近畿大学理工学部物理学コースの量子制御研究室、量子多体物理学研究室、物性理論研究室が合同で運営する量子物理学および量子技術に関するセミナーです。学期中は基本的に毎週水曜日10:45-12:15に開催しています。

今後の予定

2022年度


日時:2022年6月30日13:15-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: 浅井 詩緒乃(奈良女子大学)

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

概要: 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).


日時:2022年7月6日10:45-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: 金子 隆威(量子多体)

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

概要: 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). (編集済み) 


日時:2022年7月22日10:45-

教室: 31号館5階502教室 + Zoomでのオンライン配信

発表者: 長尾 一馬(理化学研究所)

題目: Squeezed coherent state path integral methods for fermions

概要: 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.

公式には近畿大学大学院総合理工学研究科学際セミナーとして開催。


日時:2022年7月27日10:45-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: 井上 直人(一般相対論・宇宙論研究室)

題目: TBA

概要: TBA


 

過去の講演

2022年度前期


日時: 2022年4月20日10:45-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: 小久保 治哉(物性理論)

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

概要: 

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). 


日時: 2022年4月27日10:45-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: 鏡原 大地(量子多体)

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

概要: 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). 


日時:2022年5月11日10:45-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: 久木田 真吾(量子制御)

題目: Short composite operation robust against two common systematic errors

概要: 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]


日時:2022年5月18日10:45-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: 數田 裕紀(量子多体)

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

概要: 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).


日時:2022年5月25日10:45-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: Mikkelsen, Mathias(量子多体)

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

概要: 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) 


日時:2022年6月1日10:45-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: 中村 優希(京都大学)

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

概要: 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).


日時:2022年6月8日10:45-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: 宮井 誠一郎(量子多体)

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

概要: 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).


日時:2022年6月15日10:45-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: 木屋 晴貴(量子制御)

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

概要: 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]

日時:2022年6月24日10:45-

教室: 31号館3階シミュレーション実験室 + Zoomでのオンライン配信

発表者: 市川 翼(大阪大学 量子情報・量子生命研究センター)

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

概要: 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 tke 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.


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