Quantum Information Protocols with Gaussian States of Light

Quantum cryptography is widely regarded as the most mature field within the context of quantum information in the sense that its application and development has produced companies that base their products on genuine quantum mechanical principles. Examples include quantum random number generators and hardware for secure quantum key distribution. These technologies directly exploit quantum effects, and indeed this is where they offer advantages to classical products.
This thesis deals with the development and implementation of quantum information protocols that utilize the rather inexpensive resource of Gaussian states. A quantum information protocol is essentially a sequence of state exchanges between some number of parties and a certain ordering of quantum mechanical unitary operators performed by these parties. An example of this is the famous BB84 protocol for secret key generation, where photons in different polarization states are sent from one party to the other and subsequently detected.
In particular we introduce the idea of measurement device independence for continuous variable states and we present a proof-of-principle implementation of this protocol. Measurement device independence with Gaussian states is a promising avenue for the development of practical quantum key distribution with a relay network structure in environments where the distances are relatively short and there is a high number of users, such as an urban environment.
In addition to this we consider various point-to-point configurations that utilize Gaussian states to achieve security. Notably, we also present a novel experiment demonstrating the feasibility of delegated quantum computing on encrypted data, where we show that we can reliably encrypt and decrypt input and output states when a server with quantum computing capabilities performs Gaussian operations.