Complete quantum control of a single quantum dot spin using ultrafast optical pulses

A single electron spin confined within a semiconductor nanostructure is an ideal qubit for quantum computing, as it is relatively stable against decoherence and is easily manipulated electrically or optically. Full quantum control involving initialization, spin rotation and detection, has been demonstrated previously using electrically controlled radio-frequency pulses, but this method will be too slow for the construction of quantum computing circuits operating at useful clock speeds. Optical manipulation of electron spin allows much faster operations and has the added advantage that it allows for an optical interface. Press et al. now achieve ultrafast optical control of electron spin in a quantum dot and demonstrate, in combination with optical initialization and detection, a single-qubit logic gate operation, involving a sequence of two optical pulses. Such high-speed operation could conceivably lead to quantum computing devices at gigahertz clock speeds.