活性量子自旋的非互易同步
Nonreciprocal Synchronization of Active Quantum Spins
AI总结：
本文提出两种量子自旋通过手性波导实现吸引-排斥型非互易相互作用的模型，证明在热力学极限下可导致宇称-时间对称性自发破缺的时间晶体行波态，并通过连续监测输出场在有限系统中实现量子行波态。
摘要：
活性剂能够对彼此施加非互易力。例如，一个活性剂，比如$A$，可能吸引另一个活性剂$B$，而$B$排斥$A$。这种对抗性的非互易相互作用在经典系统中已被广泛研究，揭示了大量令人兴奋的现象，如新颖的相变和行波态。这些现象能否在量子多体系统中产生是一个悬而未决的问题，并且缺乏实现它们的提案。在这项工作中，我们提出了一个由两种量子自旋物种组成的模型，它们以吸引-排斥类型的对抗性非互易方式相互作用。我们提出了一种基于两个原子系综的实现方案，这些原子系综通过手性波导耦合，具有编织和非编织两种几何结构。由于存在局部增益，自旋是活性的，这使得它们能够同步。在热力学极限下，我们表明非互易相互作用导致向时间晶体行波态的非互易相变，这与宇称-时间对称性的自发破缺相关。我们确立了这种对称性如何从微观量子模型中涌现。对于有限数量的自旋，时间晶体相的特征仍然可以通过检查等时或双时关联函数来识别。值得注意的是，对波导输出场的连续监测会诱导出量子行波态：一种有限尺寸量子系统的时间晶体态，其中宇称-时间对称性被自发破缺。我们的工作为探索活性量子物质中的非互易相互作用奠定了基础。
英文摘要：
Active agents are capable of exerting nonreciprocal forces upon one another. For instance, one agent, say $A$, may attract another agent $B$ while $B$ repels $A$. These antagonistic nonreciprocal interactions have been extensively studied in classical systems, revealing a wealth of exciting phenomena such as novel phase transitions and traveling-wave states. Whether these phenomena can originate in quantum many-body systems is an open issue, and proposals for their realization are lacking. In this work, we present a model of two species of quantum spins that interact in an antagonistic nonreciprocal way of the attraction-repulsion type. We propose an implementation based on two atomic ensembles coupled via chiral waveguides featuring both braided and non-braided geometries. The spins are active due to the presence of local gain, which allows them to synchronize. In the thermodynamic limit, we show that nonreciprocal interactions result in a nonreciprocal phase transition to time-crystalline traveling-wave states, associated with spontaneous breaking of parity-time symmetry. We establish how this symmetry emerges from the microscopic quantum model. For a finite number of spins, signatures of the time-crystal phase can still be identified by inspecting equal-time or two-time correlation functions. Remarkably, continuous monitoring of the output field of the waveguides induces a quantum traveling-wave state: a time-crystalline state of a finite-size quantum system, in which parity-time symmetry is spontaneously broken. Our work lays the foundation to explore nonreciprocal interactions in active quantum matter.
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