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Low-dimensional fluctuations and pseudogap in Gaudin-Yang Fermi gases 高定-杨费米气体中的低维涨落和赝隙
Pub Date : 2020-05-25 DOI: 10.1103/PHYSREVRESEARCH.2.033441
H. Tajima, S. Tsutsui, Takahiro M. Doi
Pseudogap is a ubiquitous phenomenon in strongly correlated systems such as high-$T_{rm c}$ superconductors, ultracold atoms and nuclear physics. While pairing fluctuations inducing the pseudogap are known to be enhanced in low-dimensional systems, such effects have not been explored well in one of the most fundamental 1D models, that is, Gaudin-Yang model. In this work, we show that the pseudogap effect can be visible in the single-particle excitation in this system using a diagrammatic approach. Fermionic single-particle spectra exhibit a unique crossover from the double-particle dispersion to pseudogap state with increasing the attractive interaction and the number density at finite temperature. Surprisingly, our results of thermodynamic quantities in unpolarized and polarized gases show an excellent agreement with the recent quantum Monte Carlo and complex Langevin results, even in the region where the pseudogap appears.
赝隙是强相关系统中普遍存在的现象,如高T_{rm c}$超导体、超冷原子和核物理等。虽然已知在低维系统中诱导赝隙的配对涨落会增强,但在最基本的一维模型之一,即Gaudin-Yang模型中,这种效应尚未得到很好的探讨。在这项工作中,我们使用图解方法证明了在该系统的单粒子激发中可以看到赝隙效应。费米子单粒子谱在有限温度下,随着吸引相互作用和数密度的增加,呈现出从双粒子色散到赝隙态的独特交叉。令人惊讶的是,我们在非极化和极化气体中的热力学量的结果与最近的量子蒙特卡罗和复杂朗之万结果非常吻合,甚至在赝隙出现的区域也是如此。
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引用次数: 5
Fracton-elasticity duality of two-dimensional superfluid vortex crystals: defect interactions and quantum melting 二维超流涡旋晶体的分数-弹性二象性:缺陷相互作用和量子熔化
Pub Date : 2020-05-25 DOI: 10.21468/SCIPOSTPHYS.9.5.076
D. X. Nguyen, A. Gromov, S. Moroz
Employing the fracton-elastic duality, we develop a low-energy effective theory of a zero-temperature vortex crystal in a two-dimensional bosonic superfluid which naturally incorporates crystalline topological defects. We extract static interactions between these defects and investigate several continuous quantum transitions triggered by the Higgs condensation of vortex vacancies/interstitials and dislocations. We propose that the quantum melting of the vortex crystal towards the hexatic or smectic phase may occur via a pair of continuous transitions separated by an intermediate vortex supersolid phase.
利用分数-弹性二象性,我们建立了二维玻色子超流体中含有晶体拓扑缺陷的零温度涡旋晶体的低能有效理论。我们提取了这些缺陷之间的静态相互作用,并研究了由涡旋空位/间隙和位错的希格斯凝聚引发的几个连续量子跃迁。我们提出涡旋晶体向六相或近晶相的量子熔化可能是通过中间涡旋超固相分开的一对连续转变发生的。
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引用次数: 38
Robustness of gauge-invariant dynamics against defects in ultracold-atom gauge theories 规范不变动力学对超冷原子规范理论缺陷的鲁棒性
Pub Date : 2020-05-20 DOI: 10.1103/physrevresearch.2.033361
Jad C. Halimeh, R. Ott, I. McCulloch, Bingda Yang, P. Hauke
Recent years have seen strong progress in quantum simulation of gauge-theory dynamics using ultracold-atom experiments. A principal challenge in these efforts is the certification of gauge invariance, which has recently been realized in [B.~Yang et al., arXiv:2003.08945]. One major but poorly investigated experimental source of gauge-invariance violation is an imperfect preparation of the initial state. Using the time-dependent density-matrix renormalization group, we analyze the robustness of gauge-invariant dynamics against potential preparation defects in the above ultracold-atom implementation of a $mathrm{U}(1)$ gauge theory. We find defects related to an erroneous initialization of matter fields to be innocuous, as the associated gauge-invariance violation remains strongly localized throughout the time evolution. A defect due to faulty initialization of the gauge field leads to a mild proliferation of the associated violation. Furthermore, we characterize the influence of immobile and mobile defects by monitoring the spread of entanglement entropy. Overall, our results indicate that the aforementioned experimental realization exhibits a high level of fidelity in the gauge invariance of its dynamics at all evolution times. Our work provides strong evidence that ultracold-atom setups can serve as an extremely reliable framework for the quantum simulation of gauge-theory dynamics.
