共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
Bose–Einstein condensation of two- and three-dimensional boson gases confined in the one-dimensional gravitational field is investigated. Using the semiclassical approximation method, the expressions for the BEC transition temperature, condensate fraction, heat capacity and the entropy of the system are obtained. The heat capacities of the systems with D =1, 2, 3 (D is the dimension) at the critical temperature are discussed. We find that for the 1-D and 2-D boson systems, the heat capacities are continuous, but for the 3-D case there is a gap at the critical temperature Tc. The entropies of the systems with D=1, 2, 3 are also studied in detail. It is found that the entropies increase with the increasing of the temperature T. 相似文献
3.
By generalizing the Green’s function approach developed by Beliaev [S.T. Beliaev, Sov. Phys. JETP 7 (1958) 299; S.T. Beliaev, Sov. Phys. JETP 7 (1958) 289], we study effects of quantum fluctuations on the energy spectra of spin-1 spinor Bose–Einstein condensates, in particular, of a 87Rb condensate in the presence of an external magnetic field. We find that due to quantum fluctuations, the effective mass of magnons, which characterizes the quadratic dispersion relation of spin-wave excitations, increases compared with its mean-field value. The enhancement factor turns out to be the same for two distinct quantum phases: the ferromagnetic and polar phases, and it is a function of only the gas parameter. The lifetime of magnons in a spin-1 87Rb spinor condensate is shown to be much longer than that of phonons due to the difference in their dispersion relations. We propose a scheme to measure the effective mass of magnons in a spinor Bose gas by utilizing the effect of magnons’ nonlinear dispersion relation on the time evolution of the distribution of transverse magnetization. This type of measurement can be applied, for example, to precision magnetometry. 相似文献
4.
Zhi-Yong Jiao Zhao-Xian Yu Shuo Jin Ji-Suo Wang 《International Journal of Theoretical Physics》2007,46(11):2910-2914
We have studied the tunneling and fluctuations of a dipolar Bose–Einstein condensate in an optical lattice, it is found that
there exist the tunneling and fluctuations between lattices l and l+1, l and l−1, respectively. In particular, when the optical lattice is infinitely long and the spin excitations are in the long-wavelength
limit, tunneling effects disappear between lattices l and l+1, and that l and l−1, in this case the fluctuations are a constant, and the magnetic soliton appears. 相似文献
5.
J.O. Andersen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):389-396
We consider an interacting homogeneous Bose gas at zero temperature in two spatial dimensions. The properties of the system
can be calculated as an expansion in powers of g, where g is the coupling constant. We calculate the ground state pressure and the ground state energy density to second order in the
quantum loop expansion. The renormalization group is used to sum up leading and subleading logarithms from all orders in perturbation
theory. In the dilute limit, the renormalization group improved pressure and energy density are expansions in powers of the
T
2B and T
2Bln(T
2B), respectively, where T
2B is the two-body T-matrix.
Received 19 April 2002 Published online 13 August 2002 相似文献
6.
We present a systematic account of known rigorous results about the Bogoliubov model of weakly imperfect Bose gas (WIBG). This model is a basis of the celebrated Bogoliubov theory of superfluidity, although the physical phenomenon is, of course, more complicated than the model. The theory is based on two Bogoliubov's ansätze: the first truncates the full Hamiltonian of the interacting bosons to produce the WIBG, whereas the second substitutes some operators by c-numbers (the Bogoliubov approximation). After some historical remarks, and physical and mathematical motivations of this Bogoliubov treatment of the WIBG, we turn to revision of the Bogoliubov's ansätze from the point of view of rigorous quantum statistical mechanics. Since the exact calculation of the pressure and the behaviour of the Bose condensate in the WIBG are available, we review these results stressing the difference between them and the Bogliubov theory. One of the main features of the mathematical analysis of the WIBG is that it takes into account quantum fluctuations ignored by the second Bogoliubov ansatz. It is these fluctuations which are responsible for indirect attraction between bosons in the fundamental mode. The latter is the origin of a nonconventional Bose condensation in this mode, which has a dynamical nature. A (generalized) conventional Bose–Einstein condensation appears in the WIBG only in the second stage as a result of the standard mechanism of the total particle density saturation. It coexists with the nonconventional condensation. We give also a review of some models related to the WIBG and to the Bogoliubov theory, where a similar two-stage Bose condensation may take place. They indicate possibilities to go beyond the Bogoliubov theory and the Hamiltonian for the WIBG. 相似文献
7.
