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Functional theory for Bose-Einstein condensates 玻色-爱因斯坦凝聚体的泛函理论
Pub Date : 2020-10-13 DOI: 10.1103/PHYSREVRESEARCH.3.013282
Julia Liebert, C. Schilling
One-particle reduced density matrix functional theory would potentially be the ideal approach for describing Bose-Einstein condensates. It namely replaces the macroscopically complex wavefunction by the simple one-particle reduced density matrix, therefore provides direct access to the degree of condensation and still recovers quantum correlations in an exact manner. We eventually initiate and establish this novel theory by deriving the respective universal functional $mathcal{F}$ for general homogeneous Bose-Einstein condensates with arbitrary pair interaction. Most importantly, the successful derivation necessitates a particle-number conserving modification of Bogoliubov theory and a solution of the common phase dilemma of functional theories. We then illustrate this novel approach in several bosonic systems such as homogeneous Bose gases and the Bose-Hubbard model. Remarkably, the general form of $mathcal{F}$ reveals the existence of a universal Bose-Einstein condensation force which provides an alternative and more fundamental explanation for quantum depletion.
单粒子降密度矩阵泛函理论可能是描述玻色-爱因斯坦凝聚的理想方法。它即用简单的单粒子简化密度矩阵取代宏观上复杂的波函数,因此提供了对凝聚程度的直接访问,并且仍然以精确的方式恢复量子相关性。我们最终通过推导具有任意对相互作用的一般齐次玻色-爱因斯坦凝聚体各自的泛函$mathcal{F}$,发起并建立了这一新理论。最重要的是,成功的推导需要对Bogoliubov理论进行粒子数守恒修正,并解决泛函理论的共同相困境。然后,我们在几个玻色子系统,如均匀玻色气体和玻色-哈伯德模型中说明了这种新方法。值得注意的是,$mathcal{F}$的一般形式揭示了普遍的玻色-爱因斯坦凝聚力的存在,这为量子耗尽提供了另一种更基本的解释。
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引用次数: 10
Supervised learning of few dirty bosons with variable particle number 变粒子数脏玻色子的监督学习
Pub Date : 2020-10-08 DOI: 10.21468/SCIPOSTPHYS.10.3.073
Pere Mujal, A. Miguel, A. Polls, B. Juli'a-D'iaz, S. Pilati
We investigate the supervised machine learning of few interacting bosons in optical speckle disorder via artificial neural networks. The learning curve shows an approximately universal power-law scaling for different particle numbers and for different interaction strengths. We introduce a network architecture that can be trained and tested on heterogeneous datasets including different particle numbers. This network provides accurate predictions for the system sizes included in the training set, and also fair extrapolations to (computationally challenging) larger sizes. Notably, a novel transfer-learning strategy is implemented, whereby the learning of the larger systems is substantially accelerated by including in the training set many small-size instances.
利用人工神经网络研究了光学散斑无序中少量相互作用玻色子的监督机器学习。对于不同的粒子数和不同的相互作用强度,学习曲线显示出近似通用的幂律缩放。我们引入了一种网络架构,可以在包含不同粒子数的异构数据集上进行训练和测试。该网络提供了对训练集中包含的系统大小的准确预测,以及对(计算上具有挑战性的)更大大小的公平外推。值得注意的是,实现了一种新的迁移学习策略,通过在训练集中包含许多小型实例,大大加快了大型系统的学习。
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引用次数: 6
Finite-temperature spin dynamics of a two-dimensional Bose-Bose atomic mixture 二维玻色-玻色原子混合物的有限温度自旋动力学
Pub Date : 2020-10-05 DOI: 10.1103/PHYSREVRESEARCH.3.013161
A. Roy, Miki Ota, A. Recati, F. Dalfovo
We examine the role of thermal fluctuations in uniform two-dimensional binary Bose mixtures of dilute ultracold atomic gases. We use a mean-field Hartree-Fock theory to derive analytical predictions for the miscible-immiscible transition. A nontrivial result of this theory is that a fully miscible phase at $T=0$ may become unstable at $Tneq0$, as a consequence of a divergent behaviour in the spin susceptibility. We test this prediction by performing numerical simulations with the Stochastic (Projected) Gross-Pitaevskii equation, which includes beyond mean-field effects. We calculate the equilibrium configurations at different temperatures and interaction strengths and we simulate spin oscillations produced by a weak external perturbation. Despite some qualitative agreement, the comparison between the two theories shows that the mean-field approximation is not able to properly describe the behavior of the two-dimensional mixture near the miscible-immiscible transition, as thermal fluctuations smoothen all sharp features both in the phase diagram and in spin dynamics, except for temperature well below the critical temperature for superfluidity.
