Feedback-based control of nano- and micromechanical resonators can enable the study of macroscopic quantum phenomena and also sensitive force measurements. We have experimentally demonstrated the feedback cooling macroscopic vibrating membrane close to its quantum ground state.
Dissipation and the accompanying fluctuations are often seen as detrimental for quantum systems, since they are associated with fast relaxation and loss of phase coherence. However, a pure quantum state can in principle be prepared if external noise induces suitable downwards transitions, while exciting transitions are blocked. We demonstrate such a refrigeration mechanism in a cavity optomechanical system, where we prepare a mechanical oscillator in its ground state by a noisy electromagnetic environment. intriguingly, one could use suitably filtered ambient noise for quantum state preparation.
In studies of quantum-mechanical somewhat massive systems, deep cryogenic temperatures close to absolute zero are basically necessary. The contemporary cooling technology, "cryogen-free" dilution refrigerators, utilizes cryocoolers which produce a massive amount of acoustic noise and vibrations. This is highly detrimental for any mechanical devices or sensors. The results will be of interest also to a broader community in fundamental research, in particular in detection of gravitational waves in large interferometers which are starting to use cryogenic systems. We have implemented an acoustic low-pass filter using massive copper blocks and ring springs inside a dilution refrigerator operating at 10 millikelvin temperatures. Our membrane resonators are now immune to the strong vibrations from the cryocooler, with a relatively simple and yet efficient acoustic filter.
