Quantum gravity in tabletop experiments

Measuring the quantum nature of the gravitational field is a dream going back to the earliest days of relativity and quantum mechanics. This has long been considered impossible because it is extremely difficult to prepare a large mass in a quantum state, but recent, rapid advances in the control of the quantum state of mechanical systems have opened the possibility of experimental tests in the near future. Here we give an overview of the types of tests possible using mechanical resonators and matter-wave systems. We survey a number of theories for quantum gravity at these terrestrial energy scales: standard perturbatively quantized general relativity, as well as models where gravity is classical, or responsible for a breakdown of quantum mechanics."
You can also caption the picture attached here as follows: "A cartoon of our experimental paradigm. In the first step, a source mass M is prepared in some initial state like the ground state, which produces a particular gravitational field, here depicted as a small gravitational potential well, while a test mass m is likewise prepared in some reference state. We then prepare the source into a non-classical state, here a cat state "L + R" of two locations, each branch of which has its associated gravitational field. Finally, we let the test mass m freely interact with the source mass, and perform a measurement on either one of the masses or the joint source-test system.

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