Phys. Rev. Lett. 108, 033602 (2012)

Credit: © 2012 APS

Amir Safavi-Naeini and colleagues at the California Institute of Technology in the USA have used lasers to cool a mesoscopic optomechanical resonator down to a phonon occupancy of just 2.6 ± 0.2 — a level that allows characteristics associated with quantum zero-point fluctuations to be observed. The team used a silicon microbeam patterned with air voids that forms a Bragg cavity at the centre of the beam for both the photonic modes and the acoustic mode. The photonic modes at 1,545 nm and 1,460 nm were used for readout and optical cooling, respectively. The in-plane breathing mechanical mode, which had a frequency of around 4 GHz, was coupled to the optical modes by radiation pressure. Although photon cooling to the single-phonon level has already been achieved in related systems, the researchers say the performance of their set-up (with a minimum observed phonon number of 2–3) is currently limited by the power of the cooling laser and is therefore open to improvement. They also noted that the results deviate from ideal predictions due to optical absorption, which causes power-dependent variations in the parameters.