# Laser cooling of a nanomechanical oscillator to the zero-point energy

## TL;DR

This paper demonstrates laser cooling of a nanomechanical oscillator to near its quantum ground state using a silicon optomechanical crystal in a cryogenic environment, enabling advanced quantum experiments.

## Contribution

It achieves deep laser sideband cooling to 0.09 phonons in a well-resolved optomechanical system at 2K, surpassing previous limitations due to optical heating.

## Key findings

- Achieved 0.09 mean thermal occupancy of the oscillator.
- Demonstrated laser cooling in a cryogenic environment with minimal residual motion.
- Enabled potential for quantum optomechanical experiments in the optical domain.

## Abstract

Optomechanical cavities in the well-resolved-sideband regime are ideally suited for the study of a myriad of quantum phenomena with mechanical systems, including backaction-evading measurements, mechanical squeezing, and generation of non-classical states. For these experiments, the mechanical oscillator should be prepared in its ground state; residual motion beyond the zero-point motion must be negligible. The requisite cooling of the mechanical motion can be achieved using the radiation pressure of light in the cavity by selectively driving the anti-Stokes optomechanical transition. To date, however, laser-absorption heating of optical systems far into the resolved-sideband regime has prohibited strong driving. For deep ground-state cooling, previous studies have therefore resorted to passive cooling in dilution refrigerators. Here, we employ a highly sideband-resolved silicon optomechanical crystal in a $^3$He buffer gas environment at $\sim 2\text{K}$ to demonstrate laser sideband cooling to a mean thermal occupancy of $0.09_{-0.01}^{+0.02}$ quantum (self-calibrated using motional sideband asymmetry), which is $-7.4\text{dB}$ of the oscillator's zero-point energy and corresponds to 92% ground state probability. Achieving such low occupancy by laser cooling opens the door to a wide range of quantum-optomechanical experiments in the optical domain.