Distributed quantum computing: a new frontier in distributed systems or science fiction?

Quantum computing and distributed systems may enter a mutually beneficial partnership in the future. On the one hand, it is much easier to build a number of small quantum computers rather than a single large one. On the other hand, the best results concerning some of the fundamental problems in distributed computing can potentially be dramatically improved upon by taking advantage of the superior resources and processing power that quantum mechanics offers. This survey has the purpose to highlight both of these benefits. We first review the current results regarding the implementation of arbitrary quantum algorithms on distributed hardware. We then discuss existing proposals for quantum solutions of leader election - a fundamental problem from distributed computing. Quantum mechanics allows leader election to be solved with no communication, provided that certain pre-shared entanglement is already in place. Further, an impossibility result from classical distributed computing is circumvented by the quantum solution of anonymous leader election - a unique leader is elected in finite time with certainty. Finally, we discuss the viability of these proposals from a practical perspective. Although, theoretically, distributed quantum computing looks promising, it is still unclear how to build quantum hardware and how to create and maintain robust large-scale entangled states. Moreover, it is not clear whether the costs of creating entangled states and working with them are smaller than the costs of existing classical solutions.