Speaker: Jonathan Marcks, Argonne National Laboratory
Abstract: Defect center-based spin qubits in solid-state materials show great promise as quantum sensors and nodes in quantum networks. The success of these applications relies on precise control and understanding of the qubit host material and noise environment, which ultimately dictate qubit coherence. In this talk, I will describe our recent efforts to better understand environment-induced decoherence of the nitrogen vacancy (NV) center in diamond, an optically addressable spin qubit with coherent properties up to and above room temperature. I will focus on NV centers in nuclear spin-free diamond surrounded by low-dimensional dark electron spin baths, growth conditions achievable via in-house chemical vapor deposition (CVD) diamond growth. Introduction of unconverted nitrogen defects (P1 centers) is unavoidable in CVD growth and NV center synthesis, and it is thus critical to study NV-P1 interactions at scales relevant for quantum devices. To this end, I will first discuss quantitative computational studies of NV decoherence at the length and density scales relevant for synthesizing single NV centers, providing a reference for future NV synthesis, as well as revealing coherence behavior dependent on the spin bath dimensionality. These data are then applied to characterize nitrogen density in-situ via a statistical model, bypassing the need for unreliable bulk characterization techniques. I will then present measurements of spin bath dynamics at the single-spin level as a means to understand how microscopic processes cause decoherence. I will describe a polarization- and time-resolved measurement technique of a strongly coupled NV-P1 system that enables a probe of P1 polarization decay under arbitrary microwave and optical drives. These measurements reveal decay mechanisms on the single-spin level, allowing us to address open questions about the behavior of P1 spin baths in diamond.