th
5 IFQMSThe 5th International Forumon Quantum Metrology and Sensing

PROCEEDINGS
Short Presentation Session for Young Scientists
Part 1: SE-03A

29 November, 2022
Online Conference (Zoom)
Joint Program Session with Quantum Innovation 2022

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

Quantum Sensing Track : Short Presentation Session for Young Scientists
SE-03A. Short Presentations 6HVVLRQIRU<RXQJ6FLHQWLVWV on SE-02, 04, 06, 07 Topics [5th IFQMS]*Note: Presentation order may change within the same group.
All the times in the program are Japan Standard time (GMT+9)
Nov 29 (Tue.)
13:10-14:30

13:10-14:30

Session / Presentation

Mentor / Presenter

ID

SE-03A-Į1
Chair

Ryota Katsumi

787

Co-chairNaota Sekiguchi

Tokyo Tech

Lock-In detected ramsey magnetometry with a bulk ensemble ofdiamond NV centers for high-sensitivity DC-field measurement

Sena Tsuchiya

Tokyo Tech

SE-03A-Į1-01

Towards measurement of magnetic field generated by the brain of aliving rat using N-V centers in diamond

Naota Sekiguchi

Tokyo Tech

SE-03A-Į1-02

Identification of current multipole sources frommagnetoencephalography data

Motofumi Fushimi

UTokyoSE-03A-Į1-03

Optimization of simultaneous measurement of magnetic field andtemperature measurement by silicon vacancy quantum sensor using
simultaneous resonanceTomoaki Tanaka

QST

SE-03A-Į1-04

Spin-dependent photocarrier generation dynamics in electricallydetected NV-based quantum sensor

Hiroki Morishita

Kyoto U

SE-03A-Į1-05

Towards nanoscale zero- to ultralow-field NMR

Till Lenz

JGU

SE-03A-Į1-06

Dipole-dipole interaction between NV- centers

Chikara Shinei

NIMS

SE-03A-Į1-07

Chair

Yuta Kainuma

Tokyo Tech

Co-chairNaoya Morioka

Kyoto U

Extension of dephasing time of ensemble NV centers with acontinuous-excitation protocol

Ikuya Fujisaki

Tokyo Tech

SE-03A-ȕ1-01

Wide temperature operation of diamond quantum sensor for electricvehicle battery monitoring

Keisuke Kubota

Tokyo Tech

SE-03A-ȕ1-02

A development of wearable magnetic shield for MEG

Soichiro Shido

UTokyoSE-03A-ȕ1-03

Attempts to generate entanglement state between dipolar coupled NV
centers created by molecular implantation

Kosuke Kimura

QST

SE-03A-ȕ1-04

Charge stability of shallow single NV centers in p-type diamond

Taisuke Kageura

A,67

SE-03A-ȕ1-05

Room-temperature electrical detection of nuclear spins in siliconcarbideNaoya Morioka

Kyoto U

SE-03A-ȕ1-06

JGU

SE-03A-ȕ1-07

SE-03A-ȕ1(Near) zero-field cross-relaxation features for ensembles of NV centers
2PNDU'KXQJHOin diamond
13:10-14:30

Affiliation

SE-03A-Ȗ1
Chair

Tomoya Sato

Tokyo Tech

Co-chair

Fumihiro China

NICT

Evaluation of a superconducting nanowire single photon detector for
mid-infrared wavelengths

Satoru Mima

NICT

SE-03A-Ȗ1-01*

Efficient superconducting nanostrip single-photon detectors for 2 m
wavelength

Fumihiro China

NICT

SE-03A-Ȗ1-02

Effect of pump laser linewidth on nonlinear quantum interferometricfringes

Jasleen Kaur

Kyoto U

SE-03A-Ȗ1-03

Highly efficient and ultra-broadband photon pair source using chirped
quasiphase matching slab waveguide matching slab waveguide

Bo CaoKyoto U

SE-03A-Ȗ1-04

Optical trapping and movement control of gold nanoparticles on an
optical nanofiber

Rui SunTohoku U

SE-03A-Ȗ1-05

Electromagnetic-field analysis of the plasmon-enhanced single photon
Yining Xuanemitters on an optical nanofiber

Tohoku U

SE-03A-Ȗ1-06

Ultrafast measurement of biphoton wave packets using optical Kerr
gating

UEC

SE-03A-Ȗ1-0

Takahisa Kuwana

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)Nov 29 (Tue.)

Session / Presentation

Mentor / Presenter

Affiliation

ID

14:50-16:10 SE-03A-Į2
Chair

Naota Sekiguchi

Tokyo Tech

Co-chairRyota Katsumi

787

Growth of thick CVD diamond films containing aligned nitrogenvacancy centers for high-sensitivity quantum sensors

Takeyuki Tsuji

Tokyo Tech

SE-03A-Į2-01

Enhancement of fluorescence collection efficiency using angle-shaped
Yuta Shigenobu
diamonds for compact magnetic sensor

Tokyo Tech

SE-03A-Į2-02

Transfer-printing-based integration of SiN grating structure on diamond
Ryota Katsumi
toward highly sensitive quantum sensor

TUT

SE-03A-Į2-03

NVC-SPM system to inspect electric devices

Teruo Kohashi

HitachiSE-03A-Į2-04*

Enhancing sensitivity with entanglement in coupled nitrogen vacancy
centres

Ernst David Herbschleb

Kyoto U

SE-03A-Į2-05

Frequency-bin generation of entangled photons via quantum opticalsynthesis

Takeru Naito

UEC

SE-03A-Į2-06

Development of highly sensitive gravimeter based on atominterferometry using hybrid system for field applications

Takeshi Hojo

UEC

SE-03A-Į2-0

Chair

Naoya Morioka

Kyoto U

Co-chairYuta Kainuma

Tokyo Tech

Implementation of double quantum magnetometry to continuously
excited ramsey method

Yuta Araki

Tokyo Tech

SE-03A-ȕ2-01

Development of highly sensitive compact quantum sensor with NV
center in 12C-enriched CVD diamond for bio-medical and industrial
application

Yuta Kainuma

Tokyo Tech

SE-03A-ȕ2-02

Development of a nonmagnetic helical sensor drive multipoint
measuring mechanism for magnetocardiography in animals

Wenyu Shang

UTokyoSE-03A-ȕ2-03

Ensemble NV- center in diamond for quantum sensing created by highShuya Ishii
fluence electron beam irradiation

QST

SE-03A-ȕ2-04

Synthesis of n-type diamond using tert-butyl phosphine for highsensitivity of the NV sensor

Riku Kawase

Kyoto U

SE-03A-ȕ2-05

Decoherence phenomena in nitrogen-vacancy diamond

Aulden Jones*HRUJLD7HFK

SE-03A-ȕ2-06

Chair

Fumihiro China

NICT

Co-chairTomoya Sato

Tokyo Tech

Improvement in the long-term stability of the interferometer gyroscopeusing slow and continuous atomic beams

Naoki Nishimura

Tokyo Tech

SE-03A-Ȗ2-01

Bragg interferometer using slow and continuous atomic beam with subTomoya Sato
recoil transverse momentum widthTokyo Tech

SE-03A-Ȗ2-02*

Development of a cryogenic suspension system for TOrsion-Bar
Antennae (TOBA)

Ching Pin Ooi

UTokyoSE-03A-Ȗ2-03

Torsion-bar antenna for early earthquake alert

Yuka Oshima

UTokyoSE-03A-Ȗ2-04

Optimized Design of Quasi-phase-matched crystal for Spectrally-PureWu-Hao Cai
StateࠉGeneration at MIR Wavelengths Using Metaheuristic Algorithm

Tohoku U

SE-03A-Ȗ2-05

Experimental generalized measurement of qubits using a quantum
computer

Tohoku U

SE-03A-Ȗ2-06

14:50-16:10 SE-03A-ȕ2

14:50-16:10 SE-03A-Ȗ2

Tingrui Dong

Note: This program was created for fostering young VFLHQWLVWV. Presentations with asterisks (*) are excluded from awarding.

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į1-01

Lock-In Detected Ramsey Magnetometry with a Bulk Ensemble of Diamond
NV Centers for High-Sensitivity DC-Field Measurement
Sena Tsuchiya1, Daisuke Nishitani1, Yusei Aoki1, Takeharu Sekiguchi1, Takayuki Shibata2,
Takayuki Iwasaki1, and Mutsuko Hatano1,3
1

Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
2
DENSO CORPORATION
3
National Institutes for Quantum Science and Technology
tsuchiya.s.ag@m.titech.ac.jp

Introduction
Nitrogen-vacancy (NV) centers in diamond have attracted much attention as high sensitivity quantum magnetic sensors
that can be operated at room temperature. Our group has demonstrated magnetocardiography of living rats by combining
continuous-wave optically detected magnetic resonance (CW-ODMR) with lock-in (LI) detection1. However, further
improvement of DC-field sensitivity is necessary to detect magnetoencephalography signals. Double-quantum (DQ) Ramsey
magnetometry2 based on pulsed ODMR scheme is expected to achieve much higher sensitivity by improving both spindephasing time T2* and contrast2. Combination with LI detection of fluorescence intensity should reduce noise, remove signal
offset, and allow real-time measurement. In this study, we implemented LI detection under pulsed optical excitation anddetection with DQ Ramsey sequences to demonstrate the sensitivity improvement.
Methods
The diamond sample used was grown by HPHT with 12C-enriched source in NIMS, and the NV centers were created byelectron beam irradiation (1ൈ1017 cm-2) and annealing in QST. The concentrations of NV and P1 (substitutional nitrogen)centers were 0.05 ppm and 1.1 ppm. Fig. 1(a) shows our experimental setup. Pulsed optical excitation at 532 nm and theDQ-4-Ramsey sequence2 with resonant dual-frequency microwave (MW) were applied to a bulk ensemble of NV centers indiamond. The illumination volume was roughly (60ൈ160ൈ470) ȝm3. The fluorescence signal modulated by the DQ-4Ramsey sequence was detected and demodulated by a LI amplifier. The MW pulse width (0.22 s) for this sequence wascalibrated from the DQ-Rabi oscillation measurements.
Results and discussion
Fig. 1(b) shows the LI detected DQ-4-Ramsey fringes with microwave frequencies tuned to the central resonance of the14
N hyperfine triplet. The inset FFT spectrum shows clearly this triplet structure with the splitting doubled by the DQ
sequence. Fig. 1(c) shows MW frequency dependence of the Ramsey signal at a fixed free-precession time Ĳ using theSQ(single quantum)-2-Ramsey2 and DQ-4-Ramsey sequences. The DQ-4-Ramsey signal exhibits a 15% steeper slope thanthe SQ-2-Ramsey signal. The magnetic field sensitivity can be estimated from repeated measurements of the Ramsey signal
with a fixed ǻȞ at the steepest slope. We will discuss the sensitivity improvement factors such as lock-in detection forenhancing signal-to-noise ratio and DQ-4-Ramsey sequence for the Ramsey slope improvement.

(a)

(b)

PXIe slots
AWG

PC

(c)

IQ input

MW SG

MW SG

MW Amp

MW AmpMW antenna

Laser

MW

to PC
AOM

Lock-in Amp

diamond

PhotodiodeFIG. 1. (a) Experimental set up for LI detected Ramsey measurements. (b) DQ-4-Ramsey signal by LI detection at frequency detuning of ǻȞ = 0.0
MHz, in the time domain and frequency domain (inset). (c) Detuning sweep of the LI detected DQ-4-Ramsey (Ĳ = 0.46 ȝs) and SQ-2-Ramsey (Ĳ =0.40 ȝs). The dashed line represents the steepest slope of the DQ-4-Ramsey signal.

Acknowledgement
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395. We thank Dr. M. Miyakawa, Dr. T.
Taniguchi (NIMS), Dr. S. Ishii, S. Saiki, and S. Onoda (QST) for providing the diamond sample.
Reference
1
K. Arai et al., Commun. Phys. 5. 200 (2022). 2C. A. Hart et al., Phys. Rev. Appl. 15, 044020 (2021).

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į1-02
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Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į1-03

Identification of current multipole sources frommagnetoencephalography data
Motofumi Fushimi1, Mutsuko Hatano2, Takaaki Nara3, and Masaki Sekino1
1

Department of Bioengineering, Graduate School of Engineering, The University of Tokyo
Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
3
Department of Information Physics and Computing, Graduate School of Information Science and Technology,
The University of Tokyo
motofumi-fushimi@g.ecc.u-tokyo.ac.jp
2

Introduction
In magnetoencephalography (MEG) source identification, current sources are typically modeled as equivalent current dipoles(ECDs). However, actual neural sources have non-negligible spatial pattern, which can be accounted for using equivalentcurrent multipoles (ECMs). We extend the previously proposed algebraic method for the multipole source identification in
the two-dimensional (2D) case [1] to the three-dimensional (3D) case to enhance applicability of the framework to therealistic MEG problem. This can also be seen as an extension of the 3D dipole and dipole-quadrupole identification method[2] to general-order multipoles.


Methods
By adopting the concentric sphere head model, the radial component of the magnetic field is represented by the current
source according to the Biot-Savart law as shown in Fig. 1. The multipole expansion of the equation relates the unknown
multipole source parameters (location and moment) to the MEG data [3]. We derived an algebraic equation for multipole
parameters, the detail of which will be shown in the presentation. We validated the proposed method by numericalsimulations with two distinct current quadrupoles and octupoles.


FIG. 1. Problem formulation of the MEG current source identification in the present study.

Results and Discussion
The proposed method could stably estimate both the two quadrupoles and octupoles, which has not been achieved in previous
methods, validating the efficacy of the method. In contrast, the results of the ECD model had huge errors because the ECD
model erroneously tries to explain MEG data resulting from multipoles by dipoles. The resulting figures will also bepresented in the conference.


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

Reference
1

T. Nara et al., Phys. Med. Biol., 52(13), 3859-3879 (2007).
T. Nara et al., Math. Probl. Eng., 2013, 413980 (2014).
3
G. Nolte et al., Biophys. J., 73(3), 1253-1262 (1997).