近年来,利用超冷原子实验对量规理论动力学进行量子模拟取得了很大进展。这些努力的一个主要挑战是规范不变性的证明,最近在[B]中已经实现。[杨等,中国生物工程学报,2003.08945]。一个主要的,但很少研究的实验源的规范不变性违反是一个不完善的初始状态的准备。利用时变密度矩阵重整化群,我们分析了在上述$ mathm {U}(1)$规范理论的超冷原子实现中,规范不变动力学对潜在制备缺陷的鲁棒性。我们发现与物质场错误初始化相关的缺陷是无害的,因为相关的规范不变性违反在整个时间演化过程中仍然强烈定位。由于规范域初始化错误而导致的缺陷会导致相关违例的轻微扩散。此外,我们还通过监测纠缠熵的扩散来表征固定缺陷和移动缺陷的影响。总体而言,我们的结果表明,上述实验实现在其所有演化时间的动力学的规范不变性中表现出高水平的保真度。我们的工作提供了强有力的证据,证明超冷原子装置可以作为量规理论动力学量子模拟的极其可靠的框架。
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引用次数: 13
Beyond Lee-Huang-Yang description of self-bound Bose mixtures 超越自束缚玻色混合物的李-黄-杨描述
Pub Date : 2020-05-20 DOI: 10.21468/SCIPOSTPHYS.9.2.020
Miki Ota, G. Astrakharchik
We investigate the properties of self-bound ultradilute Bose-Bose mixtures, beyond the Lee-Huang-Yang description. Our approach is based on the determination of the beyond mean-field corrections to the phonon modes of the mixture in a self-consistent way and calculation of the associated equation of state. The newly obtained ground state energies show excellent agreement with recent quantum Monte Carlo calculations, providing a simple and accurate description of the self-bound mixtures with contact type interaction. We further show numerical results for the equilibrium properties of the finite size droplet, by adjusting the Gross-Pitaevskii equation. Our analysis is extended to the one-dimensional mixtures where an excellent agreement with quantum Monte Carlo predictions is found for the equilibrium densities. Finally, we discuss the effects of temperature on the stability of the liquid phase.
我们研究了自束缚超稀玻色-玻色混合物的性质,超出了李-黄-杨描述。我们的方法是基于以自洽方式确定混合物声子模式的超平均场修正和相关状态方程的计算。新获得的基态能量与最近的量子蒙特卡罗计算结果非常吻合,提供了具有接触型相互作用的自束缚混合物的简单而准确的描述。通过调整Gross-Pitaevskii方程,我们进一步给出了有限尺寸液滴平衡特性的数值结果。我们的分析扩展到一维混合物中,发现平衡密度与量子蒙特卡罗预测非常吻合。最后讨论了温度对液相稳定性的影响。
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引用次数: 32
Quantum simulation of extended polaron models using compound atom-ion systems 使用复合原子-离子系统的扩展极化子模型的量子模拟
Pub Date : 2020-05-18 DOI: 10.1103/PHYSREVRESEARCH.2.033326
K. Jachymski, A. Negretti
We consider the prospects for quantum simulation of condensed matter models exhibiting strong electron-phonon coupling using a hybrid platform of trapped laser-cooled ions interacting with an ultracold atomic gas. This system naturally posesses a phonon structure, in contrast to the standard optical lattice scenarios usually employed with ultracold atoms in which the lattice is generated by laser light and thus it remains static. We derive the effective Hamiltonian describing the general system and discuss the arising energy scales, relating the results to commonly employed extended Hubbard-Holstein models. Although for a typical experimentally realistic system the coupling to phonons turns out to be small, we provide the means to enhance its role and reach interesting regimes with competing orders. Extended Lang-Firsov transformation reveals the emergence of phonon-induced long-range interactions between the atoms, which can give rise to both localized and extended bipolaron states with low effective mass, indicating the possibility of fermion pairing.
