Phases of atom-molecule vortex matter

We study ground state vortex configurations in a rotating atom-molecule Bose-Einstein condensate. It is found that the coherent coupling between the atomic and molecular condensates can render a pairing of atomic and molecular vortices into a composite structure that resembles a carbon dioxide molecule. Structural phase transitions of vortex lattices are also explored through different physical parameters including the rotational frequency of the system.     

环形势阱中旋转玻色爱因斯坦凝聚体的基态

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.     

Bose–Einstein condensates in a ring optical lattices trap

The evolution of Bose–Einstein condensates (BECs) loaded into a periodic ring optical lattices (OL) trap is studied. By means of the variational method and direct numerical simulations of the Gross–Pitaevskii (GP) equation, the ground state properties and the vortex stabilities of the condensates for both repulsive and attractive cases are investigated. The results show that the bound states exist for determinate OL strength and interatomic interaction. However, the ground states of BECs undergo delocalizing–localizing transition for both attractive and repulsive cases as the strength of the OL or the interatomic interaction is decreased below the critical value. The ring OL can suppress the delocalizing transition efficiently.     

Bose-Einstein Condensates in a One-Dimensional Optical Lattice: from Superfluidity to Number-Squeezed States

We study the phase coherence property of Bose-Einstein condensates confined in a one-dimensional optical lattice formed by a standing-wave laser field. The lattice depth is determined using a method of Kapitza-Dirac scattering between a condensate and a short pulse lattice potential. Condensates are then adiabatically loaded into the optical lattice. The phase coherence property of the confined condensates is reflected by the interference patterns of the expanded atomic cloud released from the optical lattice. For weak lattice, nearly all of the atoms stay in a superfluid state. However, as the lattice depth is increased, the phase coherence of the whole condensate sample is gradually lost, which confirms that the sub-condensates in each lattice well have evolved into number-squeezed states.     

Macroscopic atom-molecule dark state and its collective excitations in fermionic systems

We show that a robust macroscopic atom-molecule dark state can exist in fermionic systems, which represents a coherent superposition between the ground molecular Bose-Einstein condensates and the atomic BCS paired state. We take advantage of the tunability offered by external laser fields, and explore this superposition for demonstrating coherent oscillations between ground molecules and atom pairs. We interpret the oscillation frequencies in terms of the collective excitations of the dark state.     

Unconditional two-mode squeezing of separated atomic ensembles

We propose schemes for the unconditional preparation of a two-mode squeezed state of effective bosonic modes realized in a pair of atomic ensembles interacting collectively with optical cavity and laser fields. The scheme uses Raman transitions between stable atomic ground states and under ideal conditions produces pure entangled states in the steady state. The scheme works both for ensembles confined within a single cavity and for ensembles confined in separate, cascaded cavities.     

Vortex phase qubit: generating arbitrary, counterrotating, coherent superpositions in Bose-Einstein condensates via optical angular momentum beams

We propose a scheme for the generation of arbitrary coherent superpositions of vortex states in Bose-Einstein condensates (BEC) using the orbital-angular-momentum states of light. We devise a scheme to generate coherent superpositions of two such counterrotating states of light using well-known experimental techniques. We show that a specially designed Raman scheme allows for transfer of the optical vortex-superposition state onto an initially nonrotating BEC. This creates an arbitrary and coherent superposition of a vortex and antivortex pair in the BEC. The ideas presented here could be extended to generate entangled vortex states, design memories for the orbital-angular-momentum states of light, and perform other quantum information tasks. Applications to inertial sensing are also discussed.     

谐振子势与高斯势联合势阱中玻色爱因斯坦凝聚体的巨涡旋态

研究谐振子势与高斯势联合势阱中玻色爱因斯坦凝聚体的基态。发现凝聚体形成巨涡旋时,其涡旋个数等于平均角动量,且凝聚体密度分布和角动量密度分布相同,进而得到凝聚体形成巨涡旋时所处基态是角动量的本征态。发现势阱从各向同性的环形势阱逐渐变为各向异性的环形势阱的过程中,凝聚体的平均角动量与涡旋个数之比先由1平缓下降,然后迅速下降,最后保持在0.5附近。同时给出凝聚体密度分布和角动量分布的特征,并作出相应解释。     

Ground states of spin-orbit-coupled Bose Einstein condensates in the presence of external magnetic field

Two different kinds of spin-orbit (SO) coupling are often investigated theoretically and experimentally in atomic Bose-Einstein condensates (BECs), namely, Rashba and Dresselhaus SO couplings. We show that ground states for these two SO-coupled BECs share lots of similarities and it is impossible to distinguish them from the observation of ground states. We find that an Ioffe-Pritchard magnetic field can be utilized as a tool to distinguish them. In the presence of the Ioffe-Pritchard magnetic field, ground states manifest distinctively for the Rashba and Dresselhaus SO-coupled BECs.     

Jaynes-Cummings dynamics with a matter wave oscillator

We propose to subject two Bose-Einstein condensates to a periodic potential, so that one condensate undergoes the Mott-insulator transition to a state with precisely one atom per lattice site. We show that photoassociation of heteronuclear molecules within each lattice site is described by the quantum optical Jaynes-Cummings Hamiltonian. In analogy with studies of this Hamiltonian with cavity fields and trapped ions, we are thus able to engineer quantum optical states of atomic matter wave fields and we are able to reconstruct these states by quantum state tomography.     

