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Spontaneous Emission Decay and Excitation in Photonic Time Crystals

Jagang Park1,*, Kyungmin Lee2,*, Ruo-Yang Zhang3, Hee-Chul Park4, Jung-Wan Ryu5, Gil Young Cho6, Min Yeul Lee7, Zhaoqing Zhang3, Namkyoo Park8 et al.

Wonju Jeon9, Jonghwa Shin7, C. T. Chan3, and Bumki Min2,†

  • *These authors contributed equally to this work.
  • †Contact author: bmin@kaist.ac.kr
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Phys. Rev. Lett. 135, 133801 – Published 22 September, 2025

DOI: https://doi.org/10.1103/5v2w-yg7v

Abstract

Over the last few decades, the predominant strategies for controlling spontaneous emission have involved tailoring the spatial surroundings of quantum emitters or atoms to create resonant or spatially periodic photonic structures. However, the rise of time-varying photonics has prompted a reevaluation of spontaneous emission in dynamically changing environments, especially within photonic time crystals, where optical properties undergo time-periodic modulation. Here, we apply classical light-matter interaction theory together with Floquet analysis to reveal a substantial enhancement of the spontaneous emission decay rate at the momentum gap frequency in photonic time crystals. Moreover, our findings suggest that photonic time crystals enable a nonequilibrium light-matter interaction process: the spontaneous excitation of an atom from its ground state to an excited state, accompanied by the concurrent emission of a photon, referred to as spontaneous emission excitation.

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Controlling Light Emission with Photonic Time Crystals

Published 22 September, 2025

A material whose dielectric properties vary in time could produce exotic light-emission phenomena in a nearby atom, theorists predict.

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Outline

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Phys. Rev. Lett. 135, 133801– Published 22 September, 2025
  • Received 12 February 2025
  • Revised 9 June 2025
  • Accepted 30 July 2025
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