Advanced Quantum Characterisation in Integrated Photonics

Harnessing quantum mechanics offers drastically new capabilities in computation, information security and metrology - all core technologies underpinning modern society. However, the underlying physical complexity that gives quantum systems their power also makes them incredibly difficult to characterize: to even describe a quantum system requires a number of parameters that is exponential in the number of constituent particles. To tackle this, quantum characterization has become a burgeoning field, which deals with the task of characterizing quantum systems in an efficient manner. The goal of this project is to implement in the lab quantum characterisation techniques in the integrated silicon quantum photonics technology developed in UoB's Centre for Quantum Photonics and QETlabs. Currently, the bottleneck for this technology is the ability to accurately characterise the underlying quantum processes efficiently, as the system grows in size. This project will develop and apply a technique called coherent state quantum tomography, which requires coherent states of light (for example the output of a laser) and use multiple homodyne detection modules to perform tomography on the underlying technology. The objectives of this proposal are (i) fully integrate a characterisation system based off the concept of coherent state process tomography in order to characterise multimode integrated interferometers and (ii) investigate the use of states of light other than coherent states (for example, so called "squeezed" states of light) and their effect on optical process tomography protocols. This work will lead to a better understanding of the connection between metrology (where squeezed states find traditional use) and optical quantum tomography, as well as open up questions relating to the fundamental limits of measurement.