International Workshop on 'New challenges in Reduced Density Matrix Functional Theory: Symmetries, time-evolution and entanglement'
Reduced density matrix applied to quantum thermodynamicsJamal Berakdar
Martin-Luther University Halle-Wittenberg, Germany
Coauthor(s) : L. Chotorlishvili, M. Melz, G. Lefkidis, W. Hübner
 University of Kaiserslautern, Germany
Recently considerable research efforts were devoted to study of the thermodynamic behaviour of nanoscale quantum structures  with an emphasis on the question as to which extent the quantum nature of the system, and in particular entanglement, can be exploited to enhance the performance of quantum heat engines. Motivated by the fact that entanglement entails mixedness and correlation we investigated theoretically correlated many body systems. We focus on the low-energy excitations that can be captured by an effective quantum spin model, possibly with a topologically non-trivial spin order. Thermodynamic quantities are formulated in terms of the reduced density matrices making possible to trace the role of entanglement [1,2]. For instance, we find that an efficient spin-dependent Otto heat engine can be constructed with the working substance being Ni2 dimer driven by non-resonant THz field. As evidenced by full ab-initio calculations the entanglement enhances the cycle efficiency. The same applies to quantum spin systems with non-collinear magnetic order. In particular, we studied quantum heat engines with a working substance being a helical multiferroic structure, meaning a system which is susceptible to external electric and magnetic fields allowing to perform electromagnetic work. We will discuss how to exploit the inherent spin non-collinearity to enhance the thermodynamic cycle efficiency . Practical applications such as the entanglement-assisted thermal pumping of spin currents will be presented.
 M. Horodecki and J. Oppenheim, Nat. Commun. 4 2059 (2013); P. Skrzypczyk et al., Nat. Commun. 5 4185 (2014); A. Dechant, et al., Phys. Rev. Lett. 114 183602 (2015); F. G. S. L. Brandao et al., The second laws of quantum thermodynamics PNAS 112 3275 (2015).
 M. Azimi et al. New J. Phys. 16 063018 (2014); M. Azimi et al. Phys. Rev. B 89 024424 (2014), arXiv:1703.00855.