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Related Concept Videos

Entropy02:39

Entropy

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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...
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Entropy01:18

Entropy

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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...
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Entropy and the Second Law of Thermodynamics01:20

Entropy and the Second Law of Thermodynamics

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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...
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Second Law of Thermodynamics02:49

Second Law of Thermodynamics

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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...
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Second Law of Thermodynamics00:53

Second Law of Thermodynamics

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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...
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Gibbs Free Energy02:39

Gibbs Free Energy

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One of the challenges of using the second law of thermodynamics to determine if a process is spontaneous is that it requires measurements of the entropy change for the system and the entropy change for the surroundings. An alternative approach involving a new thermodynamic property defined in terms of system properties only was introduced in the late nineteenth century by American mathematician Josiah Willard Gibbs. This new property is called the Gibbs free energy (G) (or simply the free...
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Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators
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Pseudo-Entropy in Free Quantum Field Theories.

Ali Mollabashi1,2, Noburo Shiba2, Tadashi Takayanagi2,3,4

  • 1Max-Planck-Institut for Physics, Werner-Heisenberg-Institut, 80805 Munich, Germany.

Physical Review Letters
|March 12, 2021
PubMed
Summary
This summary is machine-generated.

Pseudo-entropy, a generalization of entanglement entropy, reveals universal properties in quantum field theories. Numerical calculations show novel saturation and non-positivity behaviors, suggesting its use as a quantum order parameter.

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Area of Science:

  • Quantum Field Theory
  • Condensed Matter Physics

Background:

  • Pseudo-entropy generalizes entanglement entropy, incorporating both initial and final states.
  • It possesses a simple gravity dual, making it a subject of theoretical interest.

Purpose of the Study:

  • To investigate the fundamental properties of pseudo-entropy in quantum field theories.
  • To numerically calculate pseudo-entropy in two-dimensional free-scalar field theories and the Ising spin chain.
  • To identify universal characteristics and potential applications of pseudo-entropy.

Main Methods:

  • Extended the Gaussian method to calculate pseudo-entropy in free-scalar theories with mass (m) and dynamical exponent (z).
  • Performed numerical computations on two-dimensional free-scalar field theories.
  • Analyzed the Ising spin chain to explore pseudo-entropy's role as a quantum order parameter.

Main Results:

  • Discovered two novel properties of pseudo-entropy: saturation behavior and non-positivity of its difference from averaged entanglement entropy.
  • Confirmed an area law behavior for pseudo-entropy.
  • Numerical results for the Ising chain suggest pseudo-entropy can distinguish between quantum phases.

Conclusions:

  • Pseudo-entropy exhibits universal properties in quantum field theories, including saturation and non-positivity.
  • Pseudo-entropy adheres to an area law.
  • Pseudo-entropy shows promise as a new quantum order parameter for phase detection.