2

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į1-04

Optimization of simultaneous measurement of magnetic field and temperature
measurement by silicon vacancy quantum sensor using simultaneous resonanceTomoaki Tanaka1, Yuichi Yamazaki1, Kazutoshi Kojima2, and Takeshi Ohshima112National Institutes for Quantum Science and Technology
National Institute of Advanced Industrial Science and Technology
tanaka.tomoaki@qst.go.jp

Background and Purpose
Silicon vacancies (VSi) in silicon carbide (SiC) have attracted great attention because we can measure magnetic field andtemperature in some devices by fabricating VSi in the devices1,2. Simultaneous measurement of magnetic field andtemperature using SiC-VSi quantum sensor requires simultaneous Optically Detected Magnetic Resonance (ODMR)
measurement of the ground and excited states. However, the ODMR contrast (= sensitivity) of the excited state is about oneorder of magnitude smaller than that of the ground state. So, the temperature measurement is time-consuming. To solve thisproblem, we have proposed and demonstrated a new temperature measurement method, Simultaneous Resonance (SR)ODMR, which based on the modulation of the ODMR contrast of the ground state by simultaneous resonance of the groundand excited states3. This method converts part of the contrast of the ground state into that of the excited state. It is necessary
to optimize the RF power ratio which is related to the contrast ratio between the ground and excited states to minimize themeasurement time in magnetic field and temperature (SR) simultaneous measurement. Therefore, the purpose of our study
is to optimize the power ratio of the RF using the simultaneous measurement by SR ODMR.
Methods and Results
VSi dots were fabricated on p-type 4H-SiC epitaxial thin film (5.6 μm) using a particle beam writing (ion species: He,energy: 0.5 MeV, irradiation dose: 3×105 /dots). The size and depth of the dots are 5×5 μm2 and ~1 μm, respectively. Threesignal generators were used for the measurements, one fixed at the resonance frequency of the ground state (70 MHz) for
SR, and the others swept near those of the ground and excited states (20-170, 300-600 MHz) for the ground state and SRODMR measurements, respectively.
Figure 1 shows the spectra of ground and SR excited states by ODMR simultaneous measurements. Signal intensities
indicated by red and blue arrows are observed. The former is a resonance of the ground state, and the latter is that of theexcited states. We can find that another dip indicated by green arrow around 500 MHz exists. The sweep condition indicatesthat this frequency corresponds to 70 MHz of the ground state measurement. This suggests that the resonance of the groundstate occurs in both the ground state and SR ODMR measurements. As a result of their competition, the dip appears at aroundthe 500 MHz on the SR ODMR side. We measured the changing of ODMR contrast of the ground and excited states when
we change the RF power of signal generators. The signal intensity was almost the same at the RF power ratio of 1:9 for SR
and ground state ODMR. At this condition, the contrast of SR is more than four times that of traditional excited statemeasurement. This suggests that we achieved faster measurement than conventional simultaneous ground and excited states
measurement.









FIG. 1. Simultaneous ODMR measurement of ground and SR excited states (GS and ES) spectra.

Acknowledgement
This work was supported by MEXT Q-LEAP Grant Number JPMXS118067395, ATLA Grant number JPJ004596, and
KAKENHI Grant Number 20H00355, 21H04553.

Reference1

M. Niethammer et al., Phys. Rev. Appl. 6, 034001 (2016).
T. M. Hoang et al., Appl. Phys. Lett. 118, 044001 (2021).
3
Y. Yamazaki et al., The 69th JSAP Spring Meeting, 25a-E301 (2022).
2

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į1-05

Spin-Dependent Photocarrier Generation Dynamics in Electrically Detected
NV-Based Quantum Sensor
Hiroki Morishita,1,2 Naoya Morioka,1,2 Tetsuri Nishikawa,1,3 Hajime Yao,1,3Shinobu Onoda,4 Hiroshi Abe,4 Takeshi Ohshima,4 and Norikazu Mizuochi1,21Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
Center for Spintronics Research Network, Institute for Chemical Research, Kyoto University, Gokasho, Uji,
Kyoto 611-0011, Japan.
3
Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-Ku, Kyoto,
Kyoto, 615-8510, Japan.
4
National Institutes for Quantum Science and Technology, Takasaki, Gunma, 370-1292, Japan.
h-mori@scl.kyoto-u.ac.jp
2

A nitrogen-vacancy (NV) center in diamond is a promising candidate for room-temperature quantum sensors thanks to its
long electron spin coherence in ambient conditions [1]. In previous demonstrations, the NV electron spin was detected
optically, but another method called photoelectrically detected magnetic resonance (PDMR) is attracting attention. The
PDMR technique can read out NV electron spin [2-6] and coupled nuclear spins [7,8]. The electrical detection technique isadvantageous for developing and integrating quantum sensors and other quantum devices [7]. However, the mechanism forthe electrical detection of NV spins is not fully understood. In this study, we perform the pulsed PDMR measurements using
the ensemble of NV centers (concentration of ~ 1.4 ×1017 cm-3) created by 2 MeV electron irradiation with a fluence of 1×1017 cmí2 at 745 °C, followed by annealing at 1000 °C for 1 h in an argon atmosphere. We observe positive contrast in
PDMR (Fig. 1(a)) even though a negative PDMR contrast is usually observed. To discuss the sign of the PDMR contrast,
we numerically analyze the dynamics of photocarrier generation by NV centers using a seven-level rate model. We foundthat the sign of the PDMR contrast depends on the difference in the photocurrent generated from the excited states and themetastable state of NV centers.
Furthermore, we demonstrate AC magnetic field sensing using spin coherence with the PDMR technique. AC magnetic
field measurement with the PDMR technique is still challenging because the noise from a fluctuating magnetic environmentis greater than the measured signal. Using a phase-cycling-based noise-canceling technique to suppress the noise, we
demonstrate AC magnetic field sensing with the PDMR technique (Fig. 1(b)). We observe electrically detected AC magnetic
field sensing with a sensitivity of ~29 nT/ξHz. In this talk, we will discuss the mechanism of the NV center's electricaldetection and the sensitivity of the electrically detected AC magnetic field sensing.


FIG.1 (a) Pulsed PDMR spectrum. (b) AC magnetic field sensing with the PDMR technique

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

Reference1

E. D. Herbschleb et al., Nat. Commun. 10, 3766 (2019). 2 E. Bourgeois et al., Nat. Commun. 6, 8577 (2015).
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 T. Murooka et al., App. Phys. Lett. 118, 253502 (2021).
7
H. Morishita et al., Sci. Rep. 10, 792 (2020). 8 M. Gulka et al., Nat. Commun, 12, 4421 (2021).
3

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į1-06

Towards nanoscale zero- to ultralow-field NMR
1,2*

Till Lenz , Omkar Dhungel1,2, Arne Wickenbrock1,2, Lykourgos Bougas1, John W. Blanchard2,3,
Gopalakrishnan Balasubramanian4, Anjusha Vijayakumar Sreeja5, Fedor Jelezko5, and Dmitry
Budker1,2,6
1

Johannes Gutenberg-Universität Mainz, 55128 Mainz, Germany
2
Helmholtz Institut Mainz, 55099 Mainz, Germany
3
Quantum Technology Center, University of Maryland, College Park, Maryland 20742, USA
4
Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Bautzner Landstr. 400, 01328 Dresden
5Institute for Quantum Optics, Ulm University, Albert-Einstein-Allee 11,89081 Ulm, Germany
6
Department of Physics, University of California, Berkeley, California 94720-7300, USA*tilllenz@uni-mainz.de, presenter
Abstract: Nuclear magnetic resonance (NMR) is a widely used tool in chemical analysis as well medical
diagnostics. While medical diagnostics is the most prominent branch of the NMR subfield magnetic
resonance imaging (MRI), chemical analysis is usually performed without imaging via NMR
spectroscopy. While we will focus on NMR spectroscopy, both techniques require strong expensive
magnets and are limited to sample sizes larger than the micron scale. To overcome these requirements
and limitations we propose nanoscale zero- to ultralow-field (ZULF) NMR [1,2]. To achieve the goal ofnanoscale ZULF NMR, we, together with our collaborators, demonstrated a technique formagnetometry with NV centers in the ZULF regime [3,4] (i.e. Zeeman interaction weaker than jcouplings) Moreover, we are exploring different potential samples and have identified some promising
candidates.

Reference[1] J. W. Blanchard, D. Budker, and Andreas Trabesinger, Lower than low: Perspectives on zero-to
ultralow-field nuclear magnetic resonance, Journal of Magnetic Resonance, 323, 106886 (2021) 1[2] D. Budker, Extreme nuclear magnetic resonance: Zero field, single spins, dark matter. . . , Journalof Magnetic Resonance, 306, Pages 66-68 (2019)[3] H. Zheng, J. Xu, G. Z. Iwata, T. Lenz, J. Michl, B. Yavkin, K. Nakamura, H. Sumiya, T. Ohshima,
J. Isoya, J. Wrachtrup, A. Wickenbrock, and D. Budker, Zero-Field Magnetometry Based on NitrogenVacancy Ensembles in Diamond, Phys. Rev. Applied, 11, 064068 (2019)[4] T. Lenz, A. Wickenbrock, F. Jelezko, G. Balasubramanian, and D. Budker, Magnetic sensing atzero field with a single nitrogen-vacancy center, Quantum Science and Technology, 6, 3 (2021)

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į1-07

Dipole-dipole interaction between NV- centers
Chikara Shinei1, Yuta Masuyama2, Masashi Miyakawa1, Hiroshi Abe2, Shuya Ishii2, Seiichi Saiki2,
Shinobu Onoda2, Takashi Taniguchi1, Takeshi Ohshima2 and Tokuyuki Teraji1
12

National Institute for Materials Science

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

Introduction
Negatively charged nitrogen vacancy center (NV-) ensemble with S=1 is a promising color center for highly sensitive
magnetometers.1 Dipole-dipole interaction (DDI) between the NV- center and paramagnetic defect is one of decoherence
mechanisms. In recent study, some studies showed the interaction between the NV- center and neutral substitutional nitrogen(Ns0) with S=1/2. The strength of DDI is usually expressed as the multiple of DDI coefficient and concentration ofparamagnetic defect. DDI coefficient of Ns0: ‫୒ܦ‬బ౩ is reported as 11.2 ms-1 ppm-1.1 For increasing the NV sensing sensitivity,
increasing of [NV-] is needed. Strength of dipole-dipole interaction between NV- centers is expected to be strong in increasingof [NV-]. The effect of interaction on coherence time T2 of NV- center is expected1 but is not still clear.
In this study, we investigated DDI coefficient of the NV- center. The DDI coefficient of the NV- center was evaluatedusing diamond single crystals with substantial amounts of NV- center being comparable to that of NS0.
MethodNitrogen doped diamond single crystals
used in this study were grown using either
HPHT synthesis or CVD method. After the
diamond growth, electron beam irradiation
was applied with the total fluences of 10171018 e/cm-2 to create vacancies in the
diamond. it was followed by vacuum
annealing at 1000ႏ for 2h to form NV
centersinthediamondcrystals.
Concentration of defects and T2 are evaluatedby EPR and Han echo method, respectively.

Result and Discussion

FIG. 1. (a) Relationship between T2 and concentration of Ns0.
(b) Relationship between T2 {NV-} and concentration of NV-.

First, we investigated dependence of [Ns0] on T2 of ensemble of NV- center. Fig. 1(a) shows relationship between T2 and[Ns0]. Most of the data indicates good inverse proportionality between T2 and [Ns0], with some exceptional data shown withsome deviation from solid line indicating. A larger ratio of [NVT] to [Ns0] would be associated with a tendency to greater
deviation. This result shows that the decoherence contribution of the spin bath of NV- and NV0 centers to the NV- center spinof interest cannot be ignored. Second, we observe ‫୒ܦ‬୚ష center using the data with relatively large [NVT]/[Ns0]. We also
obtained NV- component of T2: T2{NV-} using equation below,ଵଵషሾNV ି ሿ ൌ െ ൛‫୒ܦ‬బ౩ ሺሾNୱ଴ ሿ ൅ ሾNV ଴ ሿሻൟ.
ష ൌ ‫୒ܦ‬୚ ൈ்మ ሼ୒୚ ሽ்మ

Fig. 1(b) portrays relationship between T2{NV-} and [NV-]. The solid line represents the fitting function curve (ሾNV ି ሿ)ଵ்మ ሼ୒୚ష ሽൌwith respect to plotting data. We obtained ‫୒ܦ‬୚ష of 11.2 ms-1 ppm-1 through data fitting. This value is nearly‫୒ܦ‬୚ష ൈ
equal to that of ‫୒ܦ‬୚ష of 10 ms-1 ppm-1 estimated using the relation between DDI coefficient and spin multiplicity.1 We
observed DDI between NV- centers with [NV-] ranging from 0.2 ppm to 2 ppm.
Summary
We observed good inverse proportionality between T2{NV-} and [NV-]. This observation indicates that DDI between NVcenters occurs with [NV-] ranging from 0.2 ppm to 2 ppm.

Reference
1

J. F. Barry, J. M. Schloss, E. Bauch, M. J. Turner, C. A. Hart, L. M. Pham, and R. L. Walsworth, Rev. Mod. Phys. 92,
015004 (2020).

Acknowledgement
This work was supported by MEXT Q-LEAP (JPMXS0118068379 and JPMXS0118067395). T. Teraji acknowledges the
support of JST CREST (JPMJCR1773), MIC R&D for construction of a global quantum cryptography network(JPMI00316), and JSPS KAKENHI (Nos. 20H02187, 20H05661 and 19H02617). T. Teraji and S. Onoda acknowledge
the support of JST Moonshot R&D (JPMJMS2062).

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ1-01
Extension of dephasing time of ensemble NV centers with a continuous-excitation protocol
Ikuya Fujisaki1, Yuta Araki1, Yuji Hatano1, Takeharu Sekiguchi1, Takayuki Shibata2,
Takayuki Iwasaki1 and Mutsuko Hatano1
1
Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
2
DENSO Corporation
fujisaki.i.aa@m.titech.ac.jp
Introduction
Quantum magnetic sensors based on nitrogen-vacancy (NV) centers in diamond are expected to be applied to biologicaland chemical applications with its high sensitivity. However, the DC magnetic field sensitivity of NV centers is stillinsufficient for further applications such as magnetoencephalography (MEG). We focused on CE-Ramsey1 (Continuous
Excitation Ramsey), which is not only advantages for miniaturization thanks to its experimental simplicity, but also has highsensitivity compared to conventional Ramsey. CE-Ramsey has a technical issue of long overhead time due to low laser
power limited to suppress optical broadening. Dephasing time ܶଶ‫ כ‬is a key parameter to improve sensitivity, but ܶଶ‫ כ‬oftypical bulk diamond is limited due to high nitrogen density. In this work, we developed a protocol that combines CERamsey with double quantum (DQ) coherence and spin bath driving (SBD)2 and demonstrated that dephasing time can beextended in the CE protocol.
Methods
We built a compact sensor-head with a CPC lens. Radio frequency system and microwave system are established tomanipulate spin bath and NV centers (Fig.1 (a)). We compared dephasing time between CE-SQ-Ramsey and CE-DQRamsey, with and without SBD. The diamond sample (ሾ ି ሿ̱ͲǤͺ , ሾୗ଴ ሿ̱ͺ ) was obtained by electron
irradiation (ͷ ൈ ͳͲଵ଻  ିଶ ) and vacuum annealing (2 hours) after CVD growth (110 thick) with ଵଶ -enrichedmethane on a type-IIa substrate.
Results and discussions
We first confirmed coherent control of P1 centers in the spin bath under CE protocol by measuring their spectra andtheir Rabi oscillations (Fig.1 (b)) with CE-DEER (Double Electron-Electron Resonance) sequences based on the CEHahn-Echo. We applied SBD to CE-DQ-4-Ramsey and compared dephasing time. The results showed that the dephasingtime is about 2-fold improved by applying DQ and SBD (Fig.1 (c)).
Acknowledgement
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395.
We thank Dr. H. Kato (AIST) and Dr. S. Onoda, Dr. T. Ohshima (QST) for supplying diamond samples.
Reference
1. C. Zhang et al., Phys. Rev. Appl. 15, 1 (2021).
2. E. Bauch et al., Phys. Rev. X 8, 31025 (2018).

 (a)

(b)

(c)

Fig.1. (a) Experimental setup. Microwave and radio frequency are applied with wire and CPW(Coplanar
wave guide) respectively. (b) CE-P1 Rabi shows that coherent control of spin bath with CE protocol.
Pulse time of RF (radio frequency) is swept in CE-DEER sequences. (c) 2-fold extension of dephasingtime by applying DQ and SBD to CE-Ramsey.

