Bose-Einstein Condensation of a Stochastic Liquid

The Bogoliubov-Lee-Huang theory of superfluid 4He is modified by introducing an effective temperature scale (which accounts for the deep well of the interatomic potential) and by incorporating into the Hamiltonian a stochastic term Vl, which simulates liquidity of HeI and liquidity of the normal and superfluid component of HeII. Vl depends on two independent random angles αn, αs ∈ [0, π], which characterize the locally ordered motion of the two fluids (the normal fluid and superfluid) comprising HeII. The resulting thermodynamics improves the thermodynamic functions and excitation spectrum Ep(αn, αs) of the superfluid phase, obtained previously, leaving the heat capacity CV (T) of the normal phase, with a minimum at Tmin > 2.17K, unchanged. The theoretical velocity of sound in HeII, equal to the initial slope of Ep(π, π), agrees with experiment.

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DRESSED BOSONS AND EFFECTIVE TEMPERATURE — A FORMALISM FOR HELIUM II

International Journal of Modern Physics B ◽

10.1142/s0217979212501196 ◽

2012 ◽

Vol 26 (20) ◽

pp. 1250119 ◽

Cited By ~ 3

Author(s):

JAN MAĆKOWIAK ◽

DAWID BORYCKI

Keyword(s):

Heat Capacity ◽

Effective Temperature ◽

Hard Sphere ◽

Temperature Scale ◽

Interatomic Potential ◽

Bose Gas ◽

Quantum Gas ◽

Normal Fluid ◽

Saturated Vapour Pressure ◽

Experimental Heat

The thermodynamics of a free Bose gas with effective temperature scale [Formula: see text] and hard-sphere Bose gas with the [Formula: see text] scale are studied. [Formula: see text] arises as the temperature experienced by a single particle in a quantum gas with 2-body harmonic oscillator interaction V osc , which at low temperatures is expected to simulate, almost correctly, the attractive part of the interatomic potential V He between 4 He atoms. The repulsive part of V He is simulated by a hard-sphere (HS) potential. The thermodynamics of this system of HS bosons, with the [Formula: see text] temperature scale (HSET), and particle mass and density equal to those of 4 He , is investigated, first, by the Bogoliubov–Huang method and next by an improved version of this method, which describes He II in terms of dressed bosons and takes approximate account of those terms of the 2-body repulsion which are linear in the zero-momentum Bose operators a0, [Formula: see text] (originally rejected by Bogoliubov). Theoretical heat capacity CV(T) exhibits good agreement, below 1.9 K, with the experimental heat capacity graph observed in 4 He at saturated vapour pressure. The phase transition to the He II phase, occurs in the HSET at Tλ = 2.17 K, and is accompanied, in the modified HSET version, by a singularity of CV(T). The fraction of atoms in the momentum condensate at 0 K equals 8.86% and agrees with other theoretical estimates for He II. The fraction of normal fluid falls to 8.37% at 0 K which exceeds the value 0% found in He II.

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EXCITATIONS IN CONFINED LIQUID 4He

Modern Physics Letters B ◽

10.1142/s0217984905008189 ◽

2005 ◽

Vol 19 (04) ◽

pp. 135-156

Author(s):

FRANCESCO ALBERGAMO

Keyword(s):

Saturated Vapor Pressure ◽

Saturated Vapor ◽

Finite Size ◽

Einstein Condensation ◽

Normal Fluid ◽

Finite Size Effects ◽

Bose Einstein Condensation ◽

Bulk System ◽

Bose Einstein ◽

The Relationship

The spectacular properties of liquid helium at low temperature are generally accepted as the signature of the bosonic nature of this system. Particularly the superfluid phase is identified with a Bose–Einstein condensed fluid. However, the relationship between the superfluidity and the Bose–Einstein condensation is still largely unknown. Studying a perturbed liquid 4 He system would provide information on the relationship between the two phenomena. Liquid 4 He confined in porous media provides an excellent example of a boson system submitted to disorder and finite-size effects. Much care should be paid to the sample preparation, particularly the confining condition should be defined quantitatively. To achieve homogeneous confinement conditions, firstly a suitable porous sample should be selected, the experiments should then be conducted at a lower pressure than the saturated vapor pressure of bulk helium. Several interesting effects have been shown in confined 4 He samples prepared as described above. Particularly we report the observation of the separation of the superfluid-normal fluid transition temperature, T c , from the temperature at which the Bose–Einstein condensation is believed to start, T BEC , the existence of metastable densities for the confined liquid accessible to the bulk system as a short-lived metastable state only and strong clues for a finite lifetime of the elementary excitations at temperatures as low as 0.4 K .

