# Single Photon Detection by Cavity-Assisted All-Optical Gain

## TL;DR

This paper proposes a novel method for room temperature, photon-number-resolving single photon detection using cavity-assisted all-optical gain, achieving high efficiency and low dark counts within tens of picoseconds.

## Contribution

It introduces a new approach leveraging free carrier dispersion in semiconductor nanocavities for ultrafast, incoherent transduction and detection of single photons.

## Key findings

- Single photon can be detected within tens of picoseconds.
- Detection efficiency estimated at ~99%.
- Dark count rate on the order of kHz.

## Abstract

We consider the free carrier dispersion effect in a semiconductor nanocavity in the limit of discrete photoexcited electron-hole pairs. This analysis reveals the possibility of ultrafast, incoherent transduction and gain from a single photon signal to a strong coherent probe field. Homodyne detection of the displaced probe field enables a new method for room temperature, photon-number-resolving single photon detection. In particular, we estimate that a single photon absorbed within a silicon nanocavity can, within tens of picoseconds, be detected with $\sim 99\%$ efficiency and a dark count rate on the order of kHz assuming a mode volume $V_\text{eff}\sim 10^{-2}(\lambda/n_\text{Si})^3$ for a 4.5 micron probe wavelength and a loaded quality factor $Q$ on the order of $10^4$.