Testing whether gravity acts as a quantum entity when measured

A defining signature of classical systems is their in principle measurability without disturbance: a feature manifestly violated by quantum systems. We show that this can be used to test the non-classicality of the gravitational field generated by a source in quantum superposition. To this end, we describe a multi-interferometer experimental setup that can, in principle, reveal the non-classicality of a superposition-sourced gravitational field by showing that it is necessarily disturbed by a measurement of gravity. While one interferometer sources the field, the others are used to measure the gravitational field created by the superposition. The resulting measurement induced quantum update of the state (disturbance) is evidenced through spin measurement statistics. This test, when added to the recently proposed entanglement-witness based tests, enlarge the domain of quantum mechanical postulates being tested for gravity. Moreover, the proposed test yields a signature of quantum measurement induced disturbance for any rate of decoherence, and is device independent.

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