Resolved Sideband Limit Research Articles

Resolved-sideband and cryogenic cooling of an optomechanical resonator

Combing cryogenic and so-called sideband cooling promises to cool micrometre-scaled resonators to the point at which quantum effects take hold. Hope that this aim will soon be reached is boosted by the demonstration of a deformed silica microsphere that is cooled so that it contains only 37 phonons. Cooling a mechanical oscillator to its quantum ground state enables the exploration of the quantum nature and the quantum–classical boundary of an otherwise classical system1,2,3,4,5,6,7. In analogy to laser cooling of trapped ions8, ground-state cooling of an optomechanical system can in principle be achieved by radiation-pressure cooling in the resolved-sideband limit where the cavity photon lifetime far exceeds the mechanical oscillation period9,10,11. Here, we report the experimental demonstration of an optomechanical system that combines both resolved-sideband and cryogenic cooling. Mechanical oscillations of a deformed silica microsphere are coupled to optical whispering-gallery modes that can be excited through free-space evanescent coupling12,13. By precooling the system to 1.4 K, a final average phonon occupation as low as 37 quanta, limited by ultrasonic attenuation in silica, is achieved. With diminishing ultrasonic attenuation, we anticipate that the ground-state cooling can be achieved when the resonator is precooled to a few hundred millikelvin in a 3He cryostat.