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Summary
Masers, the precedent and radio-frequency (rf) counterpart of lasers, have many applications in metrology, communication, and spectroscopy. Jiang et al. (1) demonstrate a new type of maser in which rf radiation is amplified by stimulated emission from transitions between periodically modulated quantum states, called Floquet states (2), unlike a conventional maser, which uses transitions between stationary quantum states. The Floquet maser presents a phase-locked frequency comb equally spaced by the modulation frequency. With a modulating signal at a low frequency (1 to 100 mHz) converted to maser emission at high transition frequencies (∼10 Hz) of ultranarrow spectral linewidth (<0.3 mHz), the authors overcome the low-frequency noise problem in metrology and show that subpicotesla sensitivity of magnetometry is achievable. Conceivable applications of this work include precision clocks and detection of ultralight dark-matter particles such as axions.
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