Cavity optomechanical magnetometers

Abstract

This chapter introduces a new form of magnetometer which combines precision cavity optomechanical measurement with magnetostrictive material response. Such magnetometers can be fabricated on-chip and function both at room temperature and in earths magnetic field. Firstly, we derive the fundamental limit to sensitivity due to the thermomechanical fluctuations of the system, showing that sensitivity exceeding the current state-of-the-art is in-principle possible. We then show that bandwidths in the megahertz range are feasible. Then, we discuss the experimental implementation of these magnetometers, with demonstrated sensitivity at the level of 200 picotesla and tens of micrometer resolution. Finally, we compare both theory and experiments to the state-of-the-art. The sensitivity of current devices is less than a factor of 100 away from the best similarly sized cryogenic SQUID magnetometers, while theory suggests that sensitivity over an order of magnitude superior to those devices is possible.