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Nguyen Van Thu

Publications and source records attributed to Nguyen Van Thu.

At least 19 recordsLinked to original sources
arXiv2026

Wall tension of a Bose-Einstein condensate: Effects of quantum fluctuations and finite-range interactions

We investigate the effects of quantum fluctuations (QFs) and finite-range interatomic interactions on the ground state and wall tension of a Bose-Einstein condensate (BEC) at zero temperature by means of modified Gross-Pitaevskii equations. The QFs are shown to stiffen the condensate near the hard wall, narrowing the density profile and raising the wall tension above its mean-field value by an amount proportional to square-root of the gas parameter. Finite-range corrections always reduces the wall tension relative to the QFs correction value regardless of the effective range. We find the ordering $γ_0 < γ_{\rm II} < γ_{\rm I}$ in the dilute regime and identify a crossover condition under which the two beyond-mean-field contributions mutually cancel. These results provide an experimentally accessible way for probing beyond-LHY physics through precision measurements of the wall tension in ultracold Bose gases.

cond-mat.quant-gas↗
arXiv2026

Influence of intraspecies interactions on the nucleation and wetting phase diagram in dilute ternary Bose-Einstein condensates

Within the framework of Gross-Pitaevskii theory, we investigate the effects of intraspecies interactions on the nucleation transition and the wetting phase diagram of dilute ternary Bose-Einstein condensate in the regime of strong segregation between two components. The analyses are carried out using both the analytical double-parabola approximation (DPA) and numerical computations. Our results show that the DPA provides a reliable approximation for describing the nucleation transition. For the wetting phase diagram, we find that the DPA is in excellent agreement with numerical results in symmetric systems, particularly in the completely symmetric case, whereas it fails to provide an adequate description for asymmetric systems.

cond-mat.quant-gas↗
arXiv2025

Nucleation and wetting transitions in three-component Bose-Einstein condensates in Gross-Pitaevskii theory: exact results

Nucleation and wetting transitions are studied in a three-component Bose-Einstein condensate mixture within Gross-Pitaevskii theory. For special cases of intermediate segregation between components 1 and 2, the nucleation phase transition of a surfactant film of component 3 is obtained by exact solution. Additional exact results for the nucleation transition are derived in the limit of strong segregation between components 1 and 2. In this limit the exact first-order wetting phase boundary is obtained using analytical and numerical methods, and is contrasted with the exact nucleation and wetting phase boundary derived previously for a two-component Bose-Einstein condensate mixture at a hard optical wall. Exact results for the three-component mixture are compared with results from the double-parabola approximation used in an earlier work.

cond-mat.quant-gas↗
arXiv2025

Nucleation line in three-component Bose-Einstein condensates in Gross-Pitaevskii theory

By means of Gross-Pitaevskii theory we investigate the possibility of wetting phase transition in three-component Bose-Einstein condensates within the strong segregation between components 1 and 2. Third component plays the role of a surfactant, which can wet the interface formed by components 1 and 2. The case of symmetry of components 1 and 2, the equation for nucleation line and wetting phase diagram are studied. By linearizing the set of three-coupled Gross-Pitaevskii equations, the wave functions of the components are found. An analytical approximation for the surfactant thickness in the prewetting phase is presented. The results indicate that the surfactant thickness in the prewtting phase varies linearly with the chemical potential ratio in the logarithmic scale.

cond-mat.quant-gas↗
arXiv2025

Transition temperature of a two-component Bose-Einstein condensates in improved Hartree-Fock approximation

In this study, we investigate the transition temperature of a two-component Bose-Einstein condensates by means of Cornwall-Jackiw-Tomboulis effective action formalism within the framework of the improved Hartree-Fock approximation. Influence of intra- and interspecies interactions as well as of the thermal fluctuations to the transition temperature are considered up to leading order of the gas parameters and scattering lengths.

cond-mat.quant-gas↗
arXiv2025

Transition temperature and thermodynamic properties of homogeneous weakly interacting Bose gas in self-consistent Popov approximation

