Photonic time crystals assisted by quasi-bound states in the continuum

TL;DR

This paper demonstrates that nanophotonic structures with quasi-bound states in the continuum can enable the realization of photonic time crystals at optical frequencies by reducing the required modulation amplitude.

Contribution

It introduces a novel approach combining bound states in the continuum with time-varying metamaterials to achieve observable photonic time crystals at optical frequencies.

Findings

Significant reduction in modulation amplitude needed for momentum bandgaps.

Enhanced light-matter interaction via nanostructures supporting quasi-bound states.

Potential pathway for practical realization of optical photonic time crystals.

Abstract

Photonic time crystals are a class of artificial materials that have only recently been explored. They are characterized by the ultrafast modulation of the material properties in time, causing a momentum bandgap for light that propagates through such novel states of matter. However, the observation of these unique properties at optical frequencies remains elusive, as the necessary modulation amplitudes of the permittivity to show notable momentum bandgaps are relatively high, inaccessible with available materials. While it has been known that structuring photonic time crystals at the sub-wavelength scale can enhance the momentum bandgap, we push this concept to the extreme by leveraging the nanophotonic toolbox. Specifically, we demonstrate that nanophotonic structures composed of scatterers supporting quasi-bound states in the continuum can significantly reduce the required amplitude of temporal permittivity modulation by enhancing the interaction time between light and time-varying matter. This allows us to observe extremely wide momentum bandgaps despite the material properties having tiny modulation amplitudes. Our approach bridges the concepts of bound states in the continuum and time-varying metamaterials, paving the way toward realizable photonic time crystals at optical frequencies.