Coherent state exchange in multi-prover quantum interactive proof systems

Understand

We show that any number of parties can coherently exchange any one pure quantum state for another, without communication, given prior shared entanglement.

• Two applications of this fact to the study of multi-prover quantum interactive proof systems are given.
• First, we prove that there exists a one-round two-prover quantum interactive proof system for which no finite amount of shared entanglement allows the provers to implement an optimal strategy.
• More specifically, for every fixed input string, there exists a sequence of strategies for the provers, with each strategy requiring more entanglement than the last, for which the probability for the provers to convince the verifier to accept approaches 1.