The development of micro-electromechanical systems has presented physicists with an intriguing concept: quantum effects in macroscopic systems. One such phenomenon that could be observable in ultrasmall mechanical resonators is zero-point motion — movement of the resonator even when it is in its lowest energy state. Attempts to measure zero-point motion using electrical techniques have run into a number of problems: the high frequencies (GHz) and the low temperatures (mK) involved, plus the demand for sensitivity. Optical monitoring is an alternative that offers this higher sensitivity. It comes, however, at a price: the resonators must be larger and, as a consequence, the temperatures needed to observe the fascinating quantum effects are even lower. This temperature requirement has, up to now, put the feasibility of optical monitoring in some doubt.

The recent work of Arcizet et al. has now gone some way to showing that it may be possible after all1. The team fabricated a silicon resonator, clamped at both ends, which were 1 mm2 in area and 60 µm thick — relatively large by modern standards — and coated in a high-reflectivity dielectric to form a moveable mirror. A second, static mirror creates an optical cavity, which was interrogated with 1,064 nm laser light. The displacement of the resonator is measured from the optical signal using the so-called Pound–Drever–Hall technique — primarily used for frequency-stabilizing lasers, it is also used for interferometry with optical cavities. Arcizet et al. claim that their system is 1,000 times more sensitive than previous experiments. The primary focus of this work has been to demonstrate the sensitivity of optical detection. The next step, which this work indicates could soon be possible, is to cool the system to temperatures below 1 mK so that the zero-point state of a macroscopic mechanical resonator can be successfully experimentally measured.