南京大学夏可宇团队近日研究了非互易自发参数过程。2025年5月19日，《光：科学与应用》杂志发表了这一成果。

通过与量子真空场的相互作用，在非线性光学介质中传播的探测激光场可以通过自发参量过程在宽光谱范围内产生新的光场对。由于与方向无关的场-真空相互作用，到目前为止，这种过程本质上与光的入射方向无关，并且是相互的。在这项工作中，研究组通过实验证明，在钠原子蒸汽中，这种自发参数过程可以通过单向耦合到另一个泵浦的四波混频过程来实现非互易性。 

由于自发参量过程的宽带宽，结合多普勒和功率诱导的原子能级展宽，研究组实现了隔离比>25 dB、带宽大于100 GHz的光隔离。考虑到自发参量过程和泵浦四波混频都已在不同的固体光子平台上实现，所证明的概念可以通过非线性光学过程之间的相互作用激发对集成无磁宽带光学非互易性设计的进一步探索。

附：英文原文

Title: Nonreciprocal spontaneous parametric process

Author: Li, Changbiao, Yuan, Jiaqi, He, Ruidong, Yu, Jiawei, Zhang, Yanpeng, Xiao, Min, Xia, Keyu, Zhang, Zhaoyang

Issue&Volume: 2025-05-19

Abstract: Mediated by the interactions with quantum vacuum fields, a probe laser field propagating in a nonlinear optical medium can generate new pair of light fields over a broad spectral range via spontaneous parametric process. Such process is inherently independent of the incident direction of light and reciprocal thus far, due to the direction-independent field-vacuum interactions. In this work, we experimentally demonstrate within sodium atomic vapors that such spontaneous parametric process can be nonreciprocal by unidirectionally coupling it to another pumped four-wave mixing process. Thanks to the broad bandwidth of the spontaneous parametric process, in combination with the Doppler and power-induced broadening of atomic energy levels, we achieve optical isolation with isolation ratio >25dB over a bandwidth larger than 100GHz. Considering that both spontaneous parametric processes and the pumped four-wave mixing have been realized in diverse solid photonic platforms, the demonstrated concept can motivate further explorations in the design of integrated magnetic-free broadband optical nonreciprocity via the interactions between nonlinear optical processes.

DOI: 10.1038/s41377-025-01844-8

Source: https://www.nature.com/articles/s41377-025-01844-8