Experimental estimation of quantum discord for a polarization qubit and the use of fidelity to assess quantum correlations

摘要

We address the experimental determination of entropic quantum discord for systems made of a pair ofnpolarization qubits. We compare results from full and partial tomography and found that the two determinationsnare statistically compatible, with partial tomography leading to a smaller value of discord for depolarized states.nDespite the fact that our states are well described, in terms of fidelity, by families of depolarized or phase-dampednstates, their entropic discord may be largely different from that predicted for these classes of states, such that nonreliable estimation procedure beyond tomography may be effectively implemented. Our results, together with thenlack of an analytic formula for the entropic discord of a generic two-qubit state, demonstrate that the estimationnof quantum discord is an intrinsically noisy procedure. Besides, we question the use of fidelity as a figure ofnmerit to assess quantum correlations.