Credit: © 2008 Nature

There have been major advances in the use of lasers to cool mechanical structures such as mirrors in recent years, although the ultimate goal of observing quantum effects in these macroscopic objects has remained elusive. These experiments generally involve the mirror being part of a high-quality optical cavity. However, such cavities require the mirrors to be rigid and massive, whereas quantum behaviour is much more likely to be seen in structures that are small and flexible. Now Jack Harris and co-workers1 at Yale University and Ludwig-Maximilians University have developed an approach that allows mechanical structures and high-quality cavities to be combined without compromising the mechanical or optical properties of either.

Harris and co-workers use commercial mirrors to define their cavity, which is 6.7 cm long, and place a 50-nm-thick commercial silicon nitride membrane inside it. The cavity is then excited by a laser, and the membrane experiences radiation pressure in two directions. The team is able to cool the membrane from room temperature to 6.82 mK. The 'membrane-in-the-middle' geometry also allows the square of the membrane's displacement to be read out directly, which should make it possible to read out its energy eigenstate — something that has not been possible with existing optomechanical experiments. Harris and co-workers conclude that "it should be practical to use this scheme to observe quantum jumps of a mechanical system".