th
4 IFQMSThe 4th International Forumon Quantum Metrology and Sensing

PROCEEDINGSPart 1: SE-01, SE-03A, SE-04

December 8th, 2021
Online Conference (Zoom)

Joint Program Session with Quantum Innovation 2021

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)Organization
The 4th IFQMS (International Forum on Quantum Metrology and Sensing) is held asa Joint Program Session with Quantum Innovation 2021 (December 7-9, 2021).

Date
8 December 2021

Venue
Forum is held on-line.

Language
EnglishOrganized by
Ministry of Education, Culture, Sports, Science and Technology (MEXT)

Committee
Chairperson
Yasuhiko Arakawa (The University of Tokyo)
QI2021 Quantum Sensing Track Chair
Akinari Yokoya (National Institutes for Quantum Science and Technology (QST))QI2021 Committee Members (Quantum Sensing Track)
Takayuki Iwasaki (Tokyo Institute of Technology)
Tadashi Sakai (Tokyo Institute of Technology)

Contact
Q-LEAP Quantum Metrology and Sensing HQ Secretariat
Email: ifqms@qleap.titech.ac.jp

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

Program at a Glance
4th International Forum on Quantum Metrology and Sensing
All the times in the program are Japan Standard time (GMT+9)

Dec 8

Session / Presentation

Chairperson / Presenter

Affiliation

Abstract PDF

8:00-10:10 SE-01. Solid-State Quantum Sensors 1
Chairperson
Quantum sensing of quantum materials using NV center
8:00
microscopy
Current status and prospects of solid-state quantum sensors for
8:40
Quantum-LEAP
Nanoscale vector AC magnetometry with a single nitrogen9:10
vacancy center in diamond
Planetary magnetic field sensing via electrical readout of quantum
9:40
centers in SiC
10:10 BreakTakeshi Ohshima

QST

Amir Yacoby

Harvard U

SE-01-01

Mutsuko Hatano

Tokyo Tech

SE-01-02

Paola Cappellaro

MITSE-01-03

Corey Cochrane

JPL Caltech

SE-01-04

10:30-12:10 SE-02. Quantum Sensors for Life Sciences
Hiroshi Yukawa/Kensuke Osada

Chairperson
10:30 Production of color centers in nanodiamond
Nitrogen-vacancy centers in nanodiamonds as temperature
sensors and immunoassay reporters
Treatment responses to immune checkpoint inhibitor therapy
11:40
evaluated by MRI
12:10 Break

11:10

QST

Olga Shenderova

Adamas Nanotechnologie

SE-02-01

Huan-Cheng Chang

Academia Sinica

SE-02-02

Shun Kishimoto

NIH

SE-02-03

13:10-16:10 SE-03A. Short Presentations by Young Researchers on SE-01, 04, 06, 07 Topics
13:10 SE-A3A-α1

SE-A3A-β1

SE-A3A-γ1

SE-A3A-β2

SE-A3A-γ2

SE-A3A-δ1

14:30 Break
14:50 SE-A3A-α2

13:10-16:10 SE-03B. Short Presentations by Young Researchers on SE-02, 05 Topics
13:10 SE-A3B-01
14:30 Break
14:50 SE-A3B-02
16:10 Break
17:00-18:40 SE-04. Solid-State Quantum Sensors 2
Chairperson

Takayuki Iwasaki

Tokyo Tech

17:00 Quantum sensing enabled by spin qubits in diamondFedor Jelezko

Ulm U

SE-04-01

17:40 Programmable quantum simulators based on spins in diamond

Tim Taminiau

TU Delft

SE-04-02

Matthew Markham

Element Six

SE-04-03

Ryuji Igarashi

QST

19:00 Quantum biology: an Introduction

Johnjoe McFadden

U Surrey

SE-05-01

19:40 Avian magnetoreception – a radical sense of direction

Pete J. HoreU Oxford

SE-05-02

20:10 Surface chemistry of diamond for quantum applications

Anke Krüger

U Wurzburg

SE-05-03

ETH Zurich

SE-05-04

Development and optimisation of diamond for quantum
technologies
18:40 Break

18:10

19:00-21:10 SE-05. Quantum Sensors and Quantum Life Sciences
Chairperson

20:40

Diamond-based quantum sensors: technology and applications in
Christian Degen
physics and biology

21:10 ClosingProc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-01-01

SE-01-01

Quantum sensing of quantum materials using
NV center microscopy
Amir Yacoby
Harvard University

Abstract
The magnetic ﬁelds generated by spins and currents provide a uniquewindow into the physics of correlated-electron materials and devices.

Proposed only a decade ago, magnetometry based on the electron spin of

nitrogen-vacancy (NV) defects in diamond is emerging as a platform that is
exceptionally suited for probing condensed matter systems. It can be

operated from cryogenic temperatures to above room temperature, has adynamic range spanning from DC to GHz, and allows sensor-sample
distances as small as a few nanometers. As such, NV magnetometry

provides access to static and dynamic magnetic and electronic phenomena
with nanoscale spatial resolution. While pioneering work focused on

proof-of-principle demonstrations of its nanoscale imaging resolution andmagnetic ﬁeld sensitivity, now experiments are starting to probe thecorrelated-electron physics of magnets and superconductors and to explore
the current distributions in low-dimensional materials. In this talk, I will

review some of our recent work that uses NV center magnetometry to image
skyrmions in thin magnetic ﬁlms, measure the spin chemical potential inmagnetic insulators, and image hydrodynamic electron ﬂow inlayered materials. In addition I will describe the use of NV centers in a new
scattering platform that uses spin waves as the probing excitation.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-01-02

SE-01-02

Current status and prospects of solid-state
quantum sensors for Quantum-LEAP
Mutsuko Hatano
Tokyo Institute of Technology

Abstract
Solid-state quantum sensors using diamond and SiC are expected to havevarious applications due to their principle possibilities such as wide-ﬁeld

dynamic range, operating temperature range, and high special resolution
down to the atomic level.

In the MEXT Q-LEAP Quantum Solid-state Flagship Project, ﬁve companies,
ﬁve academia, and two national research institutes have teamed up to

develop a solid-state quantum sensor from basic science and technologies

such as materials and quantum protocols to sensor modules and application
prototypes.

In this talk, I would like to introduce the latest research topics of Q-LEAP,
such as high precision simultaneous measurement of current andtemperature in EV batteries, high-resolution magnetocardiographic imaging
of rats, probing into living cells by tip-type NV sensor. In addition,

expectations for a future "quantum leap" society based on quantum
solid-state sensor technology will be discussed.

This work was supported by MEXT Quantum Leap Flagship Program (MEXT
Q-LEAP) Grant Number JPMXS����������.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-01-03

SE-01-03

Nanoscale vector AC magnetometry witha single nitrogen-vacancy center in diamond
Paola Cappellaro
Nuclear Science and Engineering, Physics Departments,
Massachusetts Institute of Technology, USA

Abstract
Detection of AC magnetic ﬁelds at the nanoscale is critical in applications
ranging from fundamental physics to materials science. Isolated

nitrogen-vacancy centers in diamond can achieve the desired spatial

resolution with high sensitivity. Still, vector AC magnetometry currently
relies on using diﬀerent orientations of an ensemble of sensors, withdegraded spatial resolution. Here I will present a novel protocol that

exploits a single NV to reconstruct the vectorial components of an AC
magnetic ﬁeld, by tuning a continuous driving to distinct resonanceconditions. As an experimental proof-of-principle, I’ ll show how to map the
spatial distribution of an AC ﬁeld generated by a copper wire on the surfaceof the diamond.

The proposed protocol combines high sensitivity, broad dynamic range,and sensitivity to both coherent and stochastic signals, with broad
applications in condensed matter physics.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-01-04

SE-01-04

Planetary magnetic field sensing via electricalreadout of quantum centers in SiC
Corey J. Cochrane
Jet Propulsion Laboratory, California Institute of Technology, United States

Abstract
The most widely used magnetometers for scientiﬁc missions to space are
ﬂuxgate and optically-pumped atomic-gas instruments due to their highsensitivity, reliability, and proven performance. Fluxgates are simple androbust while the atomic-gas designs are highly accurate and stable.

However, it is very diﬃcult to include all of these desired speciﬁcations in asingle package with adequate size and power constraints for smaller

scientiﬁc missions that involve cubesats. This opens the door for infusion of

next-generation magnetometer technologies. In this work, we report on thedevelopment of a silicon carbide magnetometer, promising to be a low

complexity, lightweight, low power, and inexpensive alternative to these

heritage technologies. It measures magnetic ﬁeld induced changes in spin

dependent recombination (SDR) current within a pn junction. The change in
SDR current arises from the interaction of external magnetic ﬁelds with theatomic-scale defects in the SiC semiconductor. This change in current canbe detected electrically via magnetoresistance caused by zero-ﬁeld levelcrossings or low-ﬁeld electrically-detected magnetic resonance, thereby

giving the instrument the ability to self-calibrate, a signiﬁcant advantage inthe remoteness of space. The material properties of SiC, namely radiationand temperature hardness, are also very attractive for space applications inharsh environments.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03-A Program 1/3
Quantum Sensing Track : Short Presentations by Young Researchers
SE-03A. Short Presentations by Young Researchers on SE-01, 04, 06, 07 Topics [4th IFQMS]*Note: Depending on the program, the order of presentations may change within the same group.
All the times in the program are Japan Standard time (GMT+9)
Dec 8 (Wed.)
13:10-14:30

Session / Presentation

Affiliation

ID

SE-03A-α1
MentorFedor Jelezko

MentorTakeshi Ohshima

QST

Mentor

Masaki Sekino

U TokyoUlm U

MentorTakayuki Iwasaki

Tokyo Tech

Chair

Motofumi Fushimi

U TokyoCo-chairChikara Shinei

NIMS

Exploring NV center formation condition for high Econv andcharge-state ratio of NV- and NV0 centers

Chikara Shinei

NIMS

SE-03A-α1-01

Sensitive atomic magnetometer beyond the standard quantum limit

Kosuke Shibata

Gakushuin U

SE-03A-α1-02*

Uri Vool

Harvard U

SE-03A-α1-03

Xinyu CaoU TokyoSE-03A-α1-04

Hibiki Tabuchi

Keio U

SE-03A-α1-05

Peng Wang

Tokyo Tech

SE-03A-α1-06

Ryoma Matsuki

Tokyo Tech

SE-03A-α1-07

MentorSatoshi Yamasaki

Kanazawa U

MentorTokuyuki Teraji

NIMS

Imaging hydrodynamic flow in WTe_2 using cryogenic quantum
magnetometry
Toward on-board magnetoencephalography with wearable
magnetometers and active noise canceler
Continuous-wave temperature sensing using RF-dressed states ofnitrogen-vacancy centers in diamond
High-quality lead-vacancy centers in diamond by high-pressure andhigh-temperature annealing
Magnetocardiography imaging of living rats using NV centers inDiamond13:10-14:30

Mentor / Presenter

SE-03A-β1

MentorToshiharu Makino

AIST

MentorAkimichi Nakazono

YAZAKI

Chair

Hiroki Morishita

Kyoto U

Co-chairMoriyoshi Haruyama

AIST

Probing correlated phenomena in 2D materials with diamond quantum
Mark Ku
sensors
Electroluminescence observation of NV center in diamond lateral p-i-nMoriyoshi Haruyama
diode
Synthesis of HPHT diamond with controlled nitrogen concentration
Formation of diamond film containing perfectly aligned NV center
ensembles at a high growth rate by high-power density plasma CVD
High dynamic range current detection using a diamond quantum
sensorVector DC magnetic field sensing with the reference microwave fieldusing nitrogen vacancy centers in diamond
Thermal effects on generation of spin defects in hexagonal boron
nitrideU Delaware

SE-03A-β1-01

AIST

SE-03A-β1-02

Masashi Miyakawa

NIMS

SE-03A-β1-03*

Takeyuki Tsuji

Tokyo Tech

SE-03A-β1-04

Yuta Shigenobu

Tokyo Tech

SE-03A-β1-05

Takuya Isogawa

Keio U

SE-03A-β1-06

Tetta Suzuki

Saitama U, QST

SE-03A-β1-07

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03-A Program 2/3
Dec 8 (Wed.)
13:10-14:30

Session / Presentation

Affiliation

ID

SE-03A-γ1
Mentor

Keiichi Edamatsu

Tohoku U

MentorRyosuke Shimizu

UEC

MentorHirotaka Terai

NICT

MentorRyo Okamoto

Kyoto U

Chair

Fumihiro China

NICT

Co-chair

Le Bin Ho

Tohoku U

Error-disturbance uncertainty relations in faraday measurements

Le Bin Ho

Tohoku U

SE-03A-γ1-01

Hydrogen annealing effect on silicon optical waveguide

Yixin Wang

Tohoku U

SE-03A-γ1-02

Masaya Arahata

Kyoto U

SE-03A-γ1-03

Yuki Gama

Kyoto U

SE-03A-γ1-04

Phase retrieval of joint spectral amplitude

Kemeng Chen

UEC

SE-03A-γ1-05

Temporal shaping of an entangled-photon wave packet by fourier
optical synthesis

Hiroki Oshima

UEC

SE-03A-γ1-06

MentorTakuya Hirano

Gakushuin U

MentorTakashi Mukaiyama

Osaka U

Mentor

Masaki AndoU TokyoMentorTadashi Sakai

Tokyo Tech

Chair

Kiyotaka Aikawa

Tokyo Tech

Co-chairSatoru Takano

U Tokyo

Cryogenic monolithic interferometer for sensing gravity gradient

Satoru Takano

U TokyoSE-03A-δ1-01

Suspension noise measurements of cryogenic torsion pendulums with
Ching Pin Ooi
crystaline fibrfibres

U TokyoSE-03A-δ1-02

Angular sensor with a coupled cavity for gravity gradient sensing

Yuka Oshima

U TokyoSE-03A-δ1-03

Towards sensitive accelerometers with levitated single nanoparticles

Kiyotaka Aikawa

Tokyo Tech

SE-03A-δ1-04*

Interferometric gyroscope using slow and continuous atomic beam

Tomoya Sato

Tokyo Tech

SE-03A-δ1-05*

Osaka U

SE-03A-δ1-06

OIST

SE-03A-δ1-07

Wavelength-tunable broadband infrared quantum absorption
spectroscopy in the mid-infrared region 2-5 µm
Evaluation of superconducting nanowire single photon detectors for
mid-infrared wavelengths

13:10-14:30

Mentor / Presenter

SE-03A-δ1

Development of a quantum gyroscope based on a signle ion trapping
Ryoichi Saito
techniques
Exponentially enhanced quantum metrology by quenching superradiantKarol Gietka
light-matter systems beyond the critical point
14:50-16:10 SE-03A-α2
MentorFedor Jelezko

MentorTakeshi Ohshima

Ulm U
QST

Mentor

Masaki Sekino

U TokyoMentorTakayuki Iwasaki

Tokyo Tech

Chair

Chikara Shinei

NIMS

Co-chairMotofumi Fushimi

U TokyoThree-layered magnetically shielded room for ultrahigh-sensitivity
quantum sensing of biomagnetic signals

Motofumi Fushimi

U TokyoSE-03A-α2-01

Super-resolution in nanoscale NMR

Nicolas Staudenmaier

Ulm U

SE-03A-α2-02

Ryota Kitagawa

Tokyo Tech

SE-03A-α2-03

Hiroyoshi Tomioka

Tokyo Tech

SE-03A-α2-04

Shu Motoki

QST, Saitama U

SE-03A-α2-05

Ryusei Yanoshita

Kyoto U

SE-03A-α2-06

Sensitivity of weight imaging using a hybrid system based on
piezoactive magnetic material and diamond quantum sensor
Study on electron spin control method for high-sensitivity diamondquantum sensor
Optically detected magnetic resonance spectra of silicon vacancies in
4H-SiC with different temperatures
High efficiency formation of NV center inside diamond by femtosecond
laserProc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03-A Program 3/3
Dec 8 (Wed.)

Session / Presentation

Mentor / Presenter

Affiliation

ID

14:50-16:10 SE-03A-β2
MentorSatoshi Yamasaki

Kanazawa U

MentorTokuyuki Teraji

NIMS

MentorToshiharu Makino

AIST

MentorAkimichi Nakazono

YAZAKI

Chair

Moriyoshi Haruyama

AIST

Co-chair

Hiroki Morishita

Kyoto U

Hiroki Morishita

Kyoto U

SE-03A-β2-01

Hannes Kraus

NASA

SE-03A-β2-02

Kosuke Kimura

QST, Gunma U

SE-03A-β2-03

Kazuki Hirokawa

Tokyo Tech

SE-03A-β2-04

A compact quantum sensor head with side excitation of CVD diamond Yuki Nishio

Tokyo Tech

SE-03A-β2-05

Hybrid integration of Si3N4 grating structure on diamond NV substrate
Ryota Katsumi
for efficient photon extraction

Toyohashi Tech

SE-03A-β2-06

AC magnetic field sensing with ensemble NV centers using electricaldetection methods
OPuS-MAGNM - miniaturized optically pumped solid state quantum
magnetometers for space applications
Development of phthalocyanine ion beam for creation of multiple NV
centers.
Fabrication of diamond protective film using microwave plasma CVD
towards high-quality quantum emitters

14:50-16:10 SE-03A-γ2
Mentor

Keiichi Edamatsu

Tohoku U

MentorKenichi Nakagawa

UEC

MentorRyosuke Shimizu

UEC

MentorHirotaka Terai

NICT

Chair

Le Bin Ho

Tohoku U

Co-chair

Fumihiro China

NICTFumihiro China

NICT

SE-03A-γ2-01

Masayuki Hojo

Kyoto U

SE-03A-γ2-02

Hiroya Seki

UEC

SE-03A-γ2-03

Rui SunTohoku U

SE-03A-γ2-04

Yining Xuan

Tohoku U

SE-03A-γ2-05

Nicolas Schwaller

Kyoto U

SE-03A-γ2-06

Superconducting nanostrip single-photon detectors with dielectric
multilayer cavities
Estimation of the quantum efficiency of the up-conversion system
based on injection-locked dual oscillators
Selective measurement of biexciton luminescence by photon
correlation spectroscopy
Towards optical manipulation of gold-nanoparticles for efficient single
photon sources
Single photon emission from a quantum-dot-gold-nanostar coupledsystem on an optical nanofiber
Focusing constraints on coupling efficiency of collinear type-I
degenerated SPDC photon pairs into a single-mode fiber

Note: For the purpose of fostering young researchers, presentations with asterisks (*) are excluded from the short presentation awards.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α1-01
Exploring NV center formation condition for high Econv andcharge-state ratio of NV- and NV0 centers
Chikara Shinei1, Masashi Miyakawa1, Shuya Ishii2, Seiichi Saiki2, Shinobu Onoda2,
Kenji Watanabe1, Takashi Taniguchi1, Takeshi Ohshima2 and Tokuyuki Teraji1
1

National Institutes for Materials Science2

National Institutes for Quantum Science
SHINEI.Chikara@nims.go.jp

Introduction
Negatively-charged NV center (NV-) is promising color centers forhigh sensitivity magnetometer due to its long coherence time (~2 ms)
and clear Rabi and Ramsey contrast due to spin dependent
fluorescence 1. Weak DC magnetic signal detection such as detectionof single-neuron action potential 2, malarial hemozoin 3, biologicaltissue 4, and paleomagnetic in rocks 5, has been demonstrated using
ensemble of NV- center. For the weak DC magnetic signal detection,
diamond with [NT] ranged from 1 to 30 ppm and [NV-] ranged from0.1 – 4 ppm is empirically suitable. Assuming that the detectedvolume of diamond is constant, the magnetic sensitivity is
proportional to [NV-] which corresponds to the number of elementsof the magnetometer. Increasing of [NV-] is the most important for
improving the magnetic sensitivity. Generally, the conversion
FIG. 1. The relationship [NV-] / [NT] andefficiency (Econv) from substitutional nitrogen (Ns0) to NV- center,[NVT] /[NT]06[NV ] /[Ns ], must be increased in order to achieve higher [NV ] .
0
NV centers has also neutral charged state (NV ) which shows no spin dependent fluorescence. Since NV- and NV0
often coexist, fluorescence of NV0 becomes background and reduces fluorescence contrast of NV-. Thus, suppressionof NV0 formation while increasing Econv (or [NV-]) is important for improving the sensitivity.
Method and Result
Diamond single crystals used in this study were grown using either HPHT synthesis or CVD method. Substitutional
nitrogen concentration was controlled by tuning concentration of Ti in the metal solvent for the former while bychanging flow rate of nitrogen gas for the later. After the nitrogen doped diamond growth, an electron beam irradiation
was applied with the total fluence of 1017-1018 cm-2 to create vacancies in the diamond. it was followed by vacuum
annealing at 1000℃ for 2h to form NV center in the diamond crystals. The number density ratio of NV- to NV0 is
estimated from the intensity ratio of their ZPL. The [NV-] and [NT] was estimated using EPR method at room
temperature. [NVT] is equal to sum of [NV-] and [NV0].
In FIG. 1, the relationship between [NV-] / [NT] and [NVT] / [NT] measured by EPR and PL is presented. Circles
and squares respectively show synthesis method of HPHT and CVD. The color scale indicates substitutional nitrogenconcentration [NT] which was measured before electron beam irradiation process. The solid line shows the case inwhich [NV-] is equal to [NVT], indicating all NV center is negative charge state. The rate of increase of [NV-]/[NT]with respect to [NVT]/[NT] becomes smaller when [NVT]/[NT] is larger than 20 – 30%. The result indicate that the NV
centers were fully negatively charged when [NVT]/[NT] was up to about 20%. in our diamond samples. In thepresentation, we will discuss physical picture of charge state of NV center depending on [NVT] / [NT]: equilibrium
equation.
Reference
1

John F. Barry et al. Rev. Mod. Phys. 92, 015004 (2020).

