Sequential quantum measurements on entangled states2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC)

Quantum measurement is a nontrivial physical process connecting the quantum and classical worlds. However in contrast to classical measurement, any quantum detection process unavoidably introduces decoherence in the quantum system, thus leading to a detrimental effect which establish a bound on the knowledge, i.e. the information, extractable from the system. In order to avoid such problem, a partial measurement approach can be adopted, whose aim is to extract only a partial amount of information from the quantum system at cost of limited decoherence induced [1]. In general, this partial measurement consists from two steps: coupling of measured system to an available meter and projective measurement on the meter. The aim of the work is to investigate a non-demolishing measurement strategy which allows to maximize the amount of information extracted from an entangled quantum state, given a certain amount of induced decoherence on the whole system. The protocol can be applied to a single measurement step, as well as extended to a number N of sequential measurements. Furthermore we demonstrate that by implementing a sequence of non-demolishing measurement on the state, it is still possible to achieve a strategy which leads to an optimal trade off between knowledge and decoherence induced. © 2011 IEEE.