Coherent Feedback Cooling of an Ultracoherent Phononic-Crystal Membrane at Room Temperature

TL;DR

This paper demonstrates coherent feedback cooling of a high-quality phononic crystal membrane at room temperature, significantly reducing phonon occupation and approaching the quantum ground state without cryogenic cooling.

Contribution

The experimental realization of coherent feedback cooling combined with dynamical backaction to cool a high-Q membrane at room temperature is a novel achievement.

Findings

Achieved a phonon occupation reduction from 5.5 million to 166.

Demonstrated cooling factor of 3.3×10^4 at room temperature.

Showed potential for approaching the quantum ground state of high-Q membranes.

Abstract

Optomechanical systems provide a versatile platform for precision measurements and investigations of fundamental physics, where bringing macroscopic resonators into the quantum regime is a widely pursued goal. Achieving such quantum behavior of solid-state mechanical resonators at room temperature would greatly broaden their applications by removing the need for cryogenic environments. Reaching this goal requires efficient cooling of mechanical motion, among various laser cooling methods, dynamical backaction cooling (DBC) is widely utilized in experiments but fundamentally limited when operating in the sideband-unresolved regime. Coherent feedback cooling (CFC) can overcome this limitation, while avoiding state collapse and the electronic restrictions inherent to measurement-based feedback. Here, we experimentally demonstrate CFC using an ultracoherent density phononic crystal membrane. By combining CFC with strong DBC in a relatively narrow cavity, we achieve a phonon occupation reduction from $5.5\times10^{6}$ to $166\pm7$, corresponding to a cooling factor of $3.3\times10^{4}$ at room temperature, even with current experimental limitations. Our results show the potential of CFC for approaching the ground state of high-$Q$ membranes at room temperature.