# A maser based on dynamical backaction on microwave light

## TL;DR

This paper demonstrates a novel microwave maser driven by dynamical backaction in a superconducting circuit, reversing typical optomechanical roles, and achieves stabilized, low-noise maser operation through injection locking.

## Contribution

It introduces a new regime where mechanical dissipation dominates, enabling dynamical backaction on microwave light and demonstrating maser action with stabilization techniques.

## Key findings

- Achieved maser oscillation driven by mechanical backaction.
- Demonstrated injection locking to stabilize maser frequency.
- Reversed the typical optomechanical dissipation hierarchy.

## Abstract

The work of Braginsky introduced radiation pressure dynamical backaction, in which a mechanical oscillator that is parametrically coupled to an electromagnetic mode can experience a change in its rigidity and its damping rate. The finite cavity electromagnetic decay rate can lead to either amplification or cooling of the mechanical oscillator, and lead in particular to a parametric oscillatory instability, associated with regenerative oscillations of the mechanical oscillator, an effect limiting the circulating power in laser gravitational wave interferometers. These effects implicitly rely on an electromagnetic cavity whose dissipation rate vastly exceeds that of the mechanical oscillator, a condition naturally satisfied in most optomechanical systems. Here we consider the opposite limit, where the mechanical dissipation is engineered to dominate over the electromagnetic one, essentially reversing role of electromagnetic and mechanical degree of freedom. As a result, the electromagnetic field is now subject to dynamical backaction: the mechanical oscillator provides a feedback mechanism which modifies the damping rate of the electromagnetic cavity. We describe this phenomenon in the spirit of Braginsky's original description, invoking finite cavity delay and highlighting the role of dissipation. Building on previous experimental work, we demonstrate this dynamical backaction on light in a superconducting microwave optomechanical circuit. In particular, we drive the system above the parametric instability threshold of the microwave mode, leading to maser action and demonstrate injection locking of the maser, which stabilizes its frequency and reduces its noise.