Quantum thermodynamics with local control

Abstract

We investigate the limitations that emerge in thermodynamic tasks as a result of having local control only over the components of a thermal machine. These limitations are particularly relevant for devices composed of interacting many-body systems. Specifically, we study protocols of work extraction that employ a many-body system as a working medium whose evolution can be driven by tuning the on-site Hamiltonian terms. This provides a restricted set of thermodynamic operations, giving rise to alternative bounds for the performance of engines. Our findings show that those limitations in control render it, in general, impossible to reach Carnot efficiency; in its extreme ramification it can even forbid to reach a finite efficiency or finite work per particle. We focus on the one-dimensional Ising model in the thermodynamic limit as a case study. We show that in the limit of strong interactions the ferromagnetic case becomes useless for work extraction, while the antiferromagnetic case improves its performance with the strength of the couplings, reaching Carnot in the limit of arbitrary strong interactions. Our results provide a promising connection between the study of quantum control and thermodynamics and introduce a more realistic set of physical operations well suited to capture current experimental scenarios.

Non-Markov enhancement of maximum power for quantum thermal machines

“…Ruling out the possibility of using non-Markovian effects to improve the efficiency in the model [56][57][58], the power boost we reported above for the Carnot and Otto cycle can only be seen as a consequence of the latter in the reduction of thermalization timescales. We show here an argument to explain why it happens and how it is related to the non-Markovian building of correlations between the engine S and the j-th bath.…”

“…In such a set up indeed, Refs. [56][57][58] show how this mechanism can only have detrimental effects from the point of view of quasi-static Thermodynamics: that is, without external free energy injections, the 2nd Law assures the Carnot efficiency is the maximal one. Nothing instead, has been stated from the point of view of FTT: even if lowering the maximal efficiency, there is still question on the effects on power and EMP, which are, from the practical point of view, much more interesting than pure maximal efficiency.…”

Thermodynamics of Modularity: Structural Costs Beyond the Landauer Bound

“…For the feedback operation that decorrelates the system under study (SUS) and the demon in Szilard's engine, the SUS is the interacting subsystem Z i ¼ Z SUS , and the demon's memory is fixed, so that it is the stationary subsystem Z s ¼ Z demon . For this feedback step, modular control means that the externally controlled Hamiltonian [9] is the SUS's Hamiltonian:…”

“…In this setting, a modularly designed computation processes only the local component of the input, ignoring the latter's global structure. This inherent locality is a physical control restriction and, thus, can lead to thermodynamic inefficiency [9,10]. Local control in modular systems necessarily leads to irretrievable loss of global correlations during computing.…”

“…We establish this using the quantum mechanical framework appearing elsewhere on thermodynamics of control restrictions [9,10]. There, a changing Hamiltonian HðtÞ is broken into the default Hamiltonian H 0 over Z and the externally controlled Hamiltonian H ext ðtÞ, which only affects the local interacting subsystem:…”