"Kindai QPT Seminar 2022" | "Kindai QPT Seminar" | 近畿大学量子多体物理学研究室

Time and Date: 10:45-, April 20, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kokubo, Haruya (CMT)

Title: Dynamics of the wake in the Gross-Pitaevskii model with a small nonlinear coefficient

Abstract: When an object moves at a constant speed inside a fluid, a wake appears behind the object depending on the size and speed of the object. In a cold atomic gas Bose-Einstein condensate (BEC), quantum vortex generation in the wake of an obstacle has been observed when the velocity of the obstacle potential exceeds the critical velocity [1-2]. The critical velocity is strongly dependent on the shape of the obstacle potential. The critical velocity is about $0.37$ times the speed of sound if the obstacle size is sufficiently larger than the healing length of the superfluid [3-5]. Furthermore, when the obstacle is delta-functional, the critical velocity $v_c$ is near the speed of sound.
On the other hand, the critical velocity is zero in the limit that the nonlinear coefficient of the Gross-Pitaevskii equation describing the motion of the cooled atomic gas BEC is zero (linear Schrodinger limit). In this talk,we show that the critical velocity decay with decreasing the nonlinear coefficient and investigate the associated dynamics of the wake and the quantum vortex generation.

[1] G. W. Stagg, N. G. Parker, and C. F. Barenghi, J. Phys. B 47, 095304 (2014).

[2] K. Sasaki, N. Suzuki, and H. Saito, Phys. Rev. Lett. 104, 150404 (2010).

[3] S. Rica, Physica D 148, 221 (2001).

[4] C. T. Pham, C. Nore, and M.E. Brachet, Physica D 210, 203 (2005).

[5] W. J. Kwon, G. Moon, S. W. Seo, and Y. Shin, Phys. Rev. A 91, 053615 (2015).

Time and Date: 10:45-, April 27, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kagamihara, Daichi (QMB)

Title: Finite temperature phase diagram of a three-dimensional spin-dependent Fermi Hubbard model

Abstract:

Recent experimental developments in ultracold atomic physics enable us to simulate various interesting many-body systems. Combining state-dependent optical lattices [1,2], Feshbach resonances [3], and Rabi coupling between two internal states induced by microwaves or lasers [1,2], one can realize a spin-dependent Fermi Hubbard model (SDFHM) [4].

In this work, we investigate a finite temperature phase diagram of a three-dimensional SDFHM with an attractive interaction. In the ordinary Fermi Hubbard model, the so-called Bardeen-Cooper-Schrieffer (BCS)-Bose-Einstein Condensate (BEC) crossover phenomenon is expected. We first review the BCS-BEC crossover based on the Nozières-Schmitt-Rink (NSR) theory [5,6] in the standard Hubbard model. We extend the NSR approach to SDFHM and discuss how differences in hopping amplitudes and Rabi coupling affect the superfluid phase transition temperature.

[1] L. Krinner, M. Stewart, A. Pazmino, J. Kwon, and D. Schneble, Nature 559, 589 (2018).
[2] L. Riegger, Ph.D. Thesis (2019).
[3] C. Chin, R. Grimm, P. Julienne, and E. Tiesinga, Rev. Mod. Phys. 82 1225 (2010).
[4] W. V. Liu, F. Wilczek, and P. Zoller, Phys. Rev. A 70, 033603 (2004).
[5] P. Nozières and S. Schmitt-Rink, J. Low. Temp. Phys. 59, 195 (1985).
[6] H. Heiselberg, in “The BCS-BEC Crossover and the Unitary Fermi Gas”, edited by W. Zwerger (Springer, New York, 2011).

Time and Date: 10:45-, May 11, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kukita, Shingo (QC)

Title: Short composite operation robust against two common systematic errors

Abstract: Unavoidable systematic errors hinder precise quantum control. Pulse length error (PLE) and off-resonance one (ORE) are typical systematic errors that are encountered during one-qubit control. A composite operation, one of open-loop error cancellation techniques, can help compensate for the effects of systematic errors during quantum operation. Several composite operations that are robust against either PLE or ORE have been identified. However, few attempts have been made to construct composite operations that are robust against both errors (bi-robust) simultaneously. We develop a new bi-robust composite operation for controlling one-qubit, which exhibits a short operation time [1].

[1] S. Kukita, H. Kiya, Y. Kondo, arXiv: 2112.12945 [quant-ph]

Time and Date: 10:45-, May 18, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kazuta, Hironori (QMB)

Title: Towards quantum simulation of non-ergodic behavior of the one-dimension Bose-Hubbard model with a trapping potential

Abstract:

The recent development of ultracold gas experiments allows us to simulate the thermalization of isolated quantum systems. When the system satisfies the eigenstate thermalization hypothesis (ETH) [1], it thermalizes after long-time evolution. Integrable systems [2] and many-body localized systems (MBL) with random potentials [3] are known as the systems that do not satisfy the ETH. Recently, violation of the ETH has been observed in systems that neither are integrable nor have random potentials [4,5]. Typical examples include quantum many-body scar [4] and stark MBL [5]. In this presentation, I focus on another system that violates the ETH. I specifically investigate the time evolution of the initial state in the one-dimensional ultracold atoms in the trap potential. I will first reproduce the results of a previous study [6] numerically. Then, I will present some preliminary results of our attempts for observing the non-ergodic behavior with the use of a remote quantum simulator developed by the Quantum Optics group at Kyoto University.

