Quantum Technology meets Quantum Matter
Japan Standard Time (UTC+9)

Thursday, 17 September
9:00–9:10

Opening

9:00–9:40
Naoto Tsuji (RIKEN)

9:10–9:50
Katja Nowack (Cornell)“Local magnetic measurementsof unconventional
superconductors”

9:50–10:30“Spin freezing crossover inmulti-orbital systems and
SYK strange metal”

9:40–10:20
Sadashige Matsuo

Sergey Uchaikin (IBS)
Arjan van Loo (RIKEN)“Axion search with Josephsonparametric amplifiers”

10:30–10:40

Friday, 18 September

Break(RIKEN)“Control of the DC and AC
Josephson effects on theballistic InAs nanowires”

10:20–10:30

Break

10:40–11:20

10:30–11:10

Sen Yang (CUHK)

Hiroshi Imada (RIKEN)“Study pressure driven phasetransitions via NV centers indiamond”“Single-molecule investigationof charge and energy
dynamics by photon-STM”

11:20–12:00

11:10–11:50

Fan Yang (Stanford)

Kai Yang (IBM)“Imaging nematic transitions iniron-pnictide superconductors
with a quantum gas”

“Atomic-scale magnetic
resonance of quantum spins
on a surface”

11:50–12:00

Closing

https://cems.riken.jp/topicalmeeting/003_qt_meets_qm/
Organizer: Eisuke Abe (eisuke.abe@riken.jp)

Local magnetic measurements of unconventional superconductors
Katja Nowack1
1

Department of Physics, Cornell Universitykatja.nowack [at] cornell.edu

A defining property of a superconductor is its response to an applied magnetic field.
In this talk, I will discuss how we use scanning superconducting quantum interferences
devices (SQUIDs) to study the local magnetic response in two different types ofsuperconductors. First, I will discuss measurements on focus ion beam (FIB) defined
microstructures fabricated from single crystals of the heavy-fermion superconductor
CeIrIn 5 . Using scanning SQUID we observe that the superconducting transition
temperature, T c , varies throughout the structure in a complex pattern. This pattern arises
due to the interplay of a non-trivial strain field from the differential thermal contractionof the substrate and microstructure and the sensitivity of T c in CeIrIn 5 to the strengthand direction of strain. Devices with different geometry show that the spatial
modulation of T c can be tailored in agreement with predictions based on finite element
simulations. These results offer a new approach to manipulate strain-sensitive electronicorder on micrometer length scales in strongly correlated matter. Second, I will show
how we use scanning SQUID to perform local magnetic measurements of ionic gatedsuperconducting MoS 2 devices. This allows us to observe for the first time thediamagnetic response of any few layer van der Waals superconductor despite theextremely small sample volume. I will discuss how we can extract the superfluid
density and other characteristics of the superconducting state from our measurements.

Axion search with Josephson parametric amplifiers
Sergey Uchaikin1 and Arjan Ferdinand van Loo2

1Center for Axion and Precision Physics Research, Institute for Basic Science
193 Munji-ro, Yuseong-gu, Daejeon 34051, South Korea
uchaikin [at] ibs.re.kr
2
Superconducting Quantum Electronics Research Team, RIKEN Center for Emergent
Matter Science (CEMS), 2-1 Hirosawa, Wako 351-0198, Japanarjan.vanloo [at] riken.jp
Axions are hypothetical particles that have been proposed as a solution to thestrong CP problem of quantum chromodynamics. Axions with a mass between 10-3 meV
and 1 meV may also be promising cold dark matter candidates. The observed density ofaxions in the universe should be in the range of 1011−1014 per cm3. These axions can bedetected by their conversion to microwave photons in high magnetic fields inside ahigh-quality cavity due to the inverse Primakoff effect. Microwave signals from axions
are expected to be very small, and to register them a very low-noise amplifier such as aJosephson parametric amplifier is necessary.
Josephson parametric amplifiers consist of a microwave cavity containing
Josephson junctions as their nonlinear element. These devices are capable of quantumlimited amplification of microwave signals. They were first developed in the context ofcircuit QED with the aim to increase the signal-to-noise ratio in experiments relating tosuperconducting qubits, but have since been employed in other contexts where efficient
detection of weak microwave signals is important, such as the axion detection that is thetopic of this talk.
Here, a JPA with an operation frequency around 2.3 GHz is installed in arunning axion search experiment at the Center for Axion and Precision Physics
Research. The goal of the experiment is to scan the JPA operation frequency range withKSVZ sensitivity.

Study pressure driven phase transitions via NV centers in diamond
Sen Yang1
1Department of Physics, The Chinese University of Hong Kong
senyang [at] phy.cuhk.edu.hk

Strongly correlated systems are one of the most interesting and challenging fields
in physics. To understand the physics of quantum phenomena such as superconductivity
and magnetism, measurements with ultimate sensitivity is needed. Nitrogen vacancy(NV) centers in diamond are good candidates as a sensor in studying these phasetransitions. We utilize nitrogen vacancy (NV) centers in diamond as a powerful,spatially-resolved vector field sensor for material research under pressure at cryogenictemperatures. Using a single crystal of BaFe2(As0:59P0:41)2 as an example, we extract thesuperconducting transition temperature (Tc), the local magnetic field profile in theMeissner state and the critical fields (Hc1 and Hc2). The method developed in this work
will become a unique tool for tuning, probing and understanding quantum many bodysystems.

