Probing Non-Equilibrium Quantum Many-Body Dynamics with Bright Matter-Wave Solitons

碱原子的稀气体现在通常使用激光冷却到绝对零度的百万分之一以内，允许它们被限制在由于原子与外加磁场或远失谐非谐振激光束的相互作用而形成的陷阱中。以玻色子原子为例，在这样的陷阱中通过蒸发进一步冷却，就会产生一种新的物质状态，即玻色-爱因斯坦凝聚物，在这种状态下，粒子的量子力学性质支配着它们的经典行为。这种凝聚体通常被视为相干激光的原子或物质波等价物。自1995年首次观测以来，玻色-爱因斯坦凝聚体已被成功地用于研究从超流体的基础研究到光学晶格中强相关多体态的广泛物理现象，为更复杂的凝聚态系统提供了见解。这一成功源于超冷量子气体的两个重要特征。首先，从实验的角度来看，超冷原子气体很容易被外部电磁场（直流、射频、微波和光学）操纵和控制，允许在实验配置和高灵敏度检测中具有非常高的实时灵活性。其次，玻色-爱因斯坦凝聚体在理论上是容易处理的，这主要是由于它们的稀释、弱相互作用的性质，从而对实验观察结果有了更深入的理解。这使得超冷量子气体成为我们对多体量子系统行为的理论理解的前沿发展的理想试验场。在这里，我们提出了一个基础研究计划，旨在更好地理解非平衡相互作用量子多体系统的动力学，利用原子的玻色-爱因斯坦凝聚体的85Rb。具体来说，我们将利用两个85Rb原子之间的碰撞共振（称为费什巴赫共振）来调整凝聚体中的原子相互作用，使其具有吸引力，从而产生明亮的物质波孤子；鲁棒的、非色散的原子波包，限制在一维中传播，其中吸引的原子相互作用正好补偿了通常的色散。孤子是描述各种物理系统的非线性偏微分方程的解。1834年在苏格兰联合运河的浅水中首次观测到孤子，此后在许多其他领域进行了研究，包括非线性光学、生物物理学、天体物理学和粒子物理学。在原子环境中，系统的潜在量子性质激发了复杂的多体量子处理，以准确地捕捉基本物理。本提案描述了对这种“量子”明亮物质波孤子的系统的、密切相关的实验-理论研究，以期揭示明亮孤子的相干性和纠缠性，同时发展适用于其他量子多体系统的新的先进理论处理。与该领域领先的国际专家合作，我们的最终目标是评估使用量子亮孤子生成用于量子增强干涉测量的Schrödinger cat态的可行性。拟议的研究属于当前确定的两个物理学大挑战的范围，“涌现和远离平衡的物理学”和“新量子技术的量子物理学”，因此在公认的具有重大社会和经济影响潜力的领域为英国科学做出贡献。

Dilute gases of alkali atoms are now routinely cooled to within a millionth of a degree of absolute zero using laser light, permitting them to be confined in traps formed due to the interaction of the atom with either an applied magnetic field or a far-detuned off-resonant laser beam. Further cooling by evaporation in such traps leads, in the case of bosonic atoms, to the creation of a new state of matter, known as a Bose-Einstein condensate, in which the quantum mechanical nature of the particles dominates over their classical behaviour. Such condensates are often viewed as the atomic or matter-wave equivalent of coherent laser light.Since their first observation in 1995, Bose-Einstein condensates have been used with great success to investigate a vast range of physical phenomena from fundamental studies of superfluidity to strongly correlated many-body states in optical lattices, providing insight into more complicated condensed matter systems. This success stems from two important features of ultracold quantum gases. Firstly, from an experimental stand-point, ultracold atomic gases are readily manipulated and controlled with external electromagnetic fields (dc, radio-frequency, microwave and optical) permitting a very high degree of real-time flexibility in the experimental configuration and highly sensitive detection. Secondly, Bose-Einstein condensates have proved theoretically tractable, due largely to their dilute, weakly interacting nature, leading to a deeper understanding of experimental observations. This makes ultracold quantum gases an ideal testing ground for the cutting-edge developments in our theoretical understanding of the behaviour of many-body quantum systems.Here, we propose a program of fundamental research intended to yield a better general understanding of the dynamics of non-equilibrium interacting quantum many-body systems, using atomic Bose-Einstein condensates of 85Rb. Specifically, we will exploit a collision resonance (known as a Feshbach resonance) between two 85Rb atoms to tune the atomic interactions in the condensate to be attractive, thereby generating bright matter-wave solitons; robust, non-dispersive atomic wave-packets confined to propagate in one dimension, in which the attractive atomic interactions exactly compensate the usual dispersion. Solitons arise as solutions to nonlinear partial differential equations describing a diverse range of physical systems. First observed in the shallow water of the Union Canal in Scotland in 1834, solitons have since been studied in many other contexts, including nonlinear optics, biophysics, astrophysics and particle physics. In the atomic context, the underlying quantum nature of the system provokes sophisticated many-body quantum treatments to accurately capture the essential physics. This proposal describes a systematic, closely interlinked experimental-theoretical study of such "quantum" bright matter-wave solitons with a view to exposing the coherence and entanglement properties of bright solitons, whilst developing new advanced theoretical treatments applicable to other quantum many-body systems. Working together with the leading international experts in the field, we aim ultimately to assess the feasibility of using quantum bright solitons to generate Schrödinger cat states for quantum-enhanced interferometry. The proposed research falls within the remit of two of the identified current Grand Challenges in Physics, "Emergence and Physics Far From Equilibrium" and "Quantum Physics for New Quantum Technologies", and thereby contributes to UK science in areas where there is recognised potential for significant societal and economic impact.