Passive photonic time crystals

Time interfaces, which arise when an abrupt change in the properties of the host material occurs uniformly in space, have opened interesting opportunities for extreme wave manipulation, e.g., amplified emission and lasing in photonic time crystals (PTCs). Yet, altering the material properties is conventionally limited to active systems, which suffer from instabilities or saturation. In this talk, we introduce a passive path to achieving time interfaces in a switched transmission-line metamaterial. We first discuss the experimental evidence of distinct temporal boundary conditions at such passive time interfaces. Combing these unusual temporal discontinuities periodically, we then introduce passive PTCs. Unlike conventional PTCs where waves are exponentially amplified inside the momentum gaps, we demonstrate that PTCs can be achieved without parametric amplification, featuring stable momentum bandgaps. The passive PTC not only behaves as an anti-laser in time but also features momentum-filtering responses. This feature may establish a building block to realize functional time-metamaterials, with opportunities for extreme spacetime wave control, e.g., real-time waveform shaping.