[1] King Yau Yip, Kin On Ho, King Yiu Yu, Yang Chen, Wei Zhang, S. Kasahara, Y.
Mizukami, T. Shibauchi, Y. Matsuda, Swee K. Goh, Sen Yang, Science 366, 1355
(2019).
[2] Kin On Ho, Man Yin Leung, Yaxin Jiang, Kin Pong Ao, Wei Zhang, King Yau Yip,
Yiu Yung Pang, King Cho Wong Swee K. Goh, Sen Yang, Phys. Rev. Applied, 13,024041 (2020).

Imaging Nematic Transitions in Iron-Pnictide Superconductors with aQuantum Gas
Fan Yang1
1

Department of Applied Physics, Stanford University
fyang2 [at] stanford.edu

The SQCRAMscope is a recently realized Scanning Quantum CRyogenic AtomMicroscope that utilizes an atomic Bose-Einstein condensate to measure magnetic fields
emanating from solid-state samples [1]. Here, we combine the SQCRAMscope with anin situ microscope that measures optical birefringence near the surface of a sample tostudy iron-pnictide superconductors [2], where the relationship between electronic andstructural symmetry-breaking resulting in a nematic phase is under debate. We conductsimultaneous and spatially resolved measurements of both bulk and surface
manifestations of nematicity via transport and structural deformation channels,
respectively. By performing local measurements of emergent resistivity anisotropy iniron pnictides, we observe sharp, nearly concurrent transport and structural transitions.
More broadly, these measurements demonstrate the SQCRAMscope's ability to reveal
important insights into the physics of complex quantum materials.

[1] F. Yang, A. J. Kollár, S. F. Taylor, R. W. Turner, & B. L. Lev, Phys. Rev. Applied 7,034026 (2017).
[2] F. Yang, S. F. Taylor, S. D. Edkins, J. C. Palmstrom, I. R. Fisher, B. L. Lev, Nat.
Phys. 16, 514 (2020).

Spin freezing crossover in multi-orbital systems and SYK strange
metalNaoto Tsuji1
1

Quantum Condensate Research Team, RIKEN Center for Emergent Matter Science(CEMS), 2-1 Hirosawa, Wako 351-0198, Japannaoto.tsuji [at] riken.jp

Multi-orbital electron systems offer a playground of strong correlation physics,
including orbital-selective Mott transitions, non-Fermi liquids, and unconventional
superconductivity. Those physics can be successfully described by the multi-orbital
Hubbard model, which finds various material applications such as Sr2RuO4 andiron-based superconductors. In the multiorbital Hubbard model with Hund’s coupling,
there is a competition between the Kondo effect (screening of local magnetic moments)
and the Hund effect (formation of local moments), between which emerges a highly
moment-fluctuating regime called the spin freezing crossover. The spin freezing
crossover regime shows the anomalous frequency dependence of the self-energy(Σ(𝜔)~𝜔1/2) and slow relaxation of the spin correlation (⟨𝑆𝑧 (𝜏)𝑆𝑧 (0)⟩ ∼ 𝜏 −1 ).
Recently, it has been pointed out that such a spin freezing crossover state has astriking similarity to the Sachdev-Ye-Kitaev (SYK) model [1], which shows a maximallychaotic behavior as probed by out-of-time-ordered correlators (OTOCs), and is expected
to be a holographic dual to black holes. Motivated by this observation, we study OTOCs
for the Hubbard model with a new technique using an imaginary-time four-point function
with unusual time ordering [2]. The results show that in the spin freezing crossover
regime a spin-related OTOC rapidly decays without oscillations in a short time, andrelaxes more slowly as a power law in a long time. This is in a good agreement with thebehavior of OTOCs in the SYK model, providing a firm evidence that the spin freezing
crossover regime in the multiorbital Hubbard model effectively realizes the SYK strange
metal state.

[1] P. Werner, A. Kim, and S. Hoshino, Europhys. Lett. 124, 57002 (2018).
[2] N. Tsuji and P. Werner, Phys. Rev. B 99, 115132 (2019).

