Decoherence in quantum mechanics

We study decoherence in a simple quantum mechanical model using two approaches. Firstly, we follow the conventional approach to decoherence where one is interested in solving the reduced density matrix from the perturbative master equation. Secondly, we consider our novel correlator approach to decoherence where entropy is generated by neglecting observationally inaccessible correlators. We show that both methods can accurately predict decoherence time scales. However, the perturbative master equation generically suffers from instabilities which prevents us to reliably calculate the system’s total entropy increase. We also discuss the relevance of the results in our quantum mechanical model for interacting field theories.     

Observation of the second harmonic generation pumped by microscopic to extraterrestrial incoherent light sources

I report on the experimental demonstration of the second harmonic generation in bulk nonlinear crystals excited by light emitting diode, halogen lamp and the Sun. Practical application for measurement of autocorrelation functions of incoherent non-laser driven sources via second order nonlinearity is demonstrated for the first time.     

Simultaneous use of amplitude and phase to improve the validation process in a joint transform correlator

We present an alternative technique to enhance the discrimination performance in a JTC architecture, employed as a validation procedure. We define as complex objects those amplitude objects bonded to random phase masks. When using complex objects as reference inputs in a JTC optical validation system, correlation peak intensity and correlation peak shape become simultaneous key parameters to increase the discrimination ability of the system. Simulation results, comparing amplitude-only objects versus complex objects as inputs to the system, reveal the validity of our approach and show the sensitivity of the JTC architecture to the additional phase structures.     

Entropy and correlators in quantum field theory

It is well known that loss of information about a system, for some observer, leads to an increase in entropy as perceived by this observer. We use this to propose an alternative approach to decoherence in quantum field theory in which the machinery of renormalisation can systematically be implemented: neglecting observationally inaccessible correlators will give rise to an increase in entropy of the system. As an example we calculate the entropy of a general Gaussian state and, assuming the observer's ability to probe this information experimentally, we also calculate the correction to the Gaussian entropy for two specific non-Gaussian states.     

Synthetic optical processor for generalized logic realization problems

A synthetic joint Fourier transform (SJFT) correlator is proposed for the realization of generalized logic problems. As a case study, a multi-channel SJFT correlator is employed to realize a multi-output logic unit. For a given correlator set-up, this particular scheme ensures the maximal utilization of space bandwidth product. This work establishes a pragmatic approach for implementing real-time programmable content addressable memory for information processing.