[1] J. M. Deutsch, Phys. Rev. A 43, 2046 (1991).

[2] T. Kinoshita , T. Wenger & D. S. Weiss, Nature 440 900 (2006).

[3] J. Choi, S.Hild, et al. Science 352, 1547(2016)

[4] C. J. Turner, A. A. Michailidis, et al, Nat. Phys. 14, 745 (2018).

[5] E. van Nieuwenburg, Y. Baum, et al, PNAS 116, 9269 (2019).

[6] M. Kunimi and I. Danshita, Phys. Rev. A 104,043322 (2021).

Time and Date: 10:45-, May 25, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Mikkelsen, Mathias (QMB)

Title: Noise correlations and spin-structure factor for the SU(N) Hubbard model

Abstract: The realization of SU(N) Hubbard models experimentally using Alkaline-earth atoms [1] has lead to renewed theoretical interest in this model, see e.g. [2] for a review of the phase diagram. The spin-spin correlations are a natural probe for the SU(N) order in the system and measuring them experimentally is therefore important. It is well-established that the noise correlations measured by time-of-flight experiments, which corresponds to the momentum fluctuations of the initial state, can probe the spin structure factor in the Mott-limit of SU(2)-Hubbard models [3].In this talk I explicitly establish the mathematical relationship between the momentum-momentum fluctuations and spin structure factor for Mott-insulating states in the SU(N)-Hubbard model at any integer filling. The relation is confirmed numerically by DMRG calculations for 1D Fermi-Hubbard models with N=2-6 and it is shown that the momentum fluctuations still reflect the SU(N) order for weaker interactions and incommensurate filling (i.e. in the metallic phases away from the Mott-limit).

[1] A.V. Gorshkov et al. Nature Physics 6, 289–295 (2010)
[2] S. Capponi, P. Lecheminant and K. Totsuka, Ann.Phys. 367, 50 (2016)
[3] E. Altman, E. Demler, and M. D. Lukin, Phys. Rev. A 70, 013603 (2004)

Time and Date: 10:45-, June 1, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Nakamura, Yuki (Kyoto Univ.)

Title: Rydberg atoms described by the Ising model with sign-inverted next-nearest-neighbor interaction

Abstract: In recent years, taking advantages of their high controllability, Rydberg atoms confined in an optical tweezer array have been utilized as a quantum simulator of quantum spin models [1,2]. Controllable quantum simulators using up to 256 neutral atomic arrays have been realized so far, and new quantum phases and related phase transitions have been experimentally observed [2]. In the case of quantum simulators of Ising-type models, the interaction between two spins that has been realized thus far is of van der Waals type, in which the sign of the nearest neighbor interaction is the same as that of the next-nearest neighbor one.

In this talk, I propose a method to realize Ising model with sign-reversed next-nearest neighbor interactions by weakly coupling one Rydberg state to another Rydberg state. I also discuss surface criticality [3,4] as an example of interesting phenomena that can occur in this novel system. I derive Ginzburg-Landau (GL) equation describing the motion of antiferromagnetic order parameters near the first-order phase transition point. By comparing it with numerical calculations of microscopic models in the mean-field approximation, we verify the validity of the analytical calculation based on the derived GL equation for surface criticality.

[1] M.Endres et al., Science 354,6315 (2016).

[2] S.Ebadi et al., Nature 595, 227 (2021).

[3] R.Lipowsky, Phys. Rev. Lett. 49, 1575 (1982).

[4] I.Danshita et al., Phys. Rev. A 91,013630 (2015).

Time and Date: 10:45-, June 8, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Miyai, Seiichiro (QMB)

Title: Towards analysis of correlation propagation velocities in the SU(N) Hubbard model

Abstract: Quantum simulation means mimicking a quantum many-body system of interest by using another system with high controllability. Since its first proposal by Feynman in 1981 [1], quantum simulation has been realized in various experimental systems [2]. One of the most promising applications of quantum simulation is to analyze non-equilibrium dynamics of quantum many-body systems in the sense that it is in general difficult with classical computers [3]. For example, in a quantum simulator consisting of a Bose gas in an optical lattice, the time evolution of equal-time correlation functions has been measured and a mechanism of the correlation propagation based on a quasiparticle picture has been discussed [4]. These quasiparticles are composed of excess particles (doublon) and holes (holon), which can be described as slave-bosons [5].

