An opaque cloud of cold atoms becomes transparent when a few photons occupy an empty cavity, creating an optical switch for processing quantum information.
Engineered strong photon-photon interactions would enable a broad range of applications in quantum information processing. We demonstrate, using an ensemble of atoms strongly coupled to an optical cavity, that light transmission through an opaque medium may be controlled with a few photons and even with the electromagnetic vacuum field. The vacuum field induces 40% transmission, accompanied by a group delay of 25 ns, which corresponds to the light pulse propagating at 1600 m/s through the medium. The transmission increases to 80% when ~10 photons are injected into the cavity. The strong optical nonlinearity at a few-photon level observed in this system opens prospects for advanced quantum devices such as photon-number-state filters.
Photons are excellent information carriers but normally pass through each other without consequence. Engineered interactions between photons would enable applications as varied as quantum information processing and simulation of condensed matter systems. Using an ensemble of cold atoms strongly coupled to an optical cavity, we found that the transmission of light through a medium may be controlled with few photons and even by the electromagnetic vacuum field. The vacuum induces a group delay of 25 nanoseconds on the input optical pulse, corresponding to a light velocity of 1600 meters per second, and a transparency of 40% that increases to 80% when the cavity is filled with 10 photons. This strongly nonlinear effect provides prospects for advanced quantum devices such as photon number-state filters.
Photons are excellent information carriers but normally pass through each other without consequence. Engineered interactions between photons would enable applications as varied as quantum information processing and simulation of condensed matter systems. Using an ensemble of cold atoms strongly coupled to an optical cavity, we found that the transmission of light through a medium may be controlled with few photons and even by the electromagnetic vacuum field. The vacuum induces a group delay of 25 nanoseconds on the input optical pulse, corresponding to a light velocity of 1600 meters per second, and a transparency of 40% that increases to 80% when the cavity is filled with 10 photons. This strongly nonlinear effect provides prospects for advanced quantum devices such as photon number–state filters.