Autonomous phonon maser in levitated spin-mechanics

TL;DR

This paper demonstrates an autonomous phonon maser using levitated nanodiamonds with NV centers, where spin-driven gain stabilizes mechanical oscillations, confirmed by master-equation simulations.

Contribution

It introduces a method to achieve phonon maser action via spin-induced gain in levitated nanodiamonds, with analytical and numerical validation.

Findings

Achieved phonon maser threshold with percent-level spin inversion.

Demonstrated self-oscillation and coherent steady state above threshold.

Validated results with full master-equation simulations.

Abstract

Levitated nanodiamonds hosting a single nitrogen-vacancy (NV) center provide an ultra-low-frequency mechanical mode with widely tunable dissipation and spin backaction under microwave dressing and optical pumping. We demonstrate that the driven NV spin can be tuned to act as an inverted gain medium for the center-of-mass motion, thereby stabilizing an autonomous phonon maser. In the separation-of-timescales regime where spin dynamics is fast, adiabatic elimination yields a reduced mechanical master equation with closed-form, detuning-dependent transition rates and a sharp threshold given by the sign change of the phonon-number damping. For representative levitated-NV parameters, we find that a percent-level dressed-basis inversion is sufficient to reach the threshold, and the small-signal gain can exceed the intrinsic mechanical loss by orders of magnitude. Full master-equation simulations confirm above-threshold self-oscillation and a phase-diffusing, coherent steady state, whose saturation follows the Maxwell-Bloch prediction.