Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review

Coherent States in the Theory of Superfluidity

James S. Langer

Published Mar 5, 1968• 89 citations
Publisher

Abstract

It is shown that the coherent-state representation of a many-boson wave function may be identified with the order-parameter function conventionally used to describe a superfluid. The statistical mechanics of the many-boson system is reformulated in terms of the coherent states, and a theory of the Ginzburg-Landau form is recovered in an obvious approximation. The formalism is particularly useful for describing metastable states of finite superflow and the fluctuations which may cause spontaneous decay of such states.

DOI
10.1103/physrev.167.183

Related papers

Coherent States in the Theory of Superfluidity. II. Fluctuations and Irreversible Processes

James S. Langer

The coherent-state formalism is used to develop a theory of fluctuations and irreversible processes in a superfluid Bose system. Equations of motion for the density matrix are derived both for the case of an isolated system and for the system in interaction with a heat bath. The formalism allows one to go easily to the classical limit and thus to obtain equations for the probability distribution of the superfluid order parameter. The results are in a form suitable for the calculation of the decay of superflow near the $\ensuremath{\lambda}$ point and other similar phenomena.

Physical Review•Aug 5, 1969•23 citations

The macroscopic coherent state

James F. Annett

Abstract We have seen in the previous chapters that the concept of the macroscopic wave functionΨ(r), is central to understanding atomic Bose–Einstein condensates (BEC), superfluid He, and even superconductivity within the Ginzburg–Landau (GL) theory. But the connection between these ideas is not at all clear, since the atom condensates and He are bosonic systems, while super-conductivity is associated with the conduction electrons in metals which are fermions. The physical meaning of the GL order parameter was not explained until after 1957 when Bardeen Cooper and Schrieffer (BCS) published the first truly microscopic theory of superconductivity. Soon afterward the connection was finally established by Gor’ kov. He was able to show that, at least in the range of temperatures near Tc, the GL theory can indeed be derived from the BCS theory. Furthermore this provides a physical interpretation of the nature of the order parameter. Essentially it is describing a macroscopic wave function, or condensate, of Cooper pairs.

•Mar 25, 2004•0 citations

Strongly Correlated Bosons on a Lattice: A Slave-Boson Approach

K. Ziegler

The grand canonical system of hard-core bosons, subject to thermal fluctuations, is studied on a lattice. Starting from the slave-boson representation we derive an effective Ginzburg-Landau functional for the superfluid order parameter. The order parameter field is a collective field constructed from the slave-boson fields for empty and singly occupied sites. We find two phase transitions; one from a normal fluid at high density to a superfluid and another one from the superfluid to a normal fluid at low density.

Europhysics Letters (EPL)•Sep 1, 1993•16 citations

Superfluidity

Лев П. Питаевский, S. Stringari

Abstract This chapter presents a general discussion of the phenomenon of superfluidity, starting from the famous Landau criterion for the critical velocity. The Landau expression for the normal (non-superfluid) component of the gas, expressed in terms of the elementary excitations of the system, is derived. The relationship between Bose–Einstein condensation and the phenomenon of superfluidity is outlined, with special focus on the role played by the phase of the order parameter, whose gradient fixes the velocity of the superfluid. The chapter derives the hydrodynamic equations of superfluids at both zero and finite temperatures and discuss the solutions for first and second sound. The formalism of quantum hydrodynamics is presented, with an application to the Beliaev decay of phonons and to the calculation of the fluctuations of the phase. It also discusses the consequences for superfluidity on the rotational properties and the spatial structure of vortex lines.

•Jan 1, 2016•6 citations

Coherent Phonon States and Long-Range Order in Two-Dimensional Bose Systems

Gordon J. Lasher

At any finite temperature, the correlation function $〈{\ensuremath{\psi}}^{\ifmmode\dagger\else\textdagger\fi{}}(\mathcal{r})\ensuremath{\psi}(0)〉$ of a two-dimensional Bose system is known to approach zero as the separation $\mathcal{r}$ approaches infinity. This paper is devoted to supporting the point of view that superfluid phenomena may still persist in such a system. To describe the low-temperature behavior of a condensed two-dimensional Bose system, we use a coherent-state representation of the low-lying phonon excitations. The expectation of the particle field operator $〈\ensuremath{\psi}(\mathcal{r})〉$ in a coherent phonon state of the system is shown to be a well-defined function. This function has only small fluctuations in its magnitude and, therefore, it is possible to make the usual arguments for superfluid behavior based on the existence of the condensate wave function. The large phase fluctuations of the function, when the coherentphonon states are collected into the thermal ensemble, give rise to the spatial decay of the correlation function or reduced density matrix $〈{\ensuremath{\psi}}^{+}(\mathcal{r})\ensuremath{\psi}(0)〉$. It is concluded that two-dimensional Bose systems are superfluid at sufficiently low temperatures, even in the inifinite-volume limit. An analogous argument would indicate the possibility of superconductivity in a two-dimensional Fermi system.

