Balanced detection for silicon-integrated continuous-variables quantum optics

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


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.
Date of Award19 Mar 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorDylan Mahler (Supervisor) & Jonathan C F Matthews (Supervisor)

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