近日，浙江大学物理系的颜波&杨兆举及其研究小组取得一项新进展。经过不懈努力，他们研究了超冷原子的量子时间反射和折射。相关研究成果已于2023年9月18日在国际知名学术期刊《自然—光子学》上发表。
该研究团队在超冷原子的动量晶格中引入了时间边界，同时用实验证明了时间反射和折射。研究人员通过在Su-Schrieffer-Heeger原子链中发射一个高斯叠加态，观察了输入态撞击时间边界时产生的时间反射波和时间折射波。此外，他们发现随着无序强度的增加，会经历从时间反射/折射到局部化的转变，这表明时间边界效应对相当大的无序仍具有稳健性。这一研究工作为未来探索时间边界和时空晶格，以及它们与非厄米性和多体交互的相互作用开辟了新的途径。
据悉，时间反射和折射是由费马原理导出的空间边界效应的时间类比。当经典波到达一个时间边界时，介质的性质就会发生突变。时间反射波和时间折射波的主要特征是频率的变化和动量的守恒，这为操纵极端波和控制物质的相提供了新的自由度。这个概念最初是在50多年前提出的，用于操纵光波。然而，由于光学材料的超快工程面临的极端挑战，时间边界效应的实验实现仍然面临很大困难。
附：英文原文
Title: Quantum time reflection and refraction of ultracold atoms
Author: Dong, Zhaoli, Li, Hang, Wan, Tuo, Liang, Qian, Yang, Zhaoju, Yan, Bo
Issue&Volume: 2023-09-18
Abstract: Time reflection and refraction are temporal analogies of the spatial boundary effects derived from Fermat’s principle. They occur when classical waves strike a time boundary where an abrupt change in the properties of the medium is introduced. The main features of time-reflected and time-refracted waves are the shift in frequency and conservation of momentum, which offer a new degree of freedom for steering extreme waves and controlling the phases of matter. The concept was originally proposed for manipulating optical waves more than five decades ago. However, due to the extreme challenges in the ultrafast engineering of optical materials, the experimental realization of the time boundary effects remains elusive. Here we introduce a time boundary into a momentum lattice of ultracold atoms and simultaneously demonstrate time reflection and refraction experimentally. Through launching a Gaussian-superposed state into the Su–Schrieffer–Heeger atomic chain, we observe the time-reflected and time-refracted waves when the input state strikes a time boundary. Furthermore, we detect a transition from time reflection/refraction to localization with increasing strength of disorder and show that the time boundary effects are robust against considerable disorder. Our work opens a new avenue for the future exploration of time boundaries and spatiotemporal lattices, as well as their interplay with non-Hermiticity and many-body interactions.
DOI: 10.1038/s41566-023-01290-1
Source: https://www.nature.com/articles/s41566-023-01290-1