Symmetry Breaking Ground States of Bose-Einstein Condensates in 1D Double Square Well and Optical Lattice Well

We investigate the phenomena of symmetry breaking and phase transition in the ground state of Bose-Einstein condensates (BECs) trapped in a double square well and in an optical lattice well, respectively. By using standing-wave expansion method, we present symmetric and asymmetric ground state solutions of nonlinear Schrödinger equation (NLSE) with a symmetric double square well potential for attractive nonlinearity. In particular, we study the ground state wave function's properties by changing the depth of potential and atomic interactions (here we restrict ourselves to the attractive regime). By using the Fourier grid Hamiltonian method, we also reveal a phase transition of BECs trapped in one-dimensional optical lattice potential.     

From squeezed atom lasers to teleportation of massive articles

The development of the Raman atom laser promises to make available new techniques for accessing and manipulating the quantum statistical properties of Bose-Einstein condensates. In this work we show how, combined with the already existing methods for the manipulation of quantum states of light which are central to quantum optics, the Raman input-output coupling mechanisms potentially enable the production of quadrature squeezed and sub-Poissonian atomic beams, and entanglement between atomic and optical fields. We also propose a method of measuring the quantum statistics of the atomic beam by transferring them to an optical field. Finally, by combning these techniques, we propose a method of teleporting the atom laser beam from one trapped condensate to another.     

Superfluidlike motion of vortices in light condensates

We demonstrate, through numerical simulations, the generation of stable vortex lattices in light condensates. This can be achieved by propagating several concentric laser beams with nested vortices of different topological charges in an optical material with a cubic-quintic nonlinearity. We have considered several initial conditions, and in all the cases the net topological charges of the resulting lattice is equal to the topological charge of the initial outer vortex. The lattice exhibits rotation similar to vortex motion in superfluids. These vortex arrays could be used to implement all-optical photonic crystal fibers. Our results also apply to Bose-Einstein condensates in the presence of three-body elastic interactions.     

Spin-orbit coupled Bose-Einstein condensate under rotation

We examine the combined effects of Rashba spin-orbit (SO) coupling and rotation on trapped spinor Bose-Einstein condensates. The nature of single particle states is thoroughly examined in the Landau level basis and is shown to support the formation of a half-quantum vortex. In the presence of weak s-wave interactions, the ground state at strong SO coupling develops ringlike structures with domains whose number shows step behavior with increasing rotation. For the fast rotation case, the vortex pattern favors a triangular lattice, accompanied by density depletion in the central region and a weakened Skyrmionic character as the SO coupling is enhanced. Giant vortex formation is facilitated when SO coupling and rotation are both strong.     

Flat rotation curves in scalar field galaxy halos

We start with a model where the dark matter is of scalar field nature, which condensates and form the dark halos of galaxies. In this work we study Bose–Einstein condensates (BEC) where the scalar field particles are in many different states, and not only in the ground state, as in a realistic BEC. We find that this model is in better agreement with the rotation curves of galaxies than previous models with scalar field dark matter.     

Vortex precession in Bose-Einstein condensates: observations with filled and empty cores

We have observed and characterized the dynamics of singly quantized vortices in dilute-gas Bose-Einstein condensates. Our condensates are produced in a superposition of two internal states of 87Rb, with one state supporting a vortex and the other filling the vortex core. Subsequently, the state filling the core can be partially or completely removed, reducing the radius of the core by as much as a factor of 13, all the way down to its bare value of the healing length. The corresponding superfluid rotation rates, evaluated at the core radius, vary by a factor of 150, but the precession frequency of the vortex core about the condensate axis changes by only a factor of 2.     

Laser induced dynamics of atomic sublevel coherences

In atomic media, the interaction with resonant light leads to optical pumping and light shift effects which modify not only the static optical and magneto-optical properties of the media, but also the dynamics of multipole moments that are present in the electronic ground state as well as in electronically excited states. These modified dynamics include changes in precession frequencies and relaxation rates, but also laser-induced exchange of coherences between different atomic multipole moments. Using the Na ground state as an example, a theoretical analysis of these modified dynamics is presented, as well as experimental measurements of the laser induced coherence transfer.     

Effects of zero mode and thin spectrum on the life time of atomic Bose Einstein condensates

Reviewing the ideas developed in [1], the ground state life time of a finite size atomic Bose Einstein condensate is studied for coherent, squeezed coherent and thermal coherent ground states. Ground state evolution of coherent and squeezed coherent states in a double well potential is studied. Effects of thin spectrum on Bose-Einstein condensates is discussed and quasiparticle excitation lifetimes are calculated. It is shown that the effect of the states we use on the free energy vanishes in the thermodynamic limit. Possible extension to a double well potential and effect of a second broken symmetry is also discussed.     

Efficient Scheme for the Generation of Atomic Schrödinger Cat States in an Optical Cavity

An efficient scheme is proposed for the generation of atomic Schroedinger cat states in an optical cavity. In the scheme N three-level atoms are loaded in the optical cavity. Raman coupling of two ground states is achieved via a laser tield and the cavity mode. The cavity mode is always in the vacuum state and the atoms have no probability of being populated in the excited state. Thus, the scheme is insensitive to both the cavity decay and spontaneous emission.     

Ground State and Single Vortex for Bose-Einstein Condensates in Anisotropic Traps

For Bose-Einstein condensation of neutral atoms in anisotropic traps at zero temperature, we present simple analytical methods for computing the properties of ground state and single vortex of Bose-Einstein condensates, and compare those results to extensive numerical simulations. The critical angular velocity for production of vortices is calculated for both positive and negative scattering lengths a, and find an analytical expression for the large-N limit of the vortex critical angular velocity for a 〉0, and the critical number for condensate population approaches the point of collapse for a 〈 0, by using approximate variational method.