Physical Review•Aug 5, 1968•10 citations

Gross-Pitaevskii Equation for a Strongly Interacting Superfluid Boson System

Donald H. Kobe

The Gross-Pitaevskii equation for the order parameter of a superfluid boson system is derived in a form which is applicable to a system in which the two-body potential has a strong repulsive core, as is the case for liquid helium. The equation of motion for the order parameter, defined as the matrix element of the field annihilation operator between the states of an ($N\ensuremath{-}1$)-particle and an $N$-particle system, is obtained. The term describing the average potential due to the other particles is expanded in a perturbation series, in which the coherentstate representation is used. The resulting expansion is the same as using the Bogoliubov approximation and Wick's theorem, and shows that the Bogoliubov expansion is exact in the limit of an infinite number of particles. The perturbation expansion is partially resummed to give a Hartree field in which the potential has been replaced by the $T$ matrix, which gives a finite average effective field.

Physical Review A•Feb 1, 1972•5 citations
It is shown that the coherent-state representation of a many-boson wave function may be identified with the order-parameter function conventionally used to describe a superfluid. The statistical mechanics of the many-boson system is reformulated in terms of the coherent states, and a theory of the Ginzburg-Landau form is recovered in an obvious approximation. The formalism is particularly useful for describing metastable states of finite superflow and the fluctuations which may cause spontaneous decay of such states.
The coherent-state formalism is used to develop a theory of fluctuations and irreversible processes in a superfluid Bose system. Equations of motion for the density matrix are derived both for the case of an isolated system and for the system in interaction with a heat bath. The formalism allows one to go easily to the classical limit and thus to obtain equations for the probability distribution of the superfluid order parameter. The results are in a form suitable for the calculation of the decay of superflow near the $\ensuremath{\lambda}$ point and other similar phenomena.
Abstract We have seen in the previous chapters that the concept of the macroscopic wave functionΨ(r), is central to understanding atomic Bose–Einstein condensates (BEC), superfluid He, and even superconductivity within the Ginzburg–Landau (GL) theory. But the connection between these ideas is not at all clear, since the atom condensates and He are bosonic systems, while super-conductivity is associated with the conduction electrons in metals which are fermions. The physical meaning of the GL order parameter was not explained until after 1957 when Bardeen Cooper and Schrieffer (BCS) published the first truly microscopic theory of superconductivity. Soon afterward the connection was finally established by Gor’ kov. He was able to show that, at least in the range of temperatures near Tc, the GL theory can indeed be derived from the BCS theory. Furthermore this provides a physical interpretation of the nature of the order parameter. Essentially it is describing a macroscopic wave function, or condensate, of Cooper pairs.
The grand canonical system of hard-core bosons, subject to thermal fluctuations, is studied on a lattice. Starting from the slave-boson representation we derive an effective Ginzburg-Landau functional for the superfluid order parameter. The order parameter field is a collective field constructed from the slave-boson fields for empty and singly occupied sites. We find two phase transitions; one from a normal fluid at high density to a superfluid and another one from the superfluid to a normal fluid at low density.
Abstract This chapter presents a general discussion of the phenomenon of superfluidity, starting from the famous Landau criterion for the critical velocity. The Landau expression for the normal (non-superfluid) component of the gas, expressed in terms of the elementary excitations of the system, is derived. The relationship between Bose–Einstein condensation and the phenomenon of superfluidity is outlined, with special focus on the role played by the phase of the order parameter, whose gradient fixes the velocity of the superfluid. The chapter derives the hydrodynamic equations of superfluids at both zero and finite temperatures and discuss the solutions for first and second sound. The formalism of quantum hydrodynamics is presented, with an application to the Beliaev decay of phonons and to the calculation of the fluctuations of the phase. It also discusses the consequences for superfluidity on the rotational properties and the spatial structure of vortex lines.
At any finite temperature, the correlation function $〈{\ensuremath{\psi}}^{\ifmmode\dagger\else\textdagger\fi{}}(\mathcal{r})\ensuremath{\psi}(0)〉$ of a two-dimensional Bose system is known to approach zero as the separation r\mathcal{r}r approaches infinity. This paper is devoted to supporting the point of view that superfluid phenomena may still persist in such a system. To describe the low-temperature behavior of a condensed two-dimensional Bose system, we use a coherent-state representation of the low-lying phonon excitations. The expectation of the particle field operator $〈\ensuremath{\psi}(\mathcal{r})〉$ in a coherent phonon state of the system is shown to be a well-defined function. This function has only small fluctuations in its magnitude and, therefore, it is possible to make the usual arguments for superfluid behavior based on the existence of the condensate wave function. The large phase fluctuations of the function, when the coherentphonon states are collected into the thermal ensemble, give rise to the spatial decay of the correlation function or reduced density matrix $〈{\ensuremath{\psi}}^{+}(\mathcal{r})\ensuremath{\psi}(0)〉$. It is concluded that two-dimensional Bose systems are superfluid at sufficiently low temperatures, even in the inifinite-volume limit. An analogous argument would indicate the possibility of superconductivity in a two-dimensional Fermi system.
The Gross-Pitaevskii equation for the order parameter of a superfluid boson system is derived in a form which is applicable to a system in which the two-body potential has a strong repulsive core, as is the case for liquid helium. The equation of motion for the order parameter, defined as the matrix element of the field annihilation operator between the states of an ($N\ensuremath{-}1$)-particle and an NNN-particle system, is obtained. The term describing the average potential due to the other particles is expanded in a perturbation series, in which the coherentstate representation is used. The resulting expansion is the same as using the Bogoliubov approximation and Wick's theorem, and shows that the Bogoliubov expansion is exact in the limit of an infinite number of particles. The perturbation expansion is partially resummed to give a Hartree field in which the potential has been replaced by the TTT matrix, which gives a finite average effective field.