2 J. F. Barry et al. Proc. Natl. Acad. Sci. U.S.A. 113, 14133 (2016).

I. Fescenko et al. Phys. Rev. Applied 11, 034029 (2019).
H. C. Davis et al. Nat. Commun. 9, 131 (2018).
5
D. R. Glenn et al. Geochem. Geophys. Geosyst. 18, 3254 (2017).
6
J. F. Barry et al. Rev. Mod. Phys. 92, 015004 (2020).
This work was supported by MEXT Q-LEAP (JPMXS0118068379 and JPMXS0118067395). T. Terajiacknowledges the support of, JST CREST (JPMJCR1773), MIC R&D for construction of a global quantum
cryptography network (JPMI00316), JSPS KAKENHI (Nos. 20H02187, 20H05661 and 19H02617). T. Teraji and
S. Onoda acknowledge the support of JST Moonshot R&D (JPMJMS2062).
3
4

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α1-02
Sensitive atomic magnetometer beyond the standard quantum limit
Kosuke Shibata, Naota Sekiguchi, Aki Torii, Junnosuke Takai, and Takuya Hirano
Department of Physics, Faculty of Science, Gakushuin University
shibata@qo.phys.gakushuin.ac.jp
Introduction
Atoms can be used for sensitive magnetometry. While vapor magnetometers have achieved sub fT Hz-1/2 sensitivities [1,2],
cold atom gases may work as sensitive and spatially-resolved magnetometers due to small thermal diffusion. Magnetic fieldsensitivities in the state-of-art atomic magnetometers are limited by the so-called standard quantum limit (SQL), which
results from quantum noises. Reduction of the quantum noises below the SQL has attracted attentions as a tool for enhancing
performance of a magnetometer.
We have constructed a sensitive magnetometer using a Bose-Einstein condensate (BEC) of rubidium atoms [3]. Our BEC
magnetometer sensitivity is already almost limited by quantum noises, consisting of the photon shot noise at detection andatomic spin shot noise. We aim to squeeze both of them to realize a sensitive magnetometer surpassing the classical ones.

MethodWe probe a BEC exhibiting the Larmor precession using a two-polarization phase contrast imaging. This imaging setup
detects difference in phase shifts of orthogonal circular components of an off-resonant probe at 795 nm, which is proportional
to the spin projection along the probe propagation axis and gives the information on the precession phase or a magnetic fieldat the atom position. The photon shot noise, which naturally appears in this difference detection, can be reduced by adding
a squeezed light to the probe. We have successfully generated a squeezed light at the probe wavelength using waveguides
and are now constructing a new squeezed light source near the BEC experiment machine. The two-polarization phase
contrast detection will introduce spin squeezing on the basis of quantum nondemolition (QND) measurement of an atomic
spin variable. We expect that planar squeezed state, which has quantum noise smaller than that in the coherent (classical)
spin state in the plane of the Larmor precession [4,5], should be generated in our experiment. The planar squeezed state will
improve the magnetic field sensitivity. We have conducted experiments to measure the atomic spin shot noise level and thespin squeezing. I will present on the details of these topics and our recent status.
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118070326.

Reference

I.K. Kominis, T. W. Kornack, J. C. Allred, and M. V. Romalis, Nature (London), 422, 596-599 (2003).
S.-K. Lee, K. L. Sauer, S. J. Seltzer, O. Alem, and M. V. Romalis, Applied Phys. Lett., 89, 214106596-599 (2006).
3
N. Sekiguchi, K. Shibata, A. Torii, H. Toda, R. Kuramoto, D. Fukuda, and T. Hirano, Phys. Rev. A, 104, L041306 (2021).
4
Q. Y. He, Shi-Guo Peng, P. D. Drummond, and M. D. Reid, Phys. Rev. A, 84, 022107 (2011).
5
G. Puentes, G. Colangelo, R. J. Sewell, and M. W. Mitchell, New. J. Phys., 12, 053007 (2013).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α1-03
Imaging hydrodynamic flow in 𝑾𝑾𝑾𝑾𝒆𝒆𝟐𝟐 using cryogenic quantum magnetometry
Uri Vool1, 2, Assaf Hamo2, Georgios Varnavides3, 4, 5, Yaxian Wang3, Tony X. Zhou2, 3, Nitesh
Kumar6, Yuliya Dovzhenko2, Ziwei Qiu2, 3, Christina A. C. Garcia3, Andrew T. Pierce2, Johannes
Gooth2, 6, 7, Polina Anikeeva4, 5, Claudia Felser3, 6, Prineha Narang3, and Amir Yacoby2, 3,

1John Harvard Distinguished Science Fellows Program, Harvard University
2

Department of Physics, Harvard University

3

John A. Paulson School of Engineering and Applied Sciences, Harvard University

4

Department of Materials Science and Engineering, Massachusetts Institute of Technology
5

Research Laboratory of Electronics, Massachusetts Institute of Technology
6

Max-Planck-Institut für Chemische Physik Fester Stoffe, Dresden

7Institut für Festkörper- und Materialphysik, Technische Universität Dresden

Hydrodynamic electron flow, where electrons in a conductor flow collectively - akin to a fluid, is a unique signatureof strong electron interactions in a material. This effect has been observed in 2D materials, but observations in bulk
materials are intriguing as high-carrier density should screen the interactions. In this talk, I will discuss a recent
measurement of hydrodynamic flow in the semimetal WTe2, allowing us to gain insight into the microscopic originof its electron interactions1.

We image the spatial profile of the electric current by using a nitrogen-vacancy scanning tip. Using coherent quantum
sensing, we obtain magnetic field resolution of ~10nT and spatial resolution of ~100nm. The current pattern we observe
differs substantially from the flat profile of a normal metal and indicates correlated flow through the semimetal. The
pattern also shows non-monotonic temperature dependence, with hydrodynamic effects peaking at ~20 K.
We compare our results to a model which combines ab initio electron scattering rates and the electronic Boltzmanntransport equation. The model shows quantitative agreement with our measurement, allowing us to extract the strengthof electron-electron interactions in our material. Furthermore, we conclude that electron interactions are phonon-me
diated. This result opens a path for hydrodynamic flow and strong interactions in a variety of new materials.

FIG. 1. Measurement technique: imaging local current flow by the effect of its induced magnetic field on a nitrogen-vacancy
sensor in a diamond tip.

Reference

U. Vool, A. Hamo, G. Varnavides, Y. Wang et. al. Nature Physics 17 1216-1220 (2021)

1

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α1-04
Toward on-board magnetoencephalography with wearable magnetometers andactive noise canceler
Xinyu Cao1, Zonghao Xin1, Akihiro Kuwahata2, Motofumi Fushimi1, Shinichi Chikaki1, Kazuhiro
Oyama3, Yuki Anno3, Teppei Yoshida3, Takayuki Shibata3, Yuichiro Shirota4, Masato Yumoto4,
Hiromasa Sawamura4, Mutsuko Hatano5, Takashi Yatsui6, and Masaki Sekino1
1

Graduate School of Engineering, The University of Tokyo
2

Graduate School of Engineering, Tohoku University
3

4
5

DENSO Corporation

Graduate School of Medicine, The University of Tokyo

Department of Electrical and Electronic Engineering, Tokyo Institute of Technology
6

Graduate School of Engineering, Toyohashi University of Technology
caoxinyu@g.ecc.u-tokyo.ac.jp

Introduction
Magnetoencephalography (MEG) is a non-contact biosignal measurement with high temporal and spatial resolution,
which has the potential to replace electroencephalogram (EEG) in various application scenarios. This study investigated thefeasibility of using wearable magnetometers for applications in on-board MEG. The results provide guidance information
for the development of MEG on-board measurement.
Methods
In this study, we proposed the potential application of wearable sensors in on-board MEG measurement, as shown in
Figure 1. The steady state visually evoked response (SSVER) signals were measured with superconducting quantum
interference devices (SQUIDs), and the signal distribution at potential on-scalp sensor positions were reconstructed withspherical head model [1] and minimum norm estimation (MNE) method [2]. The magnetic fields inside a real car were
measured. Noise reduction strategies based on active noise canceler for on-board applications were proposed.

FIG. 1. Schematic diagram of on-board MEG
measurement based on wearable sensors.

FIG. 2. The FFT of recorded magnetic field without/with
active cancellation. Note the change of the peak at 24 Hz.

Results and Discussion
The signal of the simulated wearable sensors is about 3 times that of the SQUID signal in this experiment. After the engine
was started, the AC magnetic field inside a gasoline car in an urban environment is about 7 times larger in the verticaldirection than in the horizontal direction. The piston movement of the internal combustion engine and the engine fan may be
two of the main causes of the magnetic field noise in the car. The highest signal-to-noise ratio of SSVER is -110 dB in thiscase. A 350 mm 20-turn active cancel coil can attenuate noise by about 28 dB at the target frequency, as shown in Figure 2.
Acknowledgements
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395.
References
1
J. C. Mosher, R. M. Leahy and P. S. Lewis, IEEE. Trans. Biomed. Eng., 46, 245-259(1999).
2
S. Baillet, J. C. Mosher and R. M. Leahy, IEEE Signal Process Mag, 18, 14-30(2001).

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α1-05
Continuous-Wave Temperature Sensing
using RF-Dressed States of Nitrogen-Vacancy Centers in Diamond

Hibiki Tabuchi1,2, Yuichiro Matsuzaki3, Noboru Furuya1, Yuta Nakano4, Hideyuki Watanabe3,
Norio Tokuda4,5, Norikazu Mizuochi6, and Junko Ishi-Hayase1,2
1
2
34School of Fundamental and Technology, Keio University, Japan

Center for Spintronics Research Network, Keio University, Japan

National Institute of Advanced Industrial Science and Technology (AIST), Japan

Graduate School of Natural Science and Technology, Kanazawa University, Japan
5

Nanomaterials Research Institute, Kanazawa University, Japan
6

Institute for Chemical Research, Kyoto University, Japanhibiade0914@keio.jp
Introduction
Nowadays, there is a growing need to measure temperature with high sensitivity and special resolution to investigate theproperties of cells or nanodevices. A nitrogen-vacancy (NV) center in diamond is a promising candidate to realize a sensitive
temperature sensor with a high sensitivity and a special resolution. The temperature sensing using continuouswave_optically-detected magnetic resonance (CW-ODMR) has advantages because this can be simply implemented bycontinuous applications of a green laser and a microwave field. However, the temperature sensitivity with CW-ODMR istypically worse than that with pulsed-ODMR. Here, we propose a novel way to improve the sensitivity of temperature sensing
using CW-ODMR with a quantum state dressed by radio-frequency (RF) fields under the transverse magnetic fields.
MethodUnder applying the transverse magnetic fields with respect to the NV axis, the ground electronic spin states of NV centerare composed of |B⟩=(| + 1⟩+| − 1⟩)/√2, |D⟩=(| + 1⟩−| − 1⟩)/√2. The transition between |D⟩ and |B⟩ can be occurredby applying the resonant RF fields, which results in splitting into quantum states dressed by the RF fields as shown in Fig.1(a).
As the temperature increases, the resonant frequency of RF-dressed state shifts due to the change in the zero-field splitting 74.2 K/√Hz. Therefore, a temperature change can be estimated by measuring the temperature shift of RF-dressed state
observed in CW-ODMR spectra. The CW-ODMR spectra were measured by simultaneous application of continuous-waveof laser, MW, and RF fields as shown in Fig.1 (b).
Results and Discussion
Fig.1(c) shows the observed CW-ODMR spectra with the RF fields under the application of the transverse magnetic fields.
It is found the 4 peaks are clearly observed, which confirms the creation of RF-dressed states. The estimated sensitivity ofthe temperature sensing is calculated to be 73.0 mK/√Hz under the optimal conditions for the laser power, MW and RF
field intensities, and this value is 6 times better than that with the conventional scheme. This is because the linewidth becomesnarrower by suppressing the effect of the strain variations with increasing RF intensity. Moreover, the sharp dip structure
observed in the CW-ODMR contributes to improving the sensitivity.

FIG. 1. (a) The energy diagram of our system (b) Experimental setup to measure the CW-ODMR (c) Experimental Result
This work was supported by MEXT Q-LEAP (No. JPMXS0118067395), MEXT KAKENHI (No. 18H01502), and CSRN,
Keio University. This work was also supported by Leading Initiative for Excellent Young Researchers MEXT Japan andJST presto (Grant No. JPMJPR1919) Japan.
Reference
T. Yamaguchi, et al., Jpn. J. Appl. Phys., 58, 100901 (2019).2Y. Matsuzaki, et al., J. Phys. Condens. Matt., 28, 275302 (2016).
K. Hayashi, et al., Phys. Rev. Appl., 10, 034009 (2018). 4S. Saijo, et al., Appl. Phys. Lett., 113, 082405 (2018).

1
3

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α1-06
High-quality lead-vacancy centers in diamondby high-pressure and high-temperature annealing
Peng Wang1, Takashi Taniguchi2, Yoshiyuki Miyamoto3, Mutsuko Hatano1 and Takayuki Iwasaki1
1

Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
23International Center for Materials Nanoarchitectonics, NIMS, Japan

Research Center for Computational Design of Advanced Functional Materials, AIST, Japanwang.p.ac@m.titech.ac.jp

Introduction
Color centers in diamond have aroused great interests nowadays: especially heavy group-IV vacancy centers in diamond are expected
to possess sharp Zero phonon lines (ZPLs) and predicted long spin coherence times1, serving as promising candidates for quantum
network. However, the heavy atom (such as lead atom) suffers from difficulty in introducing into the diamond lattice during ion
implantation, resulting in strong strained environment around lead vacancy (PbV) center. Such strained environment resulted in broad
florescent emission, making it difficult to investigate properties of the PbV center. In order to observe its energetic structure and move
forward to wavelength tuning or spin measurement, there is an urgent demand for high quality PbV whose fine structure could beclearly demonstrated, which requires an efficient approach to release the strain and recover defects formed during ion implantation.

Method and Results

For the fabrication of high-quality PbV centers in diamond, we adopted high-pressure and high-temperature (HPHT) annealing after
Pb ion implantation, at 2100℃ under 7.7 GPa. Such a high temperature is considered to reduce the strain and recover defects indiamond, while the high-pressure condition maintains the stable phase of diamond. The same procedure has been proved to reduce
inhomogeneous distribution of tin-vacancy center in diamond1,2.
We show a sharp and clear spectrum of single PbV at around 6 K, in which the linewidth of C-transition was limited to thespectrometer3. By recording Hanbury Brown-Twiss (HBT) measurement at varying excitation powers, the single configuration was
confirmed by antibunching, and we were able to estimate the excited state lifetime according to time correlation4, ~3.7 ns, as shown in
Fig. 1. Besides, our major concern is the strained environment around PbVs, which can be evaluated by their spectral distribution. We
depicted the inhomogeneous distribution of the C-transition, which turned out a linewidth of 155 GHz, as shown in Fig. 2. Comparedwith former reported distribution of 10 nm with 950℃ annealing5, our experimental results indicated that the inhomogeneous energetic
distribution of PbVs were suppressed by HPHT annealing. Such narrow distribution is of vital importance for further research on photon
indistinguishability.
This work was supported by Toray Science Foundation and MEXT Q-LEAP Grant Number JPMXS0118067395.

Fig. 2 Inhomogeneous distribution of PbVs
Fig.1 Estimated excited state lifetime of a single PbV

Reference
1.
2.
3.
4.
5.

Iwasaki, T. et al. Tin-Vacancy Quantum Emitters in Diamond. Phys. Rev. Lett. 119, 253601 (2017).
Goerltz, J. et al. Spectroscopic investigations of negatively charged tin-vacancy centres in diamond. New J. Phys. 22,013048 (2020).
Wang, P., Taniguchi, T., Miyamoto, Y., Hatano, M. & Iwasaki, T. Low-Temperature Spectroscopic Investigation of LeadVacancy Centers in Diamond Fabricated by High-Pressure and High-Temperature Treatment. ACS Photonics 8, 2947–
2954 (2021).
Khalid, A. et al. Lifetime Reduction and Enhanced Emission of Single Photon Color Centers in Nanodiamond via
Surrounding Refractive Index Modification. Sci. Rep. 5, 11179 (2015).
Fröch, J. E. et al. Versatile direct-writing of dopants in a solid state host through recoil implantation. Nat. Commun. 11,5039 (2020).

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α1-07
Magnetocardiography imaging of living rats using NV centers in Diamond
Ryoma Matsuki1, Keigo Arai1,2, Akihiro Kuwahata3, Daisuke Nishitani1, Ikuya Fujisaki1, Yuki Nishio1,
Zonghao Xin3, Xinyu Cao3, Yuji Hatano1, Shinobu Onoda4, Chikara Shinei6, Masashi Miyakawa6, Takashi
Taniguchi6, Masatoshi Yamazaki7,8, Tokuyuki Teraji5, Takeshi Ohshima4, Mutsuko Hatano1,4, Masaki
Sekino3, and Takayuki Iwasaki 1
1Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
2Japan Science and Technology PRESTO, Saitama, 332-0012, Japan
3Graduate School of Engineering, The University of Tokyo, Tokyo, 113-8656, Japan
4National Institutes for Quantum and Radiological Science and Technology, Takasaki, 370-1292,Japan
5Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, 305-0044, Japan
6International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, 305-0044, Japan

Department of Cardiology, Nagano Hospital, Soja, 719-1126, Japan
Medical Device Development and Regulation Research Center, The University of Tokyo, Tokyo, 113-8656, Japanmatsuki.r.aa@m.titech.ac.jp
78

Introduction
Diamond quantum sensors based on nitrogen-vacancy (NV) centers have high spatial resolution operated at room
temperature even under large background magnetic fields. We constructed a sensor system suitable for bio-magnetic
measurement that can take advantage of the ability to bring the NV center closer to the signal source under ambient operating
conditions. In this study, we introduce magnetocardiography(MCG) signal, mm-scale MCG imaging, and reconstruction ofcurrent in living rats.[1].

Experimental procedures and Results

We constructed a compact sample holder that allows the distance between a live rat heart and a diamond sample to be as
close as about 1 mm as shown Fig.1(a), and measured MCG of living rats. Moreover, we conducted MCG imaging at
11x11=121 measurement points over 30 mm by automatically moving the XY stage with rats on it, and reconstructed thecurrent density using bfieldtools[2,3] an open-source Python software suite. As a result, we measured MCG in a living rat atseveral tens of nT as shown Fig. 1(b), and reconstructed the current density distribution from MCG imaging with mm-scalespatial resolution as shown Fig. 1(c)(d). In addition, we conducted experiments with multiple rats using this sensor system,
and confirmed that similar results could be obtained.
Acknowledgments
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395.

Reference[1] K.Arai et al., arxiv:2105.11676(2021).
[2] Mäkinen, A. J. et al., J. Appl. Phys.128, 063906 (2020)[3] Zetter, R. et al., J. Appl. Phys.128, 063905 (2020)

c

d

Fig.1

(a) Schematic of the rat MCG setup.

(b) MCG signal from a rat.

