John F. Barry MIT Lincoln Labs

Solid state spins have emerged as promising candidates for next-generation sensors. These spin systems combine the precision and repeatability inherent to more traditional atomic systems while eliminating obvious pain points such as cryogenics, vacuum and tunable single-frequency lasers. A principle difficulty with these systems is extraction of the full quantum information from the spins following a measurement. For the most popular solid state spin platform, NV defects in diamond, typical demonstrated ensemble readout fidelities are roughly two to four orders of magnitude worse than theoretical limits. This talk covers recent results demonstrating a promising alternative approach, dispersive readout of an NV spin ensemble. The NV ensemble is coupled to a high-Q microwave cavity. The ensemble quantum state is encoded in the dispersive shift of the cavity. The cavity center frequency is then interrogated via near-resonant microwaves. We achieve strong coupling between the ensemble and the high-Q microwave cavity. We show the scheme circumvents optical shot noise of conventional readout methods, achieves unity contrast and is ultimately limited by thermal noise.

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