Entangled Route to a Lab-Test for Quantum Gravity

“Is gravitation mediated by a classical channel or by a quantum one?”. It is increasingly acknowledged that such a question should be unambiguously answered well before attempting any investigation on “how” gravity is quantized. 

In a paper published in Physical Review Letters, Sougato Bose and Peter Barker from UCL Physics and Astronomy and collaborators from around the globe, propose a thought experiment that aims to settle such a fundamental question. The proposal utilises the overarching physical property that local operations (supported by classical communication) cannot create entanglement between non-interacting systems. In the proposed experimental setting, two masses, each endowed with a spin-like degree of freedom, are made to gravitationally interact as they traverse adjacent interferometers. By ensuring that gravity is the sole agent acting between the masses, the observation of entanglement between the probes, would certify the quantum nature of gravity. Quite remarkably, the proposed scheme would provide a signature of quantumness of gravity that is within the grasp of state-of-the-art experiments, despite the purported weakness of the gravitational coupling. The manuscript shows that the challenges of avoiding non-Gravitational interactions (namely electromagnetic interactions of various forms) can be met, so that the quantum nature of gravity can be concluded without ambiguity, and through the sole, experimentally friendly test of entanglement between two spins.

Links

• Spin Entanglement Witness for Quantum Gravity– Published 13 December 2017
• Synopsis: A Test of Gravity’s Quantum Side
• Professor Sougato Bose's academic profile
• Professor Peter Barker's academic profile

Figure

•  G. W. Morley/University of Warwick and APS/Alan Stonebraker