High-Dimensional Entanglement Generation with Linear Optics

Abstract

For many quantum applications we require high-fidelity entanglement between multiple pairs of solid state qubits at a distance. To achieve a high fidelity, we have to minimize the time during which the generated qubits need to stay coherent. Entanglement protocols often used in practice only generate one qubit at the same time. To generate multiple entangled pairs, the protocol is repeated. However during the time it takes for all pairs to be generated, the memory qubits will dephase. The required coherence time increases with the inverse transmission probability of the photons, which decreases exponentially with distance. This thesis is concerned with entanglement generation protocols that herald multiple entangled pairs simultaneously and in general herald N-dimensional entangled bipartite states. The main advantage of using more than 2 dimensions is that the qudits only dephase during the time in which the protocol executes. With simulations we show that the fidelity of the entangled pairs created with our protocols is higher than the fidelity of pairs created by protocols that heralds one entangled pair for distances L > 10 km. We also show a polynomial relation between the total success probability of the tailored protocol with dimension, which is an exponential improvement with respect to previous works.