Transitions between refrigeration regions in extremely short quantum cycles

Feldmann, Tova; Kosloff, Ronnie

doi:10.1103/physreve.93.052150

Cited by 10 publications

(10 citation statements)

References 32 publications

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“…Conversely, for short cycle-times the engine operation requires coherence and the strong dephasing nulls the power output ( <  0). Similar behaviour has been observed in the sudden Otto cycle and the two-stroke NV engines [27,44,62].…”

Section: Quantum Thermodynamic Signaturessupporting

confidence: 79%

“…There have been many proposals to quantify coherence [70]. In this context, two measures have been employed to analyze quantum heat engines: (i) Divergence, which becomes the difference between the energy and the von Neumann entropies [38,62,71,72], and (ii) The algebraic definition of coherence, utilized here, equation (D.1).…”

Section: Appendix C Friction Actionmentioning

confidence: 99%

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Quantum signatures in the quantum Carnot cycle

Dann

Kosloff

2020

New J. Phys.

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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 .

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Section: Quantum Thermodynamic Signaturessupporting

confidence: 79%

Section: Appendix C Friction Actionmentioning

confidence: 99%

Quantum signatures in the quantum Carnot cycle

Dann

Kosloff

2020

New J. Phys.

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“…In this framework, several recent studies have focused on employing quantum coherence in the working fluid for enhancing the performance of the engine [ 42 , 43 , 44 ]. Recently, an interesting regime called “sudden cycles” [ 45 ] has been explored in an incoherent formulation avoiding off-diagonal elements of the density matrix, characterized by finite cooling power [ 46 ].…”

Section: Introductionmentioning

confidence: 99%

Magnetic Otto Engine for an Electron in a Quantum Dot: Classical and Quantum Approach

Peña

Negrete

Barrios

et al. 2019

Entropy

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We studied the performance of classical and quantum magnetic Otto cycle with a working substance composed of a single quantum dot using the Fock–Darwin model with the inclusion of the Zeeman interaction. Modulating an external/perpendicular magnetic field, in the classical approach, we found an oscillating behavior in the total work extracted that was not present in the quantum formulation.We found that, in the classical approach, the engine yielded a greater performance in terms of total work extracted and efficiency than when compared with the quantum approach. This is because, in the classical case, the working substance can be in thermal equilibrium at each point of the cycle, which maximizes the energy extracted in the adiabatic strokes.

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“…A measure of coherence is the distance between a state

and

where

is the diagonal part of the density operator

in the energy representation. We can quantify this distance by

so it becomes the difference between the von Neumann entropy and the energy entropy [ 27 , 28 ]:

For a thermal state

the divergence vanishes. Under unitary transformation

is conserved but the energy entropy

can increase and with it the divergence

, therefore maximizing

will lead to maximum coherences.…”

Section: General Aspects Of Coherence Measurment: Information and mentioning

confidence: 99%

Quantifying the Unitary Generation of Coherence from Thermal Quantum Systems

Kallush

Aroch

Kosloff

2019

Entropy

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The unitary generation of coherence from an incoherent thermal state is investigated. We consider a completely controllable Hamiltonian allowing to generate all possible unitary transformations. Optimizing the unitary control to achieve maximum coherence leads to a micro-canonical energy distribution on the diagonal energy representation. We demonstrate such a control scenario starting from a Hamiltonian utilizing optimal control theory for unitary targets. Generating coherence from an incoherent initial state always costs external work. By constraining the amount of work invested by the control, maximum coherence leads to a canonical energy population distribution. When the optimization procedure constrains the final energy too tightly local suboptimal traps are found. The global optimum is obtained when a small Lagrange multiplier is employed to constrain the final energy. Finally, we explore constraining the generated coherence to be close to the diagonal in the energy representation.

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Transitions between refrigeration regions in extremely short quantum cycles

Cited by 10 publications

References 32 publications

Quantum signatures in the quantum Carnot cycle

Quantum signatures in the quantum Carnot cycle

Magnetic Otto Engine for an Electron in a Quantum Dot: Classical and Quantum Approach

Quantifying the Unitary Generation of Coherence from Thermal Quantum Systems

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