Ian Walmsley

Abstract:

Full characterization of detectors in the quantum regime is presented. We determine the POVM elements of a photon-number-resolving detector. A method for precise calibration of detector efficiency is demonstrated. © 2009 IEEE.

Abstract:

We present the joint photon-number statistics of a locally photon-subtracted two-mode vacuum squeezed state of light. Comparison to the unsubtracted statistics shows a successful photon subtraction and the expected shift by one photon number. © 2008 Optical Society of America.

Abstract:

We experimentally demonstrate photon pair production in standard single-mode optical fibers via spontaneous four-wave mixing. The process utilizes birefringent phase matching to control the photon pair joint spectral structure. © 2009 Optical Society of America.

Abstract:

We present the first complete characterization of a heralded two-photon N00N state in the presence of losses, including the one-photon and vacuum components. Reconstruction shows large vacuum and one-photon components resulting from loss. © 2008 Optical Society of America.

Abstract:

We propose and evaluate experimentally an approach to quantum process tomography that completely removes the scaling problem plaguing the standard approach. The key to this simplification is the incorporation of prior knowledge of the class of physical interactions involved in generating the dynamics, which reduces the problem to one of parameter estimation. This allows part of the problem to be tackled using efficient convex methods, which, when coupled with a constraint on some parameters, allows globally optimal estimates for the Krauss operators to be determined from experimental data. Parameterizing the maps provides further advantages: it allows the incorporation of mixed states of the environment as well as some initial correlation between the system and environment, both of which are common physical situations following excitation of the system away from thermal equilibrium. Although the approach is not universal, in cases where it is valid it returns a complete set of positive maps for the dynamical evolution of a quantum system at all times. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.