Towards Gigabaud Discretely Modulated Continuous Variable Quantum Key Distribution with Integrated Photonic and Electronic Devices

Abstract

Continuous Variable Quantum Key Distribution (CV-QKD) is an effective tool in quantum cryptography as it allows the implementation of QKD without the need for single photon sources or single photon detectors and can be implemented with standard telecoms fibre optic components. To further improve these QKD systems in various metrics such as maximum key rates, improved size weight and power (SWaP), and cost, the work in this thesis investigates the application of co-integrated photonic and electronic integrated circuits in CV-QKD systems. The work focuses on discretely modulated CV-QKD protocols which are more favourable due to their comparative experimental simplicity compared with Gaussian modulated protocols.
We investigate the novel application of a hybrid photonic/electronic dual-die homodyne detection with a 3dB bandwidth of 1.255Hz. We build an experimental CV-QKD system operating at 1.25 Gbaud used to estimate the maximum theoretic secret key rates achievable with such an integrated photonic homodyne detector and a fibre optic based transmitter. We describe the implemented data processing techniques used in the experiment, including the first experimental application of a modified parameter estimation technique developed for discretely modulated CV-QKD protocols. We transmit and detect modulated quantum signals, but we conclude that positive key rates with two-state discretely modulated CV-QKD protocols are not experimentally viable without further improvement to the experimental setup.
To look at further integration of the CV-QKD system, we design novel transmitter and receiver photonic integrated circuits for implementing a ‘chip-to-chip’ CV-QKD protocol. We design a novel PCB for interfacing the transmitter and receiver circuits.
We end with a SWaP, cost and use case analysis of our integrated detector design and compare the performance of it with a comparable commercially available homodyne detector. We include a discussion on future work and practical design considerations which need to be considered when constructing photonic/electronic integrated CV-QKD systems.

Date of Award	1 Oct 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jonathan C F Matthews (Supervisor) & Euan J Allen (Supervisor)