Light-Matter Interactions and Heralding in Quantum Information

Abstract

The field of quantum information processing covers a broad range of topics including quantum communications, computing, and metrology. Implementing efficient communications and computing protocols is particularly important for many applications including fundamental physics, secure encryption, factoring large numbers, and search algorithms among others. With such a variety of future technologies, it is important to mitigate any technical problems that may include decoherence, loss, absorption, and dispersion. Because of this, optical quantum information processing requires techniques to maintain and control the quantum states in order to effectively perform the required operations. In this dissertation, we investigate methods for controlling optical information by coupling the quantum states to matter in a variety of way. First, we investigate a direct interaction between a coherent state (laser beam) and atoms, where we measure the state of the atoms which then predicts and in a sense controls the outgoing optical state such that it is either attenuated more than normal or amplified. We then use post-selection techniques to characterize and minimize sources of error in optical quantum logic operations using the Zeno effect. In this case, the measurement serves to limit the allowable output states to those in which the operation succeeded. Finally, we investigate the effectiveness of nonlocal cancellation of dispersive effects that occur when multiple entangled photons propagate in a medium. It is shown that to some degree, the coincidence of the entangled photons is protected and can even be controlled with additional heralding techniques.