Resonant Regeneration in the Sub-Quantum Regime -- A demonstration of fractional quantum interference

TL;DR

This paper demonstrates that resonant regeneration and quantum interference can be effective even at extremely low photon levels, confirming quantum mechanics principles and improving experimental sensitivity for detecting weakly coupled particles.

Contribution

It provides the first experimental evidence that resonant amplification functions at sub-quantum photon levels, validating quantum interference in this regime.

Findings

Resonant amplification is effective below one photon on average.

Thermal photons do not adversely affect the interference.

Quantum interference persists at sub-quantum levels.

Abstract

Light shining through wall experiments (in the optical as well as in the microwave regime) are a powerful tool to search for light particles coupled very weakly to photons such as axions or extra hidden sector photons. Resonant regeneration, where a resonant cavity is employed to enhance the regeneration rate of photons, is one of the most promising techniques to improve the sensitivity of the next generation of experiments. However, doubts have been voiced if such methods work at very low regeneration rates where on average the cavity contains less than one photon. In this note we report on a demonstration experiment using a microwave cavity driven with extremely low power, to show that resonant amplification works also in this regime. In accordance with standard quantum mechanics this is a demonstration that interference also works at the level of less than one quantum. As an additional benefit this experiment shows that thermal photons inside the cavity cause no adverse effects.