MEASURING QUANTUM CORRELATIONS BY MEANS OF THE CONDITIONAL PURIT

L REBÓN; J. J. M. VARGA; N. GIGENA; C. IEMMI; S. LEDESMA; R. ROSSIGNOLI; N. CANOSA

Pucón

Conferencia; RIAO/OPTILAS 2016. IX Reunión Iberoamericana de Óptica y XII Reunión Iberoamericana de Óptica, Láseres y Aplicaciones; 2016

We present a simple analytical expression for the conditional purity of a qubit A after a local measurement on a second qubit, B, including its average, . We show that this quantity allows to determine the quantum correlations in mixtures of nonorthogonal aligned two qubit states which are relevant for the description of spin pair states in interacting spin chains. In particular, we have derived clean analytical expressions for the quantum discord and geometrical discord valid for the considered states, which unveils its direct connection with the maximum value of , directly related to the purity of the final state, and an experimentally accessible quantity which does not require a tomography reconstruction of the state. We have then experimentally tested and fully verified these theoretical results using polarization-encoded photonic qubits from a source emitting a pair of photons in the same polarization state, which enables to reproduce different mixed two qubit states.