Cooling-by-measurement and mechanical state tomography via pulsed optomechanics

TL;DR

This paper demonstrates rapid, quantum-noise-limited measurements of a mechanical oscillator's position using pulsed optomechanics, enabling state tomography and cooling-by-measurement to near-quantum ground states.

Contribution

It introduces a pulsed optomechanical technique for back-action-evading measurements, state preparation, and tomography of mechanical states at room temperature.

Findings

Achieved mechanical state reconstruction with 19 pm position uncertainty.

Reduced mechanical mode temperature from 1100 K to 16 K via cooling-by-measurement.

Performed quantum-noise-limited, rapid optical measurements of mechanical motion.

Abstract

Observing a physical quantity without disturbing it is a key capability for the control of individual quantum systems. Such back-action-evading or quantum-non-demolition measurements were first introduced in the 1970s in the context of gravitational wave detection to measure weak forces on test masses by high precision monitoring of their motion. Now, such techniques have become an indispensable tool in quantum science for preparing, manipulating, and detecting quantum states of light, atoms, and other quantum systems. Here we experimentally perform rapid optical quantum-noise-limited measurements of the position of a mechanical oscillator by using pulses of light with a duration much shorter than a period of mechanical motion. Using this back-action evading interaction we performed both state preparation and full state tomography of the mechanical motional state. We have reconstructed mechanical states with a position uncertainty reduced to 19 pm, limited by the quantum fluctuations of the optical pulse, and we have performed `cooling-by-measurement' to reduce the mechanical mode temperature from an initial 1100 K to 16 K. Future improvements to this technique may allow for quantum squeezing of mechanical motion, even from room temperature, and reconstruction of non-classical states exhibiting negative regions in their phase-space quasi-probability distribution.