The purpose of this study is to analyze how the propagation velocity of the correlation in the SU (N) Hubbard model behaves by using the slave-boson method. In this presentation, as a preliminary step for this purpose, we review the derivation of the maximum group velocity, which is serves as an estimation of the upper limit of the information propagation velocity in the one-dimensional Bose-Hubbard model, on the basis of the method using auxiliary bosons [5], and the auxiliary bosons method for the Fermi-Hubbard model [6].

[1] R. P. Feynman, Int. J. Theor. Phys. 21, 467 (1982).

[2] I. M. Georgescu et al., Rev. Mod. Phys. 86, 153 (2014).

[3] K. Nagao and I. Danshita, Suurikagaku 684, 36 (2020), in Japanese.

[4] M. Cheneau et al., Nature 481, 484 (2012).

[5] P. Barmettler et al., Phys. Rev. A 85, 053625 (2012).

[6] G. Kotliar and A. E. Ruckenstein, Phys. Rev.Lett. 57, 1362 (1986).

Time and Date: 10:45-, June 15, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kiya, Haruki (QC)

Title: General off-resonance-error-robust symmetric composite pulses with three elementary operations

Abstract: The performance of quantum computing is highly dependent on the accuracy of quantum control in each process.Realistic quantum operations suffer from undesirable effects of systematic errors caused by the miscalibration of experimental apparatuses and such errors deteriorate the performance of quantum control.In one-qubit control, one mainly confronts two typical systematic errors: pulse length error (PLE) and off-resonance error (ORE).A composite pulse (CP) is a method used to compensate for such systematic errors.For one-qubit operations, several CPs that are robust against PLE have been found, such as SK1[1], BB1[2] and SCROFULOUS[3].On the other hand, ORE-robust CPs that implement arbitrary $\theta$-rotations have been less investigated. The CORPSE family is one of the simplest and most tractable ORE-robust CPs for implementing arbitrary $\theta$-ratations[4].

In this talk, I explain a systematic construction of a wide class of ORE-robust CPs that implement arbitrary $\theta$-rotations.In this class of CPs, we have one continuous free parameter to choose a CP that implements a target operation. We evaluate the performance of the CPs in this class in terms of gate fidelity(and infidelity) and the time required for operation[5].

References:

[1] K. R. Brown, A. W. Harrow, and I. L. Chuang,Phys. Rev. A \textbf{70}, 052318 (2004); K. R. Brown,A. W. Harrow, and I. L. Chuang, Phys. Rev.A \textbf{72}, 039905(E) (2005).
[2] Wimperis, S. 1994 Broadband, narrowband, and passband composite pulses for use in advanced NMR experiments. J. Magn. Reson. A \textbf{109}, 221–231. (doi:10.1006/jmra.1994.1159)
[3] Cummins, H. K. Llewellyn, G. , Jones, J. A. 2003 Tackling systematic errors in quantum logic gates with composite rotations. Phys. Rev. A \textbf{67}, 042308. (doi:10.1103/PhysRevA.67.042308)
[4] H. Cummins and J. Jones, Use of composite rotations to correct systematic errors in nmr quantum computation, New Journal of Physics \textbf{2}, 6 (2000).
[5] S. Kukita, H. Kiya, Y.Kondo, arXiv:2203.05754[quant-ph]

Time and Date: 10:45-, June 24, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Ichikawa, Tsubasa (QIQB, Osaka University)

Title: Bayenianism, Conditional Probability and Laplace Law of Succession in Quantum Mechanics

Abstract: The axioms of quantum mechanics (QM) assume the existence of a measurer.
Although this is not a problem in practical terms, it has often been pointed out
by Heisenberg and others that this is a fundamental feature that distincts
QM from classical mechanics.

QBism (Quantum Bayesianism) is a recent attempt of reconstruction of QM
with emphasis on this feature. Here, Bayesianism is the view that probability is
“a measure of one’s degree of belief on whether a given phenomenon will take place.
QBism follows this view and derives quantum probability (Born rule) as a measure
of the measurer’s degree of belief.

The research question I raise here is whether QBism can derives other relevant
concepts in probability theory such as conditional probability and relative frequency.
The answer is expected to be affirmative, since in Bayesian approach to classical
probability theory, Italian mathematician Bruno de Finetti actually derived these.

In this talk, I would like to brief review of Bruno de Finetti’s work and QBism,
followed by my recent work which derives conditional probability and relative frequency
along the line of the thought of Bruno de Finetti’s works and QBism.

Time and Date: 13:15-, June 30, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Asai, Shiono (Nara Wowen’s Univ.)

Title: Transition between vacuum and finite-density states in the Bose–Hubbard model with spatially inhomogeneous dissipation

Abstract: Recent technological advances in cold-atom experiments enable us to analyze open quantum many-body systems with widely controllable dissipation [1–3]. Previous theoretical studies have considered the dynamics of a Bose–Hubbard system with dissipation processes that tend to lock the phase difference of the particle field between nearest-neighboring sites. It has been shown that steady states reached after long time evolution exhibit a transition between a Bose condensed state and a non-condensed state when the dissipation strength is varied [4,5]. Such transition phenomena in Bose–Hubbard systems with dissipation have recently attracted much attention.

