Giulio Chiribella (University of Hong Kong): The quantum time flip
Channel: Centrum Fizyki Teoretycznej PAN
Date: 29/04/2021

Giulio Chiribella (University of Hong Kong).
 The quantum time flip 
The fundamental dynamics of quantum particles is neutral with respect to the arrow of time. And yet, our experiments are not: we observe quantum systems evolving from the past to the future, but not the other way around. A fundamental question is whether it is possible, at least in principle, to engineer mechanisms that probe quantum dynamics in the backward direction, or in more general combinations of the forward and the backward direction. To answer this question, we characterize all possible time-reversals that are compatible with four natural requirements, and we show that quantum theory is compatible with the existence of a machine that adds quantum control to the time direction of an unknown dynamics. This machine, which we call the quantum time flip, offers an advantage in a game where a referee challenges a player to identify a hidden relation between two unknown unitary gates. The quantum time flip can be experimentally simulated with photonic systems, shedding light on the information-processing capabilities of exotic scenarios in which the arrow of time between two events is in a quantum superposition of two alternative directions. 
CTP Quantum Information Days (online), 22-24 February 2021.
Center for Theoretical Physics PAS (Warsaw, Poland)