# Photon-level tuning of photonic nanocavities

## TL;DR

This paper demonstrates highly energy-efficient optical tuning of photonic nanocavities at the photon level, enabling resonance control with minimal photon energy, which is promising for future low-power photonic devices.

## Contribution

The study achieves photon-level resonance tuning in a lithium niobate nanocavity with unprecedented efficiency, combining high Q-factor and small mode volume for minimal photon energy use.

## Key findings

- Resonance tuning rate of 88.4 MHz per photon
- Tuning across the entire cavity resonance with only about 2.4 photons
- Potential applications in energy-efficient optical switching

## Abstract

Energy-efficient optical control of photonic device properties is crucial for diverse photonic signal processing. Here we demonstrate extremely efficient optical tuning of photonic nanocavities, with only photon-level optical energy. With a lithium niobate photonic crystal nanocavity with an optical Q up to 1.41 million and an effective mode volume down to 0.78$(\lambda/n)^3$, we are able to achieve a resonance tuning rate of about 88.4~MHz/photon (0.67~GHz/aJ), which allows us to tune across the whole cavity resonance with only about 2.4 photons on average inside the cavity. Such a photon-level resonance tuning is of great potential for energy-efficient optical switching, wavelength routing, and reconfiguration of photonic devices/circuits that are indispensable for future photonic interconnect.