(c) (d) MCG imaging and reconstructed current distribution combined with MRI.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β1-01
Probing correlated phenomena in 2D materials with diamond quantum sensors
Mark J.H. Ku1
1

Department of Physics and Astronomy and Department of Materials Science and Engineering, University of
Delawaremku@udel.edu

Understanding correlated spin and charge phenomena presents a rich arena for discovering exotic behaviors in materials
and plays a critical role in developing next-generation information processing capabilities. 2D systems realized with van der
Waals materials provide particularly interesting platforms for exploring correlated phenomena because of novel effects
associated with reduced dimensionality and the opportunity for drastic miniaturization and for creating new functionality.
Hence, understanding correlated phenomena in 2D materials is a frontier in condensed matter physics; however, this effort
encounters numerous challenges related to measurement techniques, including spatially-varying current or spin distribution,
small device dimension, and complex device geometry (e.g. heterostructure. Due to the ability to image magnetic field fromcurrent and spins with high spatial resolution over wide temperature range, quantum sensing with nitrogen-vacancy (NVcenters in diamond provides a transformative tool for studying condensed matter phenomena. In this talk, I will discuss two
topics in 2D materials probed with NV quantum sensing. We have directly imaged viscous flow of the Dirac electron fluidin graphene via NV magnetic imaging [1]. Understanding of the Dirac fluid presented in this work provides insight into
strongly-correlated electrons such as those in high-temperature superconductors. Via NV magnetic imaging, we have also
directly established room-temperature ferromagnetism in exfoliated flakes of Fe5GeTe2 (FGT [2] for the first time as wellas in Co-doped FGT (Co-FGT. As a step towards detecting magnons (spin excitations in 2D magnets, we have also obtained
the first ferromagnetic resonance measurement of Co-FGT bulk crystal. These results contribute towards the applications of
2D magnets in technologies and devices.

References[1] M.J.H. Ku, T.X. Zhou, Q. Li, Y.J. Shin, J.K. Shi, C. Burch, L.E. Anderson, A.T. Pierce, Y. Xie, A. Hamo, U. Vool,[2]

H. Zhang, F. Casola, T. Taniguchi, K. Watanabe, M.M. Fogler, P. Kim, A. Yacoby, and R.L. Walsworth,Nature 583, 537 (2020).

Hang Chen, Shahidul Asif, Matthew Whalen, Jeyson Tamara-Isaza, Brennan Luetke, Yang Wang, Xinhao
Wang, Millicent Ayako, Andrew F. May, Michael A. McGuire, Chitraleema Chakraborty, John Q. Xiao, andMark J.H. Ku, arXiv:2110.05314 (2021).

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β1-02
Electroluminescence Observation of NV Center in Diamond Lateral p-i-n Diode
Moriyoshi Haruyama1, Hiromitsu Kato1, Masahiko Ogura1, Yukako Kato1, Takayuki Iwasaki2,
Norikazu Mizuochi3, and Toshiharu Makino1
1
2

National Institute of Advanced Industrial Science and Technology

Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
3

Institute for Chemical Research, Kyoto University
haruyama.moriyoshi@aist.go.jp

Introduction
Nitrogen Vacancy (NV) center in diamond is one of the most studied color centers. Especially in negatively charged NV
center (NV- center), electron spin state initialization and readout can be easily performed by laser irradiation. On the other
hand, electrical manipulation of NV center without laser is required for chip-scale quantum device development. In 2013,
two papers were reported about electroluminescence of NV center, however electrical excitation of NV- center was notrealized. It can be expected that charge state of NV- center was stabilized by increasing electron concentration around NV
center. To realize this, we fabricate high concentration phosphorus doped n layer. In this study, we tried observation ofelectroluminescence from NV center in the lateral p-i-n diode and investigate the electroluminescence characteristics.

MethodResults
0

Intensity(a.u.)

Wavelength(nm)Wavelength(nm)FIG. 1. (a) PL CFM map. (b) EL CFM map. (c) PL spectrum. (d) EL
spectrum.

This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395.

Reference
N. Mizuochi et al., Nature Photonics, 6, 299 (2012)
A. Lohrmann et al., Applied Physics Letter, 99, 251106 (2011)

2

2 μm
(d)

Acknowledgement

1

0

2 μm
(c)
Intensity(a.u.)

Figure 1 (a) and (b) shows PL and EL CFM
map in i layer. The EL measurement was
performed under applied 30V of forward
bias. As shown in these figure, isolated
luminescent centers were observed at same
position. Figure 1 (c) and (d) show PL and EL
spectra of luminescence center. Zero phononline of NV- center was detected from PL
spectrum, while zero phonon line of NV0
center was detected from EL spectrum. In
theseresults,
wesucceedinelectroluminescence observation of NV
center by using lateral p-i-n diode. In
presentation, we will report analysis result
about NV– component in the EL spectrum.

Photon count (kcps)

Photon count (kcps)

We fabricated p-i-n diode by using microwave plasma enhanced chemical vaper deposition (CVD) method. The i layer
was grown on the (111) Ib high pressure high temperature diamond substrate. The i layer was slightly doped phosphorus tostabilize charge state of NV- center (P concentration: 1016 cm-3). Patterned boron doped p+ and phosphorus doped n+ layer
were grown on the i layer. Both of boron and phosphorus concentration in p+ and n+ layer was 1020 cm-3. After CVD growth,
we performed nitrogen ion implantation and post-annealing to create NV center. Acceleration energy, ion fluence andimplantation temperature were 350 keV
ELPL
5×108 cm-3 and 600oC, respectively. Post200
100
(a)
(b)
annealing temperature and time were 850oC,
30 min, respectively. After post-annealing,boiled acid mixture treatment (H2SO4 andHNO3) was performed to terminate surface
with oxygen. Electrode (Ti / Pt / Au) was
created on both p+ layer and n+ layer.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-3A-β1-03
Synthesis of HPHT diamond with controlled nitrogen concentration
Masashi Miyakawa1, Chikara Shinei1, Takashi Taniguchi2, and Tokuyuki Teraji1
1
2

Research Center for Functional Materials, National Institute for Materials Science

International Center for Materials Nanoarchitectonics, National Institute for Materials Science
MIYAKAWA.Masashi@nims.go.jp

Introduction
For developing quantum sensing devices, it is essential to utilize diamonds containing NV center with desiredconcentration. The desired concentration of NV centers varies from 1 ppb to 10 ppm, depending on applications in quantum
sensing devices. Thus, control of NV center concentration with a wide range is requested in diamond growth method. In caseof diamonds grown under high-pressure and high-temperature (HPHT), NV centers are usually formed by electron beamirradiation to nitrogen-doped diamonds followed by post-annealing treatments. Here, precise control of the substitutional
nitrogen (P1) center concentration during HPHT growth process with a wide range is a key for the concentration control of
NV center. There were reports that nitrogen impurity was reduced to the limit by adding a nitrogen getter of Ti or Al,1-4 but
continuous control of nitrogen concentrations in wide range of the order of 100 to 0.1 ppm was not. In this paper, we willreport the controllability of the nitrogen in the HPHT diamond synthesized with Co-Ti and Fe-Co-Ti base solvents by using
Ti as a nitrogen getter.

MethodSingle-crystalline diamonds were grown in Co-Ti and Fe-Co-Ti solvents by a temperature-gradient method using amodified belt-type high-pressure apparatus. Graphite and diamond with different boron impurity levels were used as carbon
sources. Pressure, temperature, and growth duration were 5.5 GPa and 1350oC for 40~80 h. Concentration of the P1 center
was evaluated by electron spin resonance (ESR) measurements using a piece of diamond with (111) faces obtained by cutting
parallel to (111) plane.

Results and discussion

ESR measurements indicated P1 center concentrations were exponentially decreased from 100 ppm to 0.1 ppm withincreasing amount of Ti additives in the Co-Ti solvent, which provides the nitrogen concentration in diamond crystals canbe controlled by optimizing amount of Ti additive. In the Fe-Co-Ti solvents, P1 concentration was decreased from ~90 ppm
to ~0.08 ppm with increasing amount of Ti additive up to 2 wt%, and efficiency of nitrogen gettering by Ti additives washigher compared with the Co-Ti solvents. Moreover, it was found that selection of carbon source became important when
the P1 concentration < ~0.2 ppm. The result of SIMS measurements indicated that residual boron concentrations in the growndiamonds were ~0.2 ppm when graphite was used as a carbon source and ~0.02 ppm when CVD diamond was used. Residualboron compensates for the P1 center, leading to an unexpected lower concentration of the P1 centers in the grown diamonds.
Therefore, utilizing a high-purity carbon source such as CVD diamonds was found to be efficient for suppressing
contamination by boron impurities in the synthesized diamonds with the P1 concentration < ~0.2 ppm.

Reference

H. Sumiya, S. Satoh, Diam. Relat. Mater., 5, 1359 (1996).
R.C. Burns, J.O. Hansen, R.A. Spits, M. Sibanda, C.M. Welbourn, D.L. Welch, Diam. Relat. Mater., 8, 1433 (1999).
3
H. Kanda, Braz. J. Phys., 30, 482 (2000).
4
A. D’Haenens-Johansson, K.S. Katrusha, P.J. Moe, W. Wang, Gems Gemol., 51, 260 (2015).
1
2

Acknowledgements
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118068379.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β1-04
Formation of diamond film containing perfectly aligned NV center ensembles at
a high growth rate by high-power density plasma CVD

Takeyuki Tsuji1, Hitoshi Ishiwata1,2, Takeharu Sekiguchi1, Takayuki Iwasaki1, and Mutsuko Hatano1
1

Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
2

PRESTO, Japan Science and Technology Agency
tsuji.t.ac@m.titech.ac.jp

Diamond film sensors with large volumes (> (0.5 mm)3) containing perfectly aligned nitrogenvacancy (NV) ensembles performing high contrast (≈ 30%) are a promising material forachieving highly sensitive quantum magnetometers such as magnetoencephalography. The stepflow growth mode in which diamonds grow laterally by microwave plasma chemical vapor
deposition (MPCVD) is required to realize aligned NV center ensembles. However, theconventional growth rate of aligned NV center ensembles was limited to a low value (0.05~ 0.5μm/h) because a low gas flow ratio CH4 / H2 (< 0.5%) is needed for step flow growth [1–3]. In
addition, the nitrogen density of the NV center film should be controlled to below 30 ppm toobtain high contrast because the high nitrogen densities shorten the life-time of the excited-state
and reduce spin polarization, which leads to decreased the contrast [4].
In this study, we achieved a high growth rate (6.6 µm/h) of diamond film containing perfectlyaligned NV ensembles with high contrast (30%) by applying high power density plasma (103
W/cm3) and precisely controlling the flow rate ratios of CH4 / H2 and N2 / CH4. For introducing
high power density plasma, we used an MPCVD with a spherical chamber to reflectively
concentrate microwaves on the diamond stage with a microwave antenna, and higher gas
pressure up to 30 kPa was introduced to concentrate the plasma on the diamond substrate. The
power density was varied as 42, 66, 103 W / cm3, which belongs to the high-density regime (>40 W/cm3) among the previous diamond CVD studies [5]. The growth temperature of 800 °C
and growth time of 4 hours are fixed during the CVD growth.
The three-dimensional island growth was observed at the CH4 / H2 of 0.32% because of thenucleation formed on the terraces. Then, the hydrogen etching of the nucleation formed on theterraces was induced by decreasing the CH4 / H2 to below 0.16% leading to step-flow growth.
Fig.1 shows that the growth rate of the diamond films with step flow growth were increased
as the power density was increased. It was considered that increasing the power density, which
can produce a large amount of carbon precursors while maintaining a low CH4 / H2 of 0.16%,
realized step-flow growth, leading to a high growth rate (6.6 µm/h) with perfectly aligned NV
center ensembles. The N2 / CH4 ratio was also controlled to be lower than 2.5%, and thenitrogen density in the diamond film was kept below 30 ppm to obtain a high Rabi contrast(30%) as shown in Fig2. Moreover, we measured the T2* of the obtained diamond sensor films
by the high growth rate with the Ramsey sequence using a large detection volume of
approximately 8000µm3. We confirmed that T2* (= 210 ns) obtained in this study is mainly
limited by nitrogen electron spin bath density of the diamond film (24 ppm) [6] and no
significant decrease in T2* due to the deterioration of the crystallinity of the diamond film
including strain gradients was observed. This result is promising for building material
technology for highly sensitive quantum sensors with large sensor volumes.

Acknowledgment

This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395. andconducted at (NanofabPF, Tokyo Tech), supported by "Nanotechnology Platform Program" ofthe Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, Grant
Number JPMXP09F-21-IT-014.

Reference

Fig.1. (a) Evolution of thegrowth rate of the CVD
diamond films with island
growth (triangular red dots) or
the step-flow growth (circle
black dots) as a function of the
MW power density.

Fig.2. The nitrogen density in
the CVD film (circle blue dots)
and Rabi contrast (triangular
red dots) dependence on N2 /CH4. To obtain high contrast (≈30%), N2 / CH4 was controlled
to be lower than 2.5%.

[1] H. Ozawa, K. Tahara, H. Ishiwata, M. Hatano, and T. Iwasaki, Appl. Phys. Express 10, 045501 (2017).
[2] H. Ishiwata, M. Nakajima, K. Tahara, H. Ozawa, T. Iwasaki, and M. Hatano, Appl. Phys. Lett. 111, 043103 (2017).
[3] P. Balasubramanian, C. Osterkamp, Y. Chen, X. Chen, T. Teraji, E. Wu, B. Naydenov, and F. Jelezko, Nano Lett. 19,6681 (2019).
[4] K. Mizuno, M. Nakajima, H. Ishiwata, M. Hatano, and T. Iwasaki, Appl. Phys. Express 14, 032001 (2021).
[5] T. Teraji, T. Yamamoto, K. Watanabe, Y. Koide, J. Isoya, S. Onoda, T. Ohshima, L. J. Rogers, F. Jelezko, P. Neumann,
J. Wrachtrup, and S. Koizumi, Phys. Status Solidi 212, 2365 (2015).
[6] E. Bauch, S. Singh, J. Lee, C. A. Hart, J. M. Schloss, M. J. Turner, J. F. Barry, L. M. Pham, N. Bar-Gill, S. F. Yelin,and R. L. Walsworth, Phys. Rev. B Condens. Matter 102, 134210 (2020).

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β1-05
High dynamic range current detection using a diamond quantum sensor
Yuta Shigenobu1, Yuji Hatano1, Jaewon Shin2, Junya Tanigawa2, Akimichi Nakazono2,

Shinobu Onoda3, Takeshi Oshima3, Keigo Arai1, Mutsuko Hatano1, 3, Takayuki Iwasaki1
1

Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
Yazaki Corporation,

2

3

National Institutes for Quantum Science and Technology
Shigenobu.y.aa@m.titech.ac.jp

Introduction
High dynamic range current detection is required to estimate the remaining charge in the battery and precisely predict
the travelable mileage of EV. The maximum current flowing bus-bars connecting the battery will reach to several hundred
amperes. Simultaneously, the measurement with 10 mA accuracy in the well-controlled temperature is required to expand
the travelable mileage up to 10 %1. Thus, 5-digit dynamic range current sensor is crucial to realize an efficient battery
system. In this study, to meet these requirements, we constructed a quantum sensor system using ensemble NV centers indiamond.

MethodExperimental set-up to measure the bus-bar current with the diamond sensor is shown in FIG.1. The diamond sensor
used was a (111) type-Ib HPHT crystal, with a size of 2.0 ✕ 2.0 ✕ 1.0 mm3 and 3.0 ✕ 1018 cm-2 EB irradiation. The
sensor was attached to one end of a multi-mode fiber to excite by green laser and to collect the red fluorescence from theNV centers. The diamond sensor was placed perpendicular to the bus-bar to coincide the current magnetic field direction
with the N-V axis. Since the magnetic field strength in the diamond sensor generated by the 1000 A bus-bar current wasestimated to be 9 mT, 15 mT static magnetic field was applied by Nd magnets. The magnetic field was measured as thedifference in the lock-in-amplifier (LIA) outputs in the two resonance frequencies generated by the microwave signal
generator (SG)2.

ResultThe obtained spectrum of the magnetic field noise measured when SG and LIA were modulated by the frequency of
Fmod = 20 kHz and the depth of Fdev = 3.5 MHz is shown in FIG.2. The noise floor of the sensor system was less than 10
nT⁄√Hz. This value is enough to measure the magnetic field generated by the 10 mA around the bus-bar. The current
measurement procedure was as follows. The feedback path from LIA through integrator circuit to SG in FIG.1 is always
stable if the magnetic field variation caused by the bus-bar current is within a few MHz, which we define as D, where theslope of CW-ODMR around the resonance frequency is monotonous. For the small range, a current pulse train withchanging amplitude from 100 mA to 10 mA was applied and the 10 mA pulse could be detected as the change of theintegrator output. Even if the current change was over D, the feedback was kept stable by repeating the intermittent
adjustment of the center frequency of SG when the integrator circuit output reaches a predetermined value below D (forexample, 𝐷𝐷 ⁄2). The current was incremented or decremented with 30 A amplitude and 2 s width steps. We confirmed thatthe feedback path could track the current variation up to ±1000A provided.
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395.

Reference

H. Sugiyama et al., OP2, IFQMS3 (2020)

2

Y. Hatano et al., Appl. Phys. Lett. 118, 034001 (2021)
Magnetic field fluctuation (nT/Hz1/2)

1

FIG.1 Experimental setup for measuring the bus-bar
current with diamond sensor (left) and its expansion
around the diamond sensor (right).

1000
100
10
1
0.1
0.01
0.1

1

100
10
Frequency (Hz)

1000

10000

FIG.2 Measured noise spectrum of the
diamond sensor at 15 mT magnetic field and100 mW laser power.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β1-06
Vector DC magnetic-field sensing with reference microwave fieldusing a single nitrogen-vacancy center in diamond
Takuya Isogawa1,*, Yuichiro Matsuzaki2,†, and Junko Ishi-Hayase1,‡
Department of Applied Physics and Physico-Informatics, Keio University, Yokohama 223-8522, Japan

1

National Institute of Advanced Industrial Science and Technology, Ibaraki 305-8568, Japan2

tisogawa@keio.jp †matsuzaki.yuichiro@aist.go.jp ‡hayase@appi.keio.ac.jp*

Introduction
The measurement of DC magnetic fields at the nanoscale is important in various fields such as condensed matter physics[1]. In particular, a single nitrogen vacancy (NV) center in diamond is a promising device to achieve high sensitivity andspatial resolution. Recent studies have shown that vector DC magnetic-field sensing using a single NV center provides higher
readout contrast and spatial resolution compared to conventional methods using NV center ensembles [2, 3]. However, thesemethods require the application of a reference DC field that may disturb the target system in order to estimate the azimuthal
angle of the target magnetic field with respect to the NV axis. This can be a severe problem for materials that are sensitive
to static magnetic fields. Here, we propose a scheme to measure vector DC fields without a reference DC field. The azimuthal
angle of the target magnetic field can be measured from the Rabi frequency, using the direction of the microwave field todrive the Rabi oscillation as a reference. The proposed scheme delivers a novel technique for sensitive vector DC magneticfield sensing with a single NV center.

Measurement of the azimuthal angle of the target DC magnetic field

The components perpendicular and parallel to the NV axis of the target magnetic field are estimated from the two
resonance frequencies. While the azimuthal angle can be determined by applying a reference DC field to the system (Fig.
1a), our method provides a way to determine the azimuthal angle of the target field using the direction of the microwave asa reference (Fig. 1b). The perpendicular component of the target magnetic field tilts the quantization axis from the NV axis.
When a linearly polarized resonant microwave is applied, Rabi oscillation occurs at the frequency proportional to thecomponent of the microwave perpendicular to the quantization axis. Therefore, the tilt of the quantization axis can be
determined from the Rabi frequency, and the direction of the applied DC magnetic field can be measured. Fig. 1c shows thesensitivity of the conventional scheme and our scheme. The simulation was performed by solving the master equation in thepresence of Markovian dephasing. Here, we have used the same decay rate in the calculation of the sensitivity of bothschemes. In the actual experiments, we expect that our scheme can achieve higher sensitivity because the coherence time of
the Rabi oscillation is usually longer than that of the Ramsey interferometry.

FIG. 1. (a) Configuration of NV axis, the target DC magnetic field, and the reference DC magnetic field. (b) Configurationof NV axis and the reference microwave field. (c) Sensitivity of the conventional scheme (blue) and our scheme (red) as afunction of the azimuthal angle 𝜙𝜙 for 𝜃𝜃 = 10° (solid), 𝜃𝜃 = 40° (dashed), and 𝜃𝜃 = 80° (dotted). Here we fix 𝐵𝐵 =8 mT, 𝐵𝐵mw = 1 mT, 𝐵𝐵𝑟𝑟 = 1 mT, and 𝜃𝜃mw = 20°. The decay rate is 1.0 × 106 .

