Photonic Time Crystals in the Quantum Regime - College of Engineering - Purdue University

The resurgence in studying time-varying media in optics is driven by recent extreme modulations in refractive index seen in transparent conducting oxides. These modulations occur rapidly, comparable to optical frequency oscillations, leading to phenomena like time-refraction, time-reflection, and photonic time crystals. While many groups focus on macroscopic aspects, quantum investigations remain limited. Classically, a sudden refractive index change in uniform media causes a Fresnel-like time-reflected wave, reflecting backward due to causality. Quantum mechanically, time-reflection involves creating a photon pair from vacuum, propagating both forward and backward. This parallels the dynamic Casimir effect, where modulated cavities influence vacuum state modes. Our program aims to explore these quantum aspects, focusing on on-demand photon-pair generation, entanglement, and vacuum state manipulation. These investigations could advance photonic quantum computing by tackling key challenges, such as shaping spontaneous emission with tailored temporal modulation, creating entangled photon cluster states through temporal modulation and nonlinear optics in time-varying media, both in classical and quantum contexts.