A digital alkali spin maser

Ingleby, Stuart and Griffin, Paul and Dyer, Terry and Mrozowski, Marcin and Riis, Erling (2022) A digital alkali spin maser. Scientific Reports, 12 (1). 12888. ISSN 2045-2322 (https://doi.org/10.1038/s41598-022-16910-z)

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Self-oscillating atomic magnetometers, in which the precession of atomic spins in a magnetic field is driven by resonant modulation, offer high sensitivity and dynamic range. Phase-coherent feedback from the detected signal to the applied modulation creates a resonant spin maser system, highly responsive to changes in the background magnetic field. Here we show a system in which the phase condition for resonant precession is met by digital signal processing integrated into the maser feedback loop. This system uses a modest chip-scale laser and mass-produced dual-pass caesium vapour cell and operates in a 50 μT field, making it a suitable technology for portable measurements of the geophysical magnetic field. We demonstrate a Cramér-Rao lower bound-limited resolution of 50 fT at 1 s sampling cadence, and a sensor bandwidth of 10 kHz. This device also represents an important class of atomic system in which low-latency digital processing forms an integral part of a coherently-driven quantum system.