Quantum signatures in the quantum Carnot cycle

Abstract

The Carnot cycle combines reversible isothermal and adiabatic strokes to obtain optimal efficiency, at the expense of a vanishing power output. Quantum Carnot-analog cycles are constructed and solved, operating irreversibly with positive power. Swift thermalization is obtained in the isotherms utilizing shortcut to equilibrium protocols and the adiabats employ frictionless unitary shortcuts. The working medium in this study is composed of a particle in a driven harmonic trap. For this system, we solve the dynamics employing a generalized canonical state. Such a description incorporates both changes in energy and coherence. This allows comparing three types of Carnot-analog cycles, Carnot-shortcut, Endo-shortcut and Endo-global. The Carnot-shortcut engine demonstrates the trade-off between power and efficiency. It posses a maximum in power, a minimum cycle-time where it becomes a dissipator and for a diverging cycle-time approaches the ideal Carnot efficiency. The irreversibility of the cycle arises from non-adiabatic driving, which generates coherence. To study the role of coherence we compare the performance of the shortcut cycles, where coherence is limited to the interior of the strokes, with the Endo-global cycle where the coherence never vanishes. The Endo-global engine exhibits a quantum signature at a short cycle-time, manifested by a positive power output while the shortcut cycles become dissipators. If energy is monitored the back action of the measurement causes dephasing and the power terminates.CA c h [4,5], which has been generalized for weak dissipation [6,7].In the quantum regime energy transfer is constrained as well by the second law of thermodynamics [8][9][10][11]. Implying that quantum heat engines are also bounded by the Carnot efficiency. Reversibility and optimal efficiency is obtained in the quantum adiabatic limit, requiring an infinite cycle-time τ cycle .

Bosons outperform fermions: The thermodynamic advantage of symmetry

“…This might explain the plethora of studies to investigate possible enhancements of engine performance through the exploitation of quantum resources including coherence [8][9][10][11][12][13][14][15], measurement effects [16], squeezed reservoirs [17][18][19], quantum phase transitions [20], and quantum many-body effects [15,[21][22][23]. Other works have examined the fundamental differences between quantum and classical thermal machines [24][25][26], finite time cycles [13,27,28], utilizing shortcuts to adiabaticity [12,22,23,[29][30][31][32][33], operating over non-thermal states [34,35], non-Markovian effects [36], magnetic systems [37][38][39][40][41][42], anharmonic potentials [43], optomechanical implementation [44], quantum dot implementation [38,40,42], implementation in 2D materials…”

Entropy Distribution in a Quantum Informational Circuit of Tunable Szilard Engines

“…Some papers describe how a string of bits can be processed by information ratchets that interact with simple physical systems with [21] or without thermal reservoirs [22]. There are differences between classical and quantum which have been discussed in several papers [23][24][25][26][27][28], although the Carnot efficiency bound is the same for both [29,30] in the limit of infinitely slow processes and thermal reservoirs. The devices that perform this transformation are known as information heat engines [1,7,[31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47].…”

The Quantum Friction and Optimal Finite-Time Performance of the Quantum Otto Cycle

“…Quantum models of heat engines and refrigerators have been investigated extensively, especially because of the relevance of these models to the problem of cooling at extremely low temperatures, i.e., near absolute zero. The most well-studied case is the quantum analog of the Otto cycle [ 1 , 2 , 3 , 4 ] for which heat-exchange and work-exchange take place in different steps of the thermodynamic cycle, although the Carnot cycle has been investigated as well [ 5 , 6 ].…”