We have created a Bose-Einstein condensate of 87 Rb atoms directly in an optical trap. We employ a quasi-electrostatic dipole force trap formed by two crossed CO2 laser beams. Loading directly from a sub-doppler laser-cooled cloud of atoms results in initial phase space densities of ∼ 1/200. Evaporatively cooling through the BEC transition is achieved by lowering the power in the trapping beams over ∼ 2 s. The resulting condensates are F = 1 spinors with 3.5 x 10 4 atoms distributed between the mF = (−1, 0, 1) states. 03.75.Fi, 32.80.Pj, The first observation of Bose Einstein condensates (BEC) in dilute atomic vapors in a remarkable series of experiments in 1995 [1][2][3] has stimulated a tremendous volume of experimental and theoretical work in this field.Condensates are now routinely created in over 30 laboratories around the world, and the pace of theoretical progress is equally impressive [4]. The recipe for forming a BEC is by now well-established [5,6]. The atomic vapor is first pre-cooled, typically by laser cooling techniques, to sub-mK temperatures and then transferred to a magnetic trap. Further cooling to BEC is then achieved by evaporatively cooling the atoms in the magnetic trap using energetically selective spin transitions [7].All-optical methods of reaching the BEC phase transition have been pursued since the early days of laser cooling. Despite many impressive developments beyond the limits set by Doppler cooling, including polarization gradient cooling [8], VSCPT [9], Raman cooling [10,12], and evaporative cooling in optical dipole force traps [13][14][15], the best efforts to-date produce atomic phase space densities nλ 3 dB a factor of 30 away from the BEC transition [12]. The principal roadblocks have been attributed to density-dependent heating and losses in laser cooling techniques, residual heating in optical dipole force traps or the unfavorable starting conditions for evaporative cooling. Hence, optical traps have played only an ancillary role in BEC experiments. The MIT group used a magnetic trap with an 'optical dimple' to reversibly condense a magnetically confined cloud of atoms evaporatively cooled to just above the phase transition [16]. Additionally, Bose condensates created in magnetic traps have been successfully transferred to shallow optical traps for further study [17][18][19]. In all these cases, however, magnetic traps provided the principle increase of phase space density (by factors up to ∼ 10 6 ) to the BEC transition.In this letter, we present an experiment in which we have created a Bose condensate of 87 Rb atoms directly in an optical trap formed by tightly focused laser beams. Following initial loading from a laser cooled gas, evaporative cooling through the BEC transition is achieved by simply lowering the depth of the optical trap. Our success is due in part to a high initial phase space density realized in the loading of our optical dipole trap and in part to the tight confinement of the atoms that permits rapid evaporative cooling to the BEC transition in ∼ 2 s....
We measure spin mixing of F=1 and F=2 spinor condensates of 87 Rb atoms confined in an optical trap. We determine the spin mixing time to be typically less than 600 ms and observe spin population oscillations. The equilibrium spin configuration in the F=1 manifold is measured for different magnetic fields and found to show ferromagnetic behavior for low field gradients. An F=2 condensate is created by microwave excitation from F=1 manifold, and this spin-2 condensate is observed to decay exponentially with time constant 250 ms. Despite the short lifetime in the F=2 manifold, spin mixing of the condensate is observed within 50 ms.PACS numbers: 03.75. Mn, 32.80.Pj, One of the hallmarks of Bose-Einstein condensation (BEC) in dilute atomic gases is the relatively weak and well-characterized inter-atomic interactions that allow quantitative comparison with theory. The vast majority of experimental work has involved single component systems, using magnetic traps confining just one Zeeman sub-level in the ground state hyperfine manifold. An important frontier in BEC research is the extension to multi-component systems, which provides a unique opportunity for exploring coupled, interacting quantum fluids. In particular, atomic BECs with internal spin degrees of freedom offer a new form of coherent matter with complex internal quantum structures. The first twocomponent condensate was produced utilizing two hyperfine states in 87 Rb, and remarkable phenomena such as phase separation were observed [1,2]. Sodium F=1 spinor BECs have been created by transferring spin polarized condensates into a far-off resonant optical trap to liberate the internal spin degrees of freedom. This allowed investigations of the ground state properties of Na spinor condensates, and observations of domain structures, metastability, and quantum spin tunneling [3,4,5].In this letter, we explore the spin dynamics and ground state properties of 87 Rb spinor condensates in an alloptical trap, by starting with well-characterized initial conditions in a known magnetic field. We focus on the F=1 case and confirm the predicted ferromagnetic behavior. We observe population oscillation between different spin states during the spin mixing and observe reduced magnetization fluctuations, pointing the way to future exploration of the underlying spin squeezing and spin entanglement predicted for the system [6]. We also create F=2 spinors using a microwave excitation, measure a decay of the condensate with a time constant of 250 ms. Despite the short lifetime, spin mixing of the spin-2 condensates is observed within 50 ms. Similar results are concurrently reported in Ref [7]; in that work, the emphasis is on the F=2 mixing, while here, we focus mainly on the F=1 manifold.A spinor BEC can be described by a multi-component order parameter which is invariant under gauge transformation and rotation in spin space [8,9,10]. For a spin-1 BEC, the condensate is either ferromagnetic or antiferromagnetic [8], and the corresponding ground state structure and dynamical prope...
