Heralded quantum imaging

Aspden, Reuben S. (2015) Heralded quantum imaging. PhD thesis, University of Glasgow.

Abstract

Imaging systems play a crucial role in shaping understanding of our surroundings. Modern imaging systems enable the acquisition of images of objects at length-scales and resolutions previously deemed impossible. However, as the drive for better images and novel applications increases, several questions fundamental to our understanding of imaging are being raised. We are familiar with images containing many millions of photons, but how many photons does it take to form an image? In scenarios requiring covert imaging, or where high-light levels damage the sample being imaged, is it possible to image a sample with a very small number of very low-energy photons? This thesis will focus on answering these two questions.
In order to answer these questions I developed a heralded quantum imaging system. The strong spatial correlations inherent between down-converted twin photons have been utilised in many quantum imaging techniques for the past 25 years. Thus far, standard quantum imaging techniques have relied on scanning a fibre detector across the field of view in order to measure the spatial information in the image. However, the scanning mechanism fundamentally limits the detection efficiency of the imaging system.
Recent years have seen an increased interest in using the latest camera technology within quantum imaging systems. The advent of single-photon-sensitive cameras has opened up new possibilities within the quantum imaging field. It is now possible to obtain images of objects by detecting very low-light illumination across the full scene simultaneously.
In the heralded quantum imaging system presented in this thesis, a combination of quantum mechanics and a high-sensitivity camera was employed to obtain high contrast images containing very few photons. This was the first such system built. Using the correlations between the twin photons generated by our down-conversion source, and our development of compressive sampling techniques to post-process the acquired data enabled the acquisition of an image containing an average of only 0.5 photons per pixel. This represents a significant reduction when compared with a conventional image that contains of order 105 photons per pixel.
I also developed this imaging system to use twin photons at vastly different wave- lengths. The object was probed with low-energy infrared photons whilst the image was developed on a camera using the correlated visible photon. This disparity in energy between the two photons enabled the acquisition of images using only several thousand photons, corresponding to an energy deposition on the sample of only a few pJ.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Quantum imaging, quantum optics, spatial correlations, heralded imaging
• Subjects: Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Padgett, Prof. Miles J.
• Date of Award: 2015
• Depositing User: Mr Reuben S. Aspden
• Unique ID: glathesis:2015-6472
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 12 Jun 2015 08:43
• Last Modified: 13 Jul 2015 10:27
• URI: https://theses.gla.ac.uk/id/eprint/6472