我们考虑了使用捕获激光冷却离子与超冷原子气体相互作用的混合平台对具有强电子-声子耦合的凝聚态模型进行量子模拟的前景。该系统自然具有声子结构,与通常使用超冷原子的标准光学晶格方案相反,其中晶格是由激光产生的,因此它保持静态。我们推导了描述一般系统的有效哈密顿量,并讨论了产生的能量尺度,将结果与常用的扩展hubard - holstein模型联系起来。虽然对于一个典型的实验现实系统,声子的耦合是很小的,但我们提供了增强其作用的方法,并达到了具有竞争阶的有趣状态。扩展的Lang-Firsov变换揭示了原子之间声子诱导的远程相互作用的出现,这种相互作用可以产生低有效质量的局域和扩展双极化子态,表明费米子配对的可能性。
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引用次数: 5
Counterdiabatic control of transport in a synthetic tight-binding lattice 合成紧密结合晶格中输运的反绝热控制
Pub Date : 2020-05-14 DOI: 10.1103/PHYSREVRESEARCH.2.043201
E. Meier, K. Ngan, Dries Sels, B. Gadway
Quantum state transformations that are robust to experimental imperfections are important for applications in quantum information science and quantum sensing. Counterdiabatic (CD) approaches, which use knowledge of the underlying system Hamiltonian to actively correct for diabatic effects, are powerful tools for achieving simultaneously fast and stable state transformations. Protocols for CD driving have thus far been limited in their experimental implementation to discrete systems with just two or three levels, as well as bulk systems with scaling symmetries. Here, we extend the tool of CD control to a discrete synthetic lattice system composed of as many as nine sites. Although this system has a vanishing gap and thus no adiabatic support in the thermodynamic limit, we show that CD approaches can still give a substantial, several order-of-magnitude, improvement in fidelity over naive, fast adiabatic protocols.
对实验缺陷具有鲁棒性的量子态变换对于量子信息科学和量子传感的应用非常重要。反非绝热(CD)方法利用底层系统哈密顿量的知识来主动校正非绝热效应,是同时实现快速稳定状态转换的强大工具。迄今为止,CD驱动协议的实验实现仅限于只有两个或三个级别的离散系统,以及具有缩放对称性的批量系统。在这里,我们将CD控制工具扩展到由多达9个位点组成的离散合成晶格系统。尽管该系统有一个消失的间隙,因此在热力学极限下没有绝热支持,但我们表明,CD方法仍然可以在保真度上提供实质性的,几个数量级的改进,而不是简单的,快速的绝热协议。
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引用次数: 2
Supersolidity in an elongated dipolar condensate 细长偶极凝聚体中的超固体
Pub Date : 2020-04-27 DOI: 10.1103/PHYSREVRESEARCH.2.043318
P. B. Blakie, D. Baillie, L. Chomaz, F. Ferlaino
We present a theory for the emergence of a supersolid state in a cigar-shaped dipolar quantum Bose gas. Our approach is based on a reduced three-dimensional (3D) theory, where the condensate wavefunction is decomposed into an axial field and a transverse part described variationally. This provides an accurate fully 3D description that is specific to the regime of current experiments and efficient to compute. We apply this theory to understand the phase diagram for a gas in an infinite tube potential. We find that the supersolid transition has continuous and discontinuous regions as the averaged density varies. We develop two simplified analytic models to characterize the phase diagram and elucidate the roles of quantum droplets and of the roton excitation.