In this work, we analyze the dynamics of the infinite-dimensional Bose–Hubbard model with spatially inhomogeneous dissipation by solving the Lindblad master equation with use of the Gutzwiller variational method [6]. We consider dissipation processes that correspond to inelastic light scattering in the case of Bose gases in optical lattices. We assume that the dissipation is applied to half of the lattice sites in a spatially alternating manner. We focus on steady states at which the system arrives after long time evolution. We find that when the average particle density is varied, the steady state exhibits a transition between a state in which the sites without dissipation are vacuum and one containing a finite number of particles at those sites. We also discuss whether this transition can occur also at finite dimensions on the basis of numerical analyses using the cluster mean field approximation.

1 A. Daley, Adv. Phys. 63, 77 (2014).

2 Y. S. Patil, S. Chakram, and M. Vengalattore, Phys. Rev. Lett. 115, 140402 (2015).

3 T. Tomita, S. Nakajima, I. Danshita, Y. Takasu, and Y. Takahashi, Sci. Adv. 3, e1701513 (2017).

4 S. Diehl, A. Tomadin, A. Micheli, R. Fazio, and P. Zoller, Phys. Rev. Lett. 105, 015702 (2010).

5 A. Tomadin, S. Diehl, and P. Zoller, Phys. Rev. A 83, 013611 (2011).

6 S. Asai, S. Goto, and I. Danshita, Prog. Theor. Exp. Phys. 2022, 033I01 (2022).

Time and Date: 10:45-, July 6, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kaneko, Ryui (QMB)

Title:　Renyi entropy after a quantum quench starting from insulating states in a free boson system

Abstract:　The concept of entanglement is indispensable for understanding quantum many-body physics these days. The entanglement entropy quantifies the degree of entanglement and is a valuable probe for characterizing states of quantum many-body systems. The protocol for measuring the Renyi entropy first proposed in 2012 [1,2] has further stimulated experimental and theoretical research on real-time dynamics of quantum many-body lattice systems. Yet, studies of the entanglement growth during the quench dynamics for (soft-core) bosons are very few, even for a quench to a noninteracting region [3,4].Here we focus on a one-dimensional free boson system and investigate the time-dependent Renyi entanglement entropy after a quantum quench starting from the Mott insulating and charge-density-wave states. We show that the second Renyi entropy is the negative of the logarithm of the permanent of a matrix consisting of time-dependent single-particle correlation functions. We obtain rigorous conditions for satisfying the volume-law entanglement using the permanent inequality [5]. We also successfully calculate the time evolution of the entropy in unprecedentedly large systems by brute-force computations of the permanent. We discuss possible applications of our findings to the real-time dynamics of noninteracting bosonic systems.

[1] A. J. Daley et al., Phys. Rev. Lett. 109, 020505 (2012).
[2] D. A. Abanin and E. Demler, Phys. Rev. Lett. 109, 020504 (2012).
[3] M. Cramer et al., Phys. Rev. Lett. 100, 030602 (2008).
[4] A. Flesch et al., Phys. Rev. A 78, 033608 (2008).
[5] R. Berkowitz and P. Devlin, Isr. J. Math. 224, 437 (2018).

Time and Date: 10:45-, July 22, 2022

Room: Rm. 31-502, 5th Floor, 31 Bldg. + Webcast via Zoom

Speaker: Nagao, Kazuma (RIKEN)

Title: Squeezed coherent state path integral methods for fermions

Abstract: Spontaneous symmetry broken phases, such as Bose-Einstein condensates of dilute bosonic atoms and superconductors of electrons, are ubiquitous and fundamental quantum phases in condensed matter physics, AMO physics, and high-energy physics. In recent years, the Higgs mode of fermionic superconductor/superfluid systems, which is an emergent amplitude excitation mode of the order parameter field, has been extensively explored in many experiments including pump-probe experiments for BCS-type superconductors [1] and a radiofrequency spectroscopy experiment for ultracold two-component Fermi gases [2].

In this work, towards establishing a versatile framework to describe those experimental systems, we develop a new path integral representation of fermionic superfluid systems that gives a unified description of the fermionic quasiparticle excitations and the bosonic collective excitations of the order parameter fluctuations. Our approach gives a direct fermionic generalization of the squeezed-coherent-state path integral method for bosons [3]. In this talk, we apply this formalism to BCS superconductors and discuss that a generalized Lagrangian defined for a squeezed fermionic coherent state shows a gapped excitation branch corresponding to the Higgs excitation mode and reproduces the well-known BCS quasiparticle gapped spectrum in a single framework [4]. Additionally, I will also talk about an ongoing project on an application of the method to contact interacting Fermi gas systems [5]. In this work, we analyze the generalized Lagrangian in terms of the momentum-shell renormalization group method and present a new finding on the ground state BCS- BEC crossover phenomenon of the dilute Fermi gas systems.

