Abstract
Recent work using tools from quantum information theory has shown that for small systems where quantum effects become prevalent, there is not one thermodynamical second law but many. Derivations of these laws assume that an experimenter has very precise control of the system and heat bath. Here we show that these multitude of laws can be saturated using two very simple operations: changing the energy levels of the system and thermalizing over any two system energy levels. Using these two operations, one can distill the optimal amount of work from a system, as well as perform the reverse formation process. What is more, using only these two operations and one ancilla qubit in a thermal state, one can transform any state into any other state allowable by the second laws. We thus have the result that the second laws hold for fine-grained manipulation of system and bath, but can be achieved using very coarse control. This brings the full array of thermal operations towards a regime accessible by experiment, and establishes the physical relevance of these second laws, potentially opening a new direction of studies.
- Received 2 December 2016
- Revised 15 October 2018
DOI:https://doi.org/10.1103/PhysRevX.8.041049
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Thermodynamics is one of the most fundamental fields of physics. And yet in the domain of atoms, molecules, and subatomic particles, what we mean by thermodynamics is very different. For example, while it is relatively easy to get ordinary engines to work efficiently, it may be impossible to do so with a quantum engine using any realistic technology. However, we show that to achieve all that is possible under the laws of quantum thermodynamics, an experimenter needs only two simple operations: the ability to change the energy levels of a system and the ability to thermalize over any two system energy levels.
Using these two operations, one can extract the optimal amount of work from a system, as well as perform the reverse formation process. With the addition of one qubit in a thermal state, one can also transform a state into any other state allowable by the various second laws of quantum thermodynamics. We thus see that the second laws hold for fine-grained manipulation of a system and its bath, but they can be achieved using very coarse control.
These results open the door to a new wave of quantum thermodynamic experiments, enabling tests of theoretical predictions and providing tools for implementing optimal microscopic machines.
