Publication details

Recycling of quantum information: Multiple observations of quantum systems

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BUŽEK Vladimír

Year of publication 2007
Type Appeared in Conference without Proceedings
MU Faculty or unit

Faculty of Informatics

Description Invited key-note talk. In my talk I will address a question how much information can be extracted from a quantum system that has already been observed. Specifically, I will assume a finite ensemble of identically prepared qubits which is measured by a sequence of non-communicating observers. The first observer performs an optimal (i.e. maximal information gain and minimal disturbance of the system) measurement of the ensemble. Then the second observer who does not know neither a result nor a specific measurement set-up of the first experiment performs his optimal measurement. I will show that not only the second but essentially arbitrary number of observers can perform measurements on a system that has been measured and can obtain results that would allow for non-trivial estimations of the original preparation of qubits. I will quantify the information obtainable by the k-th observer as a function of number of previous independent observations and the size of the ensemble.
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