Protocols and Resources for New Generation Continuous Variable Quantum Key Distribution

Abstract

Quantum optics has been developing into a promising platform for future generation communications protocols. Much of this promise so far has come from the development of quantum key distribution (QKD). The majority of the development of QKD is done with discrete variables (DV), i.e. qubits with the underlying system of single photons. This is one interpretation of an optical field. Alternatively an optical field can be interpreted as wave with the continuous variable (CV) observables of phase and amplitude. This interpretation comes with the advantage of access to high efficiency detection at room temperature and deterministic sources at the cost of susceptibility to noise in lossy channels. This thesis presents an investigation of protocols and resources for the next generation of CV QKD protocols with two directions, the development of quantum state resources and the development of QKD protocols.This thesis starts with the details on the on going development of a low loss squeezed state resource using OPA for use in future communication and estimation experiments. So far the OPA has produced 11dB of squeezing with 13dB predicted with reasonable improvements to losses and locking. Being able to perform a Bell test with a CV Bell state is also key for future CV QKD protocols. Originally developed for DV systems the Bell test is a fundamental test of quantum mechanics. Here the first experimental demonstration of an optical CV bell test is presented. The experiment violated a CHSH Bell inequality with jBj = 2:31. This violation holds promise for being able to realise new device or source independent CV protocols. The second half of this thesis proposes a channel parameter estimation protocol based on the method of moments and presents the results of a one side device independent CV QKD demonstration based on the family of Gaussian QKD protocols. The proposed channel parameter estimation protocol through the use of the method of moments is able to use information usually disregarded for estimation of an adversaries information. The result does not allow for an increase in range of a fully optimised protocol but can increase the key rate by an order of magnitude with high loss channels. Using a newly found entroptic uncertainty relation for CV tripartite states a new security proof was applied to the family of Gaussian CV QKD protocols. This resulted in the discovery of six new protocols with the special property of being one side device independent. Using the new security proof three of the protocols were demonstrated with a positive key rate.