Related Experiment Video
Updated: Apr 10, 2026
11:03
An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
Published on: December 4, 2017
9.1K
Comment on "Similarity between quantum mechanics and thermodynamics: Entropy, temperature, and Carnot cycle"
L A González-Díaz1, S Díaz-Solórzano2
1Laboratorio de Dinámica No Lineal y Sistemas Complejos, Centro de Física, Instituto Venezolano de Investigaciones Científicas, Caracas 1020-A, Venezuela.
Summary
This study refutes claims about the quantum Carnot cycle, proving that the initial state is mixed, not pure, due to energy measurement. This finding impacts quantum thermodynamics research.
Area of Science:
- Quantum thermodynamics
- Statistical mechanics
- Quantum information theory
Background:
- The quantum Carnot cycle is a theoretical framework for quantum heat engines.
- A previous study claimed the initial state of a two-state quantum system in a Carnot cycle is pure, becoming mixed upon imposing Clausius equality.
Discussion:
- This paper challenges the purity assumption of the initial state in the quantum Carnot cycle.
- The analysis focuses on a simple two-state model of a particle in a one-dimensional infinite potential well.
- The core argument revolves around the effect of energy measurement on the quantum state.
Key Insights:
- The initial state of the quantum Carnot cycle is demonstrated to be mixed, not pure.
- Energy measurement inherently introduces mixedness to the quantum state at the cycle's start.
- The claim that Clausius equality transmutes a pure state to a mixed state is shown to be incorrect.
Outlook:
- Re-evaluation of quantum heat engine models considering the mixed nature of initial states.
- Implications for understanding thermodynamic processes at the quantum level.
- Further research into the role of measurement in quantum thermodynamics.
More Related Videos
Related Concept Videos
01:14The Entropy as a State Function
115
Consider an arbitrary process that moves between two specific states (A and B) in a cyclic manner. This process is reversible and broken down into smaller parts that each follow a Carnot cycle. A Carnot cycle has two isothermal (constant temperature) processes. During these processes, the ratio of the amount of heat transferred to their respective temperature remains constant. The other two processes in the Carnot cycle are also reversible but adiabatic, which means they occur without any heat...
115
01:20Entropy and the Second Law of Thermodynamics
5.3K
The second law of thermodynamics can be stated quantitatively using the concept of entropy. Entropy is the measure of disorder of the system.
The relation between entropy and disorder can be illustrated with the example of the phase change of ice to water. In ice, the molecules are located at specific sites giving a solid state, whereas, in a liquid form, these molecules are much freer to move. The molecular arrangement has therefore become more randomized. Although the change in average...
The relation between entropy and disorder can be illustrated with the example of the phase change of ice to water. In ice, the molecules are located at specific sites giving a solid state, whereas, in a liquid form, these molecules are much freer to move. The molecular arrangement has therefore become more randomized. Although the change in average...
5.3K
01:26Entropy and the Second Law of Thermodynamics
306
Consider an isolated system in which a hot object is placed in contact with a cold one. This is an irreversible process that eventually leads both objects to reach the same equilibrium temperature. It is crucial to note that the constituents of any substance exhibit increased disorder at higher temperatures. As a cold substance absorbs heat, its constituents become more disordered. The energy transfer from a hotter object to a cooler one increases the system's disorder or randomness. This...
306
01:18Entropy
3.9K
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...
3.9K
02:39Entropy
38.1K
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...
38.1K
02:49Second Law of Thermodynamics
28.6K
In the quest to identify a property that may reliably predict the spontaneity of a process, a promising candidate has been identified: entropy. Processes that involve an increase in entropy of the system (ΔS > 0) are very often spontaneous; however, examples to the contrary are plentiful. By expanding consideration of entropy changes to include the surroundings, a significant conclusion regarding the relation between this property and spontaneity may be reached. In thermodynamic models, the...
28.6K