Influence of coherence time drift on the secret key rate

Abstract

Quantum communication provides a plethora of new possibilities compared to the realm of classical communication. Since the channels used are noisy, losses are unavoidable, and quantum repeaters are needed to transmit a signal over longer distances to overcome these exponential losses. To increase the performance of these repeaters, cutoff times can be introduced. These cutoffs limit the amount of time a qubit can be stored in the quantum memory. Based on previous work done by Avis et al., this work analyzes how a variation in the initial coherence time, called a drift in coherence time, affects the optimal cutoff, the optimal secret key rate, and the loss in secret key rate. The main conclusions are that the greater the coherence time, the less the need for accurate cutoff times. This is due to losses in the secret key rate being inherently smaller at larger coherence times. Furthermore, the loss in secret key rate can be approximated using the derivations found in this thesis. Suggestions for further work are introduced; implementing these is beyond the scope of this thesis.