  Employing the ultrafast control of electronic states of a semiconductor
quantum dot in a cavity, we introduce a novel approach to achieve on-demand
emission of single photons with almost perfect indistinguishability and photon
pairs with near ideal entanglement. Our scheme is based on optical excitation
off-resonant to a cavity mode followed by ultrafast control of the electronic
states using the time-dependent quantum-confined Stark effect, which then
allows for cavity-resonant emission. Our theoretical analysis takes into
account cavity-loss mechanisms, the Stark effect, and phonon-induced dephasing
allowing realistic predictions for finite temperatures.
