Measuring quantum correlations by means of the conditional purity

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

Pucón

Congreso; RIAO/OPTILAS 2016; 2016

Quantum correlations constituting one of the main features that distinguishes quantum fromclassical composite systems and they are recognized as the essential resource that enables quantuminformation protocols exhibiting an exponential speed-up over their classical counterparts. Whileentanglement is the strongest type of quantum correlations that can occur in a quantum compositesystem of mixed states it does not cover all their possible non-classical correlations. For such kindof systems, other measures of quantum-like correlations have been proposed, with quantum discordand information deficit playing a prominent role. In particular, the presence of discord-likecorrelations has been shown to be important for several tasks as quantum state discrimination,quantum cryptography and quantum metrology. However, the computation of the quantum discordin its original definition is a hard problem for general states due it involves a minimization over alllocal measurements on one of the subsystems. The local measurement is chosen to minimize theconditional von Neumann entropy S(A/B) of the unmeasured component (A) after the localmeasurement on the other component (B). This conditional entropy has been recently extended tomore general entropic forms [1] which can be more easily evaluated and enable a clean analyticalsolution of the minimizing measurement in general qudit-qubit systems. Such entropies can also bedirectly related to the purity of the states, an experimentally accessible quantity which does notrequire a full state tomography.