Phys. Rev. X 5, 011009 (2015)

Optical and deterministic control of qubits is at the heart of successful quantum information schemes. In this context, the spin of carriers in semiconductor quantum dots has attracted much attention. Now, Ido Schwartz and co-workers have demonstrated the suitability of the dark exciton (electron–hole pair with parallel spins) for quantum applications. Following a pump–probe experiment, they not only show that deterministic initialization is possible but they also extract the lower bound values for its lifetime (1 μsec) and coherence time (0.1 μsec). Furthermore, the researchers managed to rotate the dark exciton eigenstate around the right-hand circular polarization direction on the Bloch sphere. Given its much longer coherence time with respect to other charge carriers in quantum dots, as well as the simplicity in initializing and resetting its value, the dark exciton is shown to have potential as a solid-state spin qubit.