Quantum Computing with photonics networks

The aim of this PhD project is to develop highly efficient protocols for processing quantum information in photonic networks [1]. Sources for single photons on demand, which are based on atom-cavity systems, have already become available in the laboratory and have recently been combined with linear optics networks [2]. The isolated photons used in Ref. [2] are the result of a complete conversion of one atomic excitation into an excitation of the electromagnetic field. Due to the underlying transfer being relatively slow, photons from atom-cavity systems are usually much longer than single photons from other sources. They are also much longer than typical linear optics networks. Hence, when experimenting with several simultaneously generated photons, the amplitudes of photons can be manipulated, even after the first energy quant is detected. The resulting conditional temporal evolution is expected to strongly alter the statistical properties of the photons. Bosonic photons might become fermions [3]. Using this observation, the project plans to develop schemes for applications ranging from quantum metrology [4] and quantum computing to quantum neural networks [5].
Methodology. The goup of Almut Beige at the University of Leeds recently developed a fully-quantum mechanical model to quantise the electromagnetic field on both sides of a semi-transparent mirror [6,7]. In this project, we plan to apply our model to describe the propagation of photonic wave packets from atom-cavity systems through linear optics networks. The first step of the proposed PhD project would be to identify the possible statistical properties of the photons in the networks and to derive precise in-distinguishability criteria. Afterwards, we plan to exploit the above-described conditional dynamics for practical applications.