我们研究了在稀超冷原子气体的均匀二维二元玻色混合物中热波动的作用。我们使用平均场Hartree-Fock理论推导了混相-非混相转变的分析预测。该理论的一个重要结果是,由于自旋磁化率的发散行为,在T=0处的完全混相可能在Tneq0$处变得不稳定。我们通过使用随机(预测)Gross-Pitaevskii方程进行数值模拟来验证这一预测,其中包括超越平均场效应。我们计算了在不同温度和相互作用强度下的平衡构型,并模拟了弱外部扰动产生的自旋振荡。尽管有一些定性的一致,但两种理论之间的比较表明,平均场近似不能恰当地描述二维混合物在混相-非混相转变附近的行为,因为热涨落平滑了相图和自旋动力学中的所有尖锐特征,除了远低于超流体临界温度的温度。
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引用次数: 4
Interaction-Assisted Reversal of Thermopower with Ultracold Atoms 超冷原子热能相互作用辅助逆转
Pub Date : 2020-09-30 DOI: 10.1103/PhysRevX.11.021034
S. Häusler, P. Fabritius, Jeffrey Mohan, M. Lebrat, L. Corman, T. Esslinger
We study thermoelectric currents of neutral, fermionic atoms flowing through a mesoscopic channel connecting a hot and a cold reservoir across the superfluid transition. The thermoelectric response results from a competition between density-driven diffusion from the cold to the hot reservoir and the channel favoring transport of energetic particles from hot to cold. We control the relative strength of both contributions to the thermoelectric response using an external optical potential in both non-interacting and strongly-interacting systems. Without interactions, the magnitude of the particle current can be tuned over a broad range but is restricted to flow from hot to cold in our parameter regime. Strikingly, strong interparticle interactions additionally reverse the direction of the current. We quantitatively model ab initio the non-interacting observations and qualitatively explain the interaction-assisted reversal by the reduction of entropy transport due to pairing correlations. Our work paves the way to studying the coupling of spin and heat in strongly correlated matter using spin-dependent optical techniques with cold atoms.
我们研究了中性费米子原子在超流体跃迁中通过连接热储层和冷储层的介观通道流动的热电电流。热电响应是由密度驱动的从冷区向热区扩散和有利于高能粒子从热区向冷区输运的通道之间的竞争造成的。我们在非相互作用和强相互作用系统中使用外部光势来控制热电响应的两种贡献的相对强度。在没有相互作用的情况下,粒子电流的大小可以在很宽的范围内调整,但在我们的参数范围内仅限于从热到冷的流动。引人注目的是,强烈的粒子间相互作用还会逆转电流的方向。我们定量地从头开始模拟非相互作用的观测,并定性地解释了由于配对相关而减少熵输运的相互作用辅助反转。我们的工作为利用自旋依赖光学技术与冷原子研究强相关物质中自旋和热的耦合铺平了道路。
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引用次数: 11
Dynamical control of the conductivity of an atomic Josephson junction 原子约瑟夫逊结电导率的动态控制
Pub Date : 2020-09-24 DOI: 10.1103/PHYSREVRESEARCH.3.013111
B. Zhu, V. Singh, J. Okamoto, L. Mathey
We propose to dynamically control the conductivity of a Josephson junction composed of two weakly coupled one dimensional condensates of ultracold atoms. A current is induced by a periodically modulated potential difference between the condensates, giving access to the conductivity of the junction. By using parametric driving of the tunneling energy, we demonstrate that the low-frequency conductivity of the junction can be enhanced or suppressed, depending on the choice of the driving frequency. The experimental realization of this proposal provides a quantum simulation of optically enhanced superconductivity in pump-probe experiments of high temperature superconductors.
