Sideband Cooling Beyond the Quantum Limit with Squeezed Light

TL;DR

This paper demonstrates that using squeezed light in microwave cavity optomechanics allows cooling of a mechanical oscillator below the quantum limit, surpassing traditional laser cooling constraints and enabling quantum experiments with larger systems.

Contribution

The authors experimentally show that squeezed microwave light can cool a mechanical resonator below the quantum limit, a significant advancement over conventional cooling methods.

Findings

Achieved cooling 2 dB below the quantum limit.

Minimum phonon occupancy of 0.19 measured.

Cooling to within 15% of the quantum limit with coherent light.

Abstract

Quantum fluctuations of the electromagnetic vacuum impose an observable quantum limit to the lowest temperatures that can be reached with conventional laser cooling techniques. As laser cooling experiments continue to bring massive mechanical systems to unprecedented temperatures, this quantum limit takes on increasingly greater practical importance in the laboratory. Fortunately, vacuum fluctuations are not immutable, and can be "squeezed" through the generation of entangled photon pairs. Here we propose and experimentally demonstrate that squeezed light can be used to sideband cool the motion of a macroscopic mechanical object below the quantum limit. To do so, we first cool a microwave cavity optomechanical system with a coherent state of light to within 15% of this limit. We then cool by more than 2 dB below the quantum limit using a squeezed microwave field generated by a Josephson Parametric Amplifier (JPA). From heterodyne spectroscopy of the mechanical sidebands, we measure a minimum thermal occupancy of 0.19 phonons. With this novel technique, even low frequency mechanical oscillators can in principle be cooled arbitrarily close to the motional ground state, enabling the exploration of quantum physics in larger, more massive systems.