Spin-dependent Otto quantum heat engine based on a molecular substance

Abstract

We explore the potential of single molecules for thermodynamic cycles. To this end we propose two molecular heat engines based on the Ni 2 dimer in the presence of a static magnetic field: (a) a quantum Otto engine and (b) a modified quantum Otto engine for which optical excitations induced by a laser pulse substitute for one of the heat-exchange points. For reliable predictions and to inspect the role of spin and electronic correlations we perform fully correlated ab initio calculations of the molecular electronic structure including spin-orbital effects. We analyze the efficiency of the engines in dependence of the electronic level scheme and the entanglement and find a significant possible enhancement connected to the quantum nature and the heat capacity of the dimer, as well as to the zero-field triplet states splitting.

Magnetic Engine for the Single-Particle Landau Problem

“…On the other hand, the effects of the degeneracy of energy levels on the efficiency and power of an engine quantum machine have been reported in many works in the past [21,22,[28][29][30]. In this same framework, we highlight the work of Mehta and Ramandeep [32], who worked on a quantum Otto engine in the presence of level degeneracy, finding an enhancement of work and efficiency for two-level particles with a degeneracy in the excited state.…”

“…This is a crucial point in the discussion for our magnetic engine based in the work presented [13]. In general, a quantum adiabatic stroke does not maintain the system in a thermal state [28][29][30]. A power law potential can guarantee the thermal state condition when the degeneracy does not change, as in the treatment of [36], but not in our case under the study, because the number of states involved in the process should not increase, even if the degeneracy increases.…”

Magnetic Engine for the Single-Particle Landau Problem

“…On the other hand, the effects of the degeneracy of energy levels on the efficiency and power of an engine quantum machine have been reported in many works in the past [21,22,[28][29][30]. In this same framework, we highlight the work of Mehta and Ramandeep [31], who worked on a quantum Otto engine in the presence of level degeneracy, finding an enhancement of work and efficiency for two-level particles with a degeneracy in the excited state.…”

“…This is a crucial point in the discussion for our magnetic engine, based on the work presented [13]. In general, a quantum adiabatic stroke does not maintain the system in a thermal state [28][29][30]. A power law potential can guarantee the thermal state condition when the degeneracy does not change, as in the treatment of [36], but not in our case under the study, because the number of states involved in the process should not increase, even if the degeneracy increases.…”

“…Our system was studied to prove a concept rather than a practical implementation protocol. However, we believe the readers will find attractive the study of the "full" quantum version of this cycle following the treatment of the works [28][29][30], where treated the magnetic substance under degenerate conditions using non-equilibrium techniques. Besides, it is promising to treat the quantum version of our formulation optimized following the work of Kosloff and Rezek [25], for the case of frictionless adiabats using the methods of shortcuts to adiabaticity [37][38][39].…”