Related Experiment Video
Updated: Jan 10, 2026
09:09
Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation
Published on: February 5, 2020
7.6K
Universal efficiency boost in prethermal quantum heat engines at negative temperature
Alberto Brollo1,2, Adolfo Del Campo3,4, Alvise Bastianello5,6
1Department of Mathematics, Technical University of Munich, CIT, Garching, Germany.
Nature Communications
|November 25, 2025
Summary
Quantum heat engines with conserved quantities show reduced efficiency at positive temperatures but improved performance at negative temperatures. This study explores prethermalization effects in quantum systems.
Area of Science:
- Quantum thermodynamics
- Statistical mechanics
- Condensed matter physics
Background:
- Heat engines typically assume thermal equilibrium, but quantum systems may not thermalize due to conservation laws.
- Prethermalization occurs in quantum many-body systems with hindered thermalization, existing in exotic stationary phases.
- Understanding prethermalization's impact on quantum heat engine efficiency is crucial.
Purpose of the Study:
- To investigate whether prethermalization enhances or reduces the efficiency of quantum heat engines.
- To analyze the effect of varying numbers of conserved quantities on engine performance.
- To explore quantum Otto cycles in systems with and without prethermalization.
Main Methods:
- Investigated quantum Otto cycles in systems with different numbers of conserved quantities.
- Utilized general thermodynamic inequalities for infinitesimal cycles.
- Applied Generalized Hydrodynamics to analyze integrable models with finite cycles.
Main Results:
- Additional conservation laws decrease engine efficiency at positive temperatures.
- Additional conservation laws enhance engine efficiency in negative temperature regimes.
- Prethermalization's impact on efficiency is dependent on temperature and the number of conserved quantities.
Conclusions:
- Prethermalization's effect on quantum heat engine efficiency is complex and depends on thermodynamic conditions.
- Findings provide insights into optimizing quantum engine performance in non-equilibrium systems.
- Results are relevant for the development and application of quantum simulators.
Related Concept Videos
01:30The Carnot Cycle
3.9K
Converting work to heat is an irreversible process, and the purpose of a heat engine is to reverse the effect partially. Heat engines aim to increase the efficiency of the reversal, that is, maximize the work retrieved from heat. If the efficiency of a heat engine were 100%, it would imply reversing the process completely without introducing any other effect. Thus, it would violate the second law of thermodynamics.
What could be the theoretical limit to the efficiency of a heat engine? The...
What could be the theoretical limit to the efficiency of a heat engine? The...
3.9K
01:20The Carnot Cycle and the Second Law of Thermodynamics
3.7K
The Carnot engine works between two heat reservoirs of fixed temperatures. The Carnot cycle begs the following question: Is it possible to devise a heat engine that is more efficient than a Carnot engine between two fixed temperatures? The answer lies in designing a Carnot refrigerator.
Since the individual steps in a Carnot cycle can be reversed, the entire cycle is, thus, reversible. If a Carnot cycle is reversed, it becomes a Carnot refrigerator. It extracts heat Qc from a cold reservoir at...
Since the individual steps in a Carnot cycle can be reversed, the entire cycle is, thus, reversible. If a Carnot cycle is reversed, it becomes a Carnot refrigerator. It extracts heat Qc from a cold reservoir at...
3.7K
01:15Statements of the Second Law of Thermodynamics
4.9K
The second law of thermodynamics can be stated in several different ways, and all of them can be shown to imply the others. The Clausius’ statement of the second law of thermodynamics is based on the irreversibility of spontaneous heat flow. It states that heat will not flow from the colder body to the hotter body unless some other process is involved. Additionally, as per the Kelvin’s statement, it is impossible to convert the heat from a single source into work without any other...
4.9K
01:10Heat Engines
3.5K
A heat engine is a device used to extract heat from a source and then convert it into mechanical work used for various applications. For example, a steam engine on an old-style train can produce the work needed for driving the train.
Whenever we consider heat engines (and associated devices such as refrigerators and heat pumps), we do not use the standard sign convention for heat and work. For convenience, we assume that the symbols Qh, Qc, and W represent only the amounts of heat transferred...
Whenever we consider heat engines (and associated devices such as refrigerators and heat pumps), we do not use the standard sign convention for heat and work. For convenience, we assume that the symbols Qh, Qc, and W represent only the amounts of heat transferred...
3.5K
01:18Entropy
3.5K
The first law of thermodynamics is quantitatively formulated via an equation relating the internal energy of a system, the heat exchanged by it, and the work done on it. A quantitative formulation of the second law of thermodynamics leads to defining a state function, the entropy.
When an ideal gas expands isothermally, the disorder in the gas increases. From the molecular perspective, the gas molecules have more volume to move around in.
Consider an infinitesimal step in the expansion, which...
When an ideal gas expands isothermally, the disorder in the gas increases. From the molecular perspective, the gas molecules have more volume to move around in.
Consider an infinitesimal step in the expansion, which...
3.5K
02:39Entropy
34.8K
Salt particles that have dissolved in water never spontaneously come back together in solution to reform solid particles. Moreover, a gas that has expanded in a vacuum remains dispersed and never spontaneously reassembles. The unidirectional nature of these phenomena is the result of a thermodynamic state function called entropy (S). Entropy is the measure of the extent to which the energy is dispersed throughout a system, or in other words, it is proportional to the degree of disorder of a...
34.8K