Vector magnetometry using cavity-enhanced microwave readout of solid-state spin sensors

Abstract

Robust, high-fidelity readout is central to quantum device performance. Overcoming poor readout is therefore an increasingly urgent challenge for devices based on solid-state spin defects, particularly given their rapid adoption in quantum sensing, quantum information, and tests of fundamental physics. However, in spite of experimental progress in specific systems, solid-state spin sensors still lack a universal technique for high-fidelity readout. One leading research avenue is to engineer state-of-the-art microwave delivery systems which improve the coherent control of large spin ensembles as they are manipulated for readout. Another is to develop novel readout techniques that go beyond measuring optical fluorescence signals, which are often difficult to detect, and unique only to some solid-state spin systems. In this thesis, I discuss these two approaches, and begin by designing a three dimensional microwave resonator that overcomes the many shortcomings of conventional microwave delivery systems, which limit the readout fidelity of devices employing large spin systems. Next, I demonstrate a novel readout technique that provides high-fidelity, room-temperature readout of an ensemble of nitrogen-vacancy centers via strong coupling to a dielectric microwave cavity. This strong collective interaction allows the spin ensemble’s microwave transition to be probed directly, thereby overcoming the optical photon shot noise limitations of conventional fluorescence readout. Applying this technique to magnetometry, I first build a proof-of-concept magnetometer with the capability of measuring magnetic fields along a single vector axis, with a sensitivity better than the optical shot noise limit of the system. I then expand on the initial demonstration, by building a prototype capable of measuring three-dimensional dynamic vector fields with high sensitivity. While the current device performance is limited by technical noise, the method promises what has long been elusive for quantum sensors based on solid-state spin ensembles: a clear path to readout at the spin-projection limit.