Efficient Quantum Key Distribution

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Research questionCoherent communication with quadrature modulated light is a well-developed communication scheme for conventional 100G internet traffic. But, at extremely low signal strength, inherent quantum features of light such as vacuum noise dominate and prevent the exchange of meaningful messages. However, it is possible to harness and exploit this quantum uncertainty to make it useful for secure key distribution. Continuous Variable Quantum Key Distribution (CV-QKD) is such a quantum technology which is also highly efficient for deployment in DWDM networks such that quantum and conventional channels can co-exist.CV-QKD Local Local Oscillator (LLO) schemes that converge to coherent communication have recently been gaining interest. They open up an excellent opportunity for testing and evaluating the performance of coherent communication techniques for distributing quantum signals. However, recent demonstrations of these approaches have been limited to low loss channels with reduced key rates, due to elevated receiver noise.Approach/MethodologyThis project aims to develop new CV-QKD LLO schemes for high channel loss applications with enhanced secure key rates. One direction of this work will be to recover the quantum signal information from a noisy coherent receiver. Within this project, the student will work on measurement of the quantum channel at very low receiver noise to demonstrate the potential for high performance operation. Noise reduction and optimization of CV-QKD parameters will be the major consideration for this development. This study will be extended to multi transmitter or multidimensional quantum signal detection to enhance the secure key bandwidth.The work on the link will initially focus on measuring the noise and then extrapolating to the possible secure key rate under various quantum attacks. However, once this initial phase is complete the student will then work on a link that distils a real secure key that can be used to encode conventional channels on the existing Cambridge quantum network. Later in this project, the feasibility of extended to a national scale using the National Dark Fibre Facility will be investigated. This research is primarily experimental, using the Cambridge CV-QKD system, but moderate theoretical study is also necessary. It will be linked to the major EPSRC Quantum Technology Hub, QComm2.