This study utilizes the Cornwall-Jackiw-Tomboulis effective action approach combined with variational perturbation theory to investigate the relative shift in the transition temperature of a homogeneous, repulsive, weakly interacting Bose gas compared to that of an ideal Bose gas. By applying both the one-loop and self-consistent Popov approximations, the universal form of the relative shift in the transition temperature is derived, demonstrating its proportionality to the s-wave scattering length. The results exhibit excellent agreement with those obtained from precise Monte Carlo simulations. Furthermore, the zero-point energy and various thermodynamic properties are examined in both the condensed and normal phases. A comparison with experimental data reveals an excellent agreement, further validating the findings.

cond-mat.quant-gas↗
arXiv2025

Three-component Bose-Einstein condensates and wetting without walls

In previous work within Gross-Pitaevskii (GP) theory for ultracold gases wetting phase transitions were predicted for a phase-segregated two-component Bose-Einstein condensate (BEC) adsorbed at an optical wall. The wetting phase diagram was found to depend on intrinsic atomic parameters, being the masses and the scattering lengths, and on the extrinsic wall boundary condition. Here we study wetting transitions in GP theory without an optical wall in a setting with three phase-segregated BEC components instead of two. The boundary condition is removed by replacing the wall with the third component and treating the three phases on an equal footing. This leads to an unequivocal wetting phase diagram that depends only on intrinsic atomic parameters. It features first-order and critical wetting transitions, and prewetting phenomena. The phase boundaries are computed by numerical solution of the GP equations. In addition, useful analytic results are obtained by extending the established double-parabola approximation to three components.

cond-mat.quant-gas↗
arXiv2025

Surface tension of Bose-Einstein condensate at finite temperature

We examine the influence of nonzero temperature on a bounded surface of a dilute Bose gas confined by a hard wall, utilizing the Gross-Pitaevskii theory and the Bogoliubov-de Gennes equation to describe surface excitations. The theoretical calculations are compared with experimental data for liquid helium II, demonstrating excellent agreement. An empirical relation is found for the temperature-dependence of the surface tension. Furthermore, our findings indicate that the contribution of surface excitations remains below 0.7\% in the most of recent experiments on Bose-Einstein condensate.

cond-mat.quant-gas↗
arXiv2024

Transition temperature of the homogeneous imperfect Bose gas

Beyond standard approaches in existing literature, we explore the relative shift in the transition temperature of a homogeneous dilute Bose gas using the Cornwall-Jackiw-Tomboulis effective action formalism within the improved Hartree-Fock approximation. The first correction to the enhancement of the transition temperature, as compared to that of the ideal Bose gas, is expressed in a universal form: it is linear with respect to the scattering length. The slope of this linear relationship shows excellent agreement with the exact numerical calculations presented in previous studies. Additionally, we identify non-universal terms contributing to the shift.

cond-mat.quant-gas↗
arXiv2024

Critical temperature and thermodynamic properties of a homogeneous dilute weakly interacting Bose gas within the improved Hartree-Fock approximation at finite temperature

By means of Cornwall-Jackiw-Tomboulis effective action approach we investigate a homogeneous dilute weakly interacting Bose gas at finite temperature in vicinity of critical region. A longstanding debate, the shift of critical temperature, is considered and obtained in the universal form $ΔT_C/T_C^{(0)} = cn_0^{1/3}a_s$ with constants $c$ and $a$. The non-condensate fraction is contributed by quantum fluctuations as well as thermal exitations and can be expressed in sum of three terms. These terms correspond to the quantum fluctuations, thermal fluctuations and both. Indeed, the specific heat capacity and critical exponents are calculated and in excellent agreement with those in previous works and experimental data.

cond-mat.quant-gas↗
arXiv2023

Effect of nonzero temperature to condensed fraction of a homogeneous dilute weakly interacting Bose gas

