Abstract
Quantum states of the electromagnetic field which possess reduced noise properties due to correlations between photons are a fundamental resource in continuous-variable quantum information processing. In this thesis, we study several methods for generating and detecting these ‘squeezed’ states of light using silicon, silicon nitride and silicon dioxide as nonlinear media.First, we consider the generation of squeezed states in silicon, whose advanced CMOS fabrication processes offer significant potential for scalability of quantum sources. We simulate the effects of nonlinear loss in the platform, and attempt to generate reduced-noise states from silicon waveguide nonlinear interferometers, measuring them using integrated germanium photodiodes. We observe and characterise excess noise generated by the photonic integrated circuits and compare it to noise sources from the literature. We also demonstrate a method to generate a bichromatic local oscillator using phase modulation and optical filtering. In light of the issues with silicon, we designed an experiment to use heterogeneous integration to generate a squeezed state in a silicon nitride microring resonator, filter the state using silicon waveguides, and detect it using germanium photodiodes, all on a single device. We characterise the device, simulating the theoretical squeezing achievable, and
demonstrate techniques to achieve the frequency stabilisation of two lasers required for detection of the state. We also use this heterogeneous platform to demonstrate a temperature sensor using a Mach-Zehnder interferometer consisting of waveguides of silicon and silicon nitride. This sensor is highly CMOS-compatible and demonstrates high figures of merit in both wavelength scanning and ‘side-of-fringe, constant power’ detection schemes, significantly outperforming the limits of designs using a single material.
Finally we design and characterise a low-frequency silicon photodetector for an experiment generating a correlated twin beam number-squeezed state using optical fibres. We measure this source at microwatts of power for the first time and consider difficulties arising from the local statistics of each beam. We measure the electronic noise of the detector and show quantum efficiencies in excess of 80%.
Date of Award | 27 Sept 2022 |
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Original language | English |
Awarding Institution |
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Supervisor | Jonathan C F Matthews (Supervisor) & Peter S Turner (Supervisor) |