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ1-02
Wide temperature operation of diamond quantum sensor
for electric vehicle battery monitoring
Keisuke Kubota1, Yuji Hatano1, Yuta Kainuma1, Daisuke Nishitani1,
Takashi Taniguchi2, Tokuyuki Teraji2, Shinobu Onoda3, Takeshi Ohshima3, Takayuki Iwasaki1,
and Mutsuko Hatano1,3
1

Department of Electrical and Electronic Engineering, School of Engineering, Tokyo institute of technology,
2-12-1 Ookayama, Meguro, Tokyo 152-8552, Japan
2
National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
3
National Institutes for Quantum Science and Technology, 1233 Watanuki-machi, Takasaki, Gunma 370-1292, Japankubota.k.ai@m.titech.ac.jp
Introduction
The diamond quantum sensors containing NV centers for electric vehicle(EV) battery monitoring are realized [1].
Sensors for EV batteries require a wide range of operating temperatures; however, the dependence of the sensitivity of the
diamond quantum sensor system on its wide operating temperature has not been reported. Therefore, we measured themagnetic field sensitivity in the temperature range from -150° to 150°C to investigate its potential for battery monitoring.

Methods
The overall configuration of the measurement system used in the experiment, including the sensor head, is shown in Fig.1(a). The diamond sensor was a (111) HPHT crystal with the size of approximately 3.6 mm3. 11018 electrons/cm2 electron
beam irradiation and 1000 Υ for 1 hour annealing after it realized 5 ppm NV density. The diamond sensor was attached tothe top of the multimode fiber and the surrounding microwave antenna with copper belt was attached to realize the sensor
head with a size of 1 × 1 × 0.5 cm3. The green excitation light from the fiber, with an intensity of approximately 200 mW at
the end of the fiber, was irradiated to the diamond sensor. Liquid nitrogen and a heater were used to vary the temperature.

Result and discussion
Fig.1 (b) shows the temperature dependence of the measured sensitivity of the magnetic field. The sensitivity of
approximately 5 nT/Hz1/2 was confirmed in the temperature range of -150–150 °C in the measurement system at atmosphericpressure as shown in Fig.1 (a). This sensitivity means that 10 mA current can be measured almost in 500 Hz bandwidth in
the temperature range between -150 and 150 °C. The confirmed current sensitivity in such a wide temperature range makes
it suitable for the batteries that are currently used or under development. Fig.1 (c) shows the temperature dependence of theshot noise sensitivity obtained from the contrast, line width, and photodiode (PD) current. On the high temperature side, as
we had expected, the sensitivity deteriorated with increasing temperature. This deterioration is mainly due to the contrast
deterioration, which can be attributed to the accelerated initialization of the spin state due to the faster singlet state transition
rate [2]. On the low temperature side, we had expected that the sensitivity would be improved, but it deteriorated.
Deterioration in contrast was the main cause, but it is difficult to explain the physical reasons. Considering that the line width
is thinner at lower temperatures, water vapor condensation at microwave antenna may have increased antenna loss because
this experimental setup was open to the atmosphere.
This work was supported by MEXT Quantum Leap Flagship Program (Q-LEAP) Grant Number JPMXS 0118067395
and JPMXS0118068379.

References[1] Y. Hatano et al., Sci. Rep. 12, 13991 (2022)
(a)

(b)

[2] D. Toyli et al., Phys. Rev. X 2, 031001 (2012)(c)

Fig.1 (a) Structure of the entire sensitivity measurement system. The dimension of the sensor head was approximately 1× 1 × 0.5 cm3. (b) Temperature dependence of the measured sensitivity. It was confirmed that the current sensitivity
requirements for EV batteries were obtained in the measured temperature range. (c) Measured temperature dependence ofshot noise sensitivity obtained from contrast, line width, and PD current.

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

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Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ1-04

Attempts to generate entanglement state between dipolar coupled NV centerscreated by molecular implantation
Kosuke Kimura1,2, Shinobu Onoda1, Keisuke Yamada1, Wataru Kada2, Tokuyuki Teraji 3,
Junichi Isoya4, Nozomu Kosuge1,2, Tomoya Baba1,2, Osamu Hanaizumi2, and Takeshi Ohshima112National Institutes for Quantum Science and Technology
Graduate School of Science and Technology, Gunma University
3
National Institute for Materials Science
4

Faculty of Pure and Applied Sciences, University of Tsukuba
kimura.kosuke@qst.go.jp, t222d002@gunma-u.ac.jp.

Introduction
Generating quantum entanglement states is one of the most important steps in quantum technologies such as quantum
information processing and quantum sensing, etc. The generation of entanglement states has been demonstrated on thevarious quantum systems. Among them, the entanglement between some solid-state spin qubits has the generation advantage
at room temperature. Generation of entanglement state between Nitrogen-Vacancy (NV) centers in diamond, known as solidstate electron spin qubits, has been demonstrated by Double Electron-Electron Resonance (DEER)1,2. The decoherence ofNV center limits the fidelity of entanglement state. It is expected that the short free evolution time for entanglement (ʹ߬௘௡௧ )reduce the limitations caused by decoherence. The spin state reaches the maximum quantum entanglement state at the freeevolution time ʹ߬௘௡௧ ൌ ͳȀ߭ௗ௜௣ by DEER, where ߭ௗ௜௣ is dipole coupling strength. By making the dipole-dipole interaction
as strong as possible, high fidelity due to short free evolution time is expected. We have created the strongly coupled NV
centers by molecular ion implantation3,4. In this study, we report the generation of entanglement state between dipolar
coupled double NV centers created by implanting C5N4Hn ions. In addition, we report the attempts to shorten ʹ߬௘௡௧ bychanging DEER pulse sequence.

Experiments and Results
To create dipolar coupled NV centers, C5N4Hn ions were accelerated at
65 keV and implanted into diamond. A C5N4Hn ion decomposes into
individual atoms by collision with diamond, and each nitrogen atom is
implanted 9±4 nm apart. The implanted nitrogen atom was combined witha vacancy by annealing process (1000°C, 2h) to create NV centers.
The created NV centers were observed using confocal fluorescencemicroscopy (CFM). The measurement of DEER was performed with a
532 nm pulsed laser and pulsed microwaves at room temperature in thestatic magnetic field (FIG. 1). The electron spins of two NV centers withdifferent resonance frequencies (2.6279 GHz for NVA, 2.6778 GHz for
NVB) able to be manipulated individually. Preparing both NV centers instate ห݉ௌǡ஺ ൌ Ͳǡ ݉ௌǡ஻ ൌ Ͳൿ by optical pumping, an echo measurement iscarried out on NVA. To apply ʌ/2 pulse on NVB before the second ʌ/2 on
NVA, fluorescence is a periodical signal of ܿ‫ݏ݋‬൫ʹߨ߭ௗ௜௣ ߬൯. The result of
the DEER measurement is shown in FIG. 2. The measured ߭ௗ௜௣ was 99.9
kHz and ʹ߬௘௡௧ ൌ ͳȀ߭ௗ௜௣ was calculated as 10 ȝs. In the presentation, theentanglement generation with other pulse sequences will be discussed.

Initialization

NVA
ȷ/2
NVB

Readout

ȷ

ȷ/2
ĳ
ȷ/2

FIG. 1 DEER pulse sequence.
Ǎdip=99.9 kHz

Acknowledgments
This work was supported by JST Support for Pioneering Research
Initiated by the Next Generation JPMJSP2146, JSPS KAKENHI No.
FIG. 2 Typical DEER spectrum.
21H04646, 20H02187, 20H05661, JST moonshot R&D Grant Number
JPMJMS2062, MIC R&D for construction of a global quantum
cryptography network JPMI00316, and MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) Grant Number
JPMXS0118067395 and JPMXS0118068379.

References
1
3

P. Neumann, et al., Nat. Phys. 6, 249 (2010). 2 F. Dolde, et al., Nat. Phys. 9, 139 (2013).
M. Haruyama, et al., Nat. Commun. 10, 2664 (2019). 4 K. Kimura, et al., Appl. Phys. Express 15, 066501 (2022).

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ1-05

Charge stability of shallow single NV centers in p-type diamond
Taisuke Kageura1,2, Yosuke Sasama1, Chikara Shinei1, Tokuyuki Teraji1,
Keisuke Yamada3, Shinobu Onoda3, and Yamaguchi Takahide1
1

National Institute for Materials Science (NIMS)
National Institute of Advanced Industrial Science and Technology (AIST)
3
National Institutes for Quantum and Radiological Science and Technology (QST)
kageura.taisuke@aist.go.jp
2

Introduction
A stable negatively charged state of nitrogen vacancy (NV) centers in diamond is important for diamond quantum
applications such as highly sensitive quantum sensing and high-performance quantum information processing. However, it
has been found that the charge state of single NV centers near the surface, called shallow single NV centers, is quite unstablecompared with NV centers in bulk1. Shallow single NV centers are significant to realize high-performance quantum devices
such as nanoscale NMR, so the origin of the charge instability needs to be revealed. Here we investigated how the presenceof small amounts of boron acceptors in bulk and surface states affect the charge stability of shallow single NV centers2.

Results and Discussion
We prepared four lightly boron-doped diamond thin films ([B]ӊ1×1015 cm-3,[N]<6×1011 cm-3) synthesized by microwave plasma chemical vapor deposition
method and formed single NV centers at about 3.6 nm from the diamond surface
by ion implantation. We have investigated the charge-state stability of the shallow
single NV centers by using photoluminescence spectra and optically detectedmagnetic resonance (ODMR) measurements. Surprisingly, we found thatnegatively charged state can be created despite the existence of boron acceptors;
Among 20 NV centers for which CW-ODMR was measured, 19 NV centers showed adecrease in fluorescence intensity at a frequency corresponding to the appliedmagnetic field of 1-2 mT. This negatively charged state could not be explained by
the conventional band-bending model, but it could be explained by photoexcitationinduced by green laser irradiation. Then we evaluated the charge stability underpulse measurement in the presence of laser non-irradiation time by Rabi oscillation
contrast values (Fig. 1). Clear Rabi oscillations were observed except for the
sample with higher boron concentration ([B]=1×1015 cm-3) and acid boiled surface,which means that negatively charged state can be created even under pulse
measurement. The variation of contrast values in Fig. 1(b) indicates the differencein charge stability of individual NV centers. This charge instability in lightly doped
diamond can be explained by electron transfer between the NV center and the local
environment. The charge stability is determined by whether the donor or theacceptor is closer to the NV center.
This study provides a new insight into the charge stability of a single NV centerin low-doped diamond and contributes to the further development of NV quantum
devices.
This work was partially supported by MEXT Q-LEAP Grant Number
JPMXS0118068379 and JPMXS0118067395, JST CREST (JPMJCR1773), JST
Moonshot R&D (JPMJMS2062), MIC R&D for construction of a global quantum
cryptography network (JPMI00316), JSPS KAKENHI (No. 20H02187,
20H05661, 19H02617 and 21J01804).

Reference
1
2

D. Bluvstein et al., Physical Review Letters, 122, 076101 (2019)
T, Kageura et. al, Carbon, 192, 473 (2022).

FIG. 1. (a) Typically observed
Rabi oscillations and (b) the
distributions of Rabi contrast

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ1-06
Room-temperature electrical detection of nuclear spins in silicon carbide
Naoya Morioka1,2, Tetsuri Nishikawa1, Hiroshi Abe3, Hiroki Morishita1,2,
Takeshi Ohshima3, and Norikazu Mizuochi1,212Institute for Chemical Research, Kyoto University
Center for Spintronics Research Network, Institute for Chemical Research, Kyoto University
3
National Institutes for Quantum Science and Technology
morioka.naoya.8j@kyoto-u.ac.jp

Spin-active color centers in silicon carbide (SiC) are promising candidates for scalable quantum sensors and quantum
information devices operating at room temperature due to their excellent spin coherence properties and the maturity of SiC's
wafer-scale semiconductor technology. By making use of the excellent controllability of semiconductor properties anddevice operation of SiC, the realization of electrical detection of spin information in SiC can benefit in developing integrated
quantum devices compared with conventional optical spin detection techniques. Recently, electrical detection of electron
spins of the V2 center in 4H-SiC1 was reported by photoelectrically detected magnetic resonance2 (PDMR). However, in theprevious demonstration, the PDMR spectra of V2 centers were broad due to the inhomogeneous magnetic field caused bymagnetized Ni electrodes, which is a typical ohmic contact material for SiC. The broad linewidth inhibited resolving thesignal of nuclear spins, which are useful resources as quantum memories for quantum information processing3 andsensitivity-enhanced quantum sensing.4 In this study, we optimized the contact and the device structures, and we obtained
the PDMR spectrum of an ensemble of V2 centers with a linewidth of 2.8 MHz, which is narrow enough to observe thehyperfine split resonance peaks coupled to the next-nearest-neighbor (NNN) 29Si nuclear spins (Fig. 1). By addressing thehyperfine split peaks, nuclear-spin-state-dependent spin control and its electrical detection are possible. By applying thesetechniques, the nuclear magnetic resonance signal of 29Si was successfully detected electrically at room temperature with
PDMR-based electron-nuclear double resonance (ENDOR) (Fig. 2).5 This is an achievement of electron spin coherence andnuclear spin detection in an identical device. In the ENDOR spectrum in Fig. 2, three peaks were observed, probably
originating from three nonequivalent NNN sites.6 These results suggest that room-temperature PDMR would enable selective
coherent control of nuclear spins, facilitating the development of electrically-driven integrated quantum devices.

FIG. 1. PDMR spectrum of V2 centers in 4HSiC.

FIG. 2. PDMR-ENDOR spectrum of NNN 29Si
nuclear spins coupled to V2 centers in 4H-SiC.

Acknowledgments
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395, JSPS KAKENHI Grant Numbers
JP20H00355, JP21H04553, JP21K20502, and JP22H01526, JST SPRING Grant Number JPMJSP2110, and Kyoto
University Nanotechnology Hub in MEXT ARIM project.
Reference1
M. Niethammer et al., Nat. Commun., 10, 5569 (2019).
2
E. Bourgeois et al., Nat. Commun., 6, 8577 (2015).
3
C. E. Bradley et al., Phys. Rev. X, 9, 031045 (2019).
4
M. Pfender et al., Nat. Commun., 10, 594 (2019).
5
T. Nishikawa et al., Appl. Phys. Lett., accepted (2022).
6
V. Ivády et al., Phys. Rev. B, 96, 161114 (2017).

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ1-07(Near) zero-field cross-relaxation features for ensembles of NV centers indiamondOmkar Dhungel1, Till Lenz1, and Dmitry Budker1,21Johannes Gutenberg University Mainz, Germany
Helmholtz Institute Mainz 55128, Germany

2

Department of Physics, University of California, Berkeley, California 94720-300, USA
budker.uni-mainz.de

Conventional magnetometry using NV centers in diamond relies on the application of microwaves and bias magnetic field.
However, there are applications, for example, the study of high-temperature superconductors, zero- to ultralow-field (ZULF)
NMR, investigation of biological samples, and magnetic materials where either the microwaves or the bias magnetic fieldmight disturb the system. To overcome such limitations, we study the zero-field cross-relaxation feature [1] for ensemblesof NV centers. A study of cross-relaxation features with respect to the sample cut and, NV density will be presented. Multiple
cross-relaxation features [2,3] are observed when transverse field is present and these features follow a specific pattern when
the azimuthal angle of a transverse field is changed, which is useful for vector-magnetometry applications.


