In work package 1, we developed new quantum hardware: photon sources, integrated components and used superconducting detectors. Experiments were performed both in the near-infrared wavelength and in the telecom wavelength regime.
In work package 2, we implemented protocols for quantum information processing and studied fundamental properties of few-particle states of light. In particular, we performed experiments on hybrid quantum-classical multiparty computing, quantum walks in photonic networks, and multiphoton interference.
Hybrid quantum-classical multiparty computing: A longstanding question is whether it is possible to delegate computational tasks securely—such that neither the computation nor the data is revealed to the server. In this part of the project, we demonstrated a new protocol that harnesses quantum resources to perform secure classical multiparty computation between a number of clients. In our setting, the clients had limited resources, restricted to single-qubit gates and linear classical processing. With the help of simple quantum resources provided by a server the clients were able to jointly compute a non-linear multivariable function that lies beyond their individual capabilities.
Quantum information processing in photonic networks: We demonstrated a platform for implementing quantum walks that overcame many of the barriers associated with photonic implementations. We used coupled fibre-optic cavities to implement time-bin encoded walks in an integrated system. We showed that this platform can achieve very low losses combined with high-fidelity operations, enabling an unprecedented large number of steps.
Study of multiphoton interference: Quantum interference of two independent particles in pure quantum states is fully described by the particles’ distinguishability; when more than two particles are involved, the situation becomes more complex. In this part of the project, we studied many-particle interference using three photons. We showed that the distinguishability between pairs of photons was not sufficient to fully describe the photons’ behaviour in a scattering process, but that a collective phase, plays a role. We were able to explore the full parameter space of three-photon interference by generating heralded single photons and interfering them in a fibre tritter. Our experiment showed that pairwise two-photon distinguishability is not sufficient to uniquely determine the degree of non-classical many-particle interference.
