Stimulated absorption of single gravitons: First light on quantum gravity

In a recent work we showed that the detection of the exchange of a single graviton between a massive quantum resonator and a gravitational wave can be achieved. Key to this ability are the experimental progress in preparing and measuring massive resonators in the quantum regime, and the correlation with independent detections of gravitational waves (GWs) that induce stimulated absorption, such as by the Laser Interferometer Gravitational Wave Observatory (LIGO). But can stimulated single-graviton processes shed light on the quantization of gravity? Here we analyze this question and make a historic analogy to the early days of quantum theory. We discuss in what ways such experiments can indeed probe key features of the quantized interaction between gravity and matter. We outline five experimental tests utilizing stimulated emission and absorption processes of single gravitons, opening the first window into experimental exploration of the fundamentals of quantum gravity.