Observation of discrete-light temporal refraction by moving potentials with broken Galilean invariance

Qin, Chengzhi; Ye, Han ; Wang, Shulin; Zhao, Lange ; Liu, Menglin; Li, Yinglan ; Hu, Xinyuan ; Liu, Chenyu ; Wang, Bing ; Longhi, Stefano; Lu, Peixiang
Nature Communications 15, 5444 (1-11) (2024)

Refraction is a basic beam bending effect at two media’s interface. While traditional studies focus on stationary boundaries, moving boundaries or potentials could enable new laws of refractions. Meanwhile, media’s discretization plays a pivotal role in refraction owing to Galilean invariance breaking principle in discrete-wave mechanics, making refraction highly moving-speed dependent. Here, by harnessing a synthetic temporal lattice in a fiber-loop circuit, we observe discrete time refraction by a moving gauge-potential barrier. We unveil the selection rules for the potential moving speed, which can only take an integer v = 1 or fractional v = 1/q (odd q) value to guarantee a well-defined refraction. We observe reflectionless/reflective refractions for v = 1 and v = 1/3 speeds, transparent potentials with vanishing refraction/reflection, refraction of dynamic moving potential and refraction for relativistic Zitterbewegung effect. Our findings may feature applications in versatile time control and measurement for optical communications and signal processing.

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