The aim of this paper is studying from an alternative point of view the integrability of the spin chain with long-range elliptic interactions introduced by Inozemtsev. Our analysis relies on some well-established conjectures characterizing the chaotic vs. integrable behavior of a quantum system, formulated in terms of statistical properties of its spectrum. More precisely, we study the distribution of consecutive levels of the (unfolded) spectrum, the power spectrum of the spectral fluctuations, the average degeneracy, and the equivalence to a classical vertex model. Our results are consistent with the general consensus that this model is integrable, and that it is closer in this respect to the Heisenberg chain than to its trigonometric limit (the Haldane–Shastry chain). On the other hand, we present some numerical and analytical evidence showing that the level density of Inozemtsev’s chain is asymptotically Gaussian as the number of spins tends to infinity, as is the case with the Haldane–Shastry chain. We are also able to compute analytically the mean and the standard deviation of the spectrum, showing that their asymptotic behavior coincides with that of the Haldane–Shastry chain. 相似文献
8.
T. P. Simula 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(3):453-455
We consider a quantized vortex excitation in a two-dimensional, harmonically trapped Bose gas and derive an equation for the
Berezinskii-Kosterlitz-Thouless transition temperature based on a simple free-energy argument. We relate the critical phase-space
density at the transition to the ratio between the entropy gain and the corresponding cost in energy of creating a free vortex
excitation in the system. 相似文献
9.
在加速光晶格中玻色-爱因斯坦凝聚体(BEC),当同时考虑两体和三体相互作用时,其能级结构、隧穿率出现了独特的特性.在一维加速光晶格中的BEC,当两体和三体相互作用参数满足一定条件时,非线性两能级体系的能级结构中出现了圈结构,研究得出了圈的宽度随两体和三体相互作用参数变化的关系,并由此分析圈结构的出现及其大小对BEC隧穿率的影响. 相似文献
10.
J. Tempere J.T. Devreese 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):27-33
A sum rule for the first frequency moment of the optical absorption of a many-polaron system is derived, taking into account
many-body effects in the system of constituent charge carriers of the many-polaron system. In our expression for the sum rule,
the electron-phonon coupling and the many-body effects in the electron (or hole) system formally decouple, so that the many-body
effects can be treated to the desired level of approximation by the choice of the dynamical structure factor of the electron
(hole) gas. We calculate correction factors to take into account both low and high experimental cutoff frequencies.
Received 26 April 2000 and Received in final form 5 December 2000 相似文献
11.
Based on Bose-Einstein condensation at minimized momentum state, we get the expressions for the critical temperature and condensed fraction of Bose-Einstein condensation (BEC) in an external potential in the three-dimensional (3D) case. For the 1D and 2D cases, we present not only the critical temperature and corresponding particles but also the condition of BEC occurrence. 相似文献
12.
13.
Engineering entanglement of a general three-level system interacting with a correlated two-mode nonlinear coherent state 总被引:2,自引:0,他引:2
Mahmoud Abdel-Aty Abdel-Shafy F. Obada 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(1):155-165
In this article a treatment of a three-level atom interacting with two modes of light in a cavity with arbitrary forms of
nonlinearities of both the fields and the intensity-dependent atom-field coupling is presented. A factorization of the initial
density operator is assumed, with the privileged field modes being in a pair-coherent state. We derive and illustrate an exact
expression for the time evolution of the density operator, by means of which we identify and numerically demonstrate the region
of parameters where significantly large entanglement can be obtained. We show that entanglement can be significantly influenced
by different kinds of nonlinearities. The nonlinear medium yields the superstructure of atomic Rabi oscillation. We propose
a generation of Bell-type states having a simple initial state preparation of the present system.
Received 29 July 2002 / Received in final form 18 October 2002 Published online 21 January 2003
RID="a"
ID="a"e-mail: abdelaty@uni-flensburg.dePresent address: Institut für Mathematik, Universit?t Flensburg, Germany. 相似文献
14.
T. Mercouris C.A. Nicolaides 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):241-248
By implementing a time-independent, nonperturbative many-electron, many-photon theory (MEMPT), cycle-averaged complex eigenvalues
were obtained for the He atom, whose real part gives the field-induced energy shift, Δ(ω
1, F
1;ω
2, F
2,ϕ), and the imaginary part is the multiphoton ionization rate, Γ(ω
1, F
1;ω
2, F
2,ϕ), where ω is the frequency, F is the field strength and ϕ is the phase difference. Through analysis and computation we show that, provided the intensities
are weak, the dependence of Γ(ω
1, F
1;ω
2, F
2,ϕ) on ϕ is simple. Specifically, for odd harmonics, Γ varies linearly with cos(ϕ) whilst for even harmonics it varies linearly
with cos(2ϕ). In addition, this dependence on ϕ holds for Δ(ω
1, F
1;ω
2, F
2,ϕ) as well. These relations may turn out to be applicable to other atomic systems as well, and to provide a definition of
the weak field regime in the dichromatic case. When the combination of (ω
1, F
1) and (ω
2, F
2) is such that higher powers of cos(ϕ) and cos(2ϕ) become important, these rules break down and we reach the strong field
regime. The herein reported results refer to Γ(ω
1, F
1;ω
2, F
2,ϕ) and Δ(ω
1, F
1;ω
2, F
2,ϕ) for He irradiated by a dichromatic ac-field consisting of the fundamental wavelength λ = 248 nm and its 2nd, 3rd and 4th
higher harmonics. The intensities are in the range 1.0×1012-3.5×1014 W/cm2, with the intensity of the harmonics being 1-2 orders of magnitude smaller. The calculations incorporated systematically
electronic structure and electron correlation effects in the discrete and in the continuous spectrum, for 1S, 1P, 1D, 1F, 1G, and 1H two-electron states of even and odd parity.
