ABSTRACT
Photonic cluster states are a resource for quantum computation based solely on single-photon measurements. We use semiconductor quantum dots to deterministically generate long strings of polarization-entangled photons in a cluster state by periodic timed excitation of a precessing matter qubit. In each period, an entangled photon is added to the cluster state formed by the matter qubit and the previously emitted photons. In our prototype device, the qubit is the confined dark exciton, and it produces strings of hundreds of photons in which the entanglement persists over five sequential photons. The measured process map characterizing the device has a fidelity of 0.81 with that of an ideal device. Further feasible improvements of this device may reduce the resources needed for optical quantum information processing.
ABSTRACT
Preparation of a specific quantum state is a required step for a variety of proposed quantum applications. We report an experimental demonstration of optical quantum state inversion in a single semiconductor quantum dot using adiabatic rapid passage. This method is insensitive to variation in the optical coupling in contrast with earlier work based on Rabi oscillations. We show that when the pulse power exceeds a threshold for inversion, the final state is independent of power. This provides a new tool for preparing quantum states in semiconductor dots and has a wide range of potential uses.
