Towards a fully integrated quantum optic circuit

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Quantum technologies walk the line between fundamental science and state-of-the-art engineering. Quantum photonics is revolutionising quantum information and communication, providing complex, integrated photonic circuity that can control flying qubits (photons), in parallel computational advancements are realised by processing and controlling quantum systems on large scales. Flying qubits are a qubit that can be freely send from one node to the other. The quantum internet will be a network of quantum devices that exchange information harnessing quantum mechanics. With these new advancements, protocols, tools and machines have provided multiple methods to communicate using fundamental laws [1–3]. The challenge to push the technology further to multiple end-to-end communication users is on the horizon. Few of the engineering feats have been mastered to overcome the large number of devices needed to interconnect and power such a global network.
This thesis reports on progress towards a large-scale fully integrated quantum systems based
on integrated quantum photonic devices. We demonstrate the capability to communicate quantum states across three silicon photonic devices using high dimensional (4D) communication protocols in a multi-core fibre optical network. We review the engineering challenges faced to distribute entangled photons, dimensionally separated in space, using active phase stabilisation to provide
the quantum computational basis for communications. A three device integrated silicon network is demonstrated for the first time.
With proof of the network, we then address maximising the number of users. Superconducting Nanowire Single Photon Detectors (SNSPDs) provide high detection efficiencies, low dark counts and timing jitter, proving to be ideal choices for quantum communications. SNSPDs require cryogenic temperatures for operation, and housing hundreds of detectors in a single cryogenic
station is required to ensure the scalability of quantum communication networks using nodes.
This has never been achieved due thermal power constraints caused by number of devices and
high speed electrical connections required to control and manipulate the optical circuity as well as direct communication with the detectors and electrical circuits that produce tangible information.
We present the engineering feats in operation of such a cryogenic station and SNSPD models
that bring us closer to this, as well as using cryogenically operational Field Programmable Gate Arrays (FPGAs) to process qubit readings.
Lastly, we present models of a ring cavity SNSPD optimised for short wave infrared (SWIR)
photons. SWIR can be used to reach increased numbers of photons per circuit and therefore
increased communication and computations rates. Photon in the SWIR spectrum benefit from a higher transparency in silicon, alongside a reduction of other non-linear undesirable interactions such as two-photon absorption and exploits optical non-linear effects that drive photon pair production, the cornerstone of quantum photonic technologies. The detectors presented here show increased measurement efficiencies and tailor-ability of photons, offering a route to improve the performance of state-of-the-art devices.
Date of Award28 Sep 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorMark G Thompson (Supervisor) & Dondu Sahin (Supervisor)

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