Reference
1

S. Anishchik, V. Vins, A. Yelisseyev, N. Lukzen, N. Lavrik, and V. Bagryansky, “Low-field feature in the magnetic spectraof nv- centers in diamond,” New Journal of Physics, vol. 17, no. 2, p. 023040, 2015.
2

R. Akhmedzhanov, L. Gushchin, N. Nizov, V. Nizov, D. Sobgayda, I. Zelensky, and P. Hemmer, “Microwave-freemagnetometry based on cross-relaxation resonances in diamond nitrogen-vacancy centers,” Physical Review A, vol. 96, no.
1, p. 013806, 2017.
3

R. Akhmedzhanov, L. Gushchin, N. Nizov, V. Nizov, D. Sobgayda, I. Zelensky, and H. Philip, “Magnetometry by crossrelaxation-resonance detection in ensembles of nitrogen-vacancy centers,” Phys. Rev. A, vol. 100, p. 043844, Oct 2019.

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Ȗ1-01

Evaluation of a superconducting nanowire single photon detector for midinfrared wavelengths
Satoru Mima 1, Fumihiro China 1, Masahiro Yabuno 1, Shigeyuki Miyajima 1, Shigehito Miki 1, 2,
Yuki Gama 3, Toshiyuki Tashima 3, Masaya Arahata 3, Yu Mukai 3, Ryo Okamoto 3, Shigeki
Takeuchi 3 , Hirotaka Terai 1
1

Advanced ICT Research Institute, National Institute of Information and Communications Technology
2
3

Graduate School of Engineering, Kobe University

Graduate School of Engineering, Kyoto University
mima@nict.go.jp

Introduction
Superconducting nanowire single photon detectors (SNSPDs) have attractive features such as high efficiency, low jitter,
low dark counts, and high counts rates, and are expected to be applied in various fields. Recently, quantum technologies
utilizing photons in the mid-infrared region have attracted much attention[1]. However, there are no single-photon detectors
in the mid-infrared wavelengths. SNSPD is one of best candidate for high detection efficiency in the mid-infrared region.
In the mid-infrared region, the photon energy is smaller than in the near-infrared region, so the superconducting thin film
used in the detector must be thinner and superconducting nanowire must be narrower. In addition, for highly efficient midinfrared photon detection, the introduced light must be efficiently absorbed by the superconducting nanowire. We employ
an approach to enhancing the optical absorptance at target wavelength is integrating the nanowire with the dielectric
multilayer cavity[2]. In this study, superconducting nanowire were fabricated on a dielectric multilayer of Ta2O5 and Si films
designed to maximize light absorption in the mid-infrared region and evaluated.
We cooled down the fabricated detector by a sorption refrigerator capable of cooling down to 0.8 K and evaluate theoptical properties using a QCL light source (wavelength ~ 4.3 ȝm) in the mid-infrared region. We reduced optical efficiency
between the fiber and the superconducting nanowire for the evaluation of internal efficiency because of the intensity of
blackbody radiation in the mid-infrared region. The figure 1 shows the dependence of the internal efficiency of thesuperconducting nanowire on the bias current measured at different intensities of the mid-infrared light source. We also
evaluated the optical efficiency of the same superconducting nanowire in the near-infrared region (1300 nm to 1600 nm) andconfirmed that the spectra are consistent with the design.

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

Reference
1

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).
2

Fig 1. Comparison of the intensity dependenceof the internal efficiency in the mid-infrared.

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Ȗ1-02

Efficient superconducting nanostrip single-photon detectors for 2 Pm
wavelength
Fumihiro China1, Satoru Mima1, Shigehito Miki1,2, Masahiro Yabuno1, Shigeyuki Miyajima1 and
Hirotaka Terai11Advanced ICT Research Institute, National Institute of Information and Communications Technology
2

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

Introduction
In recent years, single-photon detection technology in the mid-infrared wavelength region has attracted attention. In
particular, at the 2 Pm wavelength band, highly efficient single-photon detectors are required for various applications suchas light detection and ranging (LIDAR), satellite-based quantum communications, and silicon-based quantum optics.
However, semiconductor avalanche photodiodes and photomultiplier tubes are limited to a sensitive wavelength ofapproximately 1.8 Pm by the energy gap of the semiconductor. On the other hand, superconducting nanostrip single-photon
detectors (SNSPDs) are promising detectors because of their wideband sensitivity including the mid-infrared region [1]. To
obtain high system detection efficiency (SDE) using SNSPDs, the following three factors should be maximized: optical
coupling efficiency, optical absorptance, and internal detection efficiency. The optical coupling efficiency can be maximized
by increasing the active area of the SNSPD, and the optical absorptance of superconducting nanostrips is improved by
implementing an optical cavity in the SNSPD. The internal detection efficiency can be improved by optimizing nanostrip
parameters such as nanostrip width and thickness. In this study, we developed SNSPDs with a dielectric multilayer cavity(DMC) and attempted to maximize the three factors to achieve high SDE in the 2 Pm wavelength.

Device design and experimental results
We developed NbTiN-SNSPDs with a DMC. Figure 1 shows the schematic of designed SNSPDs with a DMC comprisedof 11 periodic SiO2/Si bilayers on a Si wafer. Each dielectric layer of DMC is one-quarter of the optical thickness for the
2 Pm wavelength. The DMC enhances the optical absorptance by concentrating the electric field of incident photons on thenanostrips. In the simulation results by finite element analysis, we confirmed that the optical absorptance at the 2 Pm
wavelength reaches over 99%. Based on the SNSPD designs, we fabricated NbTiN-nanostrips with a line width ofapproximately 110 nm on the DMC. The active area of the fabricated SNSPDs, 30 Pm × 30 Pm, is enough larger than themode field diameter of a single mode fiber for the 2 Pm wavelength band. Subsequently, we tested the fabricated SNSPDs
using a sorption-based cryocooler with an operating temperature of 0.77 K and an optical system composed of a laser source,
a beam splitter, valuable optical attenuators (VOAs), neutral-density (ND) filters, a polarization controller, and power meters.
We adjusted the optical input power to -110 dBm using three VOAs and two ND filters, and all five attenuators were carefully
calibrated before SDE measurements. Figure 2 shows the measurement results of SDE and the dark count rate (DCR) of the
SNSPD. We succeeded to demonstrate a high SDE of 79% at a 2 Pm wavelength. In addition, we estimated the measurement
uncertainty of SDE as ±5.075% by measuring all possible uncertainties of VOAs, ND filters, laser power, the count rate,
DCR, and a power meter.

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

Reference
1

F. Marsili et al., Nano Lett, 12, 4799-4804 (2012).


FIG. 1. Schematic of the device structure of
an SNSPD with a DML.

FIG. 2. Bias current dependences of system
detection efficiency (SDE) and dark count rate
(DCR).

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Ȗ1-03

Effect of pump laser linewidth on nonlinear quantum interferometric fringes
Jasleen Kaur1, Yu Mukai1, Ryo Okamoto1 and Shigeki Takeuchi1*
1Department of Electronic Science and Engineering, Graduate School of Engineering, Kyoto University*takeuchi@kuee.kyoto-u.ac.jp

Introduction
 Infrared spectroscopy is a non-invasive technique used for the identification of materials by analyzing their infrared
spectrum. This technique finds applications in chemical industries, environmental sensing, and life sciences, etc. However,conventional infrared spectroscopy techniques suffer from low directivity of infrared sources and thermal background noise
deteriorating the sensitivity of IR detectors. Therefore, quantum infrared spectroscopy (QIRS) [1] is being widely
investigated as this quantum sensing technology enables IR spectroscopy using a light source and detector in the visible
region. In this technique, by utilizing the quantum correlation between visible and IR photon pairs and the quantum
interference of their generation processes, we can extract the optical properties of the IR absorptive sample.
The generation of correlated photon pairs in QIRS relies on the spontaneous parametric down-conversion (SPDC) process.
Since the current QIRS experiments have been demonstrated using a continuous wave (CW) laser [2,3], the probe photon
flux generated is low, leading to an inferior signal-to-noise ratio (SNR) thus limiting the sensitivity of this technique.
Achieving high generation efficiency of the PDC process can aid in increasing the SNR of the system. One of the possible
ways is to use a short pulse pump laser as the excitation source. The temporal confinement of energy in a pulse laser helps
in increasing the parametric gain of the PDC process. However, it is important to note that the pulse laser possesses a finite
spectral linewidth which leads to a partial frequency correlation between the generated photon pairs, leading to increased
distinguishability between the photons, thus lower interference contrast.
In this work, we report a quantitative analysis of how the pump laser linewidth affects the nonlinear quantum
interferometer. As shown in fig.1, we excite a nonlinear quantum interferometer with both CW and pulse laser sources andcompare the contrast of fringes using a dispersive spectrometer. We further derive the mathematical relationship between
the interferometric pattern obtained by CW and pulse laser.

FIG. I. Schematic of the nonlinear quantum interferometer

Reference
1

D. A. Kalashnikov et al. Nat. Photonics, vol. 10, no. 2, p. 98–101 (2016)2

Y. Mukai et al. Phys. Rev. Appl., vol. 15, no. 3, p. 034019 (2021)

3

P. Kaufmann et al. Opt. Express, vol. 30, no. 4, p. 5926 (2022)

Acknowledgment
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067634, JST-CREST Grant Number
JPMJCR1674, JSPS KAKENHI Grant Number 21H04444, and WISE Program, MEXT

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

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SE-03A-Ȗ1-05

Optical trapping and movement control of gold nanoparticles onan optical nanofiber
Rui Sun1,2, Yining Xuan1,2, Soyoung Baek1, and Keiichi Edamatsu1
1

2

Research Institute of Electrical Communication, Tohoku University
Department of Electronic Engineering, Graduate School of Engineering, Tohoku University
sun.rui.p6@dc.tohoku.ac.jp

Introduction
Optical nanofiber has drawn lots of interests in past few years as a promising tool in quantum optics and quantum
metrology for its unique properties1,2. Our research focus on the single photon source based on quantum-dot-goldnanoparticle coupled system on optical nanofiber3. With this experimental system, we have realized a single photon source
which is much better than directly exciting the quantum dot with laser. For instance, significant Purcell enhancement of thesingle photon emission rate was observed4.
However, the current experimental system still has some drawbacks. The position of gold-nanoparticle on nanofiber isentirely random, which makes it difficult to quantitatively study the single-photon emission rate. Thus, we propose a noncontact method to control the position of a gold-nanoparticle on the nanofiber. In the past research, we have realized tocontrol the motion of liposome particles in solution by changing the intensity of evanescent light field on the optical nanofiber
surface5. Here, following a similar approach, we report on a protocol to achieve the control of gold nanoparticles on an
optical nanofiber to further improve the properties of single photon source. As shown in Figure 2, the optical nanofiber isimmersed in the solution containing gold nanoparticles, and 785 nm laser and 530 nm laser are injected at both ends of thenanofiber respectively. 785 nm laser is used to generate evanescent light field, and 530 nm laser is used to detect the
movement of the gold nanoparticles on the surface of optical nanofiber. By adjusting the laser intensity, we can control the
movement of the gold nanoparticles on the nanofiber surface. We will introduce optical tweezer to this system to achieve
more precise position control of gold nanoparticles.
This work is supported by MEXT Q-LEAP Grant Number JPMXS0118067581.

FIG. 1. The movement of a liposome
along the nanofiber5.

FIG. 2. The scheme of experimental setup.

Reference
1

M. Joos, A. Bramati, and Q. Glorieux, Opt. Express, 27, 18818-18830 (2019).
C. Lee, M. A. Buyukkaya, S. Harper, S. Aghaeimeibodi, C. J. K. Richardson, and E. Waks, Nano Letters, 21, 323-329(2021).
3
M. Sadgrove, M. Sugawara, Y. Mitsumori and K. Edamatsu, Sci Rep, 7, 17085 (2017).
4
M. Sugawara, Y. Xuan, Y. Mitsumori, K. Edamatsu and M. Sadgrove, Phys. Rev. Research, (in press) (2022).
5
T. Yoshino, D. Yamaura, M. Komiya, M. Sugawara, Y. Mitsumori, M. Niwano, A. Hirano-Iwata, K. Edamatsu, and M.
Sadgrove, Opt. Express, 28, 38527-38538 (2020).

2

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Ȗ1-06

Electromagnetic-field analysis of the plasmon-enhanced single photon emitterson an optical nanofiber
Yining Xuan1,2, Rui Sun1,2, Soyoung Baek1, and Keiichi Edamatsu1
1

2

Research Institute of Electrical Communication, Tohoku University
Department of Electronic Engineering, Graduate School of Engineering, Tohoku University
xuan.yining.t8@dc.tohoku.ac.jp

Single photon emitter has many applications in quantum information, communication, and metrology. Therefore, brightsingle photon emitters with enhanced quantum efficiency are very important for practical quantum applications and havebeen studied using various systems [1]. To achieve an enhanced, polarized single photon source that can be coupled into thefiber network directly, we studied on a gold nanoparticle-quantum-dot (GNP-QD) coupled system [2,4], as shown in Fig.1.
The single photon source in this research is based on a semiconductor quantum dot (QD) with the emission wavelengtharound 800 nm. The surface plasmon resonance of gold nanoparticles (GNP) provide large Purcell enhancement relative toconventional cavities and can also provide enhancement of degree-of-polarization (DOP) depending on the type ofnanoparticle. In addition, optical nanofibers have the advantages of low optical loss when coupling to conventional fiber
networks, and low cost as they can be fabricated from standard single mode optical fibers. Furthermore, through theevanescent field of the nanofiber, photons from QDs can be coupled directly into the nanofiber and hence an optical fiber
network.
To understand the distribution of electric field and the impact of incident light on gold nanoparticles on the nanofiber, we
carried out electromagnetic-field analysis (FDTD: Finite-difference time-domain method). We analyze the background field
distribution, reflection coefficient, absorption and scattering cross section of gold nanoparticles on the fiber surface at various
incident angles. Through the analysis of electric field distribution and localized surface plasmon response of gold
nanoparticles in Fig.2, the performance of gold nanoparticles on the surface of nanofiber is obtained and discussed. The
single photon source with GNP-QD structure can enhance the luminous efficiency of quantum dot due to the Purcell effect.
We plan to add a quantum dot in the vicinity of the gold nanoparticle and perform the simulation.

This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067581.
     FIG. 1. SEM image of the quantum-dot-gold-nanorod
coupled system on an optical nanofiber.

FIG. 2. Localized plasmon resonance of gold
nanorod using FDTD simulation.



