Levitating diamonds towards a test of the quantum nature of gravity

Quantum mechanics and general relativity are the two fundamental theories in physics, but it is not known how to combine them and experiments are needed to make progress with this. We have proposed that experiments using levitated diamonds could access this crucial open problem by putting a diamond into a quantum superposition of being in two places at once. In this PhD project we will take key steps towards this by building an experiment with a levitated diamond in vacuum, and controlling the quantum state of nitrogen-vacancy (NV) spins inside of it. The diamond will not be optically levitated as this heats the diamond too much, and we will not use ion trapping as this requires the diamond to be charged which makes it too sensitive to electromagnetic decoherence. Instead we will use diamagnetic trapping. No-one has been able to demonstrate control of an NV spin in a diamagnetically trapped diamond. As part of this we will work on improving the NV-doped diamond material that we will levitate. This work should also lead to better sensors, both by improving the existing sensing that is done with NV centres in diamond, and by creating a new class of sensor based on levitated diamonds. We will continue our collaborations on this work with Sougato Bose, Anupam Mazumdar, David Moore and Andrew Geraci.