Acknowledgements

This work was supported by MEXT Q-LEAP (No. JPMXS0118067395), MEXT KAKENHI (No. 18H01502), and CSRN,
Keio University. This work was also supported by Leading Initiative for Excellent Young Researchers MEXT Japan andJST presto (Grant No. JPMJPR1919) Japan.

Reference

F. Casola, T. Van Der Sar, and A. Yacoby, Nature Reviews Materials 3, 1 (2018).
X.-D. Chen, F.-W. Sun, C.-L. Zou, J.-M. Cui, L.-M. Zhou, and G.-C. Guo, Europhysics letters 101, 67003 (2013).
3
Y.-X. Liu, A. Ajoy, P. Cappellaro, Physical Review Letters 122, 100501 (2019).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β1-07
Thermal effects on generation of spin defects in hexagonal boron nitride
Tetta suzuki1,2, Yuichi Yamazaki2, Takashi Taniguchi3, Kenji Watanabe3,
Yu-Ichiro Matsushita4, Yuta Masuyama2, Yasuto Hijikata1, Takeshi Ohshima2
1

Saitama Univ, 2QST, 3NIMS, 4Tokyo Techt.suzuki.838@ms.saitama-u.ac.jp

Introduction
There has been a lot of research on quantum sensors based on spin defects in wide gap semiconductors such as nitrogenvacancy complex defect (known as NV center) in diamond, silicon vacancy in silicon carbide. Recently, hexagonal boron
nitride (hBN), a 2D material, has been attracting attention as a new mother material for spin defect1,2. Energetic particle(electron, ion and neutron) irradiation is the most typical method to generate spin defects. However, such a method also
introduce unnecessary defects degrading spin property of spin defect. Thermal treatment is a useful method to anneal residual
defects. The effect after irradiation as well as during irradiation (high temperature irradiation) has been studied 3,4. In thispaper, we investigated the thermal effect on generation of boron vacancy defect (VB) in hBN.
MethodWe used hBN flakes on SiO2/Si substrate formed by tape transfer method which is commonly used in graphene research.
40 keV-N2 ions were irradiated with the optimized fluence of 1×1015 cm-2 at room temperature. Then, the irradiated sample
was isochronally annealed up to 800 °C. For comparison, 40 keV-N2 ion irradiation at elevated temperature up to 800 °C
was carried out. The photoluminescence (PL) spectra were measured using a HORIBA LabRAM HR Evolition (laser
wavelength: 532 nm, laser power: 0.1 mW). Optically detected magnetic resonance (ODMR) measurements were performed
using a home-made confocal microscope. We used a software-based the lock-in detection for the ODMR measurements.
ResultPL intensity and ODMR signal contrast as a function of treatment temperature were shown in Fig. 1 and 2. In the postannealing experiment, the PL intensity remained almost the same up to 400 °C and then began to decrease at 500 °C, finallydisappeared above 600 °C. ODMR signal contrast showed the similar trend and was maximized on 400 °C annealed sample.
On the other hand, for high temperature irradiation, the PL intensity was maintained up to 600 °C, and no PL was shown
above 700 °C. The 600 °C irradiated sample showed higher ODMR signal contrast from all other samples. These results
concluded that high temperature irradiation is also useful for spin defect in 2D material.

FIG. 1. Change of PL intensity

FIG. 2. Change of ODMR signal contrast

Acknowledgement
This research is supported by QST President’s Strategic Grant QST Creative Research and JSPS KAKENHI No. 20K05352.
Reference
1
A.Gottsholl et al., Nat Mater. 19, 540 (2020). 2M.Kianinia et al., ACS Photonics. 7, 2147 (2020).
3
M.Capelli et al., Carbon 143, 714 (2019). 4Y.Chiba et al., Mater. Sci. Forum 1004, 337 (2020).

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ1-01
Error-Disturbance uncertainty relations in Faraday measurements
Le Bin Ho1, and Keiichi Edamatsu1
1Research Institute of Electrical Communication, Tohoku University
binho@riec.tohoku.ac.jp

Introduction
Quantum measurement plays a crucial role in the characterization of physical systems, which elucidate hidden quantum
properties to the classical world. One of its important intrinsic properties is the uncertainty relation which is infeasible tomeasure incompatible observables with arbitrary precision. Heisenberg was first formulated an uncertainty relation between
the position and momentum and later generalized by Arthurs and Kelly
𝜖𝜖𝐴𝐴 𝜂𝜂𝐵𝐵 ≥ 𝒞𝒞𝐴𝐴𝐴𝐴 ,that we call the Heisenberg-Arthurs-Kelly uncertainty. Here, 𝜖𝜖𝐴𝐴 is the error when measuring A and 𝜂𝜂𝐵𝐵 is the disturbancecauses to B measurement, 𝒞𝒞𝐴𝐴𝐴𝐴 = |⟨ψ|[A, B]|ψ⟩|/2, where |ψ⟩ the system state to be measured.
Furthermore, Ozawa [1] and Branciard [2, 3], have considered a rigorous relation reads
22≥ 𝒞𝒞𝐴𝐴𝐴𝐴,𝜖𝜖𝐴𝐴2 𝜎𝜎𝐵𝐵2 + 𝜎𝜎𝐴𝐴2 𝜂𝜂𝐵𝐵2 + 2𝜖𝜖𝐴𝐴 𝜂𝜂𝐵𝐵 �𝜎𝜎𝐴𝐴2 𝜎𝜎𝐵𝐵2 − 𝒞𝒞𝐴𝐴𝐴𝐴

that hereafter we call the Branciard-Ozawa uncertainty, where 𝜎𝜎Λ = �〈Λ2 〉 − 〈Λ〉2 represents the standard deviation of Λ.
Recently, Faraday measurements of spin based on an atom-light interface framework have been studied actively. It hascontributed to our understating of quantum measurement of spin systems and has various applications in quantum metrology
of atoms and spins, quantum information processing, strongly correlated systems, and many-body systems. The Faraday
effect causes the rotation of the polarized light by the spin and thus allows indirect measurement of it via the polarized light.
Such a measurement contains fundamental limits in the sensitivity caused by the quantum nature of light. Likewise, the backaction of the polarized light perturbs the spin state, which causes disturbance on the subsequent measurements of the spin.
In this work, we formulate an atom-light interface scheme for evaluating uncertainty relations.

MethodThe atom is a single spin-1/2 particle interacting with a classical coherent
polarized light. In this way, we derive the error and disturbance, and observe thecyclic oscillations as a result of the Faraday rotation and spin rotation as show in
Fig. 1. Due to the rotation of the polarized light, the square error first is gradually
decreases and then gradually reduces to the minimum at g = π/4 and increases again
at g = π/2. The behavior is then repeated when increasing g. Likewise, the squaredisturbance increases quadratically with the interaction strength and reaches the
maximum at g = π/2 and then decreases to zero for g varies from 0 to π. Thisbehavior is the imprint of the back-action effect on the spin system that disturbs(rotates) the spin on its Bloch sphere.
Similarly, we investigate the case of polarization squeezed light using the phaseFIG. 1. The plot of the square error
space approximation for the light, where the squeezing parameter takes place as ameasurement strength. Larger squeezed parameter means broader Gaussian shapeand square disturbance as functionsin the class of the polarization squeezed state, which is equivalent to “weakof interaction strength.
measurement”, while small squeezed parameter refers to the narrow of Gaussian
shape which results in a strong measurement.
We finally formulate the error-disturbance relations in these cases above and provide that the Heisenberg-Arthurs-Kelly
uncertainty can be violated while the tight Branciard-Ozawa uncertainty [2] always holds.
In conclusion, we evaluated the error, disturbance and uncertainty relations in quantum measurement in the atom-lightinterface framework of Faraday measurements. Our analysis would contribute to the understanding of the error anddisturbance as well as the uncertainty principle in the spin measurements under the atom-light interface framework.
This work was supported by MEXT Q-LEAP Grant Number MXS0118067581.

Reference

M. Ozawa, Error-disturbance relations in mixed states, arXiv:1404.3388 [quant-ph] (2014).
C. Branciard, Proceedings of the National Academy of Sciences 110, 6742 (2013).
3
C. Branciard, Phys. Rev. A 89, 022124 (2014).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ1-02
Hydrogen Annealing Effect on Silicon Optical Waveguide
Yixin Wang1, Kohei Haji2, Shunsuke Abe2, Takuya Inagaki2, Yoshiaki Kanamori3,
Keiichi Edamatsu1, Hirohito Yamada2, Nobuyuki Matsuda2
1

Research Institute of Electrical Communication, Tohoku University

2

Department of Communications Engineering, Graduate School of Engineering, Tohoku University
3

Department of Robotics, Graduate School of Engineering, Tohoku University
wangyixin@quantum.riec.tohoku.ac.jp

Introduction
In recent years, micro-optical waveguides such as silicon optical waveguides have been attracting attention for large-scale
integration of optical circuits. The main cause of propagation loss in silicon optical waveguides is light scattering due to theroughness of the surface of the waveguide core, especially at the side walls [1]. It is expected that the propagation loss of thesilicon optical waveguide will be improved by minimizing the roughness of the silicon surface. Hydrogen annealing has
been reported as one of the effective techniques for smoothing the silicon surface [2]. In this work, we applied hydrogenannealing to a silicon optical waveguide and evaluated the effect on a silicon optical waveguide.

Method and Results
The channel waveguides were fabricated in 220-nm silicon on insulator (SOI) substrates. The resist pattern of the
waveguides was formed by electron beam lithography. The pattern was transferred to silicon by using inductively-coupledplasma based reactive ion etching. The width of the waveguide was 440 nm, while both facets were designed to be as wide
as 3 μm for the effective coupling between a lensed fiber and the waveguide for transverse-electric (TE) mode.
The waveguides chip was then annealed in a hydrogen atmosphere. The temperature, pressure and annealing time were
800 °C, 5 kPa and 2 minutes, respectively. The optical properties of the waveguides were measured with an amplified
spontaneous emission (ASE) light source before and after annealing. FIG.1 shows the waveguide insertion loss as a functionof the waveguide length. In the measurement the input ASE light was filtered by a 1 nm band-pass filter with the center
wavelength of 1550 nm before the waveguide. We see that the propagation loss increased after annealing. By using the cutback method, we estimate that the propagation loss increased by 14.5 dB/cm while the coupling loss of the waveguidedecreased by 1.17 dB/facet. The possible cause of the increase in propagation loss is that silicon may be oxidized at a hightemperature [3] due to the presence of oxygen contained in the exposed SiO2 layer near the waveguide. FIG.2 shows thetransmission spectra of the 1 cm long waveguide before and after annealing. After hydrogen annealing, the insertion loss of
the waveguide increased significantly over the whole measurement range. However, the spectral ripple reduced after
annealing, which may be due to the low Fabry-Perot interference caused by high propagation loss.
-15

-10

Before annealing
After annealing

Transmittance [dB]

-20

-30

Transmittance (dB)

Before annealing
After annealing

-20

-40

-25
-30
-35
-40

-50
0

0.5

1

1.5

-45
1530

1540

1550

1560

Waveguide length (cm)Wavelength [nm]FIG. 1. Insertion loss vs. waveguide length.

FIG.2. Transmission spectra.

Acknowledgement
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067581.

Reference
T. Horikawa et al., MRS Communications 6, 9 (2016).
T. Okatani et al., Opt. Mater. Express 11, 189 (2021).
3
K. Hofman et al., Appl. Surf. Sci. 30, 25 (1987).
1
2

1570

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ1-03
Wavelength-tunable broadband infrared quantum absorption spectroscopy
in the mid-infrared region 2-5 µm
Masaya Arahata1, Yu Mukai1, Toshiyuki Tashima1, Ryo Okamoto1, and Shigeki Takeuchi1
1

Department of Electronic Science and Engineering, Kyoto University, Japanarahata.masaya.34c@st.kyoto-u.ac.jp

Introduction
Infrared spectroscopy is a powerful technique enabling the noninvasive analysis of the dynamics of the molecular vibration
and rotation modes, and an essential tool for material science and life sciences. However, a conventional infrared
spectrometer has the problems that infrared light sources have large thermal noise and low directivity and infrared detectors
need the cryogenic cooling for the high sensitivity. To overcome these problems, recently, infrared quantum absorption
spectroscopy (IRQAS) has been proposed and experimentally demonstrated [1]. IRQAS enables the spectral measurementin the infrared region only with a low-cost and high-performance visible light source and detector using the quantum
interference between the generation processes of entangled visible-infrared photon pairs. For the broadband IRQAS, somemethods of broadening the generation bandwidths of photon pairs such as the group velocity phase matching were used to
the IRQAS measurement [2]. However, the measurable wavelength ranges of IRQAS were limited to less than 1 µm at most.
Therefore, there are no IRQAS systems covering the mid-infrared (MIR) region 2-5 µm.
Here, we report a wavelength-tunable IRQAS system covering the MIR region 1.9-5.2 µm. The generation wavelengthsof visible-infrared photon pairs can be tuned by rotating a nonlinear crystal with respect to the pump beam to control thephase matching condition [3]. We show the quantum interference is observed in the wavelength region of 2-5 µm just bycontinuously rotating a crystal without the fine realignment. We also experimentally demonstrate the transmission spectrum
measurement of a silica glass sample from the ratio of visibilities of interferogram with and without a sample. Furthermore,
we demonstrate the transmittance measurement with a higher resolution with quantum Fourier-transform infrared
spectroscopy (QFTIR), which enables the measurement in the whole spectrum of photon pairs from the Fourier analysis of
the quantum interferogram [4].

MethodFigure 1 shows our experimental setup of wavelength-tunable IRQAS system with the continuous crystal rotation. A 0.5mm-thick type-I MgO:LiNbO3 crystal with a cut angle of 57.9° is pumped by a CW laser beam with a wavelength of 532
nm. The pump beam is focused into the crystal by a lens (𝑓𝑓=200 mm). Signal (visible) photons with a wavelength of 692
nm and idler (infrared) photons with a wavelength of 2300 nm are generated in the case of the normal incidence of the pumpbeam on the crystal. The SPDC wavelengths can be tuned by rotating the crystal on a rotational stage with respect to thepump beam. When being separated by a dichroic mirror, the signal and pump photons pass through, while the idler photons
are reflected. Then, the signal and pump photons are together reflected back to the crystal by a concave mirror (𝑓𝑓=100 mm).
The idler photons are collimated by a lens (𝑓𝑓=100 mm) and then pass through an ultra-violet fused silica glass window withthe thickness of 1 mm as a sample and are reflected by a mirror on a high-accurate translation stage with the position
repeatability ±2 nm. Then, at the crystal, the second SPDC generation process occurs by the reflected pump beam. Afterbeing collimated by a lens (𝑓𝑓=250 mm) and passing through a long pass filter, an iris as a spatial filter, and a tunable band
pass filter on a translation stage to eliminate the residual pump beam and the background light, signal photons are coupled
to a multimode fiber and then guided to a Si avalanche photodiode and a photon counter to measure the interference of thesingle photon counts. In this presentation, we will report on the results of transmittance measurement of the sample with thewavelength-tunable IRQAS system. This
work was supported in part by the foundationof MEXT Q-LEAP Grant Number
JPMXS0118067634, JST-CREST Grant
Number JPMJCR1674, JSPS KAKENHI
Grant Number 21H04444, Grant-in-Aid for
JSPS Fellows Grant Number 20J23408, and
WISE Program, MEXT.

Reference

FIG. 1. Schematic of wavelength-tunable IR-QAS system. APD: Avalanche photodetector.

D. Kalashnikov, A. Paterova, S. Kulik, and L. Krivitsky, Nat. Photonics, 10, 98 (2016).
C. Lindner, J. Kunz, S. J. Herr, S. Wolf, J. Kießling, and F. Kühnemann, Opt. Express, 29, 4035-4047 (2021).
3
M. Arahata, Y. Mukai, B. Cao, T. Tashima, R. Okamoto, and S. Takeuchi, J. Opt. Soc. Am. B, 38, 1934-1941 (2021).
4
Y. Mukai, M. Arahata, T. Tashima, R. Okamoto, and S. Takeuchi, Phys. Rev. Applied, 15, 034019 (2021).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ1-04
Evaluation of superconducting nanowire single photon detectors
for mid-infrared wavelengths
Yuki Gama1, Toshiyuki Tashima1, Masaya Arahata1, Yu Mukai1, Fumihiro China2, Masahiro Yabuno2,
Satoru Mima2, Shigeyuki Miyajima2, Shigehito Miki2, Hirotaka Terai2, Ryo Okamoto1, and Shigeki Takeuchi1
1

Department of Electronic Science and Engineering, Kyoto University
2

National Institute of Information and Communication Technology
takeuchi@kuee.kyoto-u.ac.jp

Introduction
Recently, single-photon detection in the mid-infrared spectral region has attracted attention as a fundamental techniquefor many technologies such as infrared quantum absorption spectroscopy1,2 and light detection and ranging (LIDAR)3.
However, the single-photon detectors operating in that region suffers from the limited operating wavelength and low
detection efficiency. One of the solutions is to use superconducting nanowire single-photon detector (SNSPD) which
possesses single-photon detection ability and low dark count. Some researchers have developed SNSPDs for the mid-infrared
spectral region and, for example, Verma et al. evaluated the detection performance of SNSPDs fabricated from WSi up to awavelength of 10 𝜇𝜇m4. However, the detection efficiency of such mid-infrared single-photon detectors has not been fully
evaluated so far. In this presentation, we report the experimental evaluation of a NbTiN SNSPD working in the mid-infrared
spectral region. We evaluated dark count and the linearity of detection count by changing the input photon number and thebias current. We also investigated the detection efficiency and obtained the value of 1.20 ± 0.40 % at the wavelength of
4.33 𝜇𝜇m with the bias current of 21.0 𝜇𝜇A.

MethodWe developed a NbTiN SNSPD for the mid-infrared single-photon detection. To improve the sensitivity for the midinfrared single-photons, we fabricated the nanowire with thinner line width of 50 nm instead of typical 80 to 100 nm used
for the SNSPD working in visible and telecommunication spectral region. The SNSPD also has a meander structure and theactive area of 15 × 15 𝜇𝜇m2 (see figure 1(a) inset).
The experimental setup for evaluating SNSPD is shown in FIG. 1(a). We used quantum cascade laser (QCL) with awavelength of 4.33 𝜇𝜇m. The laser power was attenuated to the single photon level with the combination of neutral density
filters and polarizers. The light was coupled to a single mode fiber and passed through a polarization controller which consistsof a polarizer, a half-wave plate, and a quarter-wave plate. Using this system, the input photon polarization was optimized
to maximize the detection count by the SNSPD. The output port of SNSPD was connected to an oscilloscope to observe thewaveform of the output voltage pulse from SNSPD or a pulse counter to obtain the detection count. Here, FIG. 1(b) shows
the waveform of the output voltage pulse from the SNSPD. We set threshold voltage of a pulse counter for each bias current
with this result. Using these voltages, we evaluated dark count and the linearity of detection count by changing the input
photon number and the bias current. In this presentation, we will report the evaluation results in more detail.
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067634. JST-CREST Grant Number

JPMJCR1674, Grant-in-Aid for JSPS Fellows Grant Number 20J23408

FIG. 1. (a) Experimental setup for the evaluation of mid-infrared SNSPD. ND filter: Neutral density filter, SMF: Single mode
fiber. The inset shows the schematic of SNSPD. (b) The waveform of the output voltage pulse from mid-infrared SNSPD.

Reference

D. Kalashnikov, A. Paterova, S. Kulik, and L. Krivitsky, Nat. Photonics, 10, 98 (2026).
Y. Mukai, M. Arahata, T. Tashima, R. Okamoto, and S. Takeuchi, Phys. Rev. Applied, 15 (2021).
3
G. Taylor, D. Morozov, N. Gemmell, K. Erotokritou, S. Miki, H. Terai, and R. Hadfield, Opt. Express 27 (2019)4
V. B. Verma et al., APL Photonics, 6, 056101 (2021).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ1-05
Phase retrieval of joint spectral amplitude
Kemeng Chen and Ryousuke Shimizu
The University of Electro-Communications Fundamental Science and Engineeringc2033074@edu.cc.uec.ac.jp
Introduction
Tailored and energy tunable entangled photons are required rather than polarization entanglement on
quantum information and communication technologies. To characterize the entanglement in a qubit system,
such as polarization entanglement, quantum state tomography has been developed. On the other hand, theevaluation of entanglement for infinite dimension can be achieved by von Neumann entropy obtained by
Schmidt decomposition. However, to implement Schmidt decomposition, the complex probability amplitudeof a two-photon state should be required. Today, we can measure the two-photon spectral or temporal
distributions in 2D space, but it is still challenging to evaluate phase distributions of the two-photon state.
Here we develop Gerchburg-Saxton (GS) algorism to retrieve the phase distribution. In addition, theoriginal intensity data should be corrected by Wiener filter to suppress the noise fluctuation of the retrieved
data.

