Recurring coherence A finite isolated system should return almost to its initial state if it evolves for long enough. For a large system, “long enough” is often unfeasibly long. Rauer et al. found just the right conditions to observe the recurrence of the initial state in a system of two one-dimensional superfluids with thousands of atoms in each. The superfluids were initially coupled—locking their quantum mechanical phases together—and then allowed to evolve independently. After the uncoupling, the researchers observed their phases regaining coherence two more times. Science, this issue p. 307 Two 1D superfluids in box potentials are used to show the recurrence of coherence in a system with thousands of particles. The complexity of interacting quantum many-body systems leads to exceedingly long recurrence times of the initial quantum state for all but the smallest systems. For large systems, one cannot probe the full quantum state in all its details. Thus, experimentally, recurrences can only be determined on the level of the accessible observables. Realizing a commensurate spectrum of collective excitations in one-dimensional superfluids, we demonstrate recurrences of coherence and long-range order in an interacting quantum many-body system containing thousands of particles. Our findings will enable the study of the coherent dynamics of large quantum systems even after they have reached a transient thermal-like state.

中文翻译：

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孤立量子多体系统中的递归

反复出现的相干性 如果有限的孤立系统演化足够长的时间，它应该几乎恢复到它的初始状态。对于大型系统，“足够长”通常是不可行的。劳尔等人。找到了合适的条件来观察两个一维超流体系统中初始状态的重现，每个系统都有数千个原子。超流体最初是耦合的——将它们的量子力学相位锁定在一起——然后允许独立演化。解耦后，研究人员观察到它们的相位又恢复了两次相干性。科学，这个问题 p。307 盒势中的两个一维超流体用于显示具有数千个粒子的系统中相干性的重现。相互作用的量子多体系统的复杂性导致除了最小系统之外的所有系统的初始量子态的重复时间都非常长。对于大型系统，人们无法探索完整量子态的所有细节。因此，在实验上，重复只能在可访问的可观察量的水平上确定。在一维超流体中实现了相应的集体激发谱，我们证明了在包含数千个粒子的相互作用量子多体系统中相干性和长程有序的重现。我们的发现将使大型量子系统的相干动力学研究成为可能，即使它们已经达到瞬态热状态。重复只能在可访问的可观察对象的级别上确定。在一维超流体中实现了相应的集体激发谱，我们证明了在包含数千个粒子的相互作用量子多体系统中相干性和长程有序的重现。我们的发现将使大型量子系统的相干动力学研究成为可能，即使它们已经达到瞬态热状态。重复只能在可访问的可观察对象的级别上确定。在一维超流体中实现了相应的集体激发谱，我们证明了在包含数千个粒子的相互作用量子多体系统中相干性和长程有序的重现。我们的发现将使大型量子系统的相干动力学研究成为可能，即使它们已经达到瞬态热状态。