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Stochastic Bose superfluid

International Journal of Modern Physics B ◽

10.1142/s0217979215500447 ◽

2015 ◽

Vol 29 (07) ◽

pp. 1550044 ◽

Cited By ~ 2

Author(s):

Jan Maćkowiak

Keyword(s):

Heat Capacity ◽

Liquid Phase ◽

Convex Function ◽

Temperature Scale ◽

Reduction Procedure ◽

Atomic Momentum ◽

Stochastic Term ◽

State Of Matter ◽

Ordered Motion ◽

Bose Superfluid

The ideas of Mitus et al. are exploited to define the liquid state as a state of matter, in which particles perform locally ordered motion. The presence of the liquid phase is accounted for by a stochastic term in the Hamiltonian, which simulates this property of a liquid. The Bogoliubov–Lee–Huang theory of He II, recently modified by use of effective temperature scale and more stringent reduction procedure (DHSET theory) is extended, by incorporating this term into the 4 He Hamiltonian. The resulting thermodynamics accounts for effects, which are beyond the scope of other He I and He II theories, e.g., the atomic momentum distribution and excitation spectrum have the form of diffused bands, similarly as in He II; the He I, theoretical heat capacity CV(T) is a convex function, with a minimum at T min > Tλ, which qualitatively simulates experimental He I heat capacity. Other thermodynamic functions are similar to those of DHSET theory.

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Is FeSe a superconductor in the Bose-Einstein condensation limit?

10.36471/jccm_november_2017_01 ◽

2017 ◽

Keyword(s):

Einstein Condensation ◽

Bose Einstein Condensation ◽

Bose Einstein

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Strong Coupling: Polariton Bose Condensation

10.1093/oso/9780198782995.003.0008 ◽

2017 ◽

Author(s):

Alexey V. Kavokin ◽

Jeremy J. Baumberg ◽

Guillaume Malpuech ◽

Fabrice P. Laussy

Keyword(s):

Strong Coupling ◽

Room Temperature ◽

Elevated Temperatures ◽

Dissipative System ◽

Bose Condensation ◽

Einstein Condensation ◽

Strong Coupling Regime ◽

Stimulated Scattering ◽

Exciton Polaritons ◽

Bose Einstein

In this Chapter we address the physics of Bose-Einstein condensation and its implications to a driven-dissipative system such as the polariton laser. We discuss the dynamics of exciton-polaritons non-resonantly pumped within a microcavity in the strong coupling regime. It is shown how the stimulated scattering of exciton-polaritons leads to formation of bosonic condensates that may be stable at elevated temperatures, including room temperature.

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Systems with Condensates and Pairing

10.1093/oso/9780198797241.003.0012 ◽

2018 ◽

Author(s):

Klaus Morawetz

Keyword(s):

Critical Parameters ◽

Einstein Condensation ◽

Cooper Pairs ◽

Pair Breaking ◽

Systematic Theory ◽

Bose Einstein Condensation ◽

T Matrix ◽

The Stability ◽

Bose Einstein

The Bose–Einstein condensation and appearance of superfluidity and superconductivity are introduced from basic phenomena. A systematic theory based on the asymmetric expansion of chapter 11 is shown to correct the T-matrix from unphysical multiple-scattering events. The resulting generalised Soven scheme provides the Beliaev equations for Boson’s and the Nambu–Gorkov equations for fermions without the usage of anomalous and non-conserving propagators. This systematic theory allows calculating the fluctuations above and below the critical parameters. Gap equations and Bogoliubov–DeGennes equations are derived from this theory. Interacting Bose systems with finite temperatures are discussed with successively better approximations ranging from Bogoliubov and Popov up to corrected T-matrices. For superconductivity, the asymmetric theory leading to the corrected T-matrix allows for establishing the stability of the condensate and decides correctly about the pair-breaking mechanisms in contrast to conventional approaches. The relation between the correlated density from nonlocal kinetic theory and the density of Cooper pairs is shown.

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Dynamics of the Creation of a Rotating Bose–Einstein Condensation by Two Photon Raman Transition Using a Laguerre–Gaussian Laser Pulse

Atoms ◽

10.3390/atoms9010014 ◽

2021 ◽

Vol 9 (1) ◽

pp. 14

Author(s):

Koushik Mukherjee ◽

Soumik Bandyopadhyay ◽

Dilip Angom ◽

Andrew M. Martin ◽

Sonjoy Majumder

Keyword(s):

Interaction Strength ◽

Transition Process ◽

Laser Pulses ◽

Harmonic Trap ◽

Einstein Condensation ◽

Raman Transition ◽

Two Photon ◽

Final Population ◽

The Creation ◽

Bose Einstein

We present numerical simulations to unravel the dynamics associated with the creation of a vortex in a Bose–Einstein condensate (BEC), from another nonrotating BEC using two-photon Raman transition with Gaussian (G) and Laguerre–Gaussian (LG) laser pulses. In particular, we consider BEC of Rb atoms at their hyperfine ground states confined in a quasi two dimensional harmonic trap. Optical dipole potentials created by G and LG laser pulses modify the harmonic trap in such a way that density patterns of the condensates during the Raman transition process depend on the sign of the generated vortex. We investigate the role played by the Raman coupling parameter manifested through dimensionless peak Rabi frequency and intercomponent interaction on the dynamics during the population transfer process and on the final population of the rotating condensate. During the Raman transition process, the two BECs tend to have larger overlap with each other for stronger intercomponent interaction strength.

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