Nonequilibrium thermal entanglement

Abstract

Results on heat current, entropy production rate and entanglement are reported for a quantum system coupled to two different temperature heat reservoirs. By applying a temperature gradient, different quantum states can be found with exactly the same amount of entanglement but different purity degrees and heat currents. Furthermore, a nonequilibrium enhancement-suppression transition behavior of the entanglement is identified.Comment: 5 pages and 5 figures(eps). Minor changes. Accepted version to be published in Phys. Rev.

Enhanced violation of a Leggett-Garg inequality under nonequilibrium thermal conditions

“…An analytical expression for the heat current under a temperature gradient, ∆T =T 1 −T 2 , as calculated from J (∆T ) = Tr Ĥ QL1 can be found in Ref. [15]. Although a closed equation relating F (0,τ , 2τ ) with the heat flow is possible, the expression is cumbersome and will be skipped here, since their relationship is still better appreciated by looking at the figures as discussed below.…”

“…(21) are given, in theσ z,i basis, by: |1 = |+, + , |2 = (|+, − − |−, + )/ √ 2, |3 = (|+, − + |−, + )/ √ 2 and |4 = |−, − . The non-equilibrium thermal steady-state density operator for the pair of qubits turns out to be diagonal in this basis taking the form of a direct product as [15] ρ ss =ρ ss…”

“…In the Born-Markov framework the system-bath couplings are essentially determined by the bath spectral density of the form J i (ω) = Γn i (ω) where Γ denotes the coupling strength (taken identical for both reservoirs) and n i (ω) = (e βiω − 1) −1 , the Bose-Einstein distribution of excitations in the i-th bath at inverse temperature β i [15]. For the sake of simplicity we limit ourselves to the symmetric-qubit case, i.e.…”

“…Despite the ubiquitous presence of non-equilibrium situations in quantum mesoscopic and macroscopic physics, few formal results about quantum correlations in such regimes are available [15][16][17][18]. Many efforts encompassing a large variety of physical systems have been directed to study the effects of spatial correlations, as measured by the concurrence [15,19,20] and quantum discord (QD) [21], under non-equilibrium gradients.…”

“…Despite the ubiquitous presence of non-equilibrium situations in quantum mesoscopic and macroscopic physics, few formal results about quantum correlations in such regimes are available [15][16][17][18]. Many efforts encompassing a large variety of physical systems have been directed to study the effects of spatial correlations, as measured by the concurrence [15,19,20] and quantum discord (QD) [21], under non-equilibrium gradients. However, LGI studies have been very scarce in systems out of thermodynamic equilibrium, although time correlations in condensed matter systems show complex and interesting behaviors, like those observed in ultracold atom systems [22], inductively (capacitively) coupled flux (charge) superconducting qubits [23], and even energy transfer processes in photosynthetic purple bacteria [24].…”