  The central question in quantum multi-prover interactive proof systems is
whether or not entanglement shared between provers affects the verification
power of the proof system. We study for the first time positive aspects of
prior entanglement and show that entanglement is useful even for honest
provers. We show how to use shared entanglement to parallelize any multi-prover
quantum interactive proof system to a one-round system with perfect
completeness, with one extra prover. Alternatively, we can also parallelize to
a three-turn system with the same number of provers, where the verifier only
broadcasts the outcome of a coin flip. This "public-coin" property is somewhat
surprising, since in the classical case public-coin multi-prover interactive
proofs are equivalent to single prover ones.