Reference
1

H. J. Kimble, Nature, 453, 7198 (2008).
M. Sadgrove, M. Sugawara, Y. Mitsumori, and K. Edamatsu, Sci. Rep., 7, 17085 (2017).
3
M. Sugawara, Y. Mitsumori, K. Edamatsu, and M. Sadgrove, Opt. Express, 28, 18938 (2020).
4
M. Sugawara, Y. Xuan, Y. Mitsumori, K. Edamatsu, M. Sadgrove, Phys. Rev. Research, (in press) (2022).
2

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Ȗ1-07

Ultrafast measurement of biphoton wave packets using optical Kerr gating
Takahisa Kuwana1, Masahiro Yabuno2, Fumihiro China2, Shigehito Miki2, Hirotaka Terai2,
Peter J. Mosley3, Rui-Bo Jin4 and Ryosuke Shimizu1
1

The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo, Japan

2

Advanced ICT Research Institute, National Institute of Information and Communications Technology,588-2 Iwaoka, Nishi-ku, Kobe 651-2492, Japan

3

Centre for Photonics and Photonic Materials, Department of Physics, University of Bath, Bath, BA2 7AY, UK

4

Hubei Key Laboratory of Optical Information and Pattern Recognition, Wuhan Institute of Technology, Wuhan 430205, China

k2133039@gl.cc.uec.ac.jp
Introduction
Single-photon detection is of importance for quantum information and sensing technologies. Improving the temporal
resolution in single-photon detection is essential for the further development of quantum technologies. Currently, asuperconducting nanowire single-photon detector has achieved ~3 ps temporal resolution, which is the best temporal
resolution as far as we know. However, there is a trade-off between detection efficiency and temporal resolution. Thus,
extending into the femtosecond range is challenging without a catastrophic reduction in detector efficiency. On the other
hand, optical gating with ultrafast laser pulses can efficiently detect photons with high temporal resolution. Up to now, wedeveloped an ultrafast single-photon detector using an optical Kerr gating (OKG) and demonstrated the single-photon
detection with 224s9 fs temporal resolution under low-gating power consumption (~20 mW)1. However, no demonstrationof a two-photon detection by the OKG has been reported. In this work, we present the development of our OKG system to a
two-photon detection toward joint temporal intensity (JTI) measurements.

Experiment'W А
Figure 1 shows the schematic diagram of the experimental 9HUWLFDO3RODUL]DWLRQ'HOD\/LQH
setup. Our PCF was specially designed to minimize the group
6DJQDF ,QWHUIHURPHWHU
velocity difference between the photons with the center'W⾫
wavelength of 1584 nm and the gating pulse with the wavelength +RUL]RQWDO3RODUL]DWLRQ3&)'HOD\/LQH
of 792 nm for efficient cross-phase modulation. Ultrafast pulses
from a mode-locked Ti:sapphire laser operating at the663'
wavelength of 792 nm were divided by a polarization beam
7L6 /DVHU
7&63&
splitter. One is sent to a periodically poled KTP (PPKTP) crystal QPIV#0+]
663'
to generate biphotons in a type-II phase-matching condition and+:34:3)LOWHU 7L6 FXW 0LUURU'&0
the other is used for gating pulses of the OKG system.
FIG.
1.
JTI measured our OKG system
Biphotons generated via PPKTP crystal were led to the OKG
system with the Sagnac interferometer configuration. Photons were propagated in either clockwise (CW) or
counterclockwise (CCW) directions. Only the photon wave packet in the CW propagation was copropagated with the gating
pulse. Then, a nonlinear phase shift by the optical Kerr effect was added to the photon overlapped with the gating pulse in
the PCF. In the case that the phase difference between CW and CCW propagation of the Sagnac interferometer is not zero,a portion of the photons are outputted to the detection port. Eventually, we can measure the envelope of the wave packet bysweeping the relative delay between the photon and the gating pulses. With the help of polarization multiplexing, wedeveloped our system to the two-photon detection. We reconstruct the JIT from coincidence counts of our Kerr gating system.
V

H

fFP

G%&RXSOHU

33.73

RXWSXW
SRUW

Results and discussion
Figure 2 shows the measured JTI. We can clearly see the two-photon temporal
distribution with a negative correlation. This is the first experimental observationof the JTI by the OKG. We achieved the maximum signal-to-noise ratio with agating power of 50 mW, meaning that the order-of-magnitude improvement of
the gating power consumption compared to the up-conversion method2.

Acknowledgment
This work was
JPMXS011806924.

supported

by

MEXT

Q-LEAP

Grant

Number

Reference
1

M. Yabuno, R. Shimizu , et al., Opt. Express 30, 4999-5007 (2022).
2
R.-B. Jin, R. Shimizu , et al.. Phys. Rev. Appl. 10, 034011/1-11 (2018).

FIG. 2. JTI measured our OKG system

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į2-01

Growth of thick CVD diamond films containing aligned nitrogen-vacancy
centers for high-sensitivity quantum sensors
Takeyuki Tsuji1, Takayuki Iwasaki1, and Mutsuko Hatano1
1

Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
tsuji.t.ac@m.titech.ac.jp

A large volume of CVD diamond films containing aligned
nitrogen-vacancy (NV) centers lead to highly sensitive quantum
sensors. To form perfectly aligned NV centers, diamonds need to
be grown using lateral growth in the [1 ࡄ1 ࡄ2] direction.[1] It isnecessary to cut and polish the diamond substrate at amisorientation angle (ߠ௠௜௦ ) to create the steps, as shown in Fig. 1.
Geometrically, as ߠ௠௜௦ increases, the maximum thickness of the
diamond film increases, as shown in Fig. 1. For example, if a 1
mm2 diamond substrate is polished at ߠ௠௜௦ =10°, the maximum
film thickness is 1 mm × sin(10°) § 170 μm, while at ߠ௠௜௦ =0.5°,
the maximum film thickness is 1 mm × sin(0.4°) § 7 μm.
Fig.1. Differences in the maximum film thicknesses
Therefore, ߠ௠௜௦ is a key parameter in determining the thickness
for different misorientation angles (ߠ௠௜௦ ).
of the diamond films. In this study, the dependence of the growthrate and NV center properties on ߠ௠௜௦ (= 0.4°–9.9°) wasinvestigated for synthesizing a thick diamond film containingaligned NV centers.
Diamond films containing NV centers were grown on Ib (111)diamond substrates (1 mm × 1 mm × 0.3 mm). The surfaces of the
diamond (111) substrates were polished in the [1 ࡄ1 ࡄ2] direction atߠ௠௜௦ of 0.4(1) °, 2.7(1) °, 3.7(1) °, 5.0(1) °, and 9.9(1) °, whichwere measured using X-ray diffraction. We used a high-power
density MPCVD where the microwave plasma was reflectively
concentrated above the diamond substrates by a sphericalchamber.[2] Hydrogen, methane, and nitrogen gases flowed in the
setup at 500, 0.5, and 0.01 sccm, respectively. The pressure,microwave power, and temperature were set to 30 kPa, 2.1 kW,
and 800 °C, respectively. The thickness and nitrogen density of the
diamond films were measured using secondary ion mass
spectrometry (SIMS). The fluorescence of the NV centers wasmeasured using a home-built confocal microscope.
The growth rate increased from 1.8 μm/h to 5.3 μm/h when ߠ௠௜௦increased from 0.4° to 5.0°, and it was 4.4 μm/h at 9.9°.( Fig.2. (a))
Fig.2. (a)–(b) Dependence of the growth rate andThis was discussed by the relationship between a migration length
NV yield on misorientation angles, respectively. (c)of carbon precursors and a terrace width. With increased ߠ௠௜௦ , theCross-sectional image of the CVD diamond filmusing the confocal microscope. (d) CW-ODMR
NV yield, a fraction of the NV center density in the nitrogen
spectra of the CVD diamond film at different
density, increased from 0.4% to 1.1%. (Fig.2. (b)) Finally, a
positions shown in (c).
diamond film was synthesized for 30 h to obtain a thick diamond2film using the 1 mm diamond substrate with ߠ௠௜௦ =9.9°. Figure 2(c) shows a cross-sectional image of the CVD diamondfilm. Considering the refractive index of diamond (2.41) and immersion oil (1.52) and the numerical aperture (NA) of theobjective lens (1.42), the distance of the detection point moved in the CVD diamond film was 1.71 times the distance theobjective lens moved.[3] Thus, the film thickness was calculated as approximately 70 μm (CVD film thickness seen by an
X-Zscan) × 1.72 § 120 μm. Figure 2(d) shows the CW-ODMR spectra of the film at different positions shown in Fig. 5(g).
Only two CW-ODMR peaks were observed, which confirmed the formation of perfectly aligned NV centers throughout the
thick diamond film. This study is useful to design high-sensitivity diamond films using NV centers.
Acknowledgment This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395. and conducted at(NanofabPF, Tokyo Tech), supported by "Nanotechnology Platform Program" of the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), Japan, Grant Number JPMXP09F-21-IT-014.
Reference [1] T. Miyazaki, et al., Appl. Phys. Lett. 105, 261601 (2014).[2] T. Tsuji, H. Ishiwata, T. Sekiguchi, T. Iwasaki
and M. Hatano, Diam. Relat. Mater. [108840], 108840 (2022). [3] E. E. Diel, J. W. Lichtman and D. S. Richardson, Nat.
Protoc. 15 [9], 2773 (2020).

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į2-02

Enhancement of fluorescence collection efficiency using angle-shaped diamonds forcompact magnetic sensor
Yuta Shigenobu1, Yuta Kainuma1, Yuji Hatano1, Takayuki Shibata2
Akimichi Nakazono3, Takeshi Ohshima4, Mutsuko Hatano1,4, Takayuki Iwasaki1
1
Department of Electrical and Electronics Engineering, Tokyo Institute of Technology
2
3

4

DENSO CORPORATION,YAZAKI CORPORATION,

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

Introduction
Nitrogen-vacancy (NV) centers in diamond work as highly sensitive magnetic field sensors with a wide dynamic range, awide operating temperature range, and the ability to simultaneously measure magnetic field and temperature, which are suitable
for applications of battery monitoring1 and biomedical sensing2. In order to improve the magnetic field sensitivity, it isimportant to develop a method to collect red fluorescence emitted from NV centers in a diamond sensor with high efficiency.
A Compound Parabolic Concentrator (CPC) lens3 has been utilized to increase the collection efficiency. In this study, we
propose a new method, which can be combined with the CPC lens, for the enhancement of the collection efficiency using athree-sided-angle-shaped diamond. We found that the efficiency can be more than doubled with a side angle of 30° or higher.

MethodThe sensor head used in the experiment and simulation model is shown in Fig.1, where the distance (t) between the CPC lensand the Photo Detector (PD) light-receiving surface is variable from 1.75 mm to 11.75 mm. First, we used light path analysis
software (LightTools) to simulate the fluorescence collection efficiency (ȕsim) when the diamond side shaping angle ș wasincreased from 0° to 50° with a step size of 10°. Experimentally, a green laser (wavelength: 532 nm) was irradiated to beperpendicular to the (111) plane of the diamond sensor, and PD current was measured. The diamond sensors used were HPHTgrown Ib (111) substrates (2.0ൈ2.0ൈ0.6 mm3). The NV centers were formed by irradiating with an electron beam with a fluenceof 1.0ൈ1018 cm-2 and subsequentlyannealing at 1000 ႏ for 2 hours. Then, the sidewalls of the samples were angle-polished.

ResultFigure 2(a) shows the simulated ȕsim while changing the side-angle and distance between the CPC lens and light-receiving
surface of PD. ȕsim decreases as increasing the distance. Thus, we investigated the dependence of ȕsim on the grinding angle ata short distance of 1.75 mm. The inset of Fig. 2(a) shows that ȕsim increased in the range from 0° to 20°, while it remained
approximately constant from 20° to 40°. The comparison between 0° and 30° polishing shows the increase in ȕsim by a factor
of about 2. The further increase in the angle above 40° again makes ȕsim higher. Then, we performed the experiments using
two samples of 0° and 30° shaping. Figure2(b) depicts the measured PD current as a function of the green laser power. The
PD current of the 30° polished sample becomes 2.4 times higher compared to the 0° sample, which agrees with the simulation.
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395.

References[1] Y. Hatano et al., Sci. Rep. 12, 13991 (2022) [2] K. Arai et al, Commun Phys 5, 200 (2022)[3] T. Wolf et al., Phys. Rev. X 5, 041001 (2015).
(a)Fig.1 Sensor head structure(b)

Fig.2 (a) Simulation of ȕsim. depending on the polishing angle and PD
position. (b) Experimentally obtained PD current for the 0° and 30°
samples.

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į2-03

Transfer-printing-based integration of SiN grating structure on diamond
toward highly sensitive quantum sensor
Ryota Katsumi1, 2, Takeshi Hizawa1, Akihiro Kuwahata2, 3, Shun Naruse1, Yuji Hatano4, Takayuki Iwasaki4,
Mutsuko Hatano4, Fedor Jelezko5, Shinobu Onoda6, Takeshi Ohshima6, Masaki Sekino2, and Takashi Yatsui1, 2
1

Graduate School of Engineering, Toyohashi University of Technology
2
Graduate School of Engineering, The University of Tokyo
3
Graduate School of Engineering, Tohoku University
4
School of Engineering, Tokyo Institute of Technology
5Institute of Quantum Optics, Ulm University
6
National Institutes for Quantum Science and Technology
katsumi.ryota.ti@tut.jp

Introduction
A nitrogen-vacancy (NV) center in diamond is one of the promising candidates for quantum sensing, especially sensitive
magnetic sensing thanks to their excellent spin property1,2. However, their demonstrated magnetic field sensitivity is far
beyond that based on conventional magnetometers including superconducting quantum-interference devices. One of thecritical issues is the poor extraction efficiency of the emitted photons from the diamond NV substrate3. This can be overcome
by implementing the nanostructure on diamond including gratings, but the fabrication of such structure on diamond has thetechnical difficulty.

Method and Result
In this work, we demonstrate the hybrid integration of a silicon nitride (SiN) circular grating structure on a single-crystal
diamond NV substrate toward sensitive magnetometers. Figure 1(a) displays an SEM image of the grating based on SiN,
which is transparent for the NV emission wavelength of ~700 nm. To pick them up, we employed the air-bridged structure
for the grating. By using the pick-and-place transfer printing4 [Fig. 1(b)], the SiN grating was integrated on the diamond NV
substrate. Figure 1(c) displays an optical microscope image of the fabricated device. The SiN grating is bonded with the
diamond NV substrate.
The fabricated device was characterized using micro-SKRWROXPLQHVFHQFH ȝ3/ VSHFWURVFRS\7KH19FHQWHUVZHUHH[FLWHG
with a 532 nm-CW laser. The red curve in Fig. 1(d VKRZVD3/VSHFWUXPPHDVXUHGIRUWKHsample with the SiN grating at
DQLQSXWODVHUSRZHURIP:)RUFRPSDULVRQZHPHDVXUHGWKH3/VSHFWUXPIRUWKHEDUHUHJLRQRIWKHGLDPRQG19
substrate near the SiN grating (blue curve in Fig. 1(d)). The collected photon counts are increased by a factor of up to 1.6
with the SiN grating structure. We also evaluated the magnetic sensitivity of the fabricated device. Figure 1(e) shows thelock-in voltage detected by the lock-in detection system2 as a function of the magnetic field strength B. The detected voltages
with the grating are higher than those in the bare region, which is consistent with the results of Fig. 1(d) and demonstrating
the improvement of the magnetic sensitivity in the fabricated device.
Acknowledgement
This work was supported by MEXT Q/($3*UDQW
1XPEHU
-30;6 and Kakenhi(+ + .
.+DQG.).
References
J. M. Taylor, et al., 1DW3K\V4
 
2
A. Kuwahata, et al., Sci Rep 10
(2020).
3'/H6DJHet al., 3K\VLFDO5HYLHZ%
85, 121202 (2012).
4
R. Katsumi, et al., Optica 5  
1),* D 6(0LPDJHRIWKHIDEULFDWHG6L1JUDWLQJ E 6FKHPDWLFVRIWUDQVIHUSULQWLQJ
of SiN grating on diamond. (c) Optical microscope image of the fabricated device. (d)0HDVXUHG3/VSHFWUD UHGSiN JUDWLQJEOXHEDUHUHJLRQ (e) /RFN-in voltage detectedby the lock-in detection system as a function of magnetic field strength (B).

