Tools for the design of quantum repeater networks

Abstract

The Internet, a global network of communicating computers, has profoundly changed our lives, both in the way we work and relax. Quantum computers are a fundamentally new type of computer which brings certain computational tasks within reach, for example chemistry simulations for a reduction in global energy consumption. The Quantum Internet, the vision of a global network of quantumcomputers, combines these two,with applications such as secure quantumcomputing in the cloud. A barrier to the realisation of a Quantum Internet is the loss of transmitted quantum information, usually encoded in particles of light. This fundamental limit can be overcome by splitting up the distance into segments and positioning so-called quantum repeaters in between. In principle, chains of quantum repeaters can extend the transmission range of quantuminformation to an arbitrarily long distance. In this thesis, we consider the type of quantum repeater closest to experimental realisation, which is based on quantum memories for storing quantum information and probabilistically succeeding operations on them. Researchers have proposed a multitude of such quantum repeater schemes on the drawing board. We develop tools to analyse how these quantum repeater schemes will perform when implemented on real hardware suffering from time-dependent noise, in particular imperfect quantum memories for storing quantum information. Such time-dependent noise is often hard to capture, due to its complex interplay with the random time that these quantum repeater schemes need to finish. Our tools thus help to bridge the gap between theoretical proposals for quantum repeaters and the hardware components that are currently experimentally available. On the one hand, they enable optimisation over the design of quantum repeaters, while on the other hand they provide us with an indication of the hardware components whose improvement will pay off most to bring quantum repeaters to realisation.