Related Experiment Video
Updated: May 11, 2026
07:17
Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry
Published on: August 1, 2017
Efficiency at maximum power of a heat engine working with a two-level atomic system.
Rui Wang1, Jianhui Wang, Jizhou He
1Department of Physics, Nanchang University, Nanchang 330031, China.
Summary
This study explores a quantum heat engine
Area of Science:
- Quantum Thermodynamics
- Atomic Physics
- Statistical Mechanics
Background:
- Quantum heat engines offer a novel approach to energy conversion at the nanoscale.
- Understanding finite-time operation is crucial for practical applications.
Purpose of the Study:
- To analyze the efficiency at maximum power output (EMP) of a quantum Otto cycle.
- To investigate the impact of process durations and internal friction on EMP.
Main Methods:
- Modeling a quantum heat engine using a two-level atomic system.
- Numerical analysis of quantum adiabatic and isochoric processes.
- Optimization of power output with respect to system frequencies.
Main Results:
- Derived an analytic upper bound for EMP based on Carnot efficiency, independent of internal friction.
- Confirmed analytic results with numerical simulations.
- Showed that internal friction reduces EMP.
Conclusions:
- The quantum Otto cycle's EMP is fundamentally limited by Carnot efficiency.
- Finite-time operation and internal friction significantly impact quantum heat engine performance.
Related Concept Videos
01:30The Carnot Cycle
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...
01:26Carnot Cycle and Efficiency
The Second Law of Thermodynamics asserts that it's impossible for any heat engine to achieve 100% efficiency. While contemplating the maximum possible efficiency, Nicolas Sadi Carnot conceptualized an ideal heat engine. This engine gets its energy from a high-temperature reservoir. It then performs some work and releases the remaining energy into a low-temperature reservoir.The Carnot cycle, named after Sadi Carnot, is fully reversible. The cycle consists of four distinct stages. In the first...
01:10Heat Engines
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...
01:20The Carnot Cycle and the Second Law of Thermodynamics
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...
01:16Efficiency of The Carnot Cycle
The hypothetical Carnot cycle consists of an ideal gas subjected to two isothermal and two adiabatic processes. Since the internal energy of an ideal gas depends only on its temperature, which is the same before and after the completion of the Carnot cycle, there is no change in its internal energy. Hence, using the first law of thermodynamics, the total heat exchanged by the ideal gas equals the total work done. Thus, we can quantify the efficiency of the Carnot cycle via the heat exchanged...
01:18Entropy
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...