Closed-Loop Control of ³He Nuclear Spin Oscillator: Implementation via Metastability Exchange Optical Pumping

Achieving long spin coherence times is crucial for quantum precision measurements, and closed-loop control techniques are often employed to accomplish this goal. Here, we demonstrate the impact of closed-loop feedback control on nuclear spin precession in a metastability exchange optical pumping (MEOP)-based polarized ^3He system. We analyze the effects of feedback theoretically and validate our predictions experimentally. With optimized feedback parameters, the spin coherence time T_2 is extended by an order of magnitude. When the feedback strength surpasses a critical threshold, robust maser oscillations are spontaneously excited, demonstrating remarkable resistance to environmental noise and maintaining stable oscillation. This proof-of-principle experiment highlights the viability of MEOP-based ^3He spin oscillators, especially in low-frequency domains. The operational simplicity and easy integration associated with MEOP-based systems make them particularly promising for fast, high-precision magnetic field measurements.