We investigate the effect of non-zero temperature to the condensate fraction of a homogeneous dilute weakly interacting Bose gas in very low-temperature region. Within inproved Hartree-Fock approximation, the Cornwall-Jackiw-Tomboulis effective action approach shows that the thermal fluctuations make the condensate fraction decrease as a second and fourth-order power law of temperature. The result is compared with experimental data. Indeed, the effect of non-infinite size of the trap is also integrated.

cond-mat.quant-gas↗
arXiv2021

The condensed fraction of a homogeneous dilute Bose gas within the improved Hartree-Fock approximation

Motivated by the recent experiment [R. Lopes et. al., Phys. Rev. Lett. 119, 190404 (2017)] with a homogeneous Bose gas, we investigate a homogeneous dilute Bose gas to calculate the quantum depletion density. By means of the Cornwall-Jackiw-Tomboulis effective action approach within an improved Hartree-Fock approximation, the condensed fraction is recovered in a simpler manner and compared with corresponding findings in experimental data. Additionally, higher-order terms are taken into account for several physical quantities, in particular for the chemical potential and free energy density.

cond-mat.quant-gas↗
arXiv2020

Casimir effect in a dilute Bose gas in canonical ensemble within improved Hartree-Fock approximation

The Casimir effect in a dilute Bose gas confined between two planar walls is investigated in the canonical ensemble at zero temperature by means of Cornwall-Jackiw-Tomboulis effective action approach within the improved Hartree-Fock approximation. Our results show that: (i) the Casimir energy and the resulting Casimir force in the canonical ensemble remarkably differ from those in the grand canonical ensemble; (ii) when the distance between two planar walls increases, the Casimir energy and Casimir force decay in accordance with a half-integer power law in the canonical ensemble instead of an integer power law in the grand canonical ensemble.

cond-mat.quant-gas↗
arXiv2020

Density of condensate of a dilute Bose gas in improved Hartree-Fock approximation

In a manner of Cornwal-Jackiw-Tomboulis effective action approach, the density of condensate of a dilute Bose gas confined between two planar walls is investigated within the framework of improved Hartree-Fock. Thereby, the quantum fluctuations are taken into account with presence of high-order terms in the momentum integrals. Our results show that the quantum fluctuations significantly belittle the density of condensate compared with square of the expectation value of the field operator. The comparison with relating results of Gross-Pitaevskii theory is made.

cond-mat.quant-gas↗
arXiv2019

Finite size effect on Bose-Einstein condensate mixtures in improved Hartree-Fock approximation

Using Cornwal-Jackiw-Tomboulis effective potential approach we found that at zero temperature, in improved Hartree-Fock approximation, the effective masses and order parameters of a two component Bose-Einstein condensates confined between two parallel plates strongly depend on the distance between two slabs. The Casimir force is also considered in this approximation and shown that this force differs from zero in limit of strong segregation.

cond-mat.quant-gas↗
arXiv2018

Casimir force of a dilute Bose gas confined by a parallel plate geometry in improved Hatree-Fock approximation

Within framework of quantum field theory, in improved Hatree-Fock (IHF) approximation, we have considered a dilute single Bose-Einstein condensate (BEC) confined between two parallel plates. We found that the effective mass and order parameter of BEC strongly depend on distance separating two plates. Our results shows that the effective mass, order parameter and the Casimir force in IHF approximation equal to their values in one-loop approximation added a corrected term due to contribution of two-loop diagrams. We also show that the one-loop approximation is enough for calculating Casimir effect in an ideal Bose gas.

cond-mat.quant-gas↗
arXiv2017

The forces on a single interacting Bose-Einstein condensate

Using double parabola approximation for a single Bose-Einstein condensate confined between double slabs we proved that in grand canonical ensemble (GCE) the ground state with Robin boundary condition (BC) is favored, whereas in canonical ensemble (CE) our system undergoes from ground state with Robin BC to the one with Dirichlet BC in small-$L$ region and vice versa for large-$L$ region and phase transition in space of the ground state is the first order. The surface tension force and Casimir force are also considered in both CE and GCE in detail.

cond-mat.stat-mech↗