Optical control of one and two hole spins in interacting quantum dots

A single hole spin in a semiconductor quantum dot has emerged as a quantum bit that is potentially superior to an electron spin. A key feature of holes is that they have a greatly reduced hyperfine interaction with nuclear spins, which is one of the biggest difficulties in working with an electron spin. It is now essential to show that holes are viable for quantum information processing by demonstrating fast quantum gates and scalability. To this end, we have developed InAs/GaAs quantum dots coupled through coherent tunnelling and charged with controlled numbers of holes. We report fast, single-qubit gates using a sequence of short laser pulses. We then take the important next step towards scalability of quantum information by optically controlling two interacting hole spins in separate dots.