[1] R. Shimano and N. Tsuji, Annu. Rev. Condens. Matter Phys. 11, 103 (2020).

[2] A. Behrle et al., Nat. Phys. 14, 781 (2018).
[3] I. M. H. Seifie, V. P. Singh, and L. Mathey, Phys. Rev. A 100, 013602 (2019).

[4] K. Nagao, D. Li, and L. Mathey, arXiv:2102.03113.

[5] K. Nagao and L. Mathey, in preparation.

Time and Date: 10:45-, August 2, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Andreas Thomasen (QunaSys)

Title: Contemporary approaches to variational quantum algorithms for quantum chemistry

Abstract: Variational quantum algorithms were initially proposed as enabling the first use-cases of quantum computers, namely determination of ground state properties of molecules, with the variational quantum eigensolver being the most familiar and well-known among them. There are signs that such algorithms have inherent short-comings that in the short term will render them unable to produce useful results on noisy intermediate-scale quantum (NISQ) devices due to noise and even for high-fidelity architectures may not converge due to the occurrence of barren plateaus in the parameter search space. In this seminar we give an overview of these problems and discuss recent approaches to mitigating and potentially overcoming them.

Time and Date: 10:45-, September 28, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Sekino, Yuta (RIKEN)

Title: Optical spin conductivity in ultracold atomic gases

Abstract: In solid-state physics, measurement of optical conductivity, which is conductivity of an alternating electric current obtained in an optical way, plays crucial roles to understand various exotic electron systems such as high-Tc superconductors, non-Fermi liquids, and Dirac electrons [1,2,3]. Similarly, conductivity of an alternating spin current (optical spin conductivity) is expected to be a useful probe to investigate various quantum many-body systems from spin degrees of freedom.

In this presentation, we report our proposal to measure optical spin conductivity of ultracold atomic gases [4]. In this proposal, an alternating spin current is induced by using a time-dependent gradient of magnetic field or the optical Stern-Gerlach effect. The generated current is measured by observing dynamics of spin density profile.

To demonstrate what information the frequency dependence of the spin conductivity can capture, we computed the conductivity of several cold-atomic systems; a spin-1/2 s-wave Fermi superfluid, spin-1 Bose Einstein condensate, Tomonaga-Luttinger liquid, and topological Fermi superfluid [4,5]. In these systems, nontrivial spin excitations result in the frequency dependence of the spin conductivity quite different from that of the conventional Drude conductivity.

References:

[1] C. C. Homes et al., Phys. Rev. Lett. 71, 1645 (1993).

[2] Y. S. Lee et al., Phys. Rev. B 66, 041104(R) (2002).

[3] R. R. Nair et al, Science 320, 1308 (2008); K. F. Mak et al., Phys. Rev. Lett. 101, 196405 (2008).

[4] Y. Sekino, H. Tajima, and S. Uchino, arXiv:2103.02418.

[5] H. Tajima, Y. Sekino, and S. Uchino, Phys. Rev. B 105, 064508 (2022).

Time and Date: 9:00-, October 5, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker 1: Yabuuchi, Yoshihiro (QMB)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 2: Kisanuki, Shingo (QMB)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 3: Yuri, Takumi (QMB)

Title: Only in Japanese.

Abstract: Only in Japanese.

Time and Date: 9:00-, October 12, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker 1: Nishida, Shou (QC)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 2: Takegami, Hibiki (QMB)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 3: Andou, Kyousuke (CMT)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 4: Yanagawa, Hayato (QMB)

Title: Only in Japanese.

Abstract: Only in Japanese.

Time and Date: 10:45-, October 26, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kaneko, Ryui (QMB)

Title: Tensor-network study of the SU(4) Heisenberg model on a plaquette lattice

Abstract: Lattice models with SU(N>2) degrees of freedom have recently attracted much interest because of possible emergent novel quantum states that do not appear in the Hubbard and Heisenberg models with SU(2) degrees of freedom. Experimental systems to realize these models include ultracold atomic gases in optical lattices [1-6] and antiferromagnets with intertwined spin and orbital degrees of freedom [7,8]. Recently, Ozawa et al. have reported that Pomeranchuk cooling facilitates the observation of antiferromagnetic correlations in SU(N) systems for sufficiently large N [6]. Miyazaki et al. have investigated the ground state of the relevant SU(4) Heisenberg model on a plaquette lattice by the cluster mean-field and spin-wave approximations [9,10]. They have found the SU(4) singlet ground state in the strongly anisotropic regime. On the other hand, the prior tensor-network study suggested that the ground state should exhibit the coexisting Neel and the valence bond crystal (VBC) order in the nearly isotropic region [5]. This observation implies the presence of the phase transition in the intermediate anisotropy region. To investigate the ground states of the SU(4) Heisenberg model on a plaquette lattice more precisely, we use the two-dimensional tensor-network method based on the infinite projected entangled pair states [11,12]. We successfully reproduce the SU(4) singlet ground state in the strongly anisotropic limit and the Neel-VBC coexisting ground state in the nearly isotropic limit. We will examine the location of the phase transition point and discuss the relevance of our results to future experiments.

