Le contenu de cette page n’est pas disponible en français. Veuillez nous en excuser.
 

Quantum Switches and Impossible Time Travels



Playing this video requires the latest flash player from Adobe.

Download link (right click and 'save-as') for playing in VLC or other f4v compatible player.


Recording Details

Speaker(s): 
Scientific Areas: 
Collection/Series: 
PIRSA Number: 
12030111

Abstract

This talk presents two results on the interplay between causality and quantum information flow. First I will discuss about the task of switching the connections among quantum gates in a network. In ordinary quantum circuits, gates are connected in a fixed causal sequence.  However, we can imagine a physical mechanism where the connections among gates are not fixed, but instead are controlled by the quantum state of a control system. Such a "quantum switch" mechanism is consistent with quantum theory but cannot be described with in the standard model of causally ordered circuits, where it would be equivalent to a deterministic time travel and hence would violate the causality principle. With respect to the standard circuit model, the quantum switch is a new primitive that enables new information-processing protocols, such as the perfect discrimination between two classes of channels that are not perfectly distinguishable in a single query by any ordinary quantum circuit. Second, I will discuss about the probabilistic simulation of impossible channels that take an input in the future and produce an output in the past. In this case, I will show that the maximum probability of success in such a simulation is determined by causality and is inversely proportional to the amount of information that the channel can transmit.