Ultracold 87 Rb atoms are delivered into a high-finesse optical micro-cavity using a translating optical lattice trap and detected via the cavity field. The atoms are loaded into an optical lattice from a magneto-optic trap (MOT) and transported 1.5 cm into the cavity. Our cavity satisfies the strong-coupling requirements for a single intracavity atom, thus permitting real-time observation of single atoms transported into the cavity. This transport scheme enables us to vary the number of intracavity atoms from 1 to >100 corresponding to a maximum atomic cooperativity parameter of 5400, the highest value ever achieved in an atom-cavity system. When many atoms are loaded into the cavity, optical bistability is directly measured in real-time cavity transmission.Many applications in quantum information science require the coherent and reversible interaction of single photon fields with material qubits such as trapped atoms. Quantum states can be transferred between light and matter-respectively offering long range communication and long-term storage of quantum information. This important paradigm is the heart of cavity QED systems, which are largely focused on creating laboratory systems capable of reversible matter-photon dynamics at the single photon level [1]. To achieve this, a small high-finesse build-up cavity is used to tremendously enhance the electric field per photon and hence the interaction strength of a single photon with the cavity medium (e.g. atoms). For a single atom in the cavity, the interaction strength is given by the single photon Rabi frequency, 2g 0 , and coherent dynamics is achieved for g 2 0 /(κΓ) ≫ 1, where κ is the the cavity field decay rate and Γ is the atomic spontaneous emission rate.There have been spectacular recent successes in cavity QED research brought about by the merging of optical cavity systems with ultracold neutral atoms [2], including real-time observation [3,4,5] and trapping [6,7,8,9] of single atoms in optical cavities, real-time feedback control on a single atom [10], and single photon generation [11,12]. Together with the remarkable experimental work in microwave cavity QED [13] and the future prospects for cavity QED with trapped ions [14,15], the field is well-poised to contribute significantly to the development of quantum information science. Indeed, current cavity QED parameters are sufficient for existing quantum gate protocols with fidelities > 99.9% percent [16,17,18,19], and the systems are principally limited by the lack of a scalable atomic trapping system to provide adequate control over atom motional degrees of freedom.Our strategy for overcoming this limitation is to employ optical dipole trapping fields independent from the cavity and orthogonal to its axis as illustrated in Fig.
We have demonstrated a storage ring for ultra-cold neutral atoms. Atoms with mean velocities of 1 m/s corresponding to kinetic energies of ∼100 neV are confined to a 2 cm diameter ring by magnetic forces produced by two current-carrying wires. Up to 10 6 atoms are loaded at a time in the ring, and 7 revolutions are clearly observed. Additionally, we have demonstrated multiple loading of the ring and deterministic manipulation of the longitudinal velocity distribution of the atoms using applied laser pulses. Applications of this ring include large area atom interferometers and cw monochromatic atomic beam generation.03.75. Be, 32.60.+i, 39.10.+j,29.20.Dh Controlling the motional degrees of freedom of neutral atoms has emerged as a major theme in modern atomic physics. The development of laser cooling and related techniques to cool atoms down to the µK regime allows trapping and manipulation of the atomic motion using interactions with the relatively weak electric and magnetic fields available in the laboratory. Complementing the 3-D trapping work, there has been considerable progress recently in developing 2-D magnetic guiding structures for ultra-cold neutral atoms-so-called guided atom optics. Much of this work is motivated by the prospects of coherent de Broglie wave transport for applications including ultrasensitive atomic interferometers and quantum information processing. A variety of simple guides have been developed based on current-carrying wires [1][2][3][4][5], and extensions of these systems have been used to demonstrate atomic beamsplitters [6,7], atom conveyors [8], and magnetic microtraps [8,9].It is compelling to extend these techniques to a ring geometry, and there have been several proposals along these lines [10][11][12], as well as a recent demonstration confining fast polar molecules to an electrostatic ring [13]. These are motivated in part by the prospects of ringbased atomic interferometry and monochromatic atomic beam generation. Similar to optical ring interferometers, the ring geometry offers greater sensitivity through increasing the effective enclosed area of the interferometer both by straightforward enlargement of the ring as well as by employing multiple-orbit interfering trajectories. This is important because the sensitivity of many interactions (e.g. Sagnac rotational phase) is proportional to the enclosed area of the interferometer [14]. This geometry also provides new opportunities to create ultra-cold and monochromatic atomic beams. For example, the ring can be multiply loaded to increase the number of atoms in the ring, and both the longitudinal and transverse velocity distributions of the atoms can be manipulated and cooled in the ring. Finally, highly directional output beams can be created by using a coherent, variable output coupler.In this work, we demonstrate the first storage ring for neutral atoms. Our ring consists of a particularly simple 2-wire magnetic guiding structure. We have developed a technique to successfully transfer atoms to the ring from an external...
In this paper, calculations are presented for the determination of the magnetic energy, assuming dipole-dipole interaction, of a macroscopic crystal possessing paramagnetic ions situated on a definite lattice, structure. Parallel and antiparallel configurations are considered as well as specimens of different shapes and lattice structures of various types. It is shown that the configuration of lowest energy cannot be strictly defined but is dependent upon the shape of the specimen. This configuration is an antiparallel one for a sphere but changes to a parallel one for a long slender specimen. The transition between the two configurations appears to take place at a certain critical value of the demagnetization factor. For specimens above this value the theory accounts qualitatively for the low values of the