Professor Ian Walmsley CBE FRS FCGI

Abstract:

We study distinguishing information in the context of photonic quantum interference tailored for practical implementations of quantum information processing schemes. In particular, we consider the character of single-photon states optimized for multiple-source interference experiments and for experiments relying on Bell-state measurement and arrive at specific design criteria for photons produced by parametric down-conversion. Such states can be realistically implemented with available technology. We describe a novel method for characterizing the mode structure of single photons, and demonstrate it in the context of coherent light.

Abstract:

We propose a design for a photon-counting detector that is capable of resolving multiphoton events. The basic element of the setup is a fiber loop, which traps the input field with the help of a fast electro-optic switch. A single weakly coupled avalanche photodiode is used to detect small portions of the signal field extracted from the loop. We analyze the response of the loop detector to an arbitrary input field and discuss both the reconstruction of the photon-number distribution of an unknown field from the count statistics measured in the setup and the application of the detector in conditional-state preparation.

Abstract:

We discuss the use of quasi-phase-matched downconversion to engineer the amount and type of space-time entanglement present in two-photon states. We also discuss a quantum positioning scheme based on a source of multiple entangled photons and report the implementation of this scheme for the case of two entangled photons.