  Unlike classical routing algorithms, quantum routing algorithms make use of
entangled states - a type of resources that have a limited lifetime and need to
be regenerated after consumption. In a nutshell, quantum routing algorithms
have to use these resources efficiently, while optimizing some objectives such
as the total waiting time. Current routing algorithms tend to keep a routing
request waiting until all of the resources on its path are available. In this
paper, we introduce a new way of managing entanglement resources in an
opportunistic fashion: a request can move forward along its path as soon as
possible (even if some resources on its path are not ready). We show that this
opportunistic approach is fundamentally better than conventional approaches. In
particular, our results indicate that this new approach achieves a 30-50%
improvement in the average total waiting time and average link waiting time
compared with several state-of-the-art routing algorithms. As a by-product of
this work, we develop a new simulator for quantum routing, which can be used to
evaluate various design choices under different scenarios.
