2014/04/23 by M. A. Yurischev, Yurischev, M. A.
Computer Science · Physics and Astronomy · #FOS: Physical sciences #Quantum Computing Algorithms and Architecture #Quantum Information and Cryptography #Quantum Physics (quant-ph) #Quantum and electron transport phenomena
paper · pdf · doi:10.48550/arxiv.1404.5735
openalex publication_date 2014/04/23 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
Quantum discord is a function of density-matrix elements (and through them, e.~g., of temperature, applied fields, time, and so forth). The domain of such a function in the case of two-qubit system with X or centrosymmetric (CS) density matrix can consist at most of three subdomains: two ones, where the quantum discord is expressed in closed analytical forms (Q0 and Qπ/2), and an intermediate subdomain in which for determining the quantum discord Qθit is required to solve numerically a one-dimensional minimization problem to find the optimal measurement angle θ∈(0,π/2). Exact equations for determining the boundaries between these subdomains are obtained and solved for a number of models. The Qθsubdomains are discovered in the anisotropic spin dimers in external field. On the other hand, coinciding boundaries and therefore sudden transitions between optimal measurement angles θ=π/2 and θ=0 are observed in dynamics of spin currying particles in closed nanopore and also in phase flip channels. In latter cases the solutions are entirely analytical.