1:30 pm MCP 201
Spin-Entanglement Witness for Quantum Gravity.
Understanding gravity in the framework of quantum mechanics is one of the great challenges in modern physics. Along this line, the prime question is whether gravity is a quantum entity subject to the rules of quantum mechanics. It is fair to say that there are no feasible ideas yet to test the quantum coherent behaviour of gravity directly in a laboratory experiment. Here, we introduce a protocol for such a test based on the principle that two objects cannot be entangled without a quantum mediator. We show that despite the weakness of gravity, the phase evolution induced by the gravitational interaction of two micron-size test masses in adjacent matter-wave interferometers can detectably entangle them even when they are placed far apart enough to keep Casimir-Polder forces at bay. We provide a prescription for witnessing this entanglement, which certifies gravity as a coherent quantum mediator through simple correlation measurements between two spins: one embedded in each test mass. A similar protocol where a massive object in a ground state can entangle the high energy photons in a cavity in a quantum-optomechanical setup. The latter experiment will witness the spin of the gravitational interaction along with its quantum origin. Fundamentally, the above entanglement is shown to certify the presence of non-zero off-diagonal terms in the coherent state basis of the gravitational field modes.