我们提出动态控制由两个弱耦合的一维超冷原子凝聚体组成的约瑟夫森结的电导率。电流是由冷凝物之间周期性调制的电位差引起的,从而获得结的导电性。利用隧道能量的参数驱动,我们证明了驱动频率的选择可以增强或抑制结的低频电导率。该方案的实验实现为高温超导体的泵探实验提供了光增强超导性的量子模拟。
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引用次数: 1
Non-equilibrium evolution of Bose-Einstein condensate deformation in temporally controlled weak disorder 时间控制弱无序状态下玻色-爱因斯坦凝聚变形的非平衡演化
Pub Date : 2020-09-22 DOI: 10.21468/SCIPOSTPHYS.10.1.008
Milan Radonji'c, A. Pelster
We consider a time-dependent extension of a perturbative mean-field approach to the dirty boson problem by considering how switching on and off a weak disorder potential affects the stationary state of an initially homogeneous Bose-Einstein condensate by the emergence of a disorder-induced condensate deformation. We find that in the switch on scenario the stationary condensate deformation turns out to be a sum of an equilibrium part and a dynamically-induced part, where the latter depends on the particular driving protocol. If the disorder is switched off afterwards, the resulting condensate deformation acquires an additional dynamically-induced part in the long-time limit, while the equilibrium part vanishes. Our results demonstrate that the condensate deformation represents an indicator of the generically non-equilibrium nature of steady states of a Bose gas in a temporally controlled weak disorder.
通过考虑打开和关闭弱无序势如何通过无序诱导的凝聚态变形的出现影响初始均匀玻色-爱因斯坦凝聚态的定态,我们考虑了脏玻色子问题的微扰平均场方法的时间依赖扩展。我们发现,在开关情况下,稳态凝析变形是平衡部分和动力诱导部分的总和,其中动力诱导部分取决于特定的驱动协议。如果随后关闭失序,则产生的凝析变形在长时间极限下获得额外的动力诱导部分,而平衡部分则消失。我们的研究结果表明,凝聚变形代表了玻色气体在时间控制的弱无序状态下稳定状态的一般非平衡性质的一个指标。
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引用次数: 0
Time-optimal variational control of a bright matter-wave soliton 明亮物质波孤子的时间最优变分控制
Pub Date : 2020-09-20 DOI: 10.1103/physreva.102.053313
Tangyou Huang, Jia Zhang, Jing Li, Xi Chen
Motivated by recent experiments, we present the time-optimal variational control of bright matter-wave soliton trapped in a quasi-one-dimensional harmonic trap by manipulating the atomic attraction through Feshbach resonances. More specially, we first apply a time-dependent variational method to derive the motion equation for capturing the soliton's shape, and secondly combine inverse engineering with optimal control theory to design the atomic interaction for implementing time-optimal decompression. Since the time-optimal solution is of bang-bang type, the smooth regularization is further adopted to smooth the on-off controller out, thus avoiding the heating and atom loss, induced from magnetic field ramp across a Feshbach resonance in practice.
在最近的实验的启发下,我们提出了通过操纵费希巴赫共振的原子吸引力来控制被困在准一维谐波陷阱中的明亮物质波孤子的时间最优变分控制。具体地说,我们首先应用时变分方法推导出捕获孤子形状的运动方程,然后结合逆工程和最优控制理论设计原子相互作用以实现时间最优解压缩。由于时间最优解是bang-bang型的,因此进一步采用平滑正则化对开关控制器进行平滑处理,从而避免了在实际操作中由于费什巴赫共振磁场斜坡引起的发热和原子损耗。
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引用次数: 2
Density Fluctuations across the Superfluid-Supersolid Phase Transition in a Dipolar Quantum Gas 偶极量子气体中超流体-超固体相变的密度波动
Pub Date : 2020-09-18 DOI: 10.1103/PHYSREVX.11.011037
J. Hertkorn, Jan-Niklas Schmidt, F. Böttcher, M. Guo, M. Schmidt, K. S. H. Ng, Sean D. Graham, H. Büchler, Tim Langen, M. Zwierlein, Tilman Pfau
Phase transitions share the universal feature of enhanced fluctuations near the transition point. Here we show that density fluctuations reveal how a Bose-Einstein condensate of dipolar atoms spontaneously breaks its translation symmetry and enters the supersolid state of matter -- a phase that combines superfluidity with crystalline order. We report on the first direct in situ measurement of density fluctuations across the superfluid-supersolid phase transition. This allows us to introduce a general and straightforward way to extract the static structure factor, estimate the spectrum of elementary excitations and image the dominant fluctuation patterns. We observe a strong response in the static structure factor and infer a distinct roton minimum in the dispersion relation. Furthermore, we show that the characteristic fluctuations correspond to elementary excitations such as the roton modes, which have been theoretically predicted to be dominant at the quantum critical point, and that the supersolid state supports both superfluid as well as crystal phonons.