MethodTo implement GS algorism, we need a pair of data connected with Fourier transformation. Recently we
proposed synthesizing time-frequency entangled photons and verified it by measuring joint spectral andtemporal intensities. We applied GS algorism to these data in the following procedure. At first, we addeda random phase distribution to the frequency domain data and applied fast Fourier transform (FFT).
Then, we extracted the transformed phase distribution in the time domain and reconstructed the joint
temporal amplitude. Next, FFT was performed on the joint temporal amplitude repeatedly applied thesame operation in the time and frequency domains. The transformed amplitudes were compared with themeasured amplitudes and estimated an error. FFT was continued until the error values were below 5%,
and eventually, the retrieved phase distribution was obtained. After the algorism was completed, theresolution of the measured data should be considered to correct the retrieved result. Compared with timedomain data, the resolution in the frequency domain can be ignored and the time domain resolution was
about 200 fs. So, we created ten point-spread functions (PSF) and use the Wiener filter to recorrect theoriginal data. While the noise signal rate is 18, the best retrieval result was shown as the resolution is
197 fs. Figure 2 shows the retrieved phase distribution extracting the area that exceeds 50% of maximum
intensity. Additionally, the retrieved phase distribution can be used on Hong-Ou-Mandle (HOM)
interference conjecture. We also tried to evaluate the visibility of the retrieved result and compare it to
its HOM interference experiment result.
This work was supported by MEXT Q-LEAP Grant Number JPMXS011806924.

Fig. 1 Amplitude on time domain after phaseretrieval and recorrected through point spectral
function with 197 fs resolution

Fig. 2 Retrieved relative phase on frequency
domain corrected by point spectral function
with 197 fs resolution

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ1-06
Temporal shaping of an entangled-photon wave packet by Fourier opticalsynthesis
H. Oshima1, F. China2 M. Yabuno2, S. Miki2, H. Terai2, and R. Shimizu1
1

Univ. of Electro-Comm, 2NICT
o2033021@edu.cc.uec.ac.jp

Introduction
Temporal waveform control of ultrashort optical pulses is based on the one-dimensional Fourier transform relationshipbetween the time and frequency domains, known as "optical synthesis" (OS). On the other hand, we have demonstrated thata two-dimensional Fourier transform (2D-FT) connects two-photon probability distributions of entangled photon pairs intime and frequency domains [1]. Based on this, we have developed manipulating the two-photon wave packet via 2D-FT,
termed "quantum optical synthesis" (QOS) [2]. In this experiment, we created two discrete modes in 2D frequency space.
However, the two-mode manipulation allows us to control the temporal waveform of entangled photons only in sinusoidal
modulations. Our research aims to arbitrarily shape the time-domain structure of two photons with the 2D-FT manner. In
this work, we present the extension of the frequency mode of the entangled photons toward arbitrary waveform shaping.

MethodThe experimental results are shown in Fig. 1. Figure 1 (a) is a two-photon spectral distribution, bidirectionally pumped for
one nonlinear crystal. We can see two discrete frequency modes in the -45° direction. The corresponding temporal
distribution of the two-photon is shown in Fig. 1(b), which has a sinusoidal modulation in the -45° direction. The temporal
distribution with the sub-picosecond resolution was measured by up-conversion detection of single-photon with ultrashortpulses. Figure 1(c) is the measurement results obtained when creating four frequency modes using two nonlinear crystals.
The corresponding time distribution is shown in Fig. 1(d). Setting the relative phase among all the frequency modes to benearly 0, we can see slightly complicated temporal modulation as represented by | cos(2𝜋 × 0.33𝜏− ) + cos(2𝜋 × 1.0𝜏− )|2This work was supported by MEXT Q-LEAP Grant Number JPMXS0118069242.

(a)

(b)

(ｃ)

(ｄ)

Fig.1 Upper plots are the experimental result of two-frequency mode (a) two-photon frequency and (b) temporal
distribution. Lower plots are the experimental result of four-frequency mode (c) two-photon frequency and (d) its
corresponding temporal distributions.
Reference

R.-B. Jin, T. Saito, and R. Shimizu, Phys. Rev. Appl. 10, 034011 (2018).
R.-B. Jin, K. Mihoshima, R. Shimizu et al., APL Photonics 6, 086104 (2021).

1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-δ1-01
Cryogenic Monolithic Interferometer for Sensing Gravity Gradient
Satoru Takano1, Ching Pin Ooi1, Yuka Oshima1, Yuta Michimura1, and Masaki Ando1
1

Department of Physics, School of Science, The University of Tokyo
satoru.takano@phys.s.u-tokyo.ac.jp

Introduction
Gravity gradient fluctuations are essential observation targets for precise measurement of motion of masses. From theirmeasurement we obtain information about their source behavior. Recently fluctuations at low frequency, around 0.1 Hz, hasbeen aimed for earthquake early alert using transient change of gravity potential [1] and for observation of GWs from mergers
of intermediate-mass black holes [2].
A torsion-bar antenna (TOBA) is a ground-based gravity gradiometer proposed for measurement of gravity gradientfluctuations in such frequencies [2]. It measures torsional rotation angle of horizontally suspended mass(es) induced bygravity gradient fluctuations. Several prototypes and related technologies have been developed [3,4], and now we areplanning to make a 30-cm scale prototype (Phase-III TOBA). Figure 1 shows the design setup of Phase-III TOBA
The goal of Phase-III TOBA is to achieve the strain sensitivity 10-15 / √Hz at 0.1 Hz and demonstrate noise reduction,
especially thermal noise by cooling the suspension system down to 4 K. To achieve this target sensitivity, reduction ofsensing noise of interferometer is necessary. One solution is to make the readout system monolithically. Figure 2 shows thebasic concept of the readout interferometer. We present development plan of the monolithic interferometer and current
situation.
September 12,Method
2018 22:59

WSPC Proceedings - 9.75in x 6.5in

mainpage 5

Monolithic interferometer consists of optical components directly glued on a plate. Thanks to this configuration we canreduce readout noise caused by vibration of optical components, thermal drift, etc. On the contrary, unlike ordinaryinterferometers we cannot adjust optics after gluing. Therefore, its construction requires special care. Recently the technology
of construction has been well studied and validity of noise suppression has been proved in many fields.
Monolithic interferometers have been studied for applications in room temperatures. However, for TOBA case theinterferometer is under cryogenic environment. Therefore, we have to revise usual way of construction of monolithic
interferometer in order to survive in cryogenic temperatures. We have tested alternatives suitable for cryogenic
environment
5
and the results will be reported in the presentation.

-12

10

total
Shot noise
Radiation pressure
RotationalTM
seismic(silicon)
Seismic cross-coupling
Suspension thermal (4K)
Bar thermal (4K)
Gas thermal (10-7 Pa)

Cryogenic
Temp.

√
Strain [/ Hz]

-13

10

-14

10

OpticalFiber

Laser2

Laser1

10-15

Monolithic Bench

10-16

Coupler
10-17
-2
10

(a)

FIG. 1. Setup of Phase-III TOBA.

Fig. 3.

-1

10Frequency [Hz]

0

10

(b)

Rotational
MotionFIG. 2. Schematic of readout interferometer.

(a) The design of phase-III TOBA. (b) The target sensitivity of phase-III TOBA.

Acknowledgement
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118070351.

The suspended pendulums will be kept at the cryogenic temperature of 4 K to
reducethermal fluctuations. The pulse-tube cryocooler is installed in the vacuum
Reference
1
2chamber,connected
to201,
the1416-1425
intermediatethepurewires (2010)
J. Harms et andal., Geophys.
J. Int.,(2015) masses
M. Andovia
et al.,
Phys.
Rev.aluminum
Lett., 105, 161101
3
4K.
Ishidoshiro
et
al.,
Phys.
Rev.
Lett.,
106,
161101(2011)
A.
Shoda
et
al.,
Phys.
Rev.
D,
95,
082004(heatlinks). The test masses are cooled via thermal radiation from the surface(2017)(300 K → 50 K) and heat conduction of the suspension wire (50 K → 4 K). The
suspension wires will be made of silicon or sapphire, which are known to have highQ values (∼ 108 ) at cryogenic temperatures 13 .
The six seismometers and the hexapod actuators are placed at the top stage tokeep it isolated from the ground by active feedback control. An additional ground

Beat
Signal/ 19

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-δ1-02
Suspension Noise measurements of Cryogenic Torsion Pendulums with
Crystalline Fibres
Ching Pin Ooi1, Satoru Takano1, Yuka Oshima1, Yuta Michimura1, and Masaki Ando1
1

Department of physics, School of Science, The University of Tokyo
ooichingpin@g.ecc.u-tokyo.ac.jp

Introduction
Thermal noise in mechanical sensors are a fundamental noise source and a limit for sensitivity. Torsion Bar Antenna(TOBA), a proposed ground-based gravity gradiometer targeting the frequencies 0.1 - 10 Hz [1], naturally has this noise
source. TOBA utilises torsion pendulums at high sensitivities to detect these gravitational fluctuations, which can be used
for early earthquake detection [2] and sensing the gravitational waves from the mergers of intermediate mass black holes [1].
In this work, we study the suspension noise of torsion pendulums, and study how the use of two key technologies, cryogenic
temperatures and crystalline fibres can reduce it.
To quantify the suspension thermal noise, we focus on measuring the Q factor, with which we can calculate the suspension
thermal noise, given other parameters such as the temperature, and the relevant frequencies.

MethodA copper beryllium torsion pendulum with a sapphire suspension fibre was placed in a cryogenic chamber. The Q factorof the torsion pendulum was then measured via the ringdown method as the setup was thermally cycled from room
temperature to 4 K and back. The radial position of the torsion pendulum was measured using an optical lever. The torsion
pendulum was excited using coil-coil actuators, to allow for the ringdown measurement to take place.

Q vs Temp for sapphire
100000
Cooldown

Q

Warm up

10000

1000
0

50

100

150

200

250

300

Temp (K)FIG 1. Graph of Q vs Temperature for a sapphire suspension fibre. The

Q values ranged from 3 000 to 70 000 at 4 K, showing a great
dependence on temperature, and follows the expectation that Q should
increase at cryogenic temperatures. The resonance frequency was at 6
Hz, within the TOBA targeted frequencies of 0.1 – 10 Hz.

FIG 2. Picture of torsion pendulum, with attachedmirror for optical lever readout, and coils for coilcoil actuation. The sapphire fibre used forsuspension is 1 mm in diameter

Acknowledgments

This work is supported by MEXT Q-LEAP Grant Number JPMXS0118070351.

Reference

M. Ando et al., Phys. Rev. Lett., 105, 161101 (2010)
J. Harms et al., Geophys. J. Int., 201, 1416-1425 (2015)

1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-δ1-03
Angular Sensor with a Coupled Cavity for Gravity Gradient Sensing
Yuka Oshima1, Satoru Takano1, Ching Pin Ooi1, Yuta Michimura1, and Masaki Ando1
1

Department of Physics, University of Tokyoyuka.oshima@phys.s.u-tokyo.ac.jp

Introduction
TOrsion-Bar Antenna (TOBA) is a highly sensitive gravity gradient sensor using torsion pendulums [1]. The resonant
frequency of torsional motion is ~1 mHz, therefore TOBA has good design sensitivity in low frequencies (0.1 – 10 Hz). A
prototype detector Phase-III TOBA with a 35 cm-scale pendulum is under development to demonstrate noise reduction [2].
The target sensitivity is set to 10-15 /√Hz at 0.1 Hz. Phase-III TOBA can detect earthquakes with magnitude 7 or larger within
10 seconds from 100 km distance, therefore Phase-III TOBA is useful for gravity-based earthquake early warning [3]. To
achieve our target sensitivity, we need to measure the pendulum rotation precisely. We propose a coupled wavefront sensor
as an angular sensor for Phase-III TOBA. We show the principle and experimental demonstration status of a coupled
wavefront sensor.
MethodFor a conventional wavefront sensor, we build a linear cavity with two mirrors (FIG. 1. Top). When a mirror tilts, a partof the zero-order Hermite-Gaussian (HG) modes converts into the first-order HG modes. We detect it as angular signal. In
the cavity, the first-order HG modes are anti-resonant since they get non-zero Gouy phase shift compared to the zero-order
HG modes.
A coupled wavefront sensor is a new wavefront sensor using an optical coupled cavity. In our method, we put one more
mirror behind a main cavity and build an auxiliary cavity (FIG. 1. Bottom). An auxiliary cavity can compensate Gouy phaseof main cavity, therefore the zero-order and the first-order HG modes are resonant simultaneously. As a result, angular signal
is enhanced in the main cavity.

FIG. 1. Top: The schematic of a conventional wavefront sensor. Bottom: The schematic of a coupled wavefront sensor.

Acknowledgments
This work was supported by MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) Grant Number
JPMXS0118070351.
Reference1
M. Ando et al., Phys. Rev. Lett., 105, 161101 (2010).
2
T. Shimoda et al., International Journal of Modern Physics D, 29, 1940003 (2020).
3
T. Shimoda, PhD thesis, The University of Tokyo (2019).

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-δ1-04
Towards sensitive accelerometers with levitated single nanoparticles
K. Aikawa1, M. Kamba1, H. Kiuchi1, K. Okuda1, N. Suyama1, and R. Shimizu1
1

Department of Physics, School of Science, Tokyo Institute of Technology
aikawa@phys.titech.ac.jp

Introduction
Single nanoparticles levitated in vacuum are a promising platform for sensitive accelerometers as well as for exploring
macroscopic quantum physics. Cooling of their motion to the ground state of a trapping potential, corresponding totemperatures of about 10 µK, has recently been demonstrated. We plan to use levitated nanoparticles as sensitive
accelerometers. For this purpose, we develop two experimental setups: one with an optical lattice, and one with an ion trap.
In this presentation, we briefly introduce the latest results from both setups.

MethodIn a setup with an optical lattice, we find that the phase noise of the trapping laser has a crucial impact on the motion along
optical lattice. When the phase noise as well as the intensity noise are decreased, the center-of-mass motion along the opticallattice is cooled to near the ground state via electric feedback cooling1. The position sensitivity demonstrated in our setup isbetter than 10 fm⁄√Hz, suggesting that nanoparticles is a promising system as a sensitive accelerometer.
In a setup with an ion trap, we design and fabricate a novel electrode geometry allowing us to place a high-numericalaperture lens, required for observing the motion of nanoparticles, close to the electrodes. In this ion trap, we demonstrate thestable confinement of nanoparticles and observe their three-dimensional motion via the high-numerical-aperture lens. Dueto the low oscillation frequency of nanoparticles in the ion trap, the ion-trap setup is also a promising setup for the sensitive
detection of acceleration.

Reference

M. Kamba, H. Kiuchi, T. Yotsuya, and K. Aikawa, Phys. Rev. A 103, L051701 (2021).

1

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-δ1-05
Interferometric gyroscope using slow and continuous atomic beam
Tomoya Sato1, Ryotaro Inoue1, Mikio Kozuma2,11

Institute of Innovative Research, Tokyo Institute of Technology

2

Department of Physics, School of Science, Tokyo Institute of Technology
sato@qnav.iir.titech.ac.jp

Introduction
A self-localization method, which does not rely on external signals, complements methods such as satellite positioning by
the GPS signal, ensuring safety and improving estimation accuracy by hybridization. Such a method is also essential fornavigation in environments where other methods cannot be applied, for example, under the sea.
One can estimate their position by integrating the angular velocity and acceleration in time. Such a self-localization method
consists of a gyroscope and accelerometer is called inertial navigation. The accuracy of the current high-end inertial
navigation system is dominated by the performance of the gyroscope, which employs the optical Sagnac effect, such as thering laser gyroscope. The magnitude of the phase difference between counter-propagating waves for the Sagnac
interferometer is inversely proportional to the product of wavelength and velocity of the wave. Thus, the matter-wave
interferometer is a promising way to improve the phase sensitivity of the gyroscope since the wavelength and velocity of thematter-wave are much smaller than those of the light wave [1]. We aim to develop the matter-wave gyroscope utilized by
the slow and continuous atomic beam interferometer, which can be mounted on a vehicle.

MethodA pair of atomic beams which is extracted from the 2D+MOT [2] is introduced into the interferometer region, where threepairs of counter-propagating Raman beams form the π/2-π-π/2 Mach-Zehnder type interferometer [3]. The Sagnac effectcauses the sinusoidal variation between populations of internal states of the atom as a function of the angular velocity on the
Sagnac loop. Thus, the rotation of the system can be deduced from the phase shift in the interference signal.
The measured phase shift reflects the rotation of the system, but at the same time, acceleration and environmental
disturbances also change the phase. It is necessary to eliminate these effects for accurate measurement. It can be achievedby using a pair of atomic interferometers with atomic beams that share Raman lights and travel in opposite directions [4].
Since the sign of phase shift induced by the rotation depends on the velocity vector, but that induced by the spurious effectis not. By measuring the differential phase shift between two interferometers, we can extract the phase shift caused by rotation
while eliminating that caused by common-mode noises.
We measured the phase shift in the interference signal as a function of the tilting angle of the optical table on which theapparatus was installed (FIG.1). The linear phase shift due to the gravitational acceleration was observed as a function of thetilting angle. It was also confirmed that the common-mode rejection reduced that linear phase shift. The remaining phaseshift after the rejection was consistent with the shift caused by the angular velocity of the Earth's rotation. To the best of ourknowledge, this is the first demonstration of a gyroscope using the slow and continuous atomic beam.

FIG. 1 Phase shift in interferometer due to the acceleration and rotation. Dashed lines indicate theoretical values.
This work was supported by JST-Mirai Program, Grant Number JPMJMI17A3 and COI-NEXT, Grant Number
JPMJPF2015.

Reference

J. F. Clauser, Physica B, 151, 262 (1988).
K. Dieckmann, R. J. C. Spreeuw, M. Weidemüller, and J. T. M. Walraven, Phys. Rev. A, 58, 3891 (1998).
3
M. Kasevich and S. Chu, Phys. Rev. Lett, 67, 181 (1991).
4
T. L. Gustavson, P. Bouyer and M. A. Kasevich, Phys. Rev. Lett, 78, 2046 (1997).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-δ1-06
Development of a quantum gyroscope based on a single ion trapping techniques
Ryoichi Saito1,2, and Takashi Mukaiyama1,2
1

Graduate school of Engineering, Osaka University
2

QIOB, Osaka University

r_saito@ee.es.osaka-u.ac.jp
Introduction

Atoms in a coherent superposition of different momentum states enable high-precision measurement ofphysical quantities. Matter-wave interferometers typically exploit entanglement between the internal
state and the motional state of matter. The accumulated matter-wave phases for different paths are
obtained from the interference signal of the internal states after the closing pulse of the interferometer.
In order to achieve precise sensing, exquisite control of internal and external states of individual quantais essential. Atoms and ions are ideal matter for such use since they provide us with the precise controlof their quantum states using optical means. So far, neutral atoms have been used for various sensing
applications such as detection of gravitational acceleration1, electric and magnetic field2, rotation3 and soon. On the other hand, a trapped ion has not been considered for a platform to realize sensing of external
perturbations until recently. This may partly be because of the difficulty in realizing a large interference
area due to the tight confinement of the ion trap, which is inextricably linked with the advantage of acapability of stable trapping. Quite recently, Campbell and Hamilton proposed to utilize a trapped ion fora precise rotation sensing application. In the proposal, a trapped ion in a circular motion constructs a
Sagnac interferometer. By taking an arbitrary number of ion rotations, the sensitivity of the rotation
sensing can be tuned, and the ions with multiple circular motions may provide us with a large interference
area and a compact physical size at the same time.