[1] C. Wu et al., Phys. Rev. Lett. 91, 186402 (2003).
[2] C. Honerkamp and W. Hofstetter, Phys. Rev. Lett. 92, 170403 (2004).
[3] M. A. Cazalilla et al., New J. Phys. 11, 103033 (2009).
[4] A. V. Gorshkov, Nat. Phys. 6, 289 (2010).
[5] P. Corboz et al., Phys. Rev. Lett. 107, 215301 (2011).
[6] H. Ozawa et al., Phys. Rev. Lett. 121, 225303 (2018).
[7] P. Corboz et al., Phys. Rev. X 2, 041013 (2012).
[8] S. Nakatsuji et al., Science 336, 559 (2012).
[9] Y. Miyazaki et al., AIP Advances 11, 025202 (2021).
[10] Y. Miyazaki et al., J. Phys. Soc. Jpn. 91, 073702 (2022).
[11] T. Nishino et al., Prog. Theo. Phys. 105, 409 (2001).
[12] F. Verstraete and J. I. Cirac, arXiv:cond-mat/0407066.

Time and Date: 10:45-, November 9, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kiya, Haruki (QC)

Title: Search for the shortest composite quantum gate

Abstract:

One of the largest problems in realizing a quantum computer is inevitable systematic device errors. We consider two types of systematic errors in single-qubit control: Pulse Length Error (PLE) and Off-Resonance Error (ORE). A composite quantum gate (CQG) is a method in order to compensate for such systematic errors [1]. CQGs use the redundancy obtained by decomposing the target operation into multiple ones. The gate fidelity and operation time are important to evaluate the performance of CQG. A shorter operation time is better for reducing the effects of decoherence and noises. There is, however, not much discussion on the lower bound of operation time [2]. We are interested in this bound.

In order to obtain a hint of the bound, we exhaustively generate high fidelity gate combinations and examine their operation times. This survey suggests the existence of nontrivial bounds on operation time for CQGs.

参考文献

[1] Malcolm H. Levitt, Ray Freeman, J. Magn. Reson.33,473 (1979)

[2] Shingo Kukita, Haruki Kiya, Yasushi Kondo, Phys. Rev. A 106, 042613 (2022)

Time and Date: 10:45-, November 16, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kazuta, Hironori (QMB)

Title: Quantum simulation of non-ergodic behavior of the Bose-Hubbard model with a trapping potential

Abstract: The development of information technology in last few decades has enabled us to do many kinds of things on the cloud via internet. Such a cloud system is advantageous in the sense that it can be used at any time, at any place, and by anyone in the world. Of our particular interest are cloud services of advanced quantum devices, such as IBMQ (Quantum computer equipped with superconducting quantum qubit provided by IBM) [1] and Albert (Platform to create and control with Bose-Einstein Condensate (BEC) provided by ColdQaunta) [2], which have become open to the public rather recently. In Japan, the Quantum Optics group at Kyoto University plans to launch a cloud service of their quantum simulator based on ultracold atoms in optical lattices. We support its development as users of a preliminary version of the service. Since optical-lattice quantum simulators are suitable for studying non-equilibrium dynamics of quantum many-body systems [3], which is difficult to access in numerical calculations on classical computers, we aim to analyze non-ergodic dynamics due to the Hilbert-space fragmentation in the 1D Bose-Hubbard system by using the quantum simulator remotely [4].

In this presentation, I focus on the time evolution of the initial state in which each odd-numbered site is doubly occupied and each even-numbered site is empty. I will first present some preliminary results of our attempts for observing the non-ergodic behavior, which have not yet been succeeded, with the use of the remote quantum simulator. I will explain several possible reasons of the failure in the observation, among which the effect of the interchain hopping seems dominant. In order to theoretically analyze the effect of the interchain hopping, we try to numerically simulate dynamics of the Bose-Hubbard model on a two-leg ladder lattice. For this purpose, I will review how to apply the time-evolving block decimation method to the two-leg ladder geometry [5].

[1] https://quantum-computing.ibm.com/

[2] https://albert.coldquanta.com/

[3] F. Schäfer, T. Fukuhara, S. Sugawa, Y. Takasu, and Y. Takahashi, Nat. Rev. Phys. 2, 411 (2020).

[4] M. Kunimi and I. Danshita, Phys. Rev. A 104, 043322 (2021).

[5] I. Danshita, J. E. Williams, C. A. R. Sá de Melo, and C. W. Clark, Phys. Rev. A 76, 043606 (2007).

