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Title: Balanced detection for silicon-integrated continuous-variables quantum optics
Author: Ferranti, Giacomo
ISNI:       0000 0004 7961 7387
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2019
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Integrated quantum photonics is a promising platform for the development of quantum technologies such as quantum computation, cryptography, simulation and metrology. The operations performed by integrated photonic quantum devices have so far largely relied on a discrete-variables approach, using probabilistically generated single photons as information carriers. Continuous-variables (CV) quantum optics offers an alternative approach, which has shown significant potential in recent years. Generation of squeezed light, which plays a central role in CV quantum information protocols, has been recently reported in lithium niobate waveguides. However, fully integrated on-chip implementations of continuous variables experiments (including on-chip detection) have yet to be demonstrated. This thesis presents a series of techniques which are aimed at developing the building blocks required to perform continuous-variables experiments on a silicon chip. First, we demonstrate a silicon-integrated homodyne detector which is suitable for performing measurements on quantum fields. The device showed comparable shot-noise clearence and speed to state-of-the art bulk implementations available at the time of its construction. Using this detector, we performed on-chip homodyne tomography of coherent states. This is followed by the introduction of an experiment aiming to perform generation and homodyne tomography of single photon states within a single optical chip. Generation of single photons with the appropriate spectral properties was demonstrated. However, the state reconstructed by the homodye tomography showed no single-photon contribution. The chapter reports a detailed characterisation of the experimental setup, which shows that the most likely causes of this result are not expected to prevent the success of the experiment at a fundamental level. Basing on the results of this characterisation, we propose a series of improvements to the setup which are expected to solve the encountered issues. We also present a proposal for an experiment aiming to use silicon waveguides as a medium for generation of squeezed light. Key to the success of this experiment is a low-noise pump field. For this reason, we present a number of improvements to a preexisting technique allowing to suppress classical noise affecting pulsed lasers. The demonstrated experimental setup relied on a balanced photodetector which exhibited high shot-noise clearance for low input field powers. The specifications measured for the balanced detector and the noise suppression setup are sufficient for performing the proposed squeezing generation experiment.
Supervisor: Matthews, Jonathan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available