共查询到20条相似文献,搜索用时 15 毫秒
1.
We propose an experimental scheme to simulate and observe relativistic Dirac fermions with cold atoms in a hexagonal optical lattice. By controlling the lattice anisotropy, one can realize both massive and massless Dirac fermions and observe the phase transition between them. Through explicit calculations, we show that both the Bragg spectroscopy and the atomic density profile in a trap can be used to demonstrate the Dirac fermions and the associated phase transition. 相似文献
2.
操控原子玻色-爱因斯坦凝聚体在双势阱中的动力学通常是通过改变势阱深度来实现,本文提出了一种基于调节原子有效质量的控制方案,可以在不改变双阱势的前提下操控凝聚体的双阱动力学.利用双模近似,本文解析地导出了超冷原子在双阱势中的隧穿强度和相互作用强度对有效质量的依赖关系,并基于平均场近似数值模拟了在有效质量调节下的凝聚体动力学演化,展示了隧穿振荡和自束缚等典型的双阱动力学行为.此外,本文的研究还发现,借助负有效质量效应,这一方案甚至可以等效地实现对负散射长度原子凝聚体双阱动力学行为的操控. 相似文献
3.
Kazuto Hirata Ajay D. Thakur Shuuichi Ooi Takashi Mochiku 《Central European Journal of Physics》2012,10(3):576-581
Vortices (magnetic flux quanta) in the superconducting networks perforated with anti-dots (holes) arrays behave as electrons
in atomic lattice of crystals. Repulsive and attractive interaction among vortices and anti-dots resemble to those among electrons
and atoms in crystals. To confirm the variety of the vortex physics similar to the solid state physics, we have fabricated
such superconducting networks with antidots array in metallic, inter-metallic and high-T
c
superconductors (HTSCs), and have measured magneto-resistance of vortex-flow. In these materials, we have observed integer-matching
at the matching fields and fractional-matching effect between them. Most of them are well explained by commensurability between
Abrikosov vortex lattice and anti-dots array. Furthermore, the effect of the anti-dots array in HTSCs appears as another kind
of phase transitions instead of to the first-order melting transition of vortex lattice in pristine samples. 相似文献
4.
We report suppression of atomic heating by light scattering due to tight binding in a 3D far-off-resonant optical lattice. We show that rescattered spontaneously emitted photons do not heat trapped atoms when the scattering rate is much less than the trap vibrational frequency. 相似文献
5.
R. Hoppeler J. Viana Gomes D. Boiron 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(1):157-162
We have studied the atomic density of a cloud confined
in an isotropic harmonic trap at the vicinity of the Bose-Einstein
transition temperature. We show that, for a non-interacting gas
and near this temperature, the ground-state density has the same
order of magnitude as the excited states density at the centre of
the trap. This holds in a range of temperatures where the
ground-state population is negligible compared to the total atom
number. We compare the exact calculations, available in a harmonic
trap, to semi-classical approximations. We show that these latter
should include the ground-state contribution to be accurate. 相似文献
6.
A charge density wave system near commensurability and with strong damping is considered, as a model for NbSe3. The observed threshold field is associated with depinning of a commensurate part of the charge density, while the excess charge, in form of phase kinks, contributes just to the ohmic conductivity. The characteristic length associated with the frequency generation is one lattice constant. 相似文献
7.
8.
We use an optical-mask technique to study the atomic density distribution in two types of optical lattices. In a two-beam lattice involving magnetic-field-induced laser cooling (MILC lattice), the measurements show, in agreement with simulations, an atomic distribution having periodicity equal to half the wavelength, λ, of the lattice fields and a modulation depth of about 20%. In a four-beam optical lattice involving Raman transitions, clear evidence of a λ/4-periodicity of the atomic distribution is found. 相似文献
9.
J. C. Li J. Zhu Z. J. Peng 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):325-330
We study analytically and numerically the properties of one-dimensional
chain of cold ions placed in a periodic potential of optical lattice
and global harmonic potential of a trap.
In close similarity with the Frenkel-Kontorova model, a transition from
sliding to pinned phase takes place with the increase of
the optical lattice potential for the density of ions
incommensurate with the lattice period. We show that at zero temperature the quantum
fluctuations lead to a quantum phase transition
and melting of pinned instanton glass phase at large values of dimensional Planck constant.
After melting the ion chain can slide in an optical lattice.
The obtained results are also relevant for a Wigner crystal placed
in a periodic potential. 相似文献
10.
Ya-Fei Yu Chuan-Jia Shan Feng Mei Zhi-Ming Zhang 《Physica B: Condensed Matter》2012,407(18):3839-3840
We propose a simple but feasible experimental scheme to simulate and detect Dirac fermions with cold atoms trapped in one-dimensional optical lattice. In our scheme, through tuning the laser intensity, the one-dimensional optical lattice can have two sites in each unit cell and the atoms around the low energy behave as massive Dirac fermions. Furthermore, we show that these relativistic quasiparticles can be detected experimentally by using atomic density profile measurements and Bragg scattering. 相似文献
11.
R. Paiva R. Muhammad R. Shiozaki A.L. de Oliveira O. Morizot V.S. Bagnato K.M.F. Magalhães 《Optics Communications》2012,285(8):2085-2089
Motivated by recent interest in low dimensional arrays of atoms, we experimentally investigated the way cold collisional processes are affected by the geometry of the considered atomic sample. More specifically, we studied the case of photoassociative ionization (PAI) both in a storage ring where collision is more unidirectional in character and in a trap with clear undefinition of collision axis. First, creating a ring shaped trap (atomotron) we investigated two-color PAI dependence with intensity and polarization of a probing laser. The intensity dependence of the PAI rate was also measured in a magneto-optical trap presenting equivalent temperature and density conditions. Indeed, the results show that in the ring trap, the value of the PAI rate constant is much lower and does not show evidences of saturation, unlike in the case of the 3D-MOT. Cold atomic collisions in storage ring may represent new possibilities for study. 相似文献
12.
