Fast, High Fidelity Quantum Dot Spin Initialization without a Strong Magnetic Field by Two-Photon Processes

Recent demonstrations of cavity quantum electrodynamics (QED) effects with semiconductor quantum dots (QDs) coupled to microcavities [1, 2, 3, 4, 5] show that these systems are robust and scalable platforms for quantum information science. The QD-cavity QED experiments performed so far treat each QD as a two-level quantum system consisting of a ground state and the single exciton excited state. However, multilevel quantum systems are necessary for fast, complex, and high fidelity quantum information processing [6]. Each of these systems should contain two stable ground states between which the transition is dipole forbidden and one or more excited states that serve as a passage for population transfer between the ground states (Λ system) [7, 8]. Initialization, coherent manipulation, and readout of these Λ systems are essential for quantum information processing including controlled phase gate [9, 10], quantum repeaters and networks [11], and remote entanglement distribution or creation [12]. Therefore, realizing a multilevel system in a QD coupled to a cavity is crucial for semiconductor cavity QED implementation of quantum computers.