Universal Quantum Rewinding Protocol with an Arbitrarily High Probability of Success.

We present a universal mechanism that, acting on any target qubit, propagates it to the state it had T time units before the experiment started. This protocol works by setting the target on a superposition of flight paths, where it is acted on by uncharacterized, but repeatable, quantum operations. Independently of the effect of each of these individual operations on the target, the successful interference of the paths causes it to leap to its past state. We prove that, for generic interaction effects, the protocol will herald a successful rewinding with probability 1 after some finite number of steps.