MethodThe Sagnac interferometer, which utilizes the single trapped
ion, is realized by circularly propagating wave packet of the ion.
The protocol to generate the two-dimensional circularinterferometer is as below. First, we apply the microwave half
pi pulse to the ion in a two-dimensional isotropic potential for
creating the superposition of the internal spin state. Then, we
irradiate a mode-locked laser at 355 nm to apply the momentum
kick, depending on the internal spin state, to generate the onedimensional interferometer5. After the generating spin-motion
entangled state by spin-dependent momentum kick, nonadiabatic trap potential shift in a perpendicular direction to themomentum kick is applied by step voltage to the electrode6.
Then, the wave packet of the ion propagates an elliptical orbit.
The rotation of the system produces the path difference between
clockwise and counterclockwise. The phase shift of the ion
matter-wave due to the rotation is measured by the detection
probability of the internal state.
FIG. 1. Schematic diagram of rotation sensing
In the presentation, we will talk about our experimental
using a trapped ion
detail and the current achievement.

Reference

M. Kasevich and S. Chu, Phys. Rev. Lett. 67, 181 (1991).
K. Zeiske, G. Zinner, F. Riehle, and J. Helmcke, Appl. Phys. B 60, 205 (1995).
3
T. L. Gustavson, P. Bouyer, and M. A. Kasevich, Phys. Rev. Lett. 78, 2046 (1997).
4
W. C. Campbell and P. Hamilton, J. Phys. B: At. Mol. Opt. Phys. 40
5
A. Shinjo, M. Baba, K. Higashiyama, R. Saito, and T. Mukaiyama, Phys. Rev. Lett. 126, 153604 (2021).
6
R. Saito and T. Mukaiyama, Phys. Rev. A 104, 053114 (2021)..
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-δ1-07
Exponentially Enhanced Quantum Metrology by Quenching SuperradiantLight-Matter Systems Beyond the Critical Point
Karol Gietka, Lewis Ruks, and Thomas BuschOkinawa Institute of Science and Technology, Quantum Systems Unit
Karol.Gietka@oist.jp
Introduction
We present a quantum metrology protocol which relies on quenching a light-matter system exhibiting a superradiantquantum phase transition beyond its critical point. In the thermodynamic limit these systems can exhibit an exponential
divergence of the quantum Fisher information in time, whose origin is the exponential growth of the number of correlated
photons on an arbitrarily fast time scale determined by the coupling strength. This provides an exponential speed-up in thegrowth of the quantum Fisher information over existing critical quantum metrology protocols observing power law behavior.
We demonstrate that the Cramer-Rao bound can be saturated in our protocol through the standard homodyne detection
scheme. We explicitly show its advantage in the archetypal setting of the Dicke model and explore a quantum gas coupled
to a single-mode cavity field as a potential platform. In this case an additional exponential enhancement of the quantum
Fisher information can in practice be observed with the number of atoms N in the cavity, despite existing works suggestinga requirement of N-body coupling terms.

Reference

K. Gietka, L. Ruks, T. Busch, arXiv, S. Schmitt, Science, 2110:04048, (2021).

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α2-01
Three-layered Magnetically Shielded Room for Ultrahigh-sensitivity
Quantum Sensing of Biomagnetic Signals
Motofumi Fushimi1, Akihiro Kuwahata2, Shinichi Chikaki1,
Takao Yamaguchi3, Yuuki Niwa3, and Masaki Sekino1
1

Graduate School of Engineering, The University of Tokyo
2

Graduate School of Engineering, Tohoku University
3

Ishida Ironwork’s Co., Ltd.

motofumi-fushimi@g.ecc.u-tokyo.ac.jp
Introduction
Measurement of biomagnetic fields generated from biological tissues such as the brain and heart has attracted great attention
since it enables us to observe physiological activities of living organisms. Quantum sensers such as the optically pumped
atomic magnetometer and the nitrogen-vacancy center in diamond have achieved ultrahigh-sensitivity sensing of magnetic
fields and opened the field of biomagnetic signal sensing at room temparature. However, to measure the extremely weakbiomagnetic signals (typically at the order of picotesla), a magnetically shielded room (MSR) that prevents the ambient
magnetic field (typically at the order of microtesla) from contaminating the target biomagnetic signals is essential [1].
In this study, we developed an MSR made of three-layered permalloy plates and measured its shielding factor to validate theefficacy of the shield in biomagnetic sensing such as magnetoencephalography (MEG) of small animals.

Methods

Figure 1 shows the developed MSR consisting of three layers of permalloy plates and one layer of aluminum plate forshielding high frequency fields. The inside dimension of the MSR is 3 m x 2 m x 2 m, and thus available for wide range of
biomedical applications including human subjects. For the measurement of the magnetic fields, we used a highly sensitive
fluxgate sensor (502A, APPLIED PHYSICS SYSTEMS). While applying the external AC magnetic fields at 0.1-100 Hz,
we evaluated the shielding factor defined here as the ratio of magnetic field strength inside to outside the MSR.

FIG. 1. Three-layered MSR developed in this study.

FIG. 2. The shielding factor at each four side of the MSR

Results and Discussion

Figure 2 shows the shielding factor of four each side of the MSR. The shielding factor increases with frequency thanks tothe aluminum layer and the factor of about 104-105 is achieved at 10 Hz, which corresponds to the frequency of the alphawave of humans. The shielding factor measured at the front side is relatively low. This is because the door of the shield
deteriorates the effect of the aluminum layer. Although the MSR greatly suppresses the magnetic field, an additionalshielding factor of about 102 is required to achieve the sensing of picotesla-scale biomagnetic signals. Introducing an active
cancelling coil in the MSR would provide the sufficient shielding capability [2,3], evaluation of which is our future work.

Acknowledgements

This work was supported by MEXT Quantum Leap Flagship Program (Q-LEAP) Grant Number JPMXS0118067395.

References

T. J. Sumner et al., J. Phys. D: Appl. Phys., 20, 1095 (1987).
K. Harakawa et al., IEEE Trans. Mag., 32(6), 5256-5260 (1996).
3
E. Boto et al., Nature, 555, 657-661 (2018).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α2-02
Super-resolution in nano-NMR
Nicolas Staudenmaier1, *, Santiago Oviedo-Casado2, Anjusha Vijayakumar-Sreeja1, Genko Genov1,
Alex Retzker2 and Fedor Jelezko1,4
1

Institute for Quantum Optics, Ulm University, D-89081 Ulm, Germany

2

Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Givat Ram, Israel
4

Center for Integrated Quantum Science and Technology, Ulm University, D-89081 Ulm, Germany*nicolas.staudenmaier@uni-ulm.de

Introduction
There is increasing interest in reducing the size of NMR and MRI devices to gain new insights to processes on thenanoscale. These include for example NMR studies of single cells, neurons1, or surfaces and surface chemistry2. Nitrogenvacancy (NV) centers in diamond show to be promising sensors for such applications. In the past years nano- to microscale
NMR has been proven using single3, 4 or ensemble NV centers5. Importantly, unlike in conventional NMR, signal pickup
with NV centers does not depend on the strength of an applied external magnetic field, allowing for the acquisition of
information-rich spectra from zero and low-field6 as well as high-field NMR. On the other side nanoscale NMR resorts tostatistical nuclear spin polarization rather than directional such as thermal polarization. For that reason, spectral resolution islimited by diffusion of a liquid sample in the detection volume. However, there is theoretical evidence that the signal
correlation does not drop off exponentially but that there is a polynomial tail for longer times allowing a sharp peaked signal
in the spectrum7, 8. We will show experimental evidence that promotes such a model that overcomes any resolution limit andultimately enables super-resolution of signals with nearby frequencies.

MethodExperimental measurements are done on a homebuilt confocal microscope using single shallow NV centers located about
10nm below the diamond surface. Hydrogen nuclear spins, naturally present in the used immersion oil, are sensed via anuclear spin sensitive dynamical decoupling sequence in combination with the quantum heterodyne (Qdyne) measurement
protocol9, that correlates all individual readouts. From the data the autocorrelation of the NMR signal is obtained andanalyzed using different statistical tools.

References
1
M. Grisi et al., Sci. reports 7, 44670 (2017).

G. A. Somorjai and Y. Li, Proc. Natl. Acad. Sci. 108, 917–924 (2011).
H. J. Mamin et al., Science 339, 557-560 (2013).
4
T. Staudacher et al., Science 339, 561-563 (2013).
5
D. Glenn et al., Nature 555, 351–354 (2018).
6
M. Ledbetter et al., J. Magn. Reson 199, 25-29 (2009).
7
D. Cohen et al., Sci. Rep. 10, 5298 (2020).
8
S. Oviedo-Casado et al., Sci. Rep. 10, 19691 (2020).
9
S. Schmitt et al., Science 356, 832-837 (2017).
2
3

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α2-03
Sensitivity of weight imaging using a hybrid system based on piezoactive
magnetic material and diamond quantum sensor
Ryota Kitagawa1, Shunsuke Nagata1, Soki Urashita1, Keigo Arai1,2, Kosuke Mizuno1,
Hitoshi Ishiwata1, 2, Yota Takamura1,
Takayuki Iwasaki1, Shigeki Nakagawa1, and Mutsuko Hatano1
Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
2
PRESTO, Japan Science and Technology Agency
kitagawa.r.ab@m.titech.ac.jp
Introduction
Imaging weight over multiple length scales from single cells to biological tissues, remaining a key challenge, introduces
a new modality for studying biological systems. Such a high dynamic range in length scale can be realized by a hybrid sensor
based on magnetostrictive(MS) magnetic material [3] and nitrogen-vacancy (NV) centers in diamonds [4]. To detect theweight of human egg cells, the weight accuracy of ~ 1 Pa is required. In this research, we evaluated the weight sensitivity of
the hybrid system. We measured weight-to-magnetic field conversion efficiency and magnetic field sensitivity.
MethodWe fabricated a hybrid sensor by gluing a MS magnetic material of a SmFe2 thin film[3], deposited on an ultra-thin quartz
substrate, and NV centers in a diamond film deposited on a type-Ib diamond (111) substrate (Fig. (a))[5]. Various weight
was applied through a rivet in an area of 3.1 mm2 by changing the number of calibrated weights (0 ~125 kPa). Due to theinverse MS effect, weight is converted into the rotation of magnetization in the MS layer (Fig. (b)). This rotation induces achange in the stray magnetic field, imaged by NV centers via optically-detected magnetic resonance (ODMR). We imaged
the magnetic field by continuous-wave ODMR while changing the weight. One pixel of the image is (4.9 µm)2.
ResultFig. (c) shows a magnetic field image at 0 kPa. We successfully imaged the magnetic field from SmFe 2. Fig. (d)shows the Bz-pressure dependence of one pixel. Weight-to-magnetic field conversion efficiency was 70 nT/kPa. The
estimation accuracy of Bz was about 2 µT per one pixel. Thus, the estimation accuracy of weight was 28 kPa.
Depositing SmFe2 on the NV center will improve the conversion efficiency by an order. Further improvement ofmagnetic field sensitivity is required, such as utilizing pulsed measurement, improvement of coherence time andgeneration rate of NV center, and spatial integration of the ODMR signal.
This work was supported by MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) Grant Number
JPMXS0118067395.
Reference
Vegas, AQ-11,5 Nov. 2019.
[1] G. Popescu et al., Lab Chip 14, 646-652 (2014).
[4] J. Cai et al., Nat. Commun. 5, 1 (2014).
[2] D. Martínez-Martín et al., Nature 550, 500-505 (2017)[5] K.Tahara et al., Appl. Phys. Lett. 107, 193110 (2015)[3] Y. Takamura, et al.,2019 Annu. Conf. on MMM, Las
1Fig. (a) Setup of hybrid weight imaging system. (b) Weight-dependent rotation of magnetization due to inverse MS effect.
(c) Magnetic field image at 0 kPa. The upper light area is off MS film. The scale bar is 100 µm. (d) Bz-pressure dependence of a
selected point. Error bar is the ±1.96𝜎 confidence interval. Weight-to-magnetic field conversion efficiency was 70 nT/kPa.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α2-04
Study on electron spin control method for high-sensitivity diamond quantum sensor
Hiroyoshi Tomioka1, Yuji Hatano1, Takeharu Sekiguchi1, Keigo Arai1, Hiromitsu Kato2,
Shinobu Onoda3, Takeshi Ohsima3, Takayuki Iwasaki1, and Mutsuko Hatano1
1

Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
23

National Institute of Advanced Industrial Science and Technology

National Institutes for Quantum and Radiological Science and Technology
tomioka.h.ac@m.titech.ac.jp

Introduction
A diamond quantum sensor utilizing the NV center, a paramagnetic defect composed of nitrogen and vacancy in diamond,is expected to be applied to life-science [1] and automotive fields due to its high sensitivity and room temperature operation.

However, further improvements in DC-field sensitivity and miniaturization are demanded for practical applications.

To achieve such improvements, we focus on CE (continuously excited)-Ramsey method [2] as an alternative to theconventional method of continuous-wave optically detected magnetic resonance (CW-ODMR) or regular Ramsey.

Methods

In CE-Ramsey measurement, the excitation light is continuously applied while the microwaves are pulsed to control theelectron spin states. Our experimental setup is shown in Fig. 1(a). In this study, we performed CW-ODMR, CE-SQ (single
quantum)-Ramsey, and CE-DQ (double quantum)-Ramsey measurements to compare the magnetic sensitivities between
them. We also estimated the shot noise limited sensitivities of CW-ODMR and CE-SQ-Ramsey methods. For this calculation,
we solved the rate equations involving only five levels [3]: two ground states, two excited states, and a metastable state. The
diamond sample used was grown by CVD (100 µm thickness) using 12C-enriched methane on a IIa substrate with a (111)
surface, followed by electron beam irradiation (5 × 1017 cm−2 ) and annealing.

Results and discussion

The magnetic sensitivities obtained by CW-ODMR, CE-SQ-Ramsey, and CE-DQ-Ramsey methods are plotted in Fig.
1(b). The CE-SQ-Ramsey and CE-DQ-Ramsey measurements showed better magnetic sensitivities than CW-ODMR for themodulation frequency between 10 and 90 kHz. Fig. 1(c) shows the calculation result of the shot noise limited sensitivity.
This sensitivity is better for CE-SQ-Ramsey than CW-ODMR at high modulation frequencies (above 20 kHz). In addition
to the sensitivity improvement, CE-Ramsey is suitable for miniaturization because it does not require pulsing of a highpower laser, which is essential for the regular Ramsey. Therefore, we expect it to be used for applications such as battery
monitoring in electric vehicles.
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395.

Reference[1] J. F. Barry et al., Proc. Natl. Acad. Sci. USA, 113, 14133 (2016). [2] C. Zhang et al., Phys. Rev. Appl. 15, 064075(2021).
[3] K. Jensen et al., Phys. Rev. B 87, 014115 (2013).

(a)

(b)

(c)

FIG. 1. (a) Schematic of the experimental setup. (b) Comparison of the experimental magnetic sensitivities with different
modulation frequencies. (c) Comparison of the shot noise limited sensitivities calculated by using five level model withdifferent modulation frequencies.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α2-05
Optically detected magnetic resonance spectra of silicon vacancies
in 4H-SiC with different temperatures
S. Motoki1, 2, S.-I. Sato2, Y. Masuyama2, Y. Yamazaki2, Y. Hijikata1, T. Ohshima2
1 1

Science and Engineering, Course in Electrical and Electronic Systems, Saitama University
2

National Institutes for Quantum Science and Technology
E-mail: s.motoki.639@ms.saitama-u.ac.jp

Introduction
Silicon vacancy (VSi −) centers in silicon carbide have attracted attention because of their potential applications to quantum
sensors (high-sensitivity magnetic field and temperature sensors). VSi − centers are also expected to be used for magnetic
sensors under harsh environments such as space and undergrounds, since they have structural stability and the potential ofhigh-fidelity spin manipulation at high temperatures1. To realize VSi − based magnetic sensors operating at high temperature,understanding of optically detected magnetic resonance (ODMR) in the ground states of VSi − centers, which is the basic
principle of magnetic sensing, is crucial. In particular, the effects of temperature on the ODMR spectra are less wellunderstood. Here, we demonstrate the potential of VSi − magnetic sensors at high temperatures by showing the ODMR
spectra with different temperatures. We also systematically investigate the effects of high energy electron irradiations on the
ODMR spectra of formed VSi − centers. The concentration of VSi − centers increases with increasing electron irradiation dose,
resulting in the enhancement of sensitivity, but increase in undesired defects which can cause decoherence is also expected.
Hence, the effects of electron irradiation dose should be clarified to obtain better sensitivity of VSi − based magnetic sensors.
MethodHigh purity semi-insulating (HPSI) 4H-SiC was irradiated with 2 MeV electrons at room temperature up to the dose of
3×1018 cm-2 to form VSi − centers. The samples were then thermally annealed at 873 K for 30 minutes in vacuum to obtainstability during measurements at high temperature. FIG. 1 shows ODMR spectra of VSi − centers in 4H-SiC at different
temperatures. The 785 nm laser at 40 mW was used for excitation and the emitted photons above 900 nm were collected by
an InGaAs photo detector. Under zero magnetic field, a resonant peak at 70 MHz due to zero-field splitting of VSi − groundstates appeared even at 600 K, being reduced with increase temperature. The resonant peak was split into two peaks byapplying external magnetic field (Zeeman splitting).
These results suggest that spin manipulation of VSi −centers is possible at 600 K and thus high temperature
operation of VSi − based magnetic sensor is feasible. At
the presentation, the mechanism of change in ODMR
spectra with different temperatures is discussed. In
addition, the relationship between the ODMR spectra
and the electron irradiation dose is reported.
Acknowledgement
This presentation is based on results obtained froma NEDO Feasibility Study Program (Uncharted
Territory Challenge 2050). Part of this study was
supported by MEXT Q-LEAP grant numbers
JPMXS0118067395, and JSPS KAKENHI grant
numbers 20H00355, and was carried out within theframework of IAEA CRP F11020.
Reference
1
H. Kraus et al., Sci. Rep. 4: 5303 (2014).

FIG. 1. ODMR spectra of VSi − centers in
4H-SiCatdifferent
temperatures.
Experimental data (symbols) are fitted by
the Lorentzian function (solid lines).

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-α2-06
High efficiency formation of NV center inside diamond by femtosecond laser
Ryusei Yanoshita1, Torataro Kurita1, Yasuhiko Shimotsuma1,
Masanori Fujiwara2, Norikazu Mizuochi2, Masahiro Shimizu1, Kiyotaka Miura1
1

Department of Material Chemistry, School of Engineering, Kyoto University
2
Institute for Chemical Research, Kyoto University
yanoshita.ryuusei.66a@st.kyoto-u.ac.jp

Introduction
The ensemble of NV centers, consisting of impurity nitrogen and adjacent vacancies in diamond, are expected as
quantum sensors due to their long coherence time and possible coherent control of a single spin at room temperature[1]. Although the single NV center formation by femtosecond laser irradiation has been reported [2], the formation
mechanism is not fully understood. Especially, the transformation of diamond to graphite [3] and the effective laser
irradiation parameters for the formation of NV center ensemble remain unexplored. More recently, we havedemonstrated that the pulse width and the number of pulses are effective to generate a higher density NV center
ensemble [4, 5]. Here we report on the relation between the impurity nitrogen concentration and the laser irradiation
parameters for the NV center formation. In particular, we focused on the efficiency of the NV center formed by the
femtosecond laser irradiation with different pulse repetition rates.
MethodA femtosecond laser beam with a central wave length of 800 nm (bandwidth 37 nm) and a pulse width of 60 fs was
focused in a diamond sample through the objective lens (50× NA 0.80). The focus was located at a depth of 50 µm below
the sample surface. In the experiments, two diamonds with different nitrogen concentrations (Sample A: CVD synthesizedType IIa diamond, [N]  1 ppm, Sample B: HPHT synthesized Type Ib diamond, [N]  33 ppm) were used. The laser
pulses were irradiated from the normal to the (100) plane. To reveal the effect of the impurity nitrogen concentration, thePL intensity originated from the NV- center ranging from 640 nm to 660 nm between the different diamond samples wascompared. Since the threshold of NV center formation by the femtosecond laser irradiation depends on the impurity
nitrogen concentration, we tuned the pulse energy (Ep) according to the samples. The Ep between 50 nJ and 200 nJ wasapplied for sample A, on the other hand, the Ep was set to 2000 nJ for sample B. Other laser parameters such as the pulse
width (60 fs), pulse repetition rate (250 kHz), and the number of pulses (2.5105) were set the same. Table 1 shows the
PL intensity (IPL) normalized by that in the unirradiated region. Despite the fact that the Ep for sample A was lower thanthat for sample B in all experiments, the PL intensity for sample A reached approximately 4.4 times higher than that for
sample B. Assuming the PL intensity is proportional to the NV center concentration, this result indicates that the formation
efficiency for the NV center is high when the impurity nitrogen concentration is low. We have also confirmed theformation efficiency of the NV center by the femtosecond laser irradiation with various pulse repetition rates ranging
from 5 kHz to 250 kHz. In the laser experiments, the irradiated number of pulses was set to be 2.5105 pulses by changing
the irradiation time. Fig. 2 shows the normalized PL intensity was changed by the pulse repetition rate, despite that thesame total pulse energy was irradiated. In particular, the NV center concentration decreased at 10 kHz or less and 100
kHz or more. In the case below 10 kHz, corresponding to the pulse interval of 100 s, such timescale is quite longer thanthat for thermalization and the lifetime of the exciton in diamond (~ 1 s). Furthermore, the decrease of NV center
concentration at 100 kHz or more could be interpreted in terms of the annihilation of NV center or the transformation into
the different defects such as H3 center.
Table1. Normalized PL intensity of NV centerin two different types of diamonds.