我们提出了一种理论来解释雪茄形偶极量子玻色气体中超固态的出现。我们的方法是基于一个简化的三维(3D)理论,其中冷凝波函数被分解为轴向场和横向部分的变化描述。这提供了一个准确的全3D描述,具体到当前的实验制度和有效的计算。我们应用这一理论来理解气体在无限管势下的相图。我们发现,随着平均密度的变化,超固体跃迁有连续和不连续的区域。我们建立了两个简化的分析模型来描述相图,并阐明了量子液滴和转子激发的作用。
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引用次数: 29
Semiclassical dynamics of a dark soliton in a one-dimensional bosonic superfluid in an optical lattice 光学晶格中一维玻色子超流体中暗孤子的半经典动力学
Pub Date : 2020-04-23 DOI: 10.1103/PHYSREVRESEARCH.2.033272
Yusuke Ozaki, Kazuma Nagao, I. Danshita, K. Kasamatsu
We study quantum dynamics of a dark soliton in a one-dimensional Bose gas in an optical lattice within the truncated Wigner approximation. A previous work has revealed that in the absence of quantum fluctuations, dynamical stability of the dark soliton significantly depends on whether its phase kink is located at a lattice site or a link of two neighboring sites. It has also shown that the dark soliton is unstable in a regime of strong quantum fluctuations regardless of the phase-kink position. To bridge the gap between the classical and strongly quantum regimes, we investigate the dynamical stability of the dark soliton in a regime of weak quantum fluctuations. We find that the position dependence of the dynamical stability gradually diminishes and eventually vanishes as the strength of quantum fluctuations increases. This classical-to-quantum crossover of the soliton stability remains even in the presence of a parabolic trapping potential. We suggest that the crossover behavior can be used for experimentally diagnosing whether the instability of a dark soliton is due to quantum fluctuations or classical dynamical instability.
在截断维格纳近似下,研究了一维玻色气体中暗孤子的量子动力学。先前的研究表明,在没有量子涨落的情况下,暗孤子的动力学稳定性很大程度上取决于它的相结是位于晶格位点还是两个相邻位点的链接。它还表明,无论相扭位置如何,暗孤子在强量子涨落状态下都是不稳定的。为了弥补经典和强量子状态之间的差距,我们研究了弱量子涨落状态下暗孤子的动力学稳定性。我们发现,随着量子涨落强度的增加,动态稳定性的位置依赖性逐渐减小并最终消失。即使在抛物线俘获势存在的情况下,孤子稳定性的经典-量子交叉仍然存在。我们认为交叉行为可以用于实验诊断暗孤子的不稳定性是由于量子涨落还是由于经典动力学不稳定性。
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引用次数: 1
Discrete truncated Wigner approach to dynamical phase transitions in Ising models after a quantum quench 量子猝灭后Ising模型中动态相变的离散截断Wigner方法
Pub Date : 2020-04-21 DOI: 10.1103/physrevb.102.014303
Reyhaneh Khasseh, A. Russomanno, M. Schmitt, M. Heyl, R. Fazio
By means of the discrete truncated Wigner approximation we study dynamical phase transitions arising in the steady state of transverse-field Ising models after a quantum quench. Starting from a fully polarized ferromagnetic initial condition these transitions separate a phase with nonvanishing magnetization along the ordering direction from a symmetric phase upon increasing the transverse field. We consider two paradigmatic cases, a one-dimensional long-range model with power-law interactions $propto 1/r^{alpha}$ decaying algebraically as a function of distance $r$ and a two-dimensional system with short-range nearest-neighbour interactions. In the former case we identify dynamical phase transitions for $alpha lesssim 2$ and we extract the critical exponents from a data collapse of the steady state magnetization for up to 1200 lattice sites. We find identical exponents for $alpha lesssim 1$, suggesting that the dynamical transitions in this regime fall into the same universality class as the nonergodic mean-field limit. The two-dimensional Ising model is believed to be thermalizing, which we also confirm using exact diagonalization for small system sizes. Thus, the dynamical transition is expected to correspond to the thermal phase transition, which is consistent with our data upon comparing to equilibrium quantum Monte-Carlo simulations. We further test the accuracy of the discrete truncated Wigner approximation by comparing against numerically exact methods such as exact diagonalization, tensor network as well as artificial neural network states and we find good quantitative agreement on the accessible time scales.