Received 9 July 2000 and Received in final form 2 November 2000 相似文献
15.
The effects of the solvent-surfactant interaction, chain length and stiffness of surfactants on the formation of aggregates
and the aggregation degree of surfactants in the two-dimension solution have been investigated using discontinuous molecular-dynamics
simulations. When the tail-water repulsion increases or the head-water attraction decreases, the aggregation degree increases.
Increasing the chain length and raising the stiffness of surfactants lead to the increment of the aggregation degree.
Received 25 July 2001 and Received in final form 7 May 2002 相似文献
16.
V. L. Lyuboshitz V. V. Lyuboshitz 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):465-467
The coherent inelastic processes of the type a→b, which may take place in the collisions of hadrons and γ-quanta with nuclei at very high energies (the nucleus remains the same), are theoretically investigated. The influence of
matter inside the nucleus is taken into account by using the optical model based on the concept of refraction index. Analytical
formulas for the effective cross-section σ
coh(a→b) are obtained, taking into account that at ultrarelativistic energies the main contribution into σ
coh(a→b) is provided by very small transferred momenta in the vicinity of the minimum longitudinal momentum transferred to the nucleus. 相似文献
17.
N. Petit V. Garnier V. Ta Phuoc R. Caillard A.-M. Frelin A. Ruyter I. Laffez J.-C. Soret A. Maignan F. Gervais 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):423-429
The reflectivity spectra of an oriented ceramic of Bi-2223 has been investigated by polarized infrared reflectivity spectroscopy
in the energy range 0.005-2.2 eV. It is shown that the data for the polarization parallel to the c axis cannot be fitted with a one-component Drude or extended-Drude model. The conductivity spectrum is then obtained from
the best fit of a “double-damping Drude” model to reflectivity spectra, itself derived from the factorized form of the dielectric
function, and by a Kramers-Kronig inversion as well. The data and their analysis give a new insight of the 2D character of
the system.
Received 26 April 2001 and Received in final form 28 August 2001 相似文献
18.
Q. Xu J. W. Yin X. M. Hu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(2):271-276
It's shown that the incoherent fluorescence spectrum from a three-level
Λ atom with orthogonal atomic transition dipole moments is comprised
of a single ultrasharp line by simulating the vacuum-induced coherence
(VIC), and the line is on resonance with the driving field. The physical
interpretation of the spectral characteristics is given in terms of dressed states. 相似文献
19.
Within the Nuclear Nambu-Jona-Lasinio model of light nuclei (the NNJL model), describing strong low-energy nuclear interactions, we compute the width of the energy level of the ground state of pionic deuterium. The theoretical value fits well the experimental data. Using the cross-sections for the reactions e + d p + p + e- and e + d p + n + e, computed in the NNJL model, and the experimental values of the events of these reactions, detected by the SNO Collaboration, we compute the boron neutrino fluxes. The theoretical values agree well with the experimental data and the theoretical predictions within the Standard Solar Model by Bahcall. We argue the applicability of the constraints on the astrophysical factor for the solar proton burning, imposed by helioseismology, to the width of the energy level of the ground state of pionic deuterium. We show that the experimental data on the width satisfy these constraints. This testifies an indirect measurement of the recommended value of the astrophysical factor for the solar proton burning in terrestrial laboratories in terms of the width of the energy level of the ground state of pionic deuterium. 相似文献
20.
C. P. Pang J. T. Lue 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):593-600
The linear refractive indices and nonlinear second-order susceptibility of
hydrated and dehydrated silica micro-spheres are studied using attenuated
total reflectance (ATR) and the second harmonic generation (SHG) method in
direct transmission, respectively. A dramatic change of the effective
dielectric constant of silica suspension under an electric bias was
observed, which is attributed to particle redistribution in the fluid.
Dielectric constants of dehydrated silica spheres change slightly under an
electric field due to Pockels effect, for which we measure a linear
electro-optical coefficient of r33 ∼3.4±0.7 pm/V. The
transmission second harmonic generation comes from the third-order
susceptibility χ(3), which is a coupling of two photons and the
electrostatic field induced by the surface –OH charges as characterized by
the Gouy-Chapman model. The SH signal from the dehydrated silica vanishes
because of the loss of –OH groups on the particle surfaces. Dehydration of
silica beads is irreversible. The optical properties of dried silica spheres
do not recover their original hydrated state when distilled water is added. 相似文献