Internal dissipation and heat leaks in quantum thermodynamic cycles

This is the final version. Available from American Physical Society via the DOI in this recordThe direction of the steady-state heat currents across a generic quantum system connected to multiple baths may be engineered to realize virtually any thermodynamic cycle. In spite of their versatility, such continuous energy-conversion systems are generally unable to operate at maximum efficiency due to non-negligible sources of irreversible entropy production. In this paper we introduce a minimal model of irreversible absorption chiller. We identify and characterize the different mechanisms responsible for its irreversibility, namely heat leaks and internal dissipation, and gauge their relative impact in the overall cooling performance. We also propose reservoir engineering techniques to minimize these detrimental effects. Finally, by looking into a known three-qubit embodiment of the absorption cooling cycle, we illustrate how our simple model may help to pinpoint the different sources of irreversibility naturally arising in more complex practical heat devices.European UnionSpanish MINECOCOST Actio

Performance bound for quantum absorption refrigerators

This is the final version. Available from American Physical Society via the DOI in this recordAn implementation of quantum absorption chillers with three qubits has been recently proposed that is ideally able to reach the Carnot performance regime. Here we study the working efficiency of such self-contained refrigerators, adopting a consistent treatment of dissipation effects. We demonstrate that the coefficient of performance at maximum cooling power is upper bounded by 3/4 of the Carnot performance. The result is independent of the details of the system and the equilibrium temperatures of the external baths. We provide design prescriptions that saturate the bound in the limit of a large difference between the operating temperatures. Our study suggests that delocalized dissipation, which must be taken into account for a proper modeling of the machine-baths interaction, is a fundamental source of irreversibility which prevents the refrigerator from approaching the Carnot performance arbitrarily closely in practice. The potential role of quantum correlations in the operation of these machines is also investigated.Spanish MICINNEuropean UnionCanary Islands GovernmentUniversity of Nottingha

Quantum-enhanced absorption refrigerators

Thermodynamics is a branch of science blessed by an unparalleled combination of generality of scope and formal simplicity. Based on few natural assumptions together with the four laws, it sets the boundaries between possible and impossible in macroscopic aggregates of matter. This triggered groundbreaking achievements in physics, chemistry and engineering over the last two centuries. Close analogues of those fundamental laws are now being established at the level of individual quantum systems, thus placing limits on the operation of quantum-mechanical devices. Here we study quantum absorption refrigerators, which are driven by heat rather than external work. We establish thermodynamic performance bounds for these machines and investigate their quantum origin. We also show how those bounds may be pushed beyond what is classically achievable, by suitably tailoring the environmental fluctuations via quantum reservoir engineering techniques. Such superefficient quantum-enhanced cooling realises a promising step towards the technological exploitation of autonomous quantum refrigerators

Laser control in open quantum systems: preliminary analysis toward the Cope rearrangement control in methyl-cyclopentadienylcarboxylate dimer

We present a preliminary simulation toward the control of theCope rearrangement of themost stable isomer of methyl-cyclopentadienylcarboxylate dimer. An experimental investigation of the dimerization of methyl-cyclopentadienylcarboxylate has been carried out. It shows that the most stable isomer of the dimer, the Thiele’s ester, is the major product of the dimerization. The simulation takes it as the initial state for the further control of the Cope reaction. The aim of the simulation is to examine the possibility of laser control to form the target product, not detected during the dimerization. The relevant stationary states have been characterized at the DFT B3LYP level, particularly the Cope transition state in which the dimer is connected only by a single bond r1. A minimum energy potential surface has been computed in a two-dimensional subspace of two bounds r2 and r3 which achieve the dimerization and have a very high weight in the reaction path from the Cope TS to the two adducts. Quantum wave packet optimal control simulation has been studied in a one-dimensionalmodel using an active coordinate r ¼ r3 r2 which nearly corresponds to the reaction path. The stability of the optimal field against dissipation is examined by a non-Markovian master equation approach, which is perturbative in the system-bath coupling but without limitation on the strength of the field