Coherence and decoherence in quantum absorption refrigerators

Kilgour, Michael; Segal, Dvira

doi:10.1103/physreve.98.012117

Cited by 65 publications

(81 citation statements)

References 82 publications

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“…In quantum thermodynamics, one of the timely questions is whether and under what conditions quantum features such as entanglement and coherence can enhance the performance of heat engines and refrigerators [1][2][3]. In many models of such machines, quantum coherence is found to be useful [4][5][6][7][8][9][10][11], whereas its adverse effect has also been reported [12][13][14][15][16] or its usefulness may even depend on the quantity of interest [17]. An interesting regime is given by sudden cycles where control parameters of the system change infinitely rapidly.…”

Section: Introductionmentioning

confidence: 99%

Supremacy of incoherent sudden cycles

et al. 2019

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We investigate theoretically a refrigerator based on a two-level system (TLS) coupled alternately to two different heat baths. Modulation of the coupling is achieved by tuning the level spacing of the TLS. We find that the TLS, which avoids quantum coherences, creates finite cooling power for one of the baths in sudden cycles, i.e. acts as a refrigerator even in the limit of infinite operation frequency. By contrast, the cycles that create quantum coherence in the sudden expansions and compressions lead to heating of both the baths. We propose a driving method that avoids creating coherence and thus restores the cooling in this system. We also discuss a physical realization of the cycle based on a superconducting qubit coupled to dissipative LC-resonators.

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Section: Introductionmentioning

confidence: 99%

Supremacy of incoherent sudden cycles

et al. 2019

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“…For simplicity, the theory was only applied to the free field case [38], in order to demonstrate the technicalities associated with coupling a different NHC thermostat [44,45] to each field mode. However, this theory is intended for situations where the field is coupled to a spin system [47][48][49][50][51][52][53][54][55][56][57]. In this case, the use of NHC thermostats in the dynamics of the thermal state of the field would make it possible to simulate processes that, to our knowledge, have not been investigated so far.…”

Section: Discussionmentioning

confidence: 99%

“…As will be explained below, this feature can be exploited to simulate the passage from a quantum thermal distribution of the modes to a classical one. The generalization of our formalism to situations where the field is coupled to a spin system [47][48][49][50][51][52][53][54][55][56][57] is left for future work. Such an endeavour could lead to new computational experiments on spin dynamics, which to the best of our knowledge, would be novel.…”

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confidence: 99%

Proposal of a Computational Approach for Simulating Thermal Bosonic Fields in Phase Space

Sergi

Grimaudo

Hanna

et al. 2019

Physics

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When a quantum field is in contact with a thermal bath, the vacuum state of the field may be generalized to a thermal vacuum state, which takes into account the thermal noise. In thermo field dynamics, this is realized by doubling the dimensionality of the Fock space of the system. Interestingly, the representation of thermal noise by means of an augmented space is also found in a distinctly different approach based on the Wigner transform of both the field operators and density matrix, which we pursue here. Specifically, the thermal noise is introduced by augmenting the classical-like Wigner phase space by means of Nosé-Hoover chain thermostats, which can be readily simulated on a computer. In this paper, we illustrate how this may be achieved and discuss how non-equilibrium quantum thermal distributions of the field modes can be numerically simulated.Published in Physics 2019, 1(3), 402-411; https://doi.org/10.3390/physics1030029 I. INTRODUCTIONAccording to quantum field theory, the vacuum is filled by fluctuating quantum fields.Such fields are present both in condensed matter systems [1-6] and, more generally, in empty space-time, where their existence is believed to be linked to dark matter and dark energy [7][8][9][10][11][12][13][14][15][16]. Universal phenomena such as the emergence of order, symmetry breaking, and phase transitions are related to the thermal degrees of freedom the first time in order to stress that we are not using the expression in a literal meaning. of the fields [17,18]. Hence, the study of the thermal excitation of the quantum vacuum is of interest to many research areas [19][20][21][22][23]. In thermo field dynamics [24][25][26], the vacuum state is generalized to a thermal vacuum state by doubling the dimension of the Fock space of the original vacuum. The additional dimension of the Fock space represent the degrees of freedom of the thermal bath, which are involved in the excitation and de-excitation processes of the thermal system.In this paper, we illustrate an approach to simulate the thermal distributions of bosonic * Electronic address: asergi@unime.it † Electronic address: roberto.grimaudo01@unipa.it ‡ Electronic address: gabriel.hanna@ualberta.ca § Electronic address: antonino.messina@unipa.it H (Q,P ) = J ω JP 2 J 2λ 2 J + ω J λ 2 JQ 2 J the Wigner transform of the field Hamiltonian in Equation (1) reads: H (Q,P ) = J P 2 J 2µ J + µ J ω 2 J Q 2 J 2 = J

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“…Therefore, large amounts of coherence (which might also imply entanglement [63]) are associated with more current and thus more cooling power, especially in the regime of weak coupling g between parts of the machine. Note, however, that this conclusion is model-dependent: in certain configurations, decoherence can actually increase cooling power by suppressing destructive interference [66], an effect that is well known in quantum biology [67].…”

Section: Quantum Performance Enhancements?mentioning

confidence: 99%

“…Therefore, while coherent effects in a given microscopic process may be found to play an important role, e.g. because additional dephasing reduces power or efficiency [66,74], it is usually possible to find another classical model that emulates the quantum machine by reproducing the same performance characteristics [75]. We thus cannot yet decisively claim a generic quantum advantage for thermal machines.…”

Section: Quantum Performance Enhancements?mentioning

confidence: 99%

Quantum thermal absorption machines: refrigerators, engines and clocks

Mitchison

2019

Contemporary Physics

149

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The inexorable miniaturisation of technologies, the relentless drive to improve efficiency and the enticing prospect of boosting performance through quantum effects are all compelling reasons to investigate microscopic machines. Thermal absorption machines are a particularly interesting class of device that operate autonomously and use only heat flows to perform a useful task. In the quantum regime, this provides a natural setting in which to quantify the thermodynamic cost of various operations such as cooling, timekeeping or entanglement generation. This article presents a pedagogical introduction to the physics of quantum absorption machines, covering refrigerators, engines and clocks in detail.

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Coherence and decoherence in quantum absorption refrigerators

Cited by 65 publications

References 82 publications

Supremacy of incoherent sudden cycles

Supremacy of incoherent sudden cycles

Proposal of a Computational Approach for Simulating Thermal Bosonic Fields in Phase Space

Quantum thermal absorption machines: refrigerators, engines and clocks

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