相变具有在过渡点附近波动增强的普遍特征。在这里,我们展示了密度波动揭示了偶极原子的玻色-爱因斯坦凝聚如何自发地打破其平移对称性并进入物质的超固体状态-一种将超流动性与晶体秩序相结合的相。我们报告了第一个直接在原位测量密度波动跨越超固-超固相变。这使我们能够引入一种通用的、直接的方法来提取静态结构因子,估计初等激励的谱,并对主要的波动模式进行成像。我们观察到静态结构因子的强烈响应,并推断出色散关系中明显的旋转最小值。此外,我们证明了特征波动对应于基本激发,如在量子临界点理论上预测占主导地位的旋转模式,并且超固体状态既支持超流体声子,也支持晶体声子。
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引用次数: 25
Twist-and-store entanglement in bimodal and spin-1 Bose-Einstein condensates 双峰态和自旋为1的玻色-爱因斯坦凝聚体中的扭曲与储存纠缠
Pub Date : 2020-09-15 DOI: 10.1103/physreva.102.053315
A. Niezgoda, E. Witkowska, Safoura S. Mirkhalaf
A scheme for dynamical stabilization of entanglement quantified by the quantum Fisher information is analyzed numerically and analytically for bimodal and spin-1 Bose-Einstein condensates in the context of atomic interferometry. The scheme consists of twisting dynamics followed by a single rotation of a state which limits further evolution around stable center fixed points in the mean-field phase space. The resulting level of entanglement is of the order or larger than at the moment of rotation. It is demonstrated that the readout measurement of parity quantifies the level of entanglement during entire evolution.
在原子干涉测量的背景下,对双峰态和自旋为1的玻色-爱因斯坦凝聚体的纠缠态动力学稳定方案进行了数值和解析分析。该方案包括扭曲动力学,然后是一个状态的单次旋转,这限制了在平均场相空间中围绕稳定中心固定点的进一步演化。由此产生的缠结水平与旋转力矩相等或更大。证明了宇称的读出测量量化了整个演化过程中的纠缠水平。
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引用次数: 1
Two Rydberg-dressed atoms escaping from an open well 两个里德堡原子从一个开着的井中逃逸
Pub Date : 2020-09-10 DOI: 10.1103/physreva.103.013304
J. Dobrzyniecki, T. Sowi'nski
A comprehensive analysis of the dynamics of two Rydberg-dressed particles (bosons or fermions) tunneling from a potential well into open space is provided. We show that the dominant decay mechanism switches from sequential tunneling to pair tunneling when the interaction strength is tuned below a certain critical value. These critical values can be modified by tuning the effective range of the interaction potential. By comparing the dynamics for bosons and fermions, we show that there are significant differences between the two cases. In particular, increasing the interaction range modifies the tunneling rate in opposite ways for fermions and bosons. Furthermore, for the fermionic system much stronger attractive interactions are needed to achieve pair tunneling. The results provide insight into the dynamics of tunnneling systems and, in light of recent realizations of tunneling few-body systems and Rydberg dressing of atoms, they offer promise for future experiments.
提供了两个里德堡装扮粒子(玻色子或费米子)从势阱隧穿到开放空间的动力学的综合分析。我们发现,当相互作用强度低于某个临界值时,主导衰变机制从顺序隧穿转变为对隧穿。这些临界值可以通过调整相互作用势的有效范围来修改。通过比较玻色子和费米子的动力学,我们发现两种情况之间存在显著差异。特别是,增加相互作用范围会以相反的方式改变费米子和玻色子的隧穿速率。此外,费米子系统需要更强的吸引相互作用来实现对隧穿。这些结果提供了对隧穿系统动力学的深入了解,并且鉴于最近隧穿少体系统和原子里德伯修饰的实现,它们为未来的实验提供了希望。
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引用次数: 2
期刊
arXiv: Quantum Gases
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