利用离散截断维格纳近似研究了量子猝灭后横场Ising模型稳态中产生的动态相变。从一个完全极化的铁磁初始条件开始,随着横向场的增加,这些转变沿着有序方向分离出具有不消失磁化的相和对称相。我们考虑了两种典型的情况,一个具有幂律相互作用$propto 1/r^{alpha}$作为距离函数的代数衰减的一维远程模型$r$和一个具有短距离近邻相互作用的二维系统。在前一种情况下,我们确定了$alpha lesssim 2$的动态相变,并从多达1200个晶格点的稳态磁化的数据崩溃中提取了临界指数。我们发现$alpha lesssim 1$的相同指数,表明该区域的动力跃迁与非遍历平均场极限属于相同的普适性类。二维伊辛模型被认为是热化的,我们也使用精确对角化来确认小系统尺寸。因此,动态转变预计对应于热相变,这与我们的数据一致,比较平衡量子蒙特卡罗模拟。通过与精确对角化、张量网络和人工神经网络状态等数值精确方法的比较,我们进一步测试了离散截断Wigner近似的准确性,并在可访问的时间尺度上找到了很好的定量一致性。
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引用次数: 11
Theoretical methods to treat a single dissipative bosonic mode coupled globally to an interacting many-body system 处理全局耦合到相互作用多体系统的单耗散玻色子模的理论方法
Pub Date : 2020-04-21 DOI: 10.1103/PHYSREVRESEARCH.2.043255
C. Halati, A. Sheikhan, C. Kollath
We present two approaches capable of describing the dynamics of an interacting many body system on a lattice coupled globally to a dissipative bosonic mode. Physical realizations are for example ultracold atom gases in optical lattice coupled to a photonic mode of an optical cavity or electronic gases in solids coupled to THz cavity fields. The first approach, applicable for large dissipation strengths and any system size, is a variant of the many-body adiabatic elimination method for investigating the long time dynamics of the system. The second method extends the time-dependent matrix product techniques to capture the global coupling of the interacting particles to the bosonic mode and its open nature. It gives numerically exact results for small to intermediate system sizes. As a benchmark for our methods we perform the full quantum evolution of a Bose-Hubbard chain coupled to a cavity mode. We show that important deviations from the mean field behavior occur when considering the full atoms cavity coupling [1].
我们提出了两种能够描述晶格上与耗散玻色子模式耦合的相互作用多体系统动力学的方法。例如,物理实现是光学晶格中的超冷原子气体耦合到光学腔的光子模式或固体中的电子气体耦合到太赫兹腔场。第一种方法是用于研究系统长时间动力学的多体绝热消去法的一种变体,适用于大耗散强度和任何系统尺寸。第二种方法扩展了时变矩阵积技术,以捕获相互作用粒子对玻色子模式及其开放性质的全局耦合。它给出了小到中等系统尺寸的精确数值结果。作为我们方法的基准,我们执行了玻色-哈伯德链耦合到腔模式的全量子演化。我们表明,当考虑全原子腔耦合时,会发生与平均场行为的重要偏差。
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引用次数: 5
期刊
arXiv: Quantum Gases
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