Event

Announcement: Ph.D. Dissertation Defense

Name: Xiechen Zheng

Committee:
Prof. Ronald L. Walsworth, Chair
Prof. Cheng Gong
Prof. Julius Goldhar
Prof. Saikat Guha
Prof. Giuliano Scarcelli, Dean's Representative

Date/Time: Monday, July 20th, 10am - 12pm

Location: E.A. Fernandez (EAF) IDEA Factory, Room 2121 (Wasmer Conference Room)
https://umd.zoom.us/j/3710503362?pwd=K2t1dzFsbEROWlg2dEZxSlNBNHVVZz09&omn=99630621952

Title:
All-Optical Quantum Diamond Magnetic Sensing

Abstract:
Nitrogen-vacancy (NV) centers in diamonds have emerged as a versatile solid-state spin defect platform for magnetic sensing under wide-ranging conditions. The negatively charged nitrogen-vacancy (NV⁻) center combines robust optical excitation and readout via spin-state-dependent photoluminescence (PL) with long spin coherence times at room temperature. This combination makes NV⁻ an attractive platform for highly sensitive magnetometry across a broad range of applications in the physical and life sciences. Conventional NV⁻ magnetic sensing protocols, such as optically detected magnetic resonance (ODMR), rely on microwave irradiation to coherently manipulate the NV⁻ spin states. Microwave irradiation, however, introduces additional experimental complexity and may perturb the sample under study.

This work pursues all-optical (AO), microwave-free magnetic sensing using NV⁻ ensembles in diamond. At low magnetic fields (<2 mT) under continuous-wave (CW) NV⁻ optical readout, we demonstrate AO-PL contrast features arising from resonant NV-NV dipolar interactions, known as NV-NV cross-relaxation, between NV⁻ centers of different crystallographic orientations. We further resolve sub-structure within these contrast features arising from NV⁻ hyperfine interaction with the nitrogen nuclear spin. To improve measurement robustness, we introduce a pulsed AO sequence that uses two PL readouts within an optical pulse to suppress common-mode noise, achieving up to 10x improvement in the low-frequency noise floor over conventional CW AO magnetometry near zero field. Beyond the low-field regime, we show that AO-PL changes induced by magnetic fields misaligned from the NV⁻ symmetry axis may be able to support AO magnetic sensing in demanding electromagnetic environments such as inside a nuclear fusion reactor, where efficient microwave delivery is impractical. Using the pulsed-sensing technique, we can detect AO-PL changes reliably in a complex optical environment, where optical intensity noise is substantial.

Given the robustness of the diamond host and NV⁻ properties, AO magnetometry may be suited to harsh environments involving extreme temperature, pressure, radiation, or chemically corrosive conditions. Finally, we develop a simple benchtop NV⁻ system capable of CW-ODMR magnetometry for educational use in a quantum hardware laboratory course. This work informs NV-diamond sample optimization for effective AO operation across diverse applications and extends the operation range of NV⁻ quantum sensing beyond controlled laboratory settings.