Description

Location: Seminar room of the Department of Theoretical Physics & the History of Science
Time      Thursday, 15 October, at 15:00 pm

Title:    Scavenging quantum information

Abstract: Given an unknown state that has already been measured optimally, can one still extract  any information about the original unknown state? Clearly, after a maximally informative measurement, the state of the system ‘collapses' into a post-measurement state from which the same observer cannot obtain further information about the original state of the system. However, the system still encodes a significant amount of information about the original preparation for a second observer who is unaware of the actions of the first one.  I present how a series of independent observers can obtain, or scavenge, information about the unknown state of a system when they sequentially measure it. I also present some interesting variants on how distribute information among observers.

In particular, I consider the scenario where a finite number of observers estimate the state with equal fidelity, regardless of their position in the measurement sequence; and the scenario where all observers use an identical measurement apparatus chosen so that a particular observer's estimation fidelity is maximized.

I finally present some recent developments where the reuse of the systems is applied in the context of discrimination of states.