Electro-optic rotating half-waveplate for a quantum dot fine-structure eraser

Abstract

Quantum dots are a promising source of entangled photon pairs. Recent advances have shown nearly dephasing-free entanglement from quantum dots embedded in semiconductor nanowires. An outstanding challenge with these sources is the presence of the so-called fine-structure splitting, which is the lifting of spin degeneracy of the exciton state due to quantum dot potential asymmetry. This fine-structure splitting causes the output state to precess rapidly, which is degrades the quality of measured entanglement due to nite detector temporal response and is undesirable for applications where preparation of a consistent state is needed. The effects of fine-structure splitting can be \erased" once the photons have been emitted using a flexible all-optical approach. This optical fine-structure eraser scheme requires a rapidly rotating half-waveplate, which cannot be implemented with commercially available off-the-shelf systems. This thesis presents the operation of an electro-optic modulator which can emulate a rotating half-waveplate at the required speeds, and demonstrates frequency conversion with an efficiency of 92%.