Time and Date: 10:45-, November 30, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kokubo, Haruya (CMT)

Title: Size dependence of a plate obstacle for vortex generation and dynamics in superfluid wake

Abstract: In classical hydrodynamics, a wake appearing behind a moving obstacle is characterized by a Reynolds number, the ratio of inertial forces to viscous forces. The Reynolds number is a quantity proportional to the characteristic length of the obstacle. As the Reynolds number increases, an unstable flow appears.
A wake appears by considering obstacles using lasers in cold atom systems [1]. Furthermore, the Reynolds number in superfluids has also been suggested [2]. The Superfluid Reynolds number includes the critical velocity of the vortex generation and is not the ratio of inertial to viscous force as in the classical system.
In this study, we study the size dependence of a plate obstacle in the Reynolds number by considering a wake in a 2D BEC system with a plate obstacle. Plate obstacle is very useful because it doesn’t need to consider density decay caused by gradient around the obstacle and size of the obstacle can be characterized only by the width of the plate. In this talk, we introduce the dynamics of the wake induced by the plate obstacle when its width is changed and discuss the future outlook.
[1]T.W. Neely, et al. Phys. Rev. Lett. 104, 160401 (2010)
[2]M.T. Reeves, et al. Phys. Rev. Lett. 114, 155302 (2015)

Time and Date: 10:45-, December 7, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kagamihara, Daichi (QMB)

Title: Entanglement entropy in a non-Hermitian linear optical system

Abstract:

Sampling complexity refers to the difficulty of sampling from a distribution close to the desired (e.g., quantum system) probability distribution and is sometimes discussed in the context of quantum supremacy. Recently, by considering the sampling problem of identical bosons time-evolving by a quadratic Hamiltonian from a product state, a transition from the state in which sampling can be done easily to that where it is difficult has been proposed[1]. Furthermore, it has been pointed out that when time evolution is extended to be non-unitary by considering open systems, there is a transition in sampling complexity that has not been observed in unitary systems[2].

The aim of this work is to clarify the relation between the sampling complexity and other complexity measures, such as entanglement entropy. We extend the method to calculate the Rényi entanglement entropy in a unitary non-interacting boson system[3] to the non-Hermitian case. We apply our method to the non-Hermitian situation discussed in Ref. [2] and calculate the Rényi entanglement entropy. We will discuss how the scaling law of the entanglement entropy and sampling complexity are related.

[1] A. Deshpande, B. Fefferman, M. C. Tran, M. Foss-Feig, and A. V. Gorshkov, Physical review letters 121, 030501 (2018).
[2] K. Mochizuki and R. Hamazaki, arXiv.2207.12624.
[3] D. Kagamihara, R. Kaneko, S. Yamashika, K. Sugiyama, R. Yoshii, S. Tsuchiya, and I. Danshita, arXiv:2207.08353.

Time and Date: 10:45-, December 14, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kukita, Shingo (QC)

Title: Lower bound on operation time of composite pulses robust against pulse length error

Abstract: Precise control of quantum systems is a cornerstone for realizing high-quality quantum technology such as quantum computing and quantum communication. The performance of control of systems often deteriorates due to systematic errors. In one-qubit control, the pulse length error (PLE) is one of typical systematic errors, which is caused by deviation of the strength of a control field. A composite pulse (CP) is a method for suppressing the effects of such systematic errors. A CP is a sequence of operations, where systematic errors in the operations cancel each other. Many CPs that are robust against the PLE have been found. However, their operation time tends to be longer than a simple one because CPs replace a simple operation with multiple ones. A longer operation time implies stronger decoherence, and thus a shorter CP is preferable from the viewpoint of noise immunity. In this talk, we discuss a lower bound on the operation time of CPs robust against the PLE. This bound is not saturable, but non-trivial.

Time and Date: 10:45-, December 21, 2022

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Kunimi, Masaya (Tokyo University of Science)

Title: Proposal for realization of the quantum-spin chain with Dzyaloshinskii-Moriya interaction using Rydberg atom quantum simulators

Abstract: Recently, the combination of optical tweezers and Rydberg atoms has enabled the realization of highly-controllable quantum simulators for quantum spin systems, and various quantum many-body phenomena have been studied. Typical quantum spin models such as the S=1/2 Ising, XY, and XXZ models have been experimentally realized by using Rydberg atoms with optical tweezers [1]. In some actual magnets, the Dzyaloshinskii-Moriya (DM) interaction exists, which originates from spin-orbit couplings. It is well known that the DM interaction causes various nontrivial phenomena. For example, skyrmion [2] and chiral soliton lattice [3] emerge due to the DM interactions. The DM interaction has not been realized in the Rydberg atom quantum simulators.

In this talk, we propose a method to experimentally realize a 1D quantum spin model with the DM interaction using the Rydberg atom systems.
Specifically, a Rydberg state (e.g., |nS>) is coupled to another Rydberg state (|n’S>) by a two-photon Raman transition. The Rabi coupling with different phases at each atom position can be realized by setting the direction of the lasers appropriately. By unitary transformation of this system and transformation to the rotating frame, we can obtain a spin Hamiltonian with the DM interaction.