Control of the DC and AC Josephson effects
on the ballistic InAs nanowires
Sadashige Matsuo1, 21

Quantum Functional System Research Group, RIKEN Center for Emergent Matter
Science (CEMS), 2-1 Hirosawa, Wako 351-0198, Japan
2JST PRESTO 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japansadashige.matsuo [at] riken.jp

The semiconductor technology provides the high electrical controllability and longmean free path in the nanostructures. Recently the transparent interfaces of thesuperconductors and semiconductors have been realized, resulting in the recent researchdevelopment of the exotic superconducting phenomena using the superconducting
proximity effect on the semiconductors as represented by the Majorana Fermionsrealized in the superconductor-semiconductor nanowire junctions [1].
Here we show the experimental results of the Josephson effect in single and double
InAs ballistic nanowires. First, we report on the Shapiro steps measured in theJosephson junctions of the single InAs nanowires. We found that steps appear at thefractional values of the quantized voltage in addition to the integer steps. These
fractional Shapiro steps are attributed to skewness of current-phase relation anticipatedin the ballistic Josephson junctions [2]. These results provide important information toestablish the phase dynamics in the ballistic Josephson junctions [3].
Second, we report on the DC Josephson effect in the ballistic double nanowire. In theexperiment, we measured the supercurrent in the gate-tunable double nanowire. From
the results, we evaluated the supercurrent carried by Cooper pair splitting (CPS), which
only appears when both the nanowires have finite conduction channels. CPS is one of
the necessary ingredients to engineer the MFs with no magnetic field in the double
nanowires [4]. Therefore, our results will provide the way to realize the robust MFs withno magnetic field in the ballistic nanowires [5].

[1] R. M. Lutchyn, et al. Nature Reviews Materials 3, 52 (2018).
[2] A. A. Golubov, et al. Rev. Mod. Phys. 76, 411 (2004).
[3] K. Ueda, S. Matsuo, et al., accepted in Phys. Rev. Research (2020).
[4] J. Klinovaja, et al. Phys. Rev. B 90, 045118 (2014).
[5] K. Ueda, S. Matsuo, et al. Sci. Adv. 5, 2194 (2019).

Single-molecule investigation ofcharge and energy dynamics by photon-STM
Hiroshi Imada1
1Surface and Interface Science Laboratory, RIKEN CPR
himada [at] riken.jp

Transfer of charge and energy in matters is an important dynamic process invarious energy-converting phenomena. Since those dynamic processes are governed bywave functions that vary on the atomic scale, it has been difficult to directly investigate
the essential physics by conventional optical methods. Recently, we have been
conducting a series of atomic-scale investigation of charge and energy transfer inmolecular systems using a scanning tunneling microscope (STM) combined with opticaltechniques (photon-STM) [1-4]. In the seminar, I will describe how an electron goes
through the molecular orbitals to form spin singlet and triplet excitons in thesingle-molecule and how the energy is dissipated by luminescence or energy transfer tothe other molecule (Figure).

Figure: Schematic illustration of a coupled molecule system investigated with scanningtunneling microscopy.
[1] H. Imada, K. Miwa, M. Imai-Imada, S. Kawahara, K. Kimura, Y. Kim, Nature, 538,
364 (2016).
[2] H. Imada, K. Miwa, M. Imai-Imada, S. Kawahara, K. Kimura, Y. Kim, Phys. Rev.
Lett., 119, 013901 (2017).
[3] K. Miwa, H. Imada, M. Imai-Imada, K. Kimura, M. Galperin, Y. Kim, Nano Lett.,
19, 2803 (2019).
[4] K. Kimura, K. Miwa, H. Imada, M. Imai-Imada, S. Kawahara, J. Takeya, M. Kawai,
M. Galperin, Y. Kim, Nature, 570, 210 (2019).

Atomic-scale magnetic resonance of quantum spins on a surface
Kai Yang1
1IBM Almaden Research Center, San Jose, CA 95120, USA
dryangk [at] gmail.com

Recently, the ability to drive electron spin resonance (ESR) of individual atoms
using a scanning tunneling microscope (STM) provided a major step forward in sensing
and manipulating magnetism at the atomic scale. In the first part, I will describe theimplementation of continuous-wave ESR in STM [1]. The ultrahigh energy resolutionof ESR has allowed the measurement of the magnetic interaction between two atoms [2],the detection of nuclear spins [3], as well as the exploration of quantum fluctuations indesigned spin arrays. Next, I will talk about coherent spin control using all-electricpulsed ESR [4]. By modulating the atomically-confined magnetic interaction between
the STM tip and surface atoms, we drive quantum Rabi oscillations of single spins in as
little as ~20 nanoseconds. Ramsey fringes and spin echo signals allow us to improve
quantum coherence. I will also show the coherent operations on engineered atomic
dimers. Coherent control of spins arranged with atomic precision thus provides asolid-state platform for quantum simulation of many-body systems.

[1] S. Baumann, W. Paul, T. Choi, C. P. Lutz, A. Ardavan, and A. J. Heinrich, Science
350, 417 (2015).
[2] F. D. Natterer, K. Yang, W. Paul, P. Willke, T. Choi, T. Greber, A. J. Heinrich, and C.
P. Lutz, Nature 543, 226 (2017).
[3] P. Willke, Y. Bae, K. Yang, J. Lado, A. Ferrón, T. Choi, A. Ardavan, J.
Fernández-Rossier, A. J. Heinrich and C. P. Lutz, Science 362, 336 (2018)[4] K. Yang, W. Paul, S.-H. Phark, P. Willke, Y. Bae, T. Choi, T, Esat, A. Ardavan, A. J.
Heinrich and C. Lutz, Science 366, 509 (2019)