Advanced data acquisition for multi-photon experiments

Abstract

The overarching theme of this thesis was to develop a state-of-the-art multi-photon experiment at telecom wavelengths. With this platform the following experiments in quantum information processing were performed: testing of local observer independence [1], multiqubit phase estimation [2], measurement-device-independent verification of quantum channels [3], assisted macroscopic quantumness [4] and experimental quantum conference key agreement [5]. My focus has been primarily on the signal processing / data analysis required in particular for the required engineering for the used single-photon sources [6] developed by our group and most prominently for the “big data” produced in measurement of the joint spectra such as our demonstration of time-frequency modes from engineered nonlinearites [7]. The analysis required for our source engineering efforts has resulted in the my development of a pair of models to determine accurate multi-photon detection rates and signal-to-noise ratios of each single-photon source. In order to extract the joint spectra from the measured “big data” I have developed a time-correlated single-photon counting toolkit. In this thesis I will outline the following, the requirements for building a high performance single-photon source, develop a pair of models for analysing the signal-to-noise ratio for a number of sources along with exploring the benefits that can be seen via multiplexing. Further, the design of time-correlated single-photon-counting hardware is discussed along with the methods needed to produced meaningful analytics from the data output from said hardware. Finally the joint spectra of a number of down-conversion based single-photon sources are reconstructed via dispersive spectroscopy allowing for the spectral purity to be estimated in each case, this is then extended by use of image processing techniques in order to determine whether our estimates can be improved. In all, this thesis discusses what we need from a single-photon source, how to optimise the experimental configuration for high detection rates and signal-to-noise ratios, how to analyse the resulting signals and then finally combining these into measurement of spectral purity resulting in a broad investigation of single-photon source performance with a view to multi-photon experiments.