Light-matter interactions in photonic temporal crystals

Bumki Min*

Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea


Over the last few decades, the prominent strategies for controlling spontaneous emission has been the use of resonant or space-periodic photonic structures. This approach, initially articulated by Purcell and later expanded upon by Yablonovitch in the context of photonic crystals, leverages the spatial surroundings to modify the spontaneous emission rate of atoms or quantum emitters. However, the rise of time-varying photonics has compelled a reevaluation of the spontaneous emission process within dynamically changing environments, especially concerning photonic temporal crystals where optical properties undergo time-periodic modulation.

In this talk, I will show that the application of classical light-matter interaction theory with Floquet analysis yields a substantially enhanced spontaneous emission rate at the edges of momentum gaps within photonic temporal crystals. This finding contrasts significantly with the recent prediction and is attributed to time-periodicity-induced loss and gain mechanisms, as well as the non-orthogonality of photonic Floquet eigenstates that are inherent to photonic temporal crystals. Intriguingly, our findings also suggest that photonic temporal crystals enable the spontaneous transition of an atom or a quantum emitter from its ground state to an excited state, accompanied by the concurrent emission of a photon. This process, which does not occur in equilibrium, represents a novel aspect of time-varying media that has not been previously addressed.

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