Workshop on

Quantum Measurements and Operations for Criptography and Information Processing

State estimation on correlated copies

aula DOTTORATO - MERCOLEdì 12 OTTOBRE, ore 14.00
  RAFAL DEMKOWICZ-DOBRZANSKI, Polish Academy of Sciences

Rafal Demkowicz-Dobrzanski did his master thesis (“Cloning of quantum states”) in 2003 at the faculty of physics, Warsaw University, under supervision of Krzysztof Wodkiewicz.
Presently he is doing a PhD at the Center for theoretical physics, Warsaw, under supervision of Marek Kus. Main areas of interests: quantum cloning, state estimation, multipartite entanglement and entanglement production in chaotic systems.

Rafal Demkowicz-Dobrzanski

State estimation is usually analyzed in the situation when copies are in a product state, either mixed or pure. I will present the concept of state estimation on correlated copies. Using a correlated state one tries to estimate as good as possible the direction of the Bloch vector of a single particle reduced density matrix. I will present the optimal fidelity of such estimation for all permutation invariant states and show the optimal state, which yields the highest estimation fidelity among the states with the same reduced density matrix.
Interestingly this state is not a product state.
It will be also pointed out that states produced by optimal universal cloning machines are the worst from the point of view of estimating the reduced density matrix.