ReferenceType

E p [nJ]

I PL

Ib

2000

8.21

IIa

50

4.05

IIa

100

17.4

IIa

200

35.8

Fig. 2. Normalized PL intensity of NV center induced by the
femtosecond laser pulses with various pulse repetition rates.

[1] A. Gruber, et al., Science 276 2012 (1997).
[2] Y. Chen, et al., Nat. Photonics 11 77 (2017).
[3] M. Sakakura, et al., J. Laser Micro/Nanoeng. 11 346 (2016).
[4] T. Kurita, et al., Appl. Phys. Lett. 113 211102 (2018).
[5] T. Kurita, et al., Appl. Phys. Lett. 118 214001 (2021).

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β2-01
AC magnetic field sensing with ensemble NV centers
using electrical detection methods

Hiroki Morishita1, Naoya Morioka1, Tetsuri Nishikawa1, Hajime Yao1, Shinobu Onoda2,
Hiroshi Abe2, Takeshi Ohshima2, and Norikazu Mizuochi1
1Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.

2

National Institutes for Quantum and Radiological Science and Technology, Takasaki, Gunma, 370-1292, Japan.
h-mori@scl.kyoto-u.ac.jp

Introduction
Nitrogen-vacancy (NV) centers in diamond have a long coherence time at room temperature, and hence they are candidates
for quantum sensors and quantum information processing devices [1]. While electrical detection of NV spins is essential todevelop and integrate these quantum devices [2-8], to the best of our knowledge, there are no demonstrations of AC magnetic
field sensing using electrical detection methods. In the electrical detection of the NV spins, the change in the photocurrent ismeasured when resonant microwaves are applied to the NV spins. In the demonstration of the AC magnetic field sensing
using electrical detection methods, the current generated by the AC magnetic field flows in the diamond sample. This current
generated by the AC magnetic field can cause an increase in noise in the electrical detection method. Thus, the AC magnetic
field sensing using the electrical detection method is still challenging. In this study, we demonstrate for the first time AC
magnetic field sensing using the electrical detection method by reducing the influence of such a current.

Method & Results

AC Signal (arb. units)

In this study, we performed the AC magnetic field sensing with an electrical detection method using the ensemble of NV
centers (concentration of ~ 1.4 ×1017 cm-3) created by electron-beam irradiation followed by annealing. Figure 1 shows aresult of AC magnetic field sensing with the electrical detection method with the bias voltage of 5 V. The result indicatesthat we observe ~ 3 × 10-8 T/√Hz of the sensitivity of the AC magnetic field. In this presentation, we discuss the results of
AC magnetic field sensing using the electrical detection method.

0

2

4

6

8

Magnetic Field (µT)

10

Fig.1 AC magnetic field sensing with an electrical detection method.

Acknowledgments

We thank T. Ono and T. Moriyama for their technical help. This work was supported by MEXT Q-LEAP (No.
JPMXS0118067395), KAKENHI (No. 15H05868，No. 19H02546), and Kyoto University Nano Hub.

References

E. D. Herbschleb et al., Nat. Commun. 10, 3766 (2019).
E. Bourgeois et al., Nat. Commun. 6, 8577 (2015).
3
F. M. Hrubesch et al., Phys. Rev. Lett. 118, 037601 (2017).
4
M. Gulka et al., Phys. Rev. Applied 7, 044032 (2017).
5
P. Siyushev, et al. Science 363, 728 (2019).
6
H. Morishita et al., Sci. Rep. 10, 792 (2020).
7
T. Murooka et al., App. Phys. Lett. 118, 253502 (2021).
8
M. Gulka et al., Nat. Commun, 12, 4421 (2021).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β2-02
OPuS-MAGNM - Miniaturized Optically Pumped Solid State Quantum
Magnetometers for Space Applications
Hannes Kraus1, Corey J. Cochrane1
1

NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
hannes.kraus@jpl.nasa.gov

The OPuS-MAGNM project proposes to develop a novel low-cost low-power rad-hard miniaturized solid-statemagnetometer for planetary magnetic field sensing. This technology leverages optically active, spin-carrying quantum
centers (QC) in wide-bandgap semiconductors such as diamond or silicon carbide. External magnetic fields cause changes
in the QC spin energy conformation, which can be detected optically. Wide-bandgap solid-state systems, in comparison togas-cell based optically pumped magnetometers are interesting because of the material’s intrinsic extensive temperature
range (QC deterioration starts above Venus surface temperatures, at about 700C), and radiation hardness (QC implantation
fluence ~1017 e/cm2 vs. Europa orbit 30 day fluence ~1013 e/cm2). Additionally, the sensor lends itself to miniaturization, as
QC are sensitive down to single emitters, i.e. small, sub-mm ensembles are sufficient sensor volumes.
The U.S. Planetary Science Decadal Survey identifies the need for a number of scientific instruments addressing the threecrosscutting themes of planetary science: (1) understanding solar system beginnings, (2) searching for the requirements forlife and (3) revealing planetary processes. Magnetometers are unassuming, but powerful tools aiding in all of these themes.
The proposed technology is an extension to the recent Silicon Carbide solid-state magnetometer (SiCMAG1), adding
substantially better sensitivities at the expense of requiring optical readout2. We leverage optical readout noise being shotnoise in nature, while all-electrical systems suffer from 1/f noise. This gives the optical readout approach a significant
advantage in low-frequency and long-term stability performance metrics.
Consider the two most commonly used magnetometer technologies flown in space: Fluxgate systems exhibit highsensitivities and all- electrical simplicity, but require multiple coils per spatial direction. Additionally, fluxgates are not selfcalibrating; drifts in absolute field values necessitate either augmenting the fluxgate system with a self-calibrating system orincorporating complicated spacecraft roll maneuvers into mission planning.
Optically pumped He cell systems can counter this issue, operating both in scalar and vector mode, also with very highsensitivities. Their downside is the added complexity of the gas cell, with Helium being notoriously prone to outgas. Also,
vector-helium systems are larger and more expensive than fluxgates. OPuS-MAGNM now marries the solid-state simplicity
of fluxgates and SiCMAG with the precision and self-calibration capabilities of an atomic gas magnetometer system, withimproving longevity over gas cells. It has the potential to provide self-calibrated, heritage-level vector magnetic field sciencein a radiation-hard and thermal/vacuum-rugged miniaturized package; well suited for all kinds of planetary science missions.
FIG. 1. Illustration of the signal genesis of the
optically detected magnetic resonance(ODMR) in wide-bandgap solid-state
semiconductors. Silicon vacancies in Silicon
Carbide (h,k)
are optically. active spincarrying quantum centers, addressable byresonant excitation of electronic and radio
frequency transitions. An exemplary ODMR
spectrum at zero magnetic field and 1mT field
ist shown at the bottom left. A calculation of
the resonance positions depending on themagnetic field is shown on the bottom right.3

References
1. C.J. Cochrane, J. Blacksberg, M.A. Anders, P.M.
Lenahan. Vectorized magnetometer for space
applications using electrical readout of atomic scale
defects in silicon carbide. Sci. Rep. 2016, 6 (1), 1239.
2. H. Zheng, J. Xu, G.Z. Iwata, et al. Zero-Field
Magnetometry Based on Nitrogen-Vacancy Ensembles
in Diamond. Phys. Rev. Applied 2019, 11 (6), 064068.
3. H. Kraus, V.A. Soltamov, F. Fuchs, et al. Magnetic
field and temperature sensing with atomic-scale spin
defects in silicon carbide. Sci. Rep. 2014, 4, 5303.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β2-03
Development of phthalocyanine ion beam for creation of multiple NV centers
Kosuke Kimura1,2, Shinobu Onoda1, Keisuke yamada1, Wataru Kada2, Tokuyuki Teraji3,
Junichi Isoya4, Osamu Hanaizumi2, and Takeshi Ohshima112National Institutes for Quantum Science and Technology

Graduate School of Science and Technology, Gunma University
3
4

National Institute for Materials Science

Faculty of Pure and Applied Sciences, University of Tsukuba
t201d208@gunma-u.ac.jp, kimura.kosuke@qst.go.jp

Introduction
A nitrogen vacancy (NV center in diamond is known as a solid-state spin qubit worked at room temperature. NV centerscoherently coupled by dipole-dipole interactions have a potential to accomplish quantum registers operatable at room
temperature. Since the dipole-dipole interaction is inversely proportional to the cube of the distance between the NV centers,
it is necessary to create NV centers in close proximity to each other. One of the methods to create NV centers in close
proximity is nitrogen (N ion implantation via a nanohole mask [1]. This method has been reported to create double coupled
NV centers. However, for reason of nanohole purification technology, it has been difficult to create multiple coupled NV
centers with this method. The other method is molecular ion implantation [2,3]. In 2013, Yamamoto et al. reported the dipolar
coupled NV center pair via nitrogen molecular ion (N2+ implantation [2]. In 2019, Haruyama et al. reported the implantationof molecular ion from an adenine (C5N5H5 ion source and demonstrated to create triple coupled NV centers [3]. It is expected
to create further multiple coupled NV center by implantation of molecular ion with a higher number of nitrogen atoms than
C5N5H5. In this study, we report to develop a phthalocyanine(C32N8H18 ion beam containing eight nitrogen atoms forcreation of multiple NV centers.

Method and result

The C32N8H18 ion beam was developed using an ion implanter. Firstly, C32N8H18 powder was vaporized and ionized by aheater at 336°C in the support gas (Ar ambient. Secondly, positive ions were electrically extracted by energy of 3 keV.
Thirdly, the extracted beam was analyzed by mass spectrometry. The result of mass spectra was showed FIG. 1. The
fragments, such as C6H4, C8H4, C8N2H5, etc., and Ar were detected in mass number ranging from 0 to 250. C32N8H18 ion was
detected around the mass number of 505. finally, the C32N8H18 ion beam extracted by mass spectrometry magnet was
accelerated at the energy of 281 keV and implanted into the sample.
The NV centers created by C32N8H18 ion implantation were observed
Ar
C H
using confocal fluorescence microscopy (CFM). The measurement of
C N H
photon counts and optically detected magnetic resonance (ODMR)
were performed with 532 nm laser and microwaves. FIG. 2(a) shows atypical image observed by a CFM with area of 20×20 μm2. Isolated
C32N8H18
spots are clearly found from C32N8H18 implanted region. FIG. 2(b)shows the ODMR spectra of the spot indicated by the circles andpentagon in FIG. 2(a). It is clear from the spectra that the spots labeled
NVA, NVB, NVC, and NVD contain a single NV center with different
axes. The spectrum labeled NVABCD is the result of the ODMR
FIG. 1. Mass spectra from the C32N8H18 ion
measurement of the spot indicated by the pentagon symbol in FIG.
source.
1(a). from the number of dips in this spectrum, the creation of four NV(a)(b)
centers with different orientation axes was observed per spot.
NV
5 µm
Therefore, we succeeded to create four NV centers in a spot by
NV
C32N8H18 ion implantation. In the presentation, I will report on theNVNVNV
probability of the creation of multiple NV centers.
NV
8

4

8

2

5

A

B

C

ABCD

Reference[1] I. Jakobi, et al., J. Phys., 752, 012001 (2016).
[2] T. Yamamoto, et al., Phys. Rev. B, 88, 201201 (2014).
[3] M. Haruyama, et al., Nat. Commun., 10, 2664 (2019).

Acknowledgement

This work was supported by MEXT Q-LEAP Grant Number
JPMXS0118067395 and JST Moonshot R&D Grant Number
JPMJMS2062.

NVA

NVD

C

D

NVABCD

NVB

FIG. 2. (a) Typical CFM image (20×20 μm2).
(b) The ODMR spectra of the single NV
centers and quadruple NV center.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β2-04
Fabrication of diamond protective film using microwave plasma CVD
towards high-quality quantum emitters
K. Hirokawa1, K. Fukuda1, P. Wang1, T. Taniguchi2, M. Hatano1 and T. Iwasaki1
1

Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
2International Center for Materials Nanoarchitectonics, National Institute for Materials Science,
hirokawa.k.ab@m.titech.ac.jp

Introduction
Quantum networks are expected to realize secure communication by using the transfer of quantum states. Quantum
emitters which can generate a quantum entanglement state are necessary to construct quantum networks. Group-IV color
centers in diamond has attracted due to the sharp zero photon line (ZPL) and resistance to external electric noise. Among thegroup-IV color centers, SnV and PbV are expected to have a long spin coherence time in the milli-seconds at Kelvintemperatures [1,2]. However, the fabrication process includes high-temperature anneal at 2100℃, resulting in deteriorationof the sample surface, which frequently etches the incorporated color centers and hinders the fabrication of nanophotonic
structures. To overcome this issue, in this study, diamond films were deposited on a diamond substrate containing SnV
centers to protect during the high- temperature anneal.

Method and Results

Figure 1 illustrates the fabrication process. We used a IIa-type diamond substrate (Element Six). Sn ions were implanted
into the substrate with an acceleration energy of 700 keV and a dose of 2×109/cm2. Then, diamond films were deposited by
two microwave plasma CVD systems for 40 hours in total. At the first growth stage, diamond films with low impurity
concentrations were synthesized at the low growth rate. Then, at the next stage, thicker diamond films were grown using ahigh-power plasma CVD system. This sample was treated at 2100℃ under 7.7 GPa to form SnV centers in the IIa-type
diamond substrate. Confocal fluorescence microscope observations were carried out at a cryogenic temperature.
The CVD film remained on the substrate after anneal at 2100℃. Figure 2 shows ZPL from the SnV centers after thehigh-temperature anneal. The two lines correspond to C- and D-peaks, originating from split energy levels of the SnV centers.
These observations indicate that the deposited diamond films worked as a protective layer to form SnV centers.

FIG.1. Schematic diagram of protective film
fabrication for the SnV center formation.

FIG.2. PL spectrum of SnV

Reference

T.iwasaki et al, Phys. Rev. Lett, 119, 253601 (2017)
P.Wang et al, ACS photonics,2947,2954(2021)

1
2

Acknowledgments

This work was supported by the Toray Science Foundation, the MEXT Quantum Leap Flagship Program (MEXT QLEAP) Grant No. JPMXS0118067395 and "Nanotechnology Platform Program" of the Ministry of Education, Culture,
Sports, Science and Technology (MEXT), Japan, Grant Number JPMXP09F-21-IT-013.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β2-05
A compact quantum sensor head with side excitation of CVD diamond
Yuki Nishio1, Yuji Hatano1, Jaewon Shin2, Daisuke Nishitani1, Ryo Matsuki1, Hiromitsu Kato3, Shinobu Onoda4,
Takeshi Oshima4, Keigo Arai1, Mutsuko Hatano1, and Takayuki Iwasaki1
1

Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
2

Yazaki Corporation

3

National Institute of Advanced Industrial Science and Technology
4National Institutes for Quantum Science and Technology
nishio.y.ac@m.titech.ac.jp

Introduction
A compact sensor system is important for practical applications of quantum diamond sensors using NV centers. There
have been reports on nanotesla to sub-nanotesla sensitivities for the small modular diamond sensor, such as 3 nT⁄√Hz byside excitation on a (100 crystal1, 310 pT⁄√Hz by perpendicular excitation on a (100 crystal2, and 344 pT⁄√Hz byperpendicular excitation on a (111 crystal3. In this report, we investigate the side excitation of a CVD diamond layer on a(111 crystal including a large volume of NV centers.

MethodThe configuration of the sensor head fabricated in this experiment is shown in FIG.1. A 110 μm-thick 12C-enriched CVD
film grow n on 2.0✕ 2.0✕ 0.3 mm3 IIa (111)substrate was used as the diamond sensor. The NV centers were formed by
5.0✕1017 cm -2EB irradiation and high-temperature anneal. The excitation green laser was introduced on a sidewall of the
CVD film, and the fluorescence emitted from the NV centers was then collected by a CPC lens and led into a photodiodethrough LPFs. The microwave antenna was made of copper tape and the microwave magnetic field was applied horizontally.
The antenna was placed on an AlN heatsink plate. In order to excite only the NV-rich region in the diamond sample, thelaser diameter was adjusted using a beam expander and focusing lens. A part of the excitation laser was extracted as areference light to cancel the laser noise from the fluorescence. The optical system was placed in a 1 mm-thick permalloy
single layer magnetic shielded box.

ResultFirst, we investigated the magnetically insensitive noise and slope of the lock-in ODMR by varying the deviation
frequency (Fig. 2a. Although the slope takes the maximum value at a deviation frequency of 500 kHz, in this experiment,
we set the deviation frequency around 350 kHz, where the noise/slope becomes small. The measured magnetic field noise
spectrum is shown in Fig. 2b. The sensitivity was estimated to be 770 pT⁄√Hz and the noise floor was 400 pT⁄√Hz
between 30-100 Hz. In this frequency range, the noise floor of magnetically sensitive is comparable to that of themagnetically insensitive. The shot-noise limit sensitivity, calculated from the contrast and linewidth measured from theODMR, is 15 pT⁄√Hz, expecting a higher magnetic field sensitivity by improving the measurement system. This work was
supported by MEXT Q-LEAP Grant Number JPMXS0118067395.

Reference

J. Webb et al., Appl. Phys. Lett. 114, 231103 (2019)
F. Stürner et al., Adv. Quantum Technol. 4, 2000111 (2021)

1
3

R. Patel et al., Phys. Rev. Appl. 14, 044058 (2020)

2(a)Optical filter
Diamond532nm laser

Antenna
AlN
1 cm

FIG.1 Sensor module for sidelaser excitation.

10

6

8

5

6

4
3

4

2

noise/slope

1

slope

0

200

300
400
500
600
Deviation frequency [kHz](b)slope [V/MHz]

Photodetector
CPC lensnoise/slope [kHz]

7

2
700

0

FIG.2 (a) Ratio of the magnetically insensitive noise to the slope of the lock-in
ODMR and the slope depending on the deviation frequency. (b) Measured FFTspectrum of sensitivity. The black dotted line indicates 400 pT⁄√Hz.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-β2-06
Hybrid integration of Si3N4 grating structure on diamond NV substrate for
efficient photon extraction
Ryota Katsumi1, 2, Takeshi Hizawa1, Akihiro Kuwahata2, 3, Takayuki Iwasaki 4, Mutsuko Hatano 4,
Fedor Jelezko5, Masaki Sekino2, and Takashi Yatsui1, 2
1

Graduate School of Engineering, Toyohashi University of Technology
Graduate School of Engineering, The University of Tokyo

2

Graduate School of Engineering, Tohoku University

3
4

School of Engineering, Tokyo Institute of Technology
Institute of Quantum Optics, Ulm University

5

katsumi.ryota.ti@tut.jp

Introduction
Nitrogen-vacancy (NV) centers in diamond is a promising candidate for a quantum sensor, especially a sensitive
magnetometer thanks to their excellent spin property1,2. However, their demonstrated magnetic field sensitivity is far beyond
those based on superconducting quantum-interference devices. One of the critical issues is the low extraction efficiency ofthe emitted photons from the diamond NV substrate3. This can be overcome by implementing the nanostructure on diamondincluding gratings, but the fabrication of such structure on diamond is technically difficult.

MethodIn this work, we demonstrate the hybrid integration of grating structure on a diamond NV substrate using transfer printing,which is based on a simple pick-and-place operation4. Figure 1(a) displays the SEM image of the grating based on Si3N4,
which is transparent for the NV emission wavelength of around 700 nm. To pick them up, we employed the air-bridged
structure for the grating. By using the transfer printing [Fig. 1(b)], the Si3N4 grating was integrated on the diamond NV
substrate. Figure 1(c) displays the optical microscope image of the fabricated device. The grating is indeed bonded with the
diamond NV substrate. The detailed design and characterization will be discussed in the presentation.