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į2-04

NVC-SPM System to Inspect Electric Devices
Teruo Kohashi1, Masanari Koguchi1, Akehito Shiotake2 and Satoshi Ono2
1

2

Hitachi, Ltd., Research & Development Group, Hatoyama, Saitama, 350-0395 JapanThe Graduate School of Informatics and Engineering, The University of Electro-Communications, Choufu,
Tokyo, 182-8585, Japanteruo.kohashi.fc@hitachi.com

Introduction
A scanning probe microscope using nitrogen-vacancy color centers in diamond (NVC) as a probe (NVC-SPM) has
been developed [1,2], taking advantage of excellent characteristics of NVC, such as high sensitivity for magnetic field
detection in three dimensions and high spatial resolutions. For now, this technique is mainly used to study fundamental
physical phenomena. On the other hand, we are developing an NVC-SPM to inspect electric devices by evaluating
magnetic fields generated from a tiny electric wiring. In this paper, we report the development of a new system including
a compact microwave antenna and mini-mirror, which makes it possible to inspect the predetermined electric circuit in awide circuit board.
Results

It is important to set the microwave antenna as close as fifty Pm to the probe in NVC-SPM, referring to the previously
published example [2]. In order to detect magnetic field generated around a minute wiring between the pads, themicrowave antenna should be inserted between the two electrical pads, which are positioned in the distance of less than
1mm. Moreover, irradiation and detection light are performed with a confocal microscope with a working distance of 4.5
mm. It means that the antenna and the probe should be set above the predetermined electric circuit in the space of 4.5mm.
We need to set these components precisely in the measurement; therefore, it is desired to confirm the position of eachcomponent in the vertical direction from the sample surface. However, the field of view is very narrow through theobjective lens (e.g., several hundred Pm) because the lens center diameter is very small. A new function for precise
position adjustment among these components was required in our SPM system.
Our new NVC-SPM is summarized in Fig. 1. We designed the microwave antenna with very tiny coil with diameter of
500Pm, and mini-mirror to confirm the position of each component from vertical direction using a camera. We developed
the above-mentioned system as shown in Fig. 2, and confirmed that this system works properly. As a next challenge, wewill inspect the actual electric circuit using this NVC-SPM system.


FIG. 1. Newly developed NVC-SPM system with mini-mirror.
FIG. 2 3D-CAD image of set up around the sample.
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395.

Reference[1] J. M. Taylor, P. Cappellaro, L. Childress, L. Jiang, D. Budker, P. R. Hemmer, A. Yacoby, R. Walsworth, M. D. Lukin,Nat. Phys. 4, 810 (2008).
[2] T. X. Zhou, R. J. Stohr and A. Yacoby, Appl. Phys. Lett 111, 163106(2017).

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į2-05

Enhancing sensitivity with entanglement in coupled nitrogen vacancy centres
Ernst David Herbschleb1, Riku Kawase1, Hiroyuki Kawashima1, Hiromitsu Kato2, Toshiharu
Makino2, Satoshi Yamasaki3, Shinobu Onoda4, Hiroshi Abe4, Takeshi Ohshima4, Norikazu
Mizuochi1
12Institute for Chemical Research, Kyoto University
National Institute of Advanced Industrial Science and Technology (AIST)
3
Nanomaterials Research Institute, Kanazawa University
4
National Institutes for Quantum Science and Technology (QST)
herbschleb@dia.kuicr.kyoto-u.ac.jp

Introduction
Quantum sensing has great potential for applications that require ultra-high sensitivities. The nitrogen-vacancy (NV)centre is an important example of a quantum sensor, since it works under ambient conditions, enables high spatial resolution,and several physical quantities can be measured. Coherence is a quantum resource that is already utilised in many quantum
sensing protocols. However, the ultimate quantum resource, entanglement, has yet to see use. This could enhance thesensitivity significantly, but it is far from straightforward.

MethodIn our research, to create NV centres that have a high chance to be coupled, we implant molecules with multiple nitrogenatoms into diamond samples, such that the distance between potential NV centres is dictated by straggling only [1]. By
choosing phosphorus-doped diamond ([P] § 5 x 1015 cm-3, created via CVD with enriched 12C [2]), we expect to have ahigher yield [3], and hence a higher chance to find NV centres with a strong coupling. Moreover, the coherence time ispotentially longer [3], which is important for various quantum protocols.
We compare results between intrinsic diamond and phosphorus-doped diamond, for which initial results show an increasein yield (Fig. 1). Moreover, the number of spots with more than one NV centre is consistent with the yield per nitrogen atom;
an example ODMR spectrum is shown in Fig. 1. Double electron-election resonance experiments give the coupling strength
between NV centres, which needs to be sufficiently strong to attempt to utilise a couple for enhanced sensing.

FIG. 1. (Left) Confocal microscope image for intrinsic diamond, showing less than 10 spots with NV centres. (Middle)
Confocal microscope image for phosphorus-doped diamond implanted with the same parameters as intrinsic diamond. There
are over 20 spots with NV centres. Moreover, the photon count per NV centre is higher compared to the intrinsic sample.
(Right) Optically detected magnetic resonance (ODMR) image for a spot with two NV centres with a different orientation.

Acknowledgement
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395.
References
1

Haruyama et al., Nature Communications 10, 2664 (2019).
E. D. Herbschleb et al., Nature Communications 10, 3766 (2019).
3
A. Watanabe et al., Carbon 178, 294-300 (2021).
2

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į2-06

Frequency-bin generation of entangled photons via quantum optical synthesis
Takeru Naito1, Masahiro Yabuno2, Fumihiro China2, Shigehito Miki2, Hirotaka Terai2,
and Ryosuke Shimizu1
1

2

The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo, Japan
Advanced ICT Research Institute, National Institute of Information and Communication Technology, 588-2
Iwaoka, Nishi-ku, Kobe Japan
n2133076@uec.ac.jp

Introduction
Entangled photons in high-dimensional Hilbert space are expected to increase information capacity. Although there areseveral approaches to realize such a high-dimensional state of the entangled photons, frequency-bin encoding is suitable for
optical-fiber-based communication systems with wavelength multiplexing technologies. Up to now, frequency-bin state
generation has been reported in some physical systems; Micro-ring resonators [1] and domain structure engineering of quasiphase-matched devices [2]. However, most of the physical characteristics of the frequency-bin state are determined by thedesigned device structures. Therefore, it may be difficult to precisely adjust the frequency-bin state to the communication
system. On the other hand, we reported manipulating the time-domain structure of a biphoton wave packet via Fourier opticalsynthesis in the frequency domain and realized an ultrafast time-bin state of the biphoton wave packet in several pico-second
ranges [3]. Since the Fourier optical approach is independent of the device structure, it would provide better flexibility inmanipulating the time-frequency structure of the biphoton wave packet. In this study, we present a proof-of-concept
experiment of a two-photon spectral modulation with Fourier optical synthesis (FOS) toward the frequency-bin state
generation with high flexibility.

Experimental results
In this experiment, photon pairs are generated by spontaneous parametric down-conversion using a periodically poled
MgO-doped stoichiometric LiTaO3 (PPMgSLT) crystal. In the earlier experiment with the PPMgSLT, broadband joint
spectral intensity (JSI) distribution with negative correlation was reported even under a type-II phase-matching condition.
Based on this scheme, we develop a spectral manipulation technique by Fourier optical synthesis in the time domain. Since
discrete joint temporal intensity (JTI) distributions are needed for our synthesis, we adopt a bidirectional pumping scheme
to the PPMgSLT crystal by reflecting the pump pulse by a concave mirror. As a result, a sequential JTI distribution withpositive temporal correlation is created. For further manipulation, we placed a dichroic mirror between the PPMgSLT andthe concave mirror to separate the biphoton wave packet, created by the first pumping, from the pump pulse. Adjusting amirror position for the biphoton wave packet, we can control the temporal separation of the two biphoton wave packets alonganti-diagonal direction. Photon pairs from the bidirectional pumped source were collected into a polarization-maintaining
fiber and were sent to a fiber-based spectrometer. We reconstructed JSIs from the arrival time of photons after passing
through the spectrometer. Photons were detected by superconducting single-photon detectors.
Figure 1 represents the resultant JSI when the two JTIs are
distributed parallel to each other to the diagonal direction(a)(b)
defined by ȟ߬௦ ൌ െȟ‫ݐ‬௜ . We can see the JSI is modulated alongઢࣇെઢ࣎െ
the anti-diagonal direction defined by ȟߥ௦ ൌ െȟߥ௜ and it
forms a frequency-bin state. The product of these modulation
periods of each bin and interval of the two JTI is ȟ ି ‫ ڄ‬ȟߥି ؆ͳǤ͵ǡ meaning successful demonstration of the FOS in the time
domain.
FIG.1. (a)Expected JTI (b) Measured JSI formed the frequency-bin state.

Acknowledgement
This work was supported by MEXT Q-LEAP Grant Number JPMXS011806924.

Reference[1] C. Joshi, A. Farsi, A. Dutt, B.Y.Kim, X. Ji, Y. Zhao, A.M. Bishop, M. Lipson, and A.L. Gaeta, “Frequency-Domain Quantum
Interference with Correlated Photons from an Integrated Microresonator,” Phys. Rev. Lett. 124, 143601/1-7 (2020).
[2] C.L. Morrison, F. Graffitti, P. Barrow, A. Pickston, J. Ho,and A. Fedrizzi, “Frequency-bin entanglement from domain-engineered
down-conversion” APL Photonics 7, 066102 (2022).
[3] R.B. Jin, K. Tazawa, N. Asamura, M. Yabuno, S. Miki, F. China, H. Terai, K. Minoshima, and R. Shimizu, “Quantum opticalsynthesis in 2D time-frequency space,” APL Photonics 6, 086104/1-7 (2021).

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Į2-07

Development of highly sensitive gravimeter based on atom interferometry using
hybrid system for field applications
Takeshi Hojo, Kaito Takamura, and Ken’ichi Nakagawa
Institute for Laser Science
University of Electro-Communication
t_houjo@ils.uec.ac.jp
Introduction
Transportable gravimeters with the sensitivity of about few micro
Gal (10-9 g) are required in the fields of geophysics and geodesy. As theatom gravimeters have favorable features for these fields such as highsensitivity and no moving elements, they will contribute to these fields.
We have developed a transportable gravimeter for these fields. Our
experimental setup is shown in Fig.1. In our experiment, using retroreflected three-beam MOT, about ͳͲ଻ laser cooled 87Rb atoms areloaded in a glass cell. One of problems to limit the sensitivity of theatom gravimeters is the vibrational noise from the floor through theretro-reflecting mirror of Raman beams (Fig. 1). Therefore, the low
frequency (< 10 Hz) vibrational noise of the mirror should be
suppressed by using passive or active vibrational systems to achieve thetarget sensitivity of the gravity measurement. In our gravimeter system,
we use a commercial passive isolation system with a resonancefrequency of about 0.5 Hz, and we can improve the signal to noise ratioof the interference fringe (Fig, 2). Without a vibrational isolator, we
could not clearly observe the interference signal for the interaction time
longer than 30 ms. By employing a vibrational isolator, we could
FIG 1. Experimental setup.
observe the interference signal for the interaction time up to 45 ms, andthe sensitivity of ȟ݃Ȁ݃ ൌ ͹Ǥʹ ൈ ͳͲି଼ was
realized. However, a residual vibrational noise
limits the sensitivity and we could not further
improve the sensitivity. To improve the sensitivity
further, we consider a hybrid approach in which
both the atom gravimeter and the mechanicalaccelerometer are employed to improve thesensitivity [1]. To realize this hybrid system, wefirst examined the correlation between the signals
from the atom gravimeter and the mechanicalaccelerometer. The phase shift of the observed
interference signal and the shift estimated from the
FIG 2. Interference signals without(red) and with vibrational
accelerometer are plotted in Fig. 3, and we could
isolation(blue)
observe the correlation between both signals. Using
the high correlation between both signals, the phaseof the interference signal is compensated by thephase shift estimated from the mechanicalaccelerometer signal, and we will be able to further
improve the sensitivity of the gravity measurement.

Acknowledgement
This work was supported by MEXT Q-LEAP
Grant Number JPMXS0118069452

Reference[1] Aopeng Xu, “vibration compensation of an atom
gravimeter”, Chinese Optics Letters Vol. 17, Issue
7, 070201(2019)

FIG3. Phase shifts of the interference signal (blue) and theaccelerometer (orange)Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ2-01

Implementation of Double Quantum Magnetometry to Continuously Excited
Ramsey Method
Yuta Araki1, Ikuya Fujisaki1, Yuji Hatano1, Takeharu Sekiguchi1, Takayuki Shibata2,
Takayuki Iwasaki and Mutsuko Hatano1
1

Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
2
DENSO Corporationaraki.y.aj@m.titech.ac.jp

Introduction
NV centers, spin qubits in diamond, have been studied for magnetic sensing applications. The continuously excited (CE)Ramsey method reported high sensitivity of 17pT/ξHz for DC magnetometry1. However, for the measurement ofmagneto-encephalo-graphy (MEG) in humans, which is our measurement target, further improvement in sensitivity is needed.
The double quantum magnetometry (DQ) is a method to improve the DC field sensitivity2. Applying DQ to the conventionalRamsey measurement not only effectively doubles the NV gyromagnetic ratio, but also improves T2* due to common-mode
noise rejection. We report the development of a measurement protocol in which DQ is applied to the CE-Ramsey method toimprove the sensitivity of the DC magnetic field.

MethodThe diamond sample was 110-m-thick 12C CVD layer deposited on a type ჟa substrate, and was irradiated with electron
beams of 5 × 1017 cm–2 and annealed. P1 and NV center concentrations were estimated to be approximately 8 ppm and 0.8
ppm. The static magnetic field of 10 mT was aligned parallel to the NV axis. A 532 nm laser was irradiated from the side of
the sample. The fluorescence was focused by a CPC lens and read by a photodetector. To implement DQ, we applied the
MW frequencies resonant to the low-frequency ݉௦ = 0 ՞ െ1 transition and the high-frequency mୱ = 0 ՞ +1
transition simultaneously. The single-quantum (SQ) Rabi frequencies for the two transitions were matched.
ResultCE-SQ-2-Ramsey and CE-DQ-4-Ramsey were performed to confirm the effect of DQ in the CE protocol. Compared to
SQ, twice the frequency of oscillation was obtained in DQ [see Fig.1 (a)], confirming that a doubling of the NV gyromagnetic
ratio was achieved. Dephasing time T2*, fitted values, were similar for SQ and DQ, confirming that common-mode noise
rejection was achieved [see Fig.1 (a)]. Next, to confirm the effect of DQ on sensitivity enhancement, we compared themeasurements of sweeping of detuning, which corresponds to an external magnetic field, between SQ and DQ. The results
confirmed that the slope was improved by the application of DQ [see Fig.1 (b)].










