Detecting single gravitons and probing their acoherence with continuous quantum sensing

Abstract

The quantization of gravity is widely believed to result in gravitons -- particles of discrete energy that populate gravitational waves. But their detection has so far been considered impossible. In this talk, I will first show that signatures of single graviton exchanges between matter and gravitational waves can be observed in laboratory experiments. Stimulated and spontaneous single-graviton processes can become relevant for massive quantum acoustic bar resonators, where the stimulated absorption of single gravitons can be resolved through continuous sensing of quantum jumps. In analogy to the discovery of the photo-electric effect for photons, such signatures can provide the first experimental clue of the quantization of gravity.
I will conclude the talk by showing that further statistical tests that probe the quantum mechanical character of radiation fields are also possible, using the counting statistics of observed quantum jumps in resonant detectors. I will present simple statistical tests which provide practical means to test the null hypothesis that a given field is "maximally classical", i.e., accurately described by a coherent state. Our findings suggest circumstances in which that hypothesis plausibly fails, notably including gravitational radiation involving non-linear or stochastic sourcing.

References:
[1] Germain Tobar*, Sreenath K. Manikandan*, Thomas Beitel, and Igor Pikovski. "Detecting single gravitons with quantum sensing."Nature Communications 15, 7229 (2024)

[2] Sreenath K. Manikandan and Frank Wilczek, Detecting Acoherence in Radiation Fields, ArXiv 2409.20378 (2024)