Workshop on: QUANTUM INFORMATION AND FOUNDATIONS OF QUANTUM MECHANICS

Quantum Mechanics: Axiomatics and connections with Computing and Information Theory

Multiple observations of quantum systems
aula DOTTORATO - MARTED' 14 SETTEMBRE ore 11.00
  Vladimir Buzek, University of Bratislava

>PRESENTATION: Vladimír Buzek has graduated at the Moscow State University (both MSc and PhD). Presently he is a head of the Research Center for Quantum Information at the Institute of Physics, Slovak Academy of Sciences. His research interests are focused on theoretical quantum optics and quantum information science. Within the field of quantum information he has been working on quantum cloning, quantum secret sharing, programmable quantum processors, quantum state and process estimation, etc. He is an author and co-author of more than 200 papers. He was visiting professor at the Imperial College London (UK), National University of Ireland, Maynooth (Ireland), University of Ulm (Germany), and in SOKEN (Japan). He is the president of the Learned society of the Slovak Academy of Sciences.

Vladimir Buzek
Abstract  
  In my talk I will present a concept of "recycling" of quantum information. Specifically, I will analyze following question: Given a finite number N of copies of an unknown qubit state that have already been measured optimally, can one still extract any information about the original unknown state? Due to information-disturbance tradeoff theorems, we know that an after-measurement quantum state may contain partial information on (average overlap with) the original pre-measurement quantum state even if the best possible single-shot estimation of the original state has taken place. Given the N-qubit state has already been measured optimally to estimate the single-qubit state, I will analyze the maximum information obtainable by a second, and subsequent, observers ignorant of important details of the previous measurements. I will quantify the information acquired by each observer as a function of N, and of the number of independent observers that in succession have independently measured the \emph{same} ensemble of qubits before him.
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