A Single-Photon LED

A single-photon LED, a light-emitting diode that fires one photon at a time, has been created, offering a potentially inexpensive and easy-to-manufacture component for quantum cryptography and a host of other applications.

At the CLEO/QELS meeting last week in Long Beach, scientists at Toshiba Research Europe Limited described a tiny, nanometer-scale indium arsenide quantum dot embedded in a gallium arsenide LED structure.

The quantum dot is so small that it can at most capture a few electrons and holes from a pulse of electric current. A single photon is created by the recombination of a single electron and single hole in the dot.

The researchers believe this is the first electrically driven single-photon source. Such single-particle-emitting sources are essential for a truly secure form of quantum cryptography. Otherwise, if several photons spill out from a device at a time, the extra ones can be siphoned off by an eavesdropper, who could then intercept a message without being detected. (Paper QTuG1 at meeting; contact Andrew Shields, andrew.shields@crl.toshiba.co.uk; see also Yuan et al., Science, 4 January 2002.)