FIG. 1. (a) Comparisons of NV Ramsey measurements (Upper) and Discrete Fourier transform (Lower). (b)Comparisons of
Detuning sweep measurements of SQ and DQ (Upper) and their calculated Slopes (Lower).
Acknowledgements
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395.
We thank Dr. Hiromitsu Kato (AIST) and Dr. Shinobu Onoda, Dr. Takeshi Ohshima (QST) for supplying diamond samples.
Reference
C. Zhang, et alPhys Rev Appl, 15, 1 (2021)
2
E. Bauch et al., Phys Rev X , 8, 31025 (2018)1

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ2-02

Development of highly sensitive compact quantum sensor with NV center in
12
C-enriched CVD diamond for bio-medical and industrial application
Yuta Kainuma1, Yuta Shigenobu1, Yuji Hatano1, Takayuki Shibata2, Akimitchi Nakazono3,
Hiromitsu Kato4, Takeshi Ohshima5, Takayuki Iwasaki1, and Mutsuko Hatano1,5
1

Department of Electrical and Electronics Engineering, School of Engineering, Tokyo Institute of Technology
2
DENSO CORPORATION
3YAZAKI CORPORATION
4
National Institute of Advanced Industrial Science and technology
5
National Institutes for Quantum Science and Technology
kainuma.y.aa@m.titech.ac.jp

Introduction
Magnetometers based on the ensemble nitrogen-vacancy (NV) centers have high magnetic sensitivity and have monitored
not only rat’s cardiac magnetism1 but also battery current over a wide dynamic range2. For these applications, especially,magnetoencephalography have required high magnetic sensitivity and multiple sensors. Thus, the development of a compact
quantum sensor is important to be implemented in the system with sufficient spatial resolution. However, these sensors havenot achieved the magnetic sensitivity required to detect magnetoencephalography.
We investigated the magnetic sensitivity of the quantum sensor head by lateral laser irradiation using 12C-enriched chemical
vapor deposition (CVD) growth diamond, which is suitable for NV centers and scalable device fabrication.

MethodFigure 1(a) shows the construction of the quantum sensor head, the inside of the dashed line is an NV diamond; The NV
centers in 12C-enriched CVD diamond were formed by electron-beam irradiation (5.01017 e/cm2) and high-temperatureannealing after it. The excitation green laser (wavelength: 532 nm) was focused on the side of the NV diamond by a lens
(focal length: 200mm). The photoluminescence from the NV center collected by compound parabolic concentrator (CPC)
lens and split laser by the beamsplitter in the optical line are detected by a photodiode (PD1) and PD2 as shown in Fig.1(a).
A laser-noise compensation is performed by an auto-balance (AB) circuit and the output signal is modulated by a lock-in
amplifier (LIA) with the modulation frequency (fmod) = 7.03 kHz. The magnetic field was adjusted to be parallel to the NV
quantum axis. The resonance frequency of the lock-in optically detected magnetic resonance (ODMR) spectra was locked
by the output microwave frequency updated. The optical setup was assembled in the magnetic shield.

Result and discussion
The measured signal spectra are shown in Fig.1(b). the floor noise of on- and off-resonance was estimated less than 60
pT/Hz0.5 and 40 pT/Hz0.5, however, electronic noise matched the off-resonance noise at 1 Hz. We confirmed that floor-noise
attenuation in the on-resonance spectra at low frequencies seems that the feedback circuit captures the resonance frequency
of ODMR. From the long-measured magnetic signal, the minimum detectable magnetic field (MDMF) was extracted with
Allan variance, reaching approximately 260 fT. MDMF can be improved by faster feedback circuit and NV diamond quality;
the use of preferentially-aligned NV center CVD diamond improves the magnetic field sensitivity by a factor of about 3 ormore3.
Acknowledgments This work was supported in part by MEXT Q-LEAP Grant Number JPMXS0118067395.
References [1] K. Arai et al., Commun. Phys. 5, 200 (2022), [2] Y. Hatano et al., Sci. Rep. 12, 13991 (2022),[3] C. Osterkamp et al., Sci. Rep. 9, 5786 (2019)

Fig .1 (a)A schematic of the construction of quantum sensor head: dashed line indicates NV diamond sensor. The diamond
was glued to the apex of the CPC lens by optical adhesives. (b) Measured FFT spectrum of magnetic sensitivity. The offresonance was measured with a microwave (fmw = 2.0 GHz) applied. Electronic noise was measured without a laser.

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ2-03

Development of a Nonmagnetic Helical Sensor Drive Multipoint Measuring
Mechanism for Magnetocardiography in Animals
Wenyu Shang1, Motofumi Fushimi1, Shinichi Chikaki1, Masaki Sekino1
1

Graduate School of Engineering, The University of Tokyo
Shangwenyu720@g.ecc.u-tokyo.ac.jp

Introduction
In the clinic, electrocardiography (ECG) and magnetocardiography (MCG) are widely known as common techniques toobserve the electrophysiological activity of the heart. Because the magnetic permeability is more uniform than the
conductivity in the organism, to obtain more accurate cardiac electrical information, MCG usually shows higher accuracy
and specificity than ECG. (for some diseases) [1]. This study will focus on MCG technology. By introducing a new type ofhelical nonmagnetic measurement device, taking animals as the measurement target, we can obtain all-around magnetic field
information to complete the depth measurement of the cardiac current source and realize 3D reconstruction.[2]Methods
In this study, we proposed a new sensor array for MCG measurement in animal to obtain more depth information about
current sources. Unlike conventional devices, we used a ring-shaped sensor array instead of a flat plane sensor array. We
designed a mechanism to realize multipoint MCG measurement and assembled it with nonmagnetic material, as shown in
Figure 1. With this mechanism, MCG data were measured using 3 OPMs.


Figure 1. Multipoint MCG measurement mechanism
Figure 2. Result of MCG measurement in rat
Results and discussion
Figure 2 shows the results of MCG measurement. 3 OPMs with six channels were used to measure the rat's MCG. The twochannels of OPM respectively detected the r and ș direction of ring. The result of additive averaging based on thesimultaneously acquired ECGs shows that the R wave can be clearly captured from directions other than the anterior chestplane. However, its signal strength is weak (about 2 pT), and the design of the mechanism needs to be improved to obtain asignal with a higher signal-to-noise ratio.

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

Reference[1] Shin, et al. (2019). Clinical Hemorheology and Microcirculation, 73(2), 283-291.
[2] R. Fenici, Expert Rev. Mol. Diagn., vol. 5, no. 3, pp. 291–313, May 2005.
Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ2-04

Ensemble NV- center in diamond for quantum sensing created by high fluenceelectron beam irradiation
Shuya Ishii1,2, Seiichi Saiki1, Shinobu Onoda1,2, Yuta Masuyama1, Hiroshi Abe1,2, Takeshi Ohshima1,2
1

Takasaki Advanced Radiation Research Institute, National Institutes for Quantum Science and Technology, 1233 Watanuki,
Takasaki, Gunma 370-1292, Japan, 2Institute for Quantum Life Science, National Institutes for Quantum Science and Technology, 49-1 Ana-gawa, Inage-ku, Chiba 263-8555, JapanISHII.shuya@qst.go.jp

Introduction
NV- center has been paid attention as a quantum sensor for highly sensitive detection of magnetic field, electric field,
temperature and strain, etc. [1]. Electron beam irradiation followed by subsequent thermal annealing is known as the effective
procedures to create NV- center in diamond. The electron irradiation generates vacancies in diamond and the annealing
enables vacancies to diffuse in the lattice. Then diffused vacancies are captured by nitrogen atoms, and as a result, NV centers
are created. In addition, substitutional nitrogen atom at a lattice site (P1 center) also acts as a donor for NV center, the charge
state of NV centers changes from neutral (NV0) to NV-. Creation high concentration of ensemble NV- centers is needed toachieve high sensitively sensing [1]. The magnetic sensitivity is proportional to the reciprocal of the number of NV centers
and T2 (spin coherence time), i.e., high concentration NV- centers with long T2 increase the sensitivity. P1 center has animportant role for being a component of NV- centers and acting as donor to the NV center. But it also plays a role asdecoherence source (decrease in magnetic field sensitivity) [1]. Therefore, it is important to create high concentration of NVcenters considering the amount of P1 centers.
In current study, we investigate irradiation fluence dependence of the creation behavior of NV centers in type-Ib diamonds
by using electron spin resonance (ESR) and photo-luminescence (PL) to understand the creation mechanism of NV- center.
The values of T2 are also evaluated by Hahn-echo measurement, since it is one of the key parameters for highly sensitive
magnetometry [1]. Then, we discuss the creation mechanism of NV centers based on concentrations of defects.

MethodThe commercial diamonds synthesized by High Pressure and High Temperature (HPHT) were used. The initial P1
concentrations ([P1]initial) for the samples were measured by ESR, 80, 72, 52, and 46 ppm, respectively. 2 MeV electrons
were irradiated with fluences up to 8.0 ×1018 cm-2 at room temperature. Then, the samples were annealed at 1000ႏ for 2
hours to create NV centers. The concentration of P1 (number of electron spins) was measured by ESR. The initialconcentration of P1 was in the range from 50 ppm to 100 ppm. The ratio of NV- to NV0 was evaluated from PL spectrum.
All these measurements were performed at room temperature. The values of T2 of NV- center ensembles were measured
using a home-built fluorescent microscope with a microwave system.
Results & Discussion
We studied the creation behavior of NV center in type-Ib diamonds with high [P1]initial under relatively high irradiation
fluences. The decrease rate of P1 centers as a function of irradiation fluence shows similar tendencies for all type-Ib diamondsamples, regardless of the initial P1 concentration in the low fluence range (~ 4.0 x 1018 e/cm2). The reduction rate of P1
centers suggests that P1 centers are consumed by recombination with introduced vacancies. However, the decrease rate of
P1 became lower in the high fluence ranges from 6.0 x 1018 e/cm2 to 8.0 x 1018 e/cm2, especially when [P1]initial is smaller,in spite that [P1] still exists even after irradiation at 8.0 x 1018 e/cm2. The process of P1 center consumption seems to shiftdepending on the residual P1 centers. Furthermore, the P1 center consumption and NV- center creation were compared andas a result, it is concluded that some amounts of the P1 centers were consumed by other defects. The conversion efficiency
from [P1]initial to the [NV-] reached ~19% at 8.0 x 1018 e/cm2 and the value confirms the usefulness of electron beamirradiation for high concentration of NV- centers in type-Ib diamonds, whereas results in this study suggests that not all P1
centers converted to NV- center and the residual defects might leads to a cause of decoherence..
Acknowledgement
This work was supported by Quantum Leap Flagship Program (Q-LEAP; JPMXS 0118067395 and
JPMXS0118068379) of MEXT.
Reference[1] J. F. Barry, J. M. Schloss, E. Bauch, M. J. Turner, C. A. Hart, L. M. Pham and R. L. Walsworth. Rev. Mod. Phys., 92,
No.1, 015004 (2020)

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ2-05

Synthesis of n-type diamond using tert-butyl phosphine
for high sensitivity of the NV sensor
Riku Kawase1, Hiroyuki Kawashima1, 2, Hiromitsu Kato2, Norio Tokuda3, Satoshi Yamasaki3,
Mikihiro Kubota1, Masahiko Ogura2, Toshiharu Makino2, Norikazu Mizuochi1, 4
1

Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
3
Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa 920-1192,Japan
kawase.riku.87n@st.kyoto-u.ac.jp

2

Introduction
Recently, ultra-long spin coherence time (T2 § 2.4 ms) of the single nitrogen-vacancy (NV) center in P-doped n-type
diamond was obtained1. The spin coherence time was the longest in room-temperature among solid-state systems. In
addition to the long T2, as a negative charge state of the NV center is stable2. Furthermore, it also reported that creation
yield of shallow NV centers formed by ion-implantation was improved in addition to longer T2 and improved charge
stability3. Due to such reports, P-doping methods for n-type diamond synthesis is getting more important.
Phosphine is usually used for P-doped diamond synthesis by chemical vapor deposition (CVD). However, phosphine
has high explosibility and toxicity, so it threatens safety of experimenters and expensive exclusion equipment was required.
Therefore, we synthesized P-doped n-type diamond with tert-butyl phosphine (TBP) whose explosibility and toxicity
were lower than phosphine's ones4, and we confirmed that the synthesized sample shows relatively long T2 (1620 ± 100
ȝs, FIG. 1). We also confirmed perfect alignment of NV axis which is also important for high sensitivity of NV quantum
sensor.

FIG. 1. Result of Hahn-echo measurement

Reference1

E. D. Herbschleb, H. Kato, Y. Maruyama, T. Danjo, T. Makino, S. Yamasaki, I. Ohki, K. Hayashi, H. Morishita, M.
Fujiwara, N. Mizuochi, Nature Communications, 10, 3766 (2019).
2
Y. Doi, T. Fukui, H. Kato, T. Makino, S. Yamasaki, T. Tashima, H. Morishita, S. Miwa, F. Jelezko, Y. Suzuki, N. Mizuochi,
Physical Review B, 93, 081203(R) (2016).
3
A. Watanabe, T. Nishikawa, H. Kato, M. Fujie, M. Fujiwara, T. Makino, S. Yamasaki, E. D. Herbschleb, N. Mizuochi,
Carbon, 178, 294-300 (2021).
4
H. Kato, S. Yamasaki, and H. Okushi, phys. stat. sol. (a) 202, 2122–2128 (2005).
This work was supported by MEXT Q-LEAP Grant Number JPMXS0118067395
Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-ȕ2-06

Decoherence Phenomena in Nitrogen-Vacancy Diamond
Aulden Jones1, Tokuyuki Teraji2, Chikara Shinei2, and Yuta Masuyama3
12School of Physics, Georgia Institute of Technology
Research Center for Functional Materials, National Institute for Materials Science3
National Institutes for Quantum and Radiological Science and Technology

Introduction
Nitrogen vacancy (NV) centers in diamond are atom-sized spin defects whose unique properties enable their use as
robust quantum sensors. Recent research efforts have focused on NV magnetometry, where both single andensemble NVs are used for highly sensitive magnetic field detection with nanoscale spatial resolution. While NV
sensors have been successfully applied to fields ranging from neuroscience to condensed matter physics, ensemble
NV diamonds are still below the sensitivity threshold needed for many more potential applications1. Presented here
is an attempt to investigate the relationship between large crystallographic strain features and the spin coherencetime ܶଶ‫ כ‬in NV-diamonds grown by chemical vapor deposition (CVD). A better understanding of this relationship can
provide valuable input for improving diamond growth methods and eventually extending ܶଶ‫ כ‬.
*This work was supported under the NSF Global Quantum Leap Program under Grant No. OISE-2020174.

Reference

1
J. F. Barry, J. M. Schloss, E. Bauch, M. J. Turner, C. A. Hart, L. M. Pham, and R. L. Walsworth, Rev. Mod. Phys. 92,
015004 (2020).

