Quantum Brayton cycle with coupled systems as working substance

Abstract

We explore the quantum version of the Brayton cycle with a composite system as the working substance. The actual Brayton cycle consists of two adiabatic and two isobaric processes. Two pressures can be defined in our isobaric process; one corresponds to the external magnetic field (characterized by F(x)) exerted on the system, while the other corresponds to the coupling constant between the subsystems (characterized by F(y)). As a consequence, we can define two types of quantum Brayton cycle for the composite system. We find that the subsystem experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized by F(x)), whereas the subsystem's cycle is quantum Otto cycle in another Brayton cycle (characterized by F(y)). The efficiency for the composite system equals to that for the subsystem in both cases, but the work done by the total system is usually larger than the sum of the work done by the two subsystems. The other interesting finding is that for the cycle characterized by F(y), the subsystem can be a refrigerator, while the total system is a heat engine. The result in this paper can be generalized to a quantum Brayton cycle with a general coupled system as the working substance.

Lipkin-Meshkov-Glick model in a quantum Otto cycle

“…In addition we compare our results with those similar studies of Heisenberg type interaction coupled spins. These studies showed the interaction enhanced work and efficiency [12,13,15,24,27,33], and elucidated the possibility of work extraction in the regimes inaccessible by the non-interacting working substances [12,13]; however they did not take into account anisotropy or LMG type coupling between the spins. Our results reveal unique advantages of anisotropy for enhancing cooperative work output, opening new working regimes, optimization of maximum work at optimal efficiency as well as bring practical advantages by extending the domain of interacting spin working substances to anisotropic systems.…”

“…QHEs can extract more work from heat baths relative to classical heat engines [4,5]; they can operate beyond the classical Carnot bound without breaking the second law by exploiting quantum resources; such as entangled [6] or quantum coherent heat reservoirs [7,8], or by regenerative steps [9]. In comparison to non-interacting working substances, such as a two level (qubit) [4,5] or a multilevel atom [10], or a simple harmonic oscillator [11], QHEs with interacting working substances, in particular coupled spins, are found to be more efficient and capable to harvest more work [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33]. Physical realizations of QHEs are proposed for a single ion [34,35], Paul trap [9], ultracold atoms [36], optomechanical systems [37], quantum dots [38], circuit and cavity quantum electrodynamic systems [7,39,40].…”

“…LMG model is relevant to particle entanglement and with the anisotropy parameter one can tune the system from single axis twisting to two-axes twisting regimes [59]. In terms of local work and heat concepts [13,15,21,24,27,33], cooperative effects and the extensitivity breakdown in the global work output [15,27,33] in the LMG system could be examined as well. These intriguing directions could be further explored but beyond the scope of our present contribution.…”

“…Since the recognition of three level maser as a heat engine [1], quantum heat engines (QHEs) have been attracted much interest recently [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40]. QHEs use quantum matter as their working substance to harvest work from classical or quantum resources through the quantum generalizations of classical thermodynamical cycles, such as Carnot, Otto, Brayton or Diesel cycles [2,3].…”

Deep-subwavelength lithography via graphene plasmons

“…Quantum heat engines are typically based on implementations of quantum Carnot, Otto [15], Brayton [16,17], Diesel [16,18] or Stirling cycles [19,20], with a succession of strokes that alternatively extract work and exchange heat with the hot and cold reservoirs. As a result the generation of work is an intermittent process.…”