FIG. 1. (a) SEM image of the fabricated Si3N4 grating. (b) Schematics of the transfer printing-based integration of Si3N4
grating on diamond. (c) Optical microscope image of the fabricated device.
Acknowledgement
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395 and Kakenhi (18H01470, 20H02197,
20H05091, 20K21118).
References
1

J. M. Taylor, et al., Nat. Phys. 4, 810 (2008).

2

A. Kuwahata, et al., Sci Rep 10, 2483 (2020).

3

D. Le Sage, et al., Physical Review B 85, 121202 (2012).

4

R. Katsumi, et al., Optica 5, 691 (2018).

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ2-01
Superconducting nanostrip single-photon detectors with dielectric multilayer
cavities
Fumihiro China1, Shigehito Miki1,2, Satoru Mima1, Masahiro Yabuno1, Shigeyuki Miyajima1 and
Hirotaka Terai11Advanced ICR Research Institute, National Institute of Information and Communications Technology
2

Graduate School of Engineering, Kobe University
f-china@nict.go.jp

Introduction
Superconducting nanostrip single-photon detectors (SNSPDs) have attractive features such as high detection efficiency,
low dark count rate, and low timing jitter, and are promising instruments in various fields, including quantum information
science [1]. The superconducting nanostrip consisting of a thin and narrow meandering line potentially has photon sensitivity
in a wide wavelength range from ultraviolet to mid-infrared, but the optical absorptance of only a single nanostrip layer is as
low as few tens of percent. The SNSPDs integrated with dielectric multilayer (DML) cavities, as shown in FIG. 1, areeffective structures to enhance the optical absorptance of the nanostrips at the target wavelengths. The DMLs are composedof two dielectric materials with different refractive indexes. By optimizing the layer structure such as the number of layers
and film thickness of each layer, the optical properties of SNSPDs can be designed flexibly according to the requirement [2].
In this presentation, we show the development of SNSPDs with DMLs for various wavelength regions.

MethodWe have designed and developed SNSPDs with DMLs using SiO2 and TiO2 for the visible wavelength, SiO2 and Si forthe telecom wavelength, and Ta2O5 and Si for the mid-infrared region, respectively. FIG. 1 shows a schematic of an SNSPD
with a DML composed of SiO2 and TiO2, which is designed for 780 nm wavelength region. First, the layer structure of the
DML was optimized for the target wavelength using a thin film calculation software. Subsequently, we simulated theabsorptance dependence on the polarization state of incident photons by finite-element analysis. As results, the optimized
number of layers and the total thickness of the DML are 17 layers and 2.02 µm, respectively. Since it was also confirmedthat the optical absorptance of the nanostrip depends on the polarization state of the incident photon, SiO film is depositedon the nanostrip to minimize the polarization sensitivity at the wavelength of 780 nm. Then, we fabricated the nanostrip
devices according to the optimized design of SNSPD with the DML and evaluated the wavelength dependence of the system
detection efficiency (DE) using a supercontinuum light source. FIG. 2 shows the wavelength dependence of the opticalabsorptance and measured system DE. The obtained dependence of the system DE well agrees with optical absorptancedependence in the simulations, and we obtained a high system DE of 85% at 780 nm. The developments of SNSPDs forother wavelengths will be talked in the presentation.

Acknowledgment

This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067634, JST CREST Grant Number
JPMJCR1671, and JST Moonshot R&D Grant Number JPMJMS2066.

Reference

R. H. Hadfield, Nat. Photon., 3, 696–705 (2009).
T. Yamashita, K. Waki, S. Miki, R. A. Kirkwood, R. H. Hadfield, H. Terai, Sci rep., 6, 35240 (2016).

1
2

FIG. 1. Schematic of the device structure of an SNSPD
with a DML. The number of layers and total thicknessof the DML are 17 layers and 2.02 µm, respectively.

FIG. 2. Comparison of the simulated opticalabsorptance of the NbTiN nanostrip and the measured
system DEs.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ2-02
Estimation of the quantum efficiency of the up-conversion system based on
injection-locked dual oscillators
Masayuki Hojo1, Shuntaro Tani2, Yohei Kobayashi2, and Koichiro Tanaka1
1

Department of Physics, School of Science, Kyoto University
2

ISSP, The University of Tokyo

hojo.masayuki.33e@st.kyoto-u.ac.jp
Introduction
Spontaneous parametric down-conversion (SPDC) is essential tool for a quantum light source in the infrared region
ranging 2-5 µm for the purpose of material identification, chemical analysis, and gas sensing. However, SPDC process
has a technical limitation of low efficiency and can be detected only by sensitive detectors. Up-conversion detecting
system has been demonstrated to bridge such a gap. So far, existing technique1 has been concentrated into the conversion
efficiency, in which the temporal duration of the light source was highly broad. In this work, we implement the upconversion detector using two Er- and Yb-doped fiber lasers (EDFL and YDFL) with the duration narrower than theconventional one.

MethodFigure 1 illustrates the schematics of the up-conversion system. The EDFL output at 1.56 µm was split into two ports,
which served as the injecting seed and the pump for down frequency generation (DFG) process in PPSLT, respectively.
The repetitions of EDFL and YDFL was synchronized at 57.9 MHz. The YDFL output had the spectral shape narrowed
by Fiber-Bragg-Grating (FBG) and was boosted to 100mW. Similarly, the amplified pulse was divided into two portions,the DFG port and the up-conversion port. In the DFG port, the two pulses at 1.03 and 1.56 μm were spatially combinedwith a wavelength division multiplexer (WDM) and produced a MIR pulse by DFG process. The MIR light source wasthen introduced into PPLN crystal. The pump for the up-conversion was focused into PPLN in the collinear configuration
with the MIR pulse. The SFG signal in the visible region was detected by a sensitive detector.
In our presentation, we will report the result of up-conversion detection and discuss about the system improvement.

Fig. 1 Schematics of the whole system.

Acknowledgement

This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067634.

Reference
1.

Huang, K. et al. Photonics Res. 9, 259 (2021).

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ2-03
Selective measurement of biexciton luminescence by photon correlation
spectroscopy
Hiroya Seki1, Keita Hashimoto2, Jun Ishihara2, Kensuke Miyajima2, Ryosuke Shimizu1
1

Department of Engineering Science, The University of Electro-Communications
2

Department of Applied Physics, Tokyo University of sciences2043006@edu.cc.uec.ac.jp

Introduction
Coincidence measurement performed by two detectors is a common technique to detect photon pairs in quantum opticalexperiments [1] and allows us to extract two-photon events from the input state of light [2]. This technique has been used indemonstrating fundamental concepts of quantum mechanics, quantum information protocols, and quantum imaging. On theother hand, we also expect the application of coincidence measurement to spectroscopy as a new development of quantum
technology. Combining the coincidence counting with frequency-resolved measurement could bring us a new approach tospectroscopy in a quantum manner. Hereafter we refer to it as photon correlation spectroscopy (PCS) [3]. The Photonnumber-resolving ability of PCS may provide a powerful tool to analyze a complex quantum system in condensed matter.
Here we present a proof-of-concept experiment of PCS with biexciton luminescence.

MethodBiexciton is generated via a two-photon resonant excitation by the second harmonic of a mode-locked Ti: sapphire laser, andthen decays into two polaritons; a higher energy polariton (HEP) and a lower energy polariton (LEP). After propagating in
the crystal, the polaritons are converted into photons at the crystal surface. In this process, the sum of the two-photon energy
should be the same as biexciton energy due to the phase-matching condition. We employed a femtosecond laser with the
bandwidth of 4.4 nm, corresponding energy width of 9.0 eV, to clarify the photon-number-resolving ability. In this situation,
the spectrum of Rayleigh scattering light of the laser overlaps that of biexciton luminescence. Therefore, it is difficult todistinguish the biexciton luminescence from the laser spectrum. In contrast, PCS enables us to observe HEP and LEP due tothe photon-number-resolving ability.
In order to characterize two-photon spectral
distributions, joint spectral intensity (JSI) plotted in a
two-dimensional space has been employed in thequantum optics field [4]. The JSI represents the twophoton probability distribution as a function of theenergy of the constituent photon. Experimentally, werecorded the coincidence counting values by scanning
the transmission frequency of two monochromaters for
the JSI measurement.
Figure 1 shows the measured JSI of biexciton
luminescence. We can see a single peak distribution
caused by coincidence counts of HEP and LEP. We
estimated the spectral width of HEP (LEP) as 0.94 (1.2)
meV from the projection of the JSI onto the vertical(horizontal) axis, which is narrower than the bandwidthof the laser. This result implies a successful
demonstration of PCS.
FIG. 1. JSI of biexciton luminescence.

Acknowledgment

This work was supported by MEXT Q-LEAP Grant Number JPMXS0118069242.

Reference

C. K. Hong, Z. Y. Ou, and L. Mandel, Phys. Rev. Lett., 59, 2044-2046 (1987).
H. Seki, K. Miyajima, R. Shimizu, arXiv:2109.03715 (2021)
3
C. M. Muñoz, and F. Schlawin, Phys. Rev. Lett., 124, 203601 (2020).
4
P. G. Evans, R. S. Bennink, W. P. Grice, and T. S. Humble, Phys. Rev. Lett., 105, 25361 (2010).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ2-04
Towards Optical Manipulation of Gold-Nanoparticles for Efficient Single
Photon Sources
Rui Sun1, Yining Xuan1, Soyoung Baek1, and Keiichi Edamatsu1
1Research Institute of Electrical Communication, Tohoku University
sun@quantum.riec.tohoku.ac.jp

Quantum dot is a promising candidate for constructing a single photon source because of its broad and continuous
excitation spectrum, adjustable wavelength, high photochemical stability, and long fluorescence lifetime1. Our research
focuses on the single photon source based on quantum-dot-gold-nanoparticle coupled system on optical nanofiber2.
Combining with the Purcell effect3, the rise time of the second order intensity correlation function for quantum dot can beenhanced. However, the position of gold-nanosphere on nanofiber is entirely random, which makes the quantitative study ofsingle-photon emission rate difficult. We propose a non-contact method to control the position of a gold-nanoparticle on thenanofiber making use of an optical tweezer. We calculate the optical responses and heating effects of a gold-nanoparticle
trapped in optical tweezer to define the optimal wavelength and laser power for the experiment.
The optical response of a gold-nanoparticle submerged in water and trapped in an optical tweezer is calculated based on
Mie theory. Figure 1 is the scattering and absorption efficiencies of a gold-nanoparticle in an optical tweezer. The red andblue curves are the scattering (Qsca)and absorption (Qabs)factors, respectively. The abscissa is the size parameter (𝑘𝑘𝑘𝑘)of thegold-nanoparticle; 𝑘𝑘 is the wave number of the light and 𝑘𝑘 is the radius of gold-nanosphere. Here, the gold-nanoparticle
size ranges from 0 to 200 nm. For the same particle size, the longer the optical wavelength is, the weaker the effect ofabsorption and scattering.
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067581.

FIG. 1. Scattering and absorbing efficiencies of gold-nanoparticle trapped in optical tweezer.

References
O. Gazzano and G. Solomon, J. Opt. Soc. Am. B, 33, C160-C175 (2016).
M. Sadgrove, M. Sugawara, Y. Mitsumori and K. Edamatsu, Sci Rep, 7, 17085 (2017).
3
Q.Gu, and Y. Fainman, Semiconductor Nanolasers, (pp. 65-90) (2017).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ2-05
Single photon emission from a quantum-dot-gold-nanostar coupled system on an
optical nanofiber
Yining Xuan1, Masakazu Sugawara1, Rui Sun1, Soyoung Baek1, Keiichi Edamatsu1, and Mark
Sadgrove2
1

Research Institute of Electrical Communication, Tohoku University

2

Department of Physics, Faculty of Science, Tokyo University of Sciencexuan@quantum.riec.tohoku.ac.jp

Single-photon emitters play an important role in many leading quantum technologies such as quantum communications
and quantum cryptography. Therefore, coupling them to existing fiber network can be a promising candidate for the various
applications in quantum network. As a carrier of photon transportation, optical nanofiber has the advantage of ultra-low loss,
low cost and high coupling efficiency [1]. Since the nanofiber has a diameter of hundreds of nanometers, photons emitted
from single photon emitters can be coupled into nanofiber through the evanescent field directly. Therefore, single-photon
source’s effective incorporation into nanofibers shows great potential in the construction of fiber-based quantum information
network. In 2012, Yalla et al. demonstrated the coupling of single photons from quantum dots into the nanofiber [2]. After
that, Liebermeister et al. succeed in coupling single photons from color centers in a diamond into the nanofiber [3].
Nevertheless, how much we can improve the coupling between the single-photon emitters and the nanofiber is still an open
question that needs to be addressed. In this research, in order to achieve Purcell-enhanced single-photon emission from aquantum dot (QD, we place gold nanoparticles, especially gold nanostars (GNS, in the vicinity of the quantum dot locatedon the surface of an optical nanofiber. By measuring the rise time of the second order correlation function 𝑔(2) (𝜏) for boththe GNS-QD system and the sole QD system, Purcell-enhancement can be verified.
We fabricate a nanofiber with the diameter of 474 nm by heating-stretch method [4][5], and place a GNS and a QD on thesurface of a nanofiber. Figure 1 shows scanning electron microscope (SEM image of GNS-QD coupled system. By scanninga laser beam spot along the nanofiber axis and measuring the photoluminescence (PL signal from the QD and the scattered
light from the GNS, we confirm the GNS and the QD is located within 1.5 𝜇m interval. Next, we measure second ordercorrelation function 𝑔(2) (𝜏) for both the GNS-QD system and the sole QD system on the same nanofiber. See Figure 2. The
obtained 𝑔(2) (0) for the GNS-QD and Sole QD was less than 0.5, a signature of anti-bunched single photons. The rise timeof 𝑔(2) (𝜏) for the GNS-QD and the SQD are obtained to be 167 ns and 107 ns, respectively; the GNS-QD exhibited ∼36 %reduction of the rise time in comparison to the SQD. Although it is likely to originate from Purcell enhancement, moredetailed and complete measurement and analysis are necessary to conclude.
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067581.

FIG. 1. SEM image of GNS-QD coupled system.

Reference

FIG. 2. 𝑔(2) (𝜏) measurement of GNS-QD coupledsystem and sole QD system, respectively.

M. Sadgrove, M. Sugawara, Y. Mitsumori, and K. Edamatsu, Sci. Rep., 7, 17085 (2017).
R. Yalla, K. Nayak, and K. Hakuta, Opt. Express, Vol. 20, Issue 3, 2932 (2012).
3
L. Liebermeister et al., Appl. Phys. Lett., 104, 031101 (2014).
4
M. Sugawara, Y. Mitsumori, K. Edamatsu, and M. Sadgrove, Opt. Express, 28, 18938 (2020).
5
M. Sadgrove, T. Yoshino, M. Sugawara, Y. Mitsumori, and K. Edamatsu, Phys. Rev. Applied, 16, 044034 (2021).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)

SE-03A-γ2-06
Focusing constraints on coupling efficiency of collinear type-I degenerated
SPDC photon pairs into a single-mode fiber
Nicolas Schwaller1,2, Geobae Park1, Ryo Okamoto1,3, and Shigeki Takeuchi1
1

Department of Electronic Science and Engineering, Kyoto University

2

Institute of Physics, Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne, Switzerland
3

Japan Science and Technology Agency, PRESTO
schwaller.nicolas.52z@st.kyoto-u.ac.jp

Introduction
Entangled photon pairs represent an essential resource for various quantum technologies, such as quantum key distribution,
quantum computing or quantum imaging. A common process to produce correlated pairs is spontaneous parametricdownconversion (SPDC) of pump photons into pairs of entangled photons which are then coupled into a single-mode (SM)fiber. For most applications, it is desirable to maximize the coupling efficiency of the entangled pairs into the SM fiber, as
well as the rate of pairs that can be collected. Systematic studies about the maximization of these quantities have been carriedout for specific parameters of SPDC, e.g. using type-II phase-matching condition [1]. However, despite advances ontheoretical modelling [2,3], other SPDC configurations still lack experimental evidence to confirm the dependence of thecoupling efficiency on the main parameters of the setup. This study focuses on collinear degenerated co-polarized SPDC
photon pairs. They are relevant for various applications such as single mode squeezed states for gaussian boson sampling,
and non-linear interferometers.

MethodWe investigate the dependence of the correlated-mode coupling efficiency ηc on pump and collection beam waists bycontinuously varying their size thanks to two beam expanders (FIG. 1). We generate type-I SPDC by pumping a bulk beta
barium borate (BBO) crystal of L= 3 mm length with a continuous wave (CW) 404 nm laser. We measure the coupling
efficiency using coincident detections from single photon counting modules (SPCMs), and study the impact of different
focusing conditions of the pump and collection beam. The estimated coupling efficiency was obtained by considering thelosses of the optics and the experimentally determined quantum efficiencies of the SPCMs. The observed ηc reached up to98%.

FIG. 1: Experimental setup enabling to change the focus ofpump and collection beam in the crystal.
This work is supported in part by JST CREST Grant Number JPMJCR1674, Japan, MEXT Quantum
Leap Flagship Program (MEXT Q-LEAP) Grant Number JP-MXS0118067634, JST-PRESTO(JPMJPR15P4), and KAHENHI Grants-in-Aid No. 21H04444.

Reference

P. Ben Dixon et al., Phys. Rev. A, 90(4), 1-9 (2014).
R. S. Bennink, R. S., Phys. Rev. A, 81(5), 1–10 (2010).
3
H. E. Guilbert et al., IEEE Journal of Selected Topics in Quantum Electronics, 21(3), 215-224 (2015).
1
2

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)SE-04-01

SE-04-01

Quantum sensing enabled by spin qubits
in diamondFedor Jelezko
Institute of Quantum Optics, Ulm University

Abstract
Single nitrogen vacancy (NV) color centers in diamond currently have

suﬃcient sensitivity for detecting single external nuclear spins and resolve
their position within a few angstroms. The ability to bring the sensor close
to biomolecules by implantation of single NV centers and attachment ofproteins to the surface of diamond enabled the ﬁrst proof of principle

demonstration of proteins labeled by paramagnetic markers and label-freedetection of the signal from a single protein. Single-molecule nuclear

magnetic resonance (NMR) experiments open the way towards unravelingdynamics and structure of single biomolecules. However, for that purpose,
NV magnetometers must reach performance comparable to that ofconventional solution state NMR. We will discuss new techniques allowing
to combine high spectral resolution and sensitivity in nanoscale NMR. The
ability to sense nuclear spins by NV centers also enables the transfer ofpolarization from optically polarized spins of NV centers to external nuclear
spins. Such diamond based techniques for dynamic nuclear spinpolarization are very promising for the enhancement of sensitivity of
conventional MRI imaging.

Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)SE-04-02

SE-04-02

Programmable quantum simulators basedon spins in diamond
Tim Taminiau
QuTech and Kavli Institute of Nanoscience, Delft University of Technology, the Netherlands

Abstract
Spins associated to optically active defects in diamond provide a versatile

platform for quantum science and technology. In this talk, I will discuss ourrecent advances in realizing programmable quantum simulators based on

individually controllable carbon-�� nuclear spins in diamond. I will present

how one can use a single nitrogen-vacancy (NV) centre to sense, characterizeand control a large number of spins in its environment [�,�,�]. By controllingthe interactions between the spins it becomes possible to create a variety of
many-body Hamiltonians with tunable parameters. As an example, I will

discuss our investigation of a discrete-time crystal stabilized by many-body
localization, a new out-of-equilibrium phase of matter [�].
[�] M. H. Abobeih et al., Nature ���, ��� (����)[�] C. E. Bradley et al., Phys. Rev. X. �, ������ (����)[�] M. J. Degen et al., Nature Commun. ��, ����, ���� (����)[�] J. Randall et al., arXiv:����.����� (����)Proc. 4th IFQMS (The 4th International Forum on Quantum Metrology and Sensing)SE-04-03

SE-04-03

Development and optimisation of diamondfor quantum technologies
Matthew Markham
Element Six

Abstract
Quantum technologies is attracting signiﬁcant investment due to the rangeof potential applications, but behind any new technology are the enablingmaterials. Diamond is one such material and ensembles ofnegatively-charged nitrogen-vacancy (NV-) centres constitutes a promising
platform for sensing applications utilizing the quantum properties of thisdefect. However, the sensitivity of present NV-ensemble devices and theneed for diamond material with reproducible properties has the potential tohinder progress toward many envisioned commercial-scale applications.
The work covered in this presentation will address the material-related

challenges associated with the development of diamond materials withreproducible properties for diamond quantum technologies.