Professor Ian Walmsley CBE FRS FCGI

Abstract:

We present an experimental method to measure the transverse spatial quantum state of an optical field in coordinate space at the single-photon level. The continuous-variable measurements are made with a photoncounting, parity-inverting Sagnac interferometer based on all-reflecting optics. The technique provides a large numerical aperture without distorting the shape of the wavefront, does not introduce astigmatism, and allows for characterization of fully or partially coherent optical fields at the single-photon level. Measurements of the transverse spatial Wigner functions for highly attenuated coherent beams are presented and compared with theoretical predictions. © 2005 Optical Society of America.

Abstract:

We show that tailored group velocity matching in non- linear chi((2)) crystal sequences interspersed with birefringent chi((1)) compensators can be used to generate time-bin entangled states. By choosing the crystal and compensator materials appropriately it is possible to generate all four time-bin Bell states without resorting to time non- stationary devices. This scheme, in addition, lends itself well to the generation of higher-dimensionality states such as time-bin qutrits.