Nature Photon. http://dx.doi.org/10.1038/nphoton.2011.208 (2011)

Mesoscopic optical cavities can alter the emission from any light sources within. Daniel Fuhrmann and colleagues have now shown that acoustic waves can tune the properties of such a cavity while a photon is still trapped inside. This concept could be useful for quantum information processing.

The authors created an optical resonator by perforating a thin membrane of gallium arsenide. An intentional defect in this otherwise regular lattice of holes trapped the light produced by embedded quantum dots. Metal electrodes driven by a radio-frequency voltage generated surface vibrations that travelled across the membrane. These 1.7-GHz sound waves expand and contract the cavity and, in doing so, change its resonant modes. The team observed the changing cavity by monitoring the light emission from the dots.

The real advantage of this approach is its speed: the properties of the photonic-crystal cavity can be altered in a fraction of a nanosecond. This is shorter than both the radiative lifetime of quantum dots and the length of time the photon remains confined in the cavity.