近日，英国剑桥大学Hadzibabic, Zoran团队研究了相干传播的普遍速度限制。相关论文于2025年11月12日发表在《自然》杂志上。
对物理过程速率基本极限的发现，从光速到信息传播的Lieb–Robinson界限，常常能带来对底层物理理解的突破。
研究组针对一个典型的多体现象——弱相互作用玻色-爱因斯坦凝聚（BEC）形成过程中的相干性传播——观测到了这样一个极限。他们研究了一个孤立的均匀原子气体中的凝聚体形成过程，该气体初始远离平衡态，处于一种非相干的低能态，并在向平衡态弛豫的过程中发生凝聚。通过调节驱动凝聚的原子间相互作用，研究组表明，相干性在系统中的传播，在相互作用较弱时初始较慢，在相互作用较强时初始较快，但最终总会达到同一个极限。
在此极限下，相干长度的平方以一个普适速率增长，该速率由普朗克常数与粒子质量的比值给出，或者，等价地，由与量子涡旋相关的速度环量量子给出。这些观测结果对初始态、气体密度和系统尺寸的变化具有鲁棒性。该结果为远离平衡态的普适性理论提供了基准，与依赖大规模相干性的量子技术息息相关，并启发在其他系统中进行类似的测量。
附：英文原文
Title: A universal speed limit for spreading of coherence
Author: Martirosyan, Gevorg, Gazo, Martin, Etrych, Ji, Fischer, Simon M., Morris, Sebastian J., Ho, Christopher J., Eigen, Christoph, Hadzibabic, Zoran
Issue&Volume: 2025-11-12
Abstract: Discoveries of fundamental limits for the rates of physical processes, from the speed of light to the Lieb–Robinson bound for information propagation1,2, often lead to breakthroughs in the understanding of the underlying physics. Here we observe such a limit for a paradigmatic many-body phenomenon, the spreading of coherence during the formation of a weakly interacting Bose–Einstein condensate3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18. We study condensate formation in an isolated homogeneous atomic gas19,20 that is initially far from equilibrium, in an incoherent low-energy state, and condenses as it relaxes towards equilibrium. Tuning the interatomic interactions that drive condensation, we show that the spreading of coherence through the system is initially slower for weaker interactions and faster for stronger ones, but always eventually reaches the same limit, at which the square of the coherence length grows at a universal rate given by the ratio of Planck’s constant and the particle mass, or, equivalently, by the quantum of velocity circulation associated with a quantum vortex. These observations are robust to changes in the initial state, the gas density, and the system size. Our results provide benchmarks for theories of universality far from equilibrium21,22,23,24,25,26,27,28,29,30,31,32,33,34, are relevant for quantum technologies that rely on large-scale coherence, and invite similar measurements in other systems.
DOI: 10.1038/s41586-025-09735-z