HOW TO REVERSE UNKNOWN QUANTUM PROCESSES

In quantum mechanics, the unitary nature of time evolution makes it intrinsically reversible, given control over the system in question. Remarkably, there have been several recent demonstrations of protocols for reverting unknown unitaries in scenarios where even the interactions with the target system are unknown. These protocols are limited by their probabilistic nature, raising the fundamental question of whether time-reversal could be performed deterministically.

In a collaboration between the University of Vienna and IQOQI, experimental physicists led by Philip Walther have successfully implemented such a universal rewinding protocol, developed by theoretical physicists led by Miguel Navascués. By combining this novel theoretical protocol with a complex optical setup, the group showed that it is indeed possible to reverse changes in a quantum system.

This demonstration of a so-called rewinding protocol was published in the journal "Optica".