13.
应用托马斯-费米近似和虚时演化数值方法研究环形势阱中旋转玻色爱因斯坦凝聚体的基态密度分布.当增加其旋转角频率,或者增加环形势阱的宽度及相应的中心高度,凝聚体基态密度分布均从涡旋晶格相转变为巨涡旋相.当旋转角频率为零时,增加环形势阱的宽度及相应的中心高度,凝聚体基态密度分布从一个圆盘变为圆环.解析结果与数值结果相互吻合. 相似文献
14.
腔内中性原子的长时间控制与俘获一直是腔量子电动力学(QED)中的一个难题,极大地制约了人们相干操控单原子及其与光相互作用的研究.基于传统Fabry-Perot光学腔,设计了一套易于内腔原子操控的强耦合腔QED系统,其典型参数为:腔长3.5 mm精细度约为57000,(g0,κ,γ)=2π×(1.48,0.375,2.61)MHz,临界光子数和原子数分别为1.54和0.89.该系统的特点是:能够在腔内直接实现冷原子磁光阱,并建立腔内光学晶格,实现腔内可控数目的中性原子的长时间俘获.通过合理选择构建光学偶极阱和原子成像系统,可实现对腔内单个原子或原子阵列的操控、探测、成像等.该系统可以克服传统腔QED系统中转移原子的困难,大幅增加腔内原子的寿命,为构建以腔QED系统为基础的量子信息演示平台提供了一种可能. 相似文献
15.
We analyze the macroscopic dynamics of a Bose gas in a harmonic trap with a superimposed two-dimensional optical lattice, assuming a weak coupling between different lattice sites. We consider the situation in which the local chemical potential at each lattice site can be considered as that provided by the Lieb-Liniger solution. Because of the weak coupling between sites and the form of the chemical potential, the three-dimensional ground-state density profile and the excitation spectrum acquire remarkable properties different from both 1D and 3D gases. We call this system a quasi-Tonks gas. We discuss the range of applicability of this regime, as well as realistic experimental situations where it can be observed. 相似文献
16.
The density functional theory (DFT) is used to study the atomic interactions in transition metal-based interstitial alloys.
The strain field is calculated in the discrete lattice model using Kanzaki method. The total energy and hence atomic forces
between interstitial hydrogen and transition metal hosts are calculated using DFT. The norm-conserving pseudopotentials for
H, Cu and Pd are generated self-consistently. The dynamical matrices are evaluated considering interaction up to first nearest
neighbors whereas impurity-induced forces are calculated with M32H shell (where M = Cu and Pd). The atomic displacements produced by interstitial hydrogen at the octahedral site in Cu and
Pd show displacements of 7.36% and 4.3% of the first nearest neighbors respectively. Both Cu and Pd lattices show lattice
expansion due to the presence of hydrogen and the obtained average lattice expansion ΔV/V = 0.177 for Cu and 0.145 for Pd.
相似文献
17.
Priyanka Verma Aranya B. Bhattacherjee Man Mohan 《Central European Journal of Physics》2012,10(2):335-341
In this work, we study parametric excitations in an elongated cigar-shaped BEC in a combined harmonic trap and a time dependent
optical lattice by using numerical techniques. We show that there exists a relative competition between the harmonic trap
which tries to spatially localize the BEC and the time varying optical lattice which tries to delocalize the BEC. This competition
gives rise to parametric excitations (oscillations of the BEC width). Regular oscillations disappear when one of the competing
factors, i.e. the strength of harmonic trap or the strength of optical lattice, dominates. Parametric instabilities (chaotic
dynamics) arise for large variations in the strength of the optical lattice. 相似文献
18.
The density–density correlation profiles obtained superimposing absorption images from atomic clouds freely expanding after the release of the confining optical lattice can be theoretically described in terms of a generalized quantum measure based on coherent-like states. We show that the corresponding density patterns differ in a testable way from those computed using standard many-body mean values, usually adopted in fitting experimental data. 相似文献
19.
We study an atomic Fermi gas interacting through repulsive contact forces in a one-dimensional harmonic trap. Bethe-ansatz solutions lead to an inhomogeneous Tomonaga-Luttinger model for the low energy excitations. The equations of motion for charge and spin density waves are analyzed both near the trap center and near the trap edges. While the center shows conventional spin-charge separation, the edges cause a giant increase of the separation between these modes. 相似文献
20.
L.J. Brillson 《Surface science》1977,69(1):62-84
Surface photovoltage spectroscopy, Auger electron spectroscopy, LEED, X-ray and ultraviolet photoemission measurements are reported for (112̄0) CdSe under a variety of ultrahigh vacuum conditions. As with CdS, all surface electronic features can be related to chemical contamination, Ar+ bombardment-induced lattice defects, or bulk trap states. Oxygen adsorption on CdSe and CdS produce qualitatively different electronic features which are attributed to different bonding at surface vacancy sites. Changes in surface atomic order show no direct effect on measured electronic features. Furthermore, CdSe exhibits no intrinsic surface state features which can account for its Schottky barrier formation with metals. 相似文献