# Nonreciprocal photon blockade in a two-mode cavity with a second-order nonlinearity

## TL;DR

This paper proposes a nanostructured toroid cavity with second-order nonlinearity to achieve nonreciprocal photon blockade via Fizeau drag, enabling directional control of photon transport with feasible system parameters.

## Contribution

It introduces a novel approach using a $^{(2)}$ nonlinear toroid cavity to realize nonreciprocal photon blockade driven by Fizeau drag effects.

## Key findings

- Photon blockade occurs when driving from one side but not the other.
- The phenomenon is achievable with small optical nonlinearity.
- The system operates effectively at fundamental and second-harmonic frequencies.

## Abstract

It is shown that the Fizeau drag can be used to cause nonreciprocity. We propose the use of a nanostructured toroid cavity made of $\chi^{(2)}$ nonlinear materials to achieve nonreciprocal photon blockade (PB) through the Fizeau drag. Under the weak driving condition, we discuss the origins of the PB based on the doubly resonant modes with good spatial overlap at the fundamental and second-harmonic frequencies. We also find that for the fundamental mode, the PB happens when we drive the system from one side but the photon-induced tunneling happens when we drive the system from the other side. However, there is no such phenomenon in the second-harmonic mode. Remarkably, the PB phenomenon occurs with a reasonably small optical nonlinearity thus bringing the system parameters closer to the reasonably achievable realm by the current technology.