Spatiotemporal Photon Blockade for Nonreciprocal Quantum Absorption

Controlling the flow of photons is crucial for advancing quantum technologies. We introduce the concept of spatiotemporal photon blockade for nonreciprocal quantum absorption, utilizing space-time-periodic metasurfaces. Our study presents a methodology for experimentally realizing this effect, where photon frequency coherence with the metasurface's space-time modulation enables one-way quantum absorption. In this system, forward-traveling photons are energetically modulated and absorbed within the slab, while backward-traveling photons are transmitted without interaction. Our analysis includes band structure, isofrequency diagrams, and nonreciprocal absorption results. These findings lay the groundwork for developing nonreciprocal quantum devices and enhancing photon management in milli-Kelvin temperature quantum systems.