In addition to the experimental proposal, we will present the numerical results for the DH model [4], whose Hamiltonian has the DM interaction and transverse magnetic field only. We investigate the nonequilibrium dynamics of quantum solitons in the DH model and find that the quantum solitons decay after a long-time evolution. Finally, we also show that the DH model has quantum many-body scar states by explicitly constructing a restricted spectrum generating algebra [5].

[1] A. Browaeys and T. Lahaye, Nature Phys. 16, 132 (2020).
[2] N. Nagaosa and Y. Tokura, Nature Nanotechnology, 8, 899 (2013).
[3] J. Kishine and A. S. Ovchinnikov, Solid State Phys. 66, 1 (2015).
[4] S. Kodama, A. Tanaka, and Y. Kato, arXiv:2209.04227 (2022).
[5] S. Moudgalya, N. Regnault, and B. A. Bernevig, Phys. Rev. B 102, 085140 (2020).

Time and Date: 9:00-, January 11, 2023

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker 1: Okuda, Kousei (CMT)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 2: Fujiwara, Hirotomo (CMT)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 3: Maruo, Kouki (CMT)

Title: Only in Japanese.

Abstract: Only in Japanese.

Time and Date: 9:00-, January 13, 2023

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker 1: Andou, Kyousuke (CMT)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 2: Yanagawa, Hayato (QMB)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 3: Yabuuchi, Yoshihiro (QMB)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 4: Kisanuki, Shingo (QMB)

Title: Only in Japanese.

Abstract: Only in Japanese.

Time and Date: 9:00-, January 18, 2023

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker 1: Takegami, Hibiki (QMB)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 2: Yuri, Takumi (QMB)

Title: Only in Japanese.

Abstract: Only in Japanese.

Speaker 3: Nishida, Shou (QC)

Title: Only in Japanese.

Abstract: Only in Japanese.

Time and Date: 10:45-, February 8, 2023

Room: Simulation and Experiment Room, 3rd Floor, 31 East Bldg. + Webcast via Zoom

Speaker: Mikkelsen, Mathias (QMB)

Title: Improved diagonalization scheme for continuum systems and chaos in two-component Bose mixtures

Abstract: Obtaining accurate numeric results for interacting continuum systems as the number of particles increase is a challenging task. In this talk I will outline how optimal truncation of the many-body basis [1] and incorporating knowledge of the exact two-body solutions into the many-body Hamiltonian through the effective interaction approach [2-4] greatly reduces the Hilbert space size required to obtain an accurate energy spectrum. Using these techniques allows us to investigate the spectrum and dynamics of 5 interacting identical bosons [5], as well as 2+2 and (with some limitations) 3+3 interacting Bose mixtures [6] in one dimensional harmonic traps. I will explain, how the latter can be used to investigate the emergence of chaos as a function of the particle-particle inter and intra -component interactions. The diagonalization scheme allows us to investigate typical indicators of chaos such as the level spacing distribution and the thermalization dynamics of few-body observables [7]. In particular we show that one can obtain strong signatures of chaos by increasing the inter-component interaction strength and breaking the symmetry of intra-component interactions.

[1] M. Plodzien, D. Wiater, A. Chrostowski, and T. Sowinski, arXiv:1803.08387 (2018)
[2] J. Rotureau, EPJ D 67, 1 (2013)
[3] E. Lindgren, J. Rotureau, C. Forssen, A. G. Volosniev and N. T. Zinner, NJP16, 063003 (2014)
[4] L. Rammelmüller, D. Huber, and A. G. Volosniev, arXiv:2202.04603 (2022)
[5] M. Mikkelsen, T. Fogarty, and T. Busch, Phys. Rev. Lett. 128, 070605 (2022)
[6] T. D. Anh-Tai, M. Mikkelsen , T. Busch, T. Fogarty, arXiv:2301.04818 (2023)
[7] L. D’Alessio, Y. Kafri, A. Polkovnikov and M. Rigol, Adv. Phys. 65,239 (2016)

Time and Date: 10:45-, March 1, 2023

Room: Room 301, 3rd Floor, 31 East Bldg.

Speaker: Aksu, Serhan (OIST)

Title: Self pinning transition of a Fermi gas immersed in a Bose gas

Abstract: In this presentation, I will be discussing about a unique quantum phase transition that can be seen in one-dimensional quantum gases. A highly density imbalance of one-dimensional Bose-Bose mixtures where a strongly-correlated minority component immersed in a weakly-correlated majority background such as a Bose-Einstein condensate can undergo an insulting self-pinned quantum state through inter-component interactions (Phys. Rev.Lett. 128, 053401) unlike previous studies of a single-component Tonks gas that can reach to a pinned phase under the presence of a commensurate lattice. In addition to that, I will be discussing about Luttinger liquid theory of one-dimensional quantum gases and manage to establish a connection between these two systems.