There is no empirical evidence yet as to “whether” gravity has a quantum mechanical origin. Motivated by this, I will present a feasible idea for testing the quantum origin of the Newtonian interaction based on the simple fact that two objects cannot be entangled without a quantum mediator. I will show that despite its weakness, gravity can detectably entangle two adjacent micron sized test masses held in quantum superpositions even when they are placed far apart enough to keep Casimir-Polder forces at bay. A prescription for witnessing this entanglement through spin correlations is also provided. Further, I clarify the assumptions underpinning the above proposal such as our reasonable definition of “classicality”, as well as relativistic causality. We note a few ways to address principal practical challenges: Decoherence, Screening EM forces and Inertial noise reduction. I will also describe how unprecedented compact sensors for classical gravity (including meter scale sensors for low frequency gravitational waves) will arise on the way to the above grand goal.

Prof. Sougato Bose is a part of the Department of Physics & Astronomy, Faculty of Maths & Physical Sciences, University College London. His research interests include Entanglement in spin chains, Quantum communication, Quantum Optics, and Foundations of Quantum Mechanics.