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Related Concept Videos

Second Law of Thermodynamics02:49

Second Law of Thermodynamics

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...
Second Law of Thermodynamics00:53

Second Law of Thermodynamics

The Second Law of Thermodynamics states that entropy, or the amount of disorder in a system, increases each time energy is transferred or transformed. Each energy transfer results in a certain amount of energy that is lost—usually in the form of heat—that increases the disorder of the surroundings. This can also be demonstrated in a classic food web. Herbivores harvest chemical energy from plants and release heat and carbon dioxide into the environment. Carnivores harvest the chemical energy...
The de Broglie Wavelength02:32

The de Broglie Wavelength

In the macroscopic world, objects that are large enough to be seen by the naked eye follow the rules of classical physics. A billiard ball moving on a table will behave like a particle; it will continue traveling in a straight line unless it collides with another ball, or it is acted on by some other force, such as friction. The ball has a well-defined position and velocity or well-defined momentum, p = mv, which is defined by mass m and velocity v at any given moment. This is the typical...
The Uncertainty Principle04:08

The Uncertainty Principle

Werner Heisenberg considered the limits of how accurately one can measure properties of an electron or other microscopic particles. He determined that there is a fundamental limit to how accurately one can measure both a particle’s position and its momentum simultaneously. The more accurate the measurement of the momentum of a particle is known, the less accurate the position at that time is known and vice versa. This is what is now called the Heisenberg uncertainty principle. He mathematically...
Entropy Change in Reversible Processes01:10

Entropy Change in Reversible Processes

In the Carnot engine, which achieves the maximum efficiency between two reservoirs of fixed temperatures, the total change in entropy is zero. The observation can be generalized by considering any reversible cyclic process consisting of many Carnot cycles. Thus, it can be stated that the total entropy change of any ideal reversible cycle is zero.
The statement can be further generalized to prove that entropy is a state function. Take a cyclic process between any two points on a p-V diagram.
Entropy and the Second Law of Thermodynamics01:20

Entropy and the Second Law of Thermodynamics

The second law of thermodynamics can be stated quantitatively using the concept of entropy. Entropy is the measure of disorder of the system.
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Related Experiment Video

Updated: May 24, 2026

Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators
09:23

Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators

Published on: May 30, 2014

Quantum and classical fluctuation theorems from a decoherent histories, open-system analysis.

Y Subaşı1, B L Hu

  • 1Maryland Center for Fundamental Physics and Joint Quantum Institute, University of Maryland, College Park, Maryland 20742, USA.

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|March 10, 2012
PubMed
Summary

This study analyzes quantum system work distributions and free energy using quantum Brownian motion, confirming fluctuation theorems (FTs) at high temperatures. It clarifies FT applicability in open quantum systems, especially at low temperatures.

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Last Updated: May 24, 2026

Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators
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Published on: December 4, 2017

Area of Science:

  • Quantum thermodynamics
  • Statistical mechanics
  • Open quantum systems

Background:

  • Quantum systems interact with environments, leading to complex dynamics.
  • Fluctuation theorems (FTs) describe nonequilibrium processes in classical and quantum systems.
  • Understanding work and free energy in quantum systems is crucial for thermodynamics.

Purpose of the Study:

  • To analyze nonequilibrium work distribution and free energy difference in quantum systems interacting with general environments.
  • To validate Jarzynski equality and Crooks' fluctuation theorem (FTs) using a quantum Brownian motion model.
  • To explore the role of decoherence and temperature on FT validity in open quantum systems.

Main Methods:

  • First-principles analysis of quantum Brownian motion model.
  • Application of decoherent histories framework for quantum trajectories.
  • Environment-induced decoherence for assessing noise strength.
  • Solving Langevin equations for stochastic dynamics.

Main Results:

  • Formal expressions for quantities in FTs derived from Langevin equation solutions.
  • Explicit proof of FT validity in the high-temperature limit.
  • Identification of conditions and parameter ranges where FTs may differ at low temperatures.

Conclusions:

  • The quantum Brownian motion model provides a microphysics basis for quantum FTs.
  • Decoherence is essential for defining work and using trajectories in open quantum systems.
  • This approach offers advantages over phenomenological models for studying quantum thermodynamics.