Optical control of single excitons in semiconductor quantum dots

The fundamental building block of quantum information processing technologies is the quantum-bit a 'qubit.' These technologies require the ability to prepare, control, and read out a qubit state. Spins confined in self-assembled quantum dots are promising candidates for a quantum bit, because semiconductors are compatible with mature modern opto- and micro-electronics. These quantum dot systems offer two more advantages: they are excellent interfaces between the spin state-an anchored qubit and a photon-a 'flying qubit' and they provide means to coherently control the spin qubit by ultrashort optical pulses. In this review, we thoroughly discuss the qubit provided by an optically-excited electron in a quantum dot-the exciton qubit. We demonstrate its spin state initialization, coherent control and read-out using ultrashort optical pulses.