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Ȗ2-01

Improvement in the long-term stability of the interferometer gyroscopeusing slow and continuous atomic beams
Naoki Nishimura1, Takuya Kawasaki2, Tomoya Sato2, Ryotaro Inoue2, Mikio Kozuma1,2
1

Department of Physics, School of Science, Tokyo Institute of Technology
2Institute of Innovative Research, Tokyo Institute of Technology
nishimura.n.ae@m.titech.ac.jp

Introduction
Gyroscopes consisting of an atom interferometer can measure angular velocity. Since their expected sensitivity is higher
than that of optical interferometers [1], many studies have paid much attention to the application of atom gyroscopes, forexample, precision measurement of physical constants [2] and inertial navigation of ships and aircraft [3]. We are developing
a matter-wave gyroscope using Raman transitions for a cold and continuous Rb atomic beam. A deadtime-free measurement
and long-stability obtained by a continuous atom beam interferometer benefit the non-GPS type of inertial navigation. In ourprevious study, we successfully measured the rotation of the Earth with our gyroscope with continuous and cold atomic
beam of Rb [4]. Currently, we are aiming to improve the accuracy of the gyroscope for the level required for inertial
navigation.


MethodIn the atom interferometer using Raman transitions, three pairs of counter-propagating Raman beams construct a ʌ/2-ʌ-ʌ/2
Mach-Zehnder type interferometer [5]. The phase in the interference signal, which reflects the Sagnac effect, is measured as
the population ratio between the ground-state hyperfine states F=1 and F=2 of 87Rb atom. The constant frequency shift ο݂in the ʌ Raman beams induces a sinusoidal change in the ratio of the population with the frequency of 2ο݂. We create areference signal of the frequency 2ο݂ based on the signal of the frequency ο݂ by a synthesizer. We estimate the phase of
the fluorescence signal by the lock-in detection with the reference signal.
If drift occurs in the relative phase of Raman beams, it worsens the long-term stability of the interferometer. To eliminate
the spurious phase shift caused by the drift in the relative phase of Raman beams, a simultaneous measurement ofinterferometers with counter-propagating atomic beams that share Raman beams is employed. The sign of the Sagnac phaseshift induced by the rotation depends on the velocity vector, while that induced by other drifts such as acceleration, movementof optical elements, and imperfections in the equipment is the same for the interferometers. Thus, the common-mode phasedrifts are canceled by taking the difference between the output phase shifts in two interferometers while enhancing the phaseshift originating from the system’s rotation. Although the common-mode rejection is a powerful method to improve longterm stability, the common-mode rejection ratio is limited in the actual system. It is desirable to suppress the relative phasedrift itself as much as possible. One of the most significant sources of long-term drift in the output phase of our interferometeris the imperfectness in the relative phase locking of Raman beams. The relative phase of counter-propagating Raman beams
is measured as the optical beat note between Raman beams. The locking of the relative phase is achieved by stabilizing thebeat note to the external RF reference using the PID feedback loop. The performance of the feedback circuit, which consistsof discrete electronic components, is vulnerable to changes in operational conditions, such as temperature. We newly
introduce the feedback circuit consisting of a field programmable gate array (FPGA). The full-digitalized feedback systemis free from the instability stemming from the change in the environmental conditions where the gyroscope is operated. As
a result, the performance of the stabilization of the relative phase of Raman beams is improved.

ResultThe stability of the interferometer as a gyroscope is evaluated by calculating the Allan deviation of the output phase of theinterferometer. The performance of the gyroscope with FPGA-based stabilization for the relative phase of Raman beams will
be reported. In addition, the changes in the response of the interferometer to the variations in the environmental condition
will be presented.

Reference
1

T. L. Gustavson, P. Bouyer, and M. A. Kasevich, Phys. Rev. Lett, 78, 2046 (1997)
G. Rosi, F. Sorrentino, L. C Acciapuoti, M. P Revedelli, G. M. Tino. Nature, 510, 518-521 (2014)
3
J.C. Fang and J. Qin Sensors, 12, 6331-6346 (2012)
4
T. Sato, R. Inoue and M. Kozuma, short presentation in 4th IFQMS, SE-03A-Ɂ1-05, 7-9 Dec. 2021
5
M. Kasevich and S. Chu, Phys. Rev. Lett, 67, 181 (1991).
2

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Ȗ2-02

Bragg interferometer using slow and continuous atomic beamwith sub-recoil transverse momentum width
Tomoya Sato1, Toshiyuki Hosoya2,3, Ryotaro Inoue1 and Mikio Kozuma1,3
1Institute of Innovative Research, Tokyo Institute of Technology
2
Japan Aviation Electronics Industry, Ltd.
3
Department of Physics, School of Science, Tokyo Institute of Technology
sato@qnav.iir.titech.ac.jp
Introduction
A gyroscope based on interferometry using a continuous atomic beam is one of the most promising candidates for nextgeneration inertial navigation to complement navigation with external references such as GPS because of their highsensitivity, deadtime-free detection, and long-term stability. In recent years, alkaline earth-like atoms have attracted attention
to improving the sensitivity and stability of interferometers [1]. In contrast to alkali atoms, which are widely used in atominterferometry [2], alkaline earth-like atoms do not possess electron spin in their ground state, making them less susceptible
to effects of environmental magnetic fields. An interferometer with Bragg diffraction, which uses only the ground state, canbenefit from this advantage. In addition, higher-order Bragg diffraction increases the area of the interferometer, thus thesensitivity of the gyroscope will be improved.
In atomic interferometry with Bragg diffraction, the interference signal is evaluated by measuring the number of atoms in
different momentum states of the same internal state. Therefore, an atomic beam whose initial momentum width is narrower
than the recoil momentum of the Bragg beam is essential for high-precision measurement. In our recent paper, we propose
a new technique to obtain the high-flux atomic beam of ytterbium (Yb) with sub-recoil momentum width [3]. Theinterferometer with such type of atomic beam will pave the way to the high-end gyroscope for inertial navigation.

MethodBy applying two-dimensional cooling using 1S0-3P1 intercombination transition to a slow atomic beam of 171Yb produced
by dipolar-allowed transition, we have successfully compressed the transverse momentum width of the atomic beam to below
4԰݇, where ԰݇ is the recoil momentum of the Bragg beam (dipolar-allowed 1S0-1P1 transition). For further reduction of
momentum width, we applied a momentum filtering technique to our atomic beam using an ultra-narrow transition between
the ground state and long-lived metastable state 3P2. The atomic beam orthogonally passes the laser light resonant on theultra-narrow transition (507nm). With our experimental condition, the spectral linewidth associated with the transverse
momentum width of the atomic beam is determined by the transit time broadening rather than the lifetime of the metastablestate. Since the transition time broadening is adjusted to correspond to the momentum width of less than ԰݇, atoms can be
excited to the metastable state in a momentum-selective manner. After blowing up the remaining atoms in the ground state,
which have unwanted momentum components, one can obtain ground state atoms within the narrow momentum width bytransporting the atoms from the metastable state to the ground state in the same momentum-selective manner.
The momentum-filtered atomic beam is introduced into the interferometer region, where three pairs of counterpropagating Bragg beams construct the ʌ/2-ʌ-ʌ/2 Mach-Zehnder type interferometer. The Sagnac effect causes the sinusoidal
variation between populations of momentum states 0԰݇ and 2݊԰݇ as a function of the acceleration and angular velocity
on the Sagnac loop, where ݊ is the order of the Bragg diffraction. For the momentum-resolved detection, the third 507nm
light, tuned to excite the 2݊԰݇ state, is introduced just after the interferometer. The change in the population of the 2݊԰݇
momentum state can be detected as the change in the loss of the atoms in the ground state.
Results
We successfully generate an atomic beam of 171Yb whose momentum width is 0.20ሺ8ሻ԰݇ by the momentum filtering.
The higher order Bragg diffraction, up to the 10th, is observed. With the obtained atomic beam with narrow momentum width,
the construction of the Bragg interferometer is ongoing. The present status of the development will be reported.
This work was supported by JST-Mirai Program, Grant Number JPMJMI17A3 and COI-NEXT, Grant Number
JPMJPF2015.

Reference
1

T. Mazzoni et al., Phys. Rev. A, 92, 053619 (2015).
D. Sayoie et al., Sci. Adv. 4, eaau7945 (2018).
3
T. Hosoya et al., Opt. Commun., 528, 129048 (2023).
2

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Ȗ2-03

Development of a cryogenic suspension system for TOrsion-Bar Antennae(TOBA)
Ching Pin Ooi1, Satoru Takano1, Yuka Oshima1, Kentaro Komori2, Yuta Michimura2,3 and Masaki
Ando1,2
1

Department of Physics, The University of Tokyo
2
RESCEU, The University of Tokyo
3
LIGO Laboratory, California Institute of Technology
ooichingpin@g.ecc.u-tokyo.ac.jp
Introduction
TOrsion-Bar Antennae (TOBA), is a proposed gravitational wave antenna1, targeted at observing intermediate mass blackhole mergers with peak sensitivity in the range 0.1 – 10 Hz, but can also be used for early earthquake warnings via measuringtransient gravitational perturbations2. TOBA phase III is currently being built, with a target sensitivity that would make it
useful for early earthquake warnings. To that end, a cryogenic suspension system is being developed to achieve the low
thermal suspension noise requirements. TOBA, as its name suggests, uses torsion bars for sensing. Thus, this work focuseson quantifying and reducing suspension thermal noise of torsion pendulums, with two key technologies, cryogenic
temperatures and crystalline fibres.


MethodOur setup consists of a copper beryllium torsion pendulum, suspended by a 1 mm thick sapphire fibre, and is cooled in acryogenic chamber to near 4 K. The Q value, a parameter which characterizes the thermal noise of the suspension, ismeasured off the setup via an optical lever. Coil-coil actuators were used to excite the torsion pendulum to start off the
ringdown for Q value measurements.

4YV7HPSIRUVDSSKLUH
&RROGRZQ

4:DUPXS


















7HPS .

Fig. 2. Range of Q values with temperature of the cryogenic chamber.
This ranges from 3000 – 70 000 across the temperatures, and we notehere that the highest values are when it is coldest.
Fig. 1. Torsion pendulum suspended by 1 mm 
sapphire fibre, in a cryogenic chamber. Coil-coilactuators provide the initial excitation for ringdown.


Acknowledgments
We would like to thank the Shigemi Otsuka and Togo Shimozawa for manufacturing the mechanical parts used.
This work is supported by MEXT Q-LEAP Grant Number JPMXS0118070351.

Reference1

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

2

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Ȗ2-04
Torsion-Bar Antenna for Early Earthquake Alert
Yuka Oshima1, Satoru Takano1, Ching Pin Ooi1,
Kentaro Komori2, Yuta Michimura2,3, and Masaki Ando1,2
1

Department of Physics, University of Tokyo
2

3

RESCEU, University of Tokyo

LIGO Laboratory, California Institute of Technology
yuka.oshima@phys.s.u-tokyo.ac.jp

Introduction
Torsion-Bar Antenna (TOBA) is a highly sensitive gravity gradient sensor using torsion pendulums [1]. We use test
masses suspended horizontally and aim to detect the torsional rotation caused by tidal forces as shown in FIG. 1. The resonant
frequency of torsional motion is ~1 mHz, therefore TOBA has good design sensitivity in low frequencies (0.1 ̽ 10 Hz).
TOBA is useful for gravity-based earthquake early warning [2], and the observation of Newtonian noise and gravitational
waves. A prototype detector Phase-III TOBA with a 35 cm-scale pendulum is under development [3]. The target sensitivity
is set to 10-15 /¥Hz at 0.1 Hz. Phase-III TOBA can detect earthquakes with a magnitude 7 or larger within 10 seconds froma 100 km distance [3].

MethodFor Phase-III TOBA, we operate torsion pendulums at cryogenic temperatures to reduce thermal noise. We havesuccessfully demonstrated cooling down test masses at 6 K [4]. Now, torsion pendulums are under development to achieve
our target sensitivity. Differential Fabry-Perot cavities are used to read out the rotational angle to the pendulums. We finisheddesigning the parameters of Fabry-Perot cavities and the mechanical parts for the pendulums.

FIG. 1. the schematic of TOBA. Test masses are suspended horizontally in the x-y plane and a suspension wire is stretchedin the z-axis. Grey lines represent tidal forces, red arrows show the rotational motion of the pendulums.

Acknowledgments
We would like to thank Shigemi Otsuka and Togo Shimozawa for manufacturing the mechanical parts used. This work
was supported by MEXT Quantum LEAP Flagship Program (MEXT Q-LEAP) Grant Number JPMXS0118070351. Y.O.
was supported by JSPS KAKENHI Grant Number JP22J21087 and JSR Fellowship, the University of Tokyo.

Reference1

M. Ando et al., Phys. Rev. Lett., 105, 161101 (2010).
J. Harms et al., Geophys. J. Int., 201, 1416 (2015).
3
T. Shimoda et al., International Journal of Modern Physics D, 29, 1940003 (2020).
4
T. Shimoda, PhD thesis, The University of Tokyo (2019).
2

Proc. 5th IFQMS (The 5th International Forum on Quantum Metrology and Sensing)

SE-03A-Ȗ2-05
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SE-03A-Ȗ2-06

Experimental generalized measurement of qubits using a quantum computer
Tingrui DONG1,2, Binho LE3, Fumihiro KANEDA1, Soyoung BAEK1 and Keiichi EDAMATSU1
1
Research Institute of Electrical Communication, Tohoku University
2
School of Engineering, Tohoku University
3
Frontier Research Institute for Interdisciplinary Sciences, Tohoku University
dong.tingrui.r7@dc.tohoku.ac.jp
Introduction
Quantum computers, which provide the ability to surpass classical computers, are also able to carry out some fundamental
experiments in quantum mechanics. For example, generalized quantum measurement protocols and their uncertainty
relations1 [1] can be realized and tested in a quantum computer. Here, we propose the implementation of generalized quantum
measurement of qubits in a noisy intermediate-scale quantum computer (NISQ). First, we demonstrate the variable-strength
measurement of a single qubit, which was once studied by photon polarization qubits2, using an NISQ (IBM-Q). The
performance of the measurement is quantified and discussed in terms of the characteristics of the noise and error of the NISQ.
We also implement the nonlocal, variable strength parity measurement of a pair of qubits we recently proposed3. The circuit
we build will also be a part of deterministic, complete Bell state measurement with arbitrary precision. To date, we made ademonstration of the strongest measurement situation by using the 7-qubit quantum computer (ibm-perth). The performanceof the measurement strategy is limited due to the noise and error in present NISQ.
This work is supported by MEXT Q-LEAP (JPMXS0118067581) and JST, the establishment of university fellowships
towards the creation of science technology innovation (JPMJFS2102).
Figures
Fig.1 The measurement circuit of measuring a pair of qubits. The qubit 0 and 1 perform as meter 1 for measurement parity
information. The qubit 2 and 3 perform the entangled system. The qubit 4 and 5 perform as the other meter for checking thephase information. The system pair is coupled with two meters by CNOT gate. Finally, the Bell-state measurement are doneon the system qubits, and the meters are projected on the calculational basis.

Reference1

M. Ozawa, Phys. Rev. A, 67, 042105 (2003).
F. Kaneda, S.-Y. Baek, M. Ozawa, and K. Edamatsu, Phy. Rev. Lett. 112, 020402 (2014).
3
P. Vidil and K. Edamatsu, New J. Phys. 23, 043004 (2021).

2