requirements for quantum information processing (QIP). A semiconductor quantum
dot is a convenient QIP platform, due to the fact that its potential well confines single
carriers, whose spins can be used as matter qubits, and optical recombination of these
confined carriers allows coupling to photonic qubits.
A quantum-dot-confined dark exciton (DE) is an electron hole pair with
parallel spins. Since photons barely interact with the electronic spin, the DE is almost
optically inactive and has a very long lifetime, making it an interesting quantum dot
qubit candidate. We demonstrate for the first time that the quantum dot-confined DE
forms a long lived (more than 1 μs) integer spin qubit which, despite its optical
inactivity, can be deterministically initiated [1-2] and fully controlled  by short
optical pulses, several orders of magnitude shorter than the life and coherence time (at
least 100 ns) of this qubit. We also demonstrate that the DE can be reset from the
quantum dot via optical pumping  and that it can be used to generate entangled
 Schwartz, Schmidgall et al. Phys. Rev. X 5, 011009 (2015).
 Schwartz et al. Phys. Rev. B 92, 201201R (2015).
 Schmidgall et al. Appl. Phys. Lett. 106, 193101 (2015).
 Lindner and Rudolph, Phys. Rev. Lett. 103, 113602 (2009).