Abstract
There are both practical and foundational motivations to consider the thermodynamics of quantum systems at small scales. Here we address the issue of autonomous quantum thermal machines that are tailored to achieve some specific thermodynamic primitive, such as work extraction in the presence of a thermal environment, while having minimal or no control from the macroscopic regime. Beyond experimental implementations, this provides an arena in which to address certain foundational aspects such as the role of coherence in thermodynamics, the use of clock degrees of freedom and the simulation of local time-dependent Hamiltonians in a particular quantum subsystem. For small-scale systems additional issues arise. Firstly, it is not clear to what degree genuine ordered thermodynamic work has been extracted, and secondly non-trivial back-actions on the thermal machine must be accounted for. We find that both these aspects can be resolved through a judicious choice of quantum measurements that magnify thermodynamic properties up the ladder of length-scales, while simultaneously stabilising the quantum thermal machine. Within this framework we show that thermodynamic reversibility is obtained in a particular Zeno limit, and finally illustrate these concepts with a concrete example involving spin systems.
Highlights
In [26, 27] the question of work extraction from an arbitrary qubit state has been analysed in a context which explicitly models the coherence resources that are required to extract work from the qubit state
The analysis recovers the expected result that one can associate the free energy difference DF to an arbitrary pure qubit state ∣yñáy ∣, but only within a particular ‘classical regime’, in which one has access to an infinite system with unbounded coherence resources. Outside of this setting it is provably impossible to extract all of the free energy from the quantum coherence
We have presented an explicit analysis of the basic requirements of a quasi-autonomous quantum thermal machine5
Summary
Commons Attribution 3.0 systems at small scales. Here we address the issue of autonomous quantum thermal machines that are licence. It is not clear to what degree genuine ordered thermodynamic work has been extracted, and secondly non-trivial back-actions on the thermal machine must be accounted for We find that both these aspects can be resolved through a judicious choice of quantum measurements that magnify thermodynamic properties up the ladder of length-scales, while simultaneously stabilising the quantum thermal machine. Within this framework we show that thermodynamic reversibility is obtained in a particular Zeno limit, and illustrate these concepts with a concrete example involving spin systems
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