Measurement of the quantum zero-point motion of a nanomechanical resonator

TL;DR

This paper reports the measurement of quantum zero-point motion in a nanomechanical resonator cooled near its ground state, using optical spectroscopy to directly observe quantum fluctuations.

Contribution

First direct measurement of quantum zero-point motion in a nanomechanical resonator using optical sideband spectroscopy.

Findings

Mechanical mode cooled close to quantum ground state

Direct measurement of zero-point motion

Calibration of phonon occupancy through photon asymmetry

Abstract

We present optical sideband spectroscopy measurements of a mesoscopic mechanical oscillator cooled near its quantum ground state. The mechanical oscillator, corresponding to a 3.99GHz acoustic mode of a patterned silicon nanobeam, is coupled via radiation pressure to a pair of co-localized 200THz optical modes. The mechanical mode is cooled close to its quantum ground state from a bath temperature of 18K using radiation pressure back-action stemming from the optical pumping of one of the optical cavity resonances. An optical probe beam, resonant with the second optical cavity resonance, is used to transduce the mechanical motion and determine the phonon occupancy of the mechanical mode. Measurement of the asymmetry between up-converted and down-converted photons of the probe beam yields directly the displacement noise power associated with the quantum zero-point motion of the mechanical oscillator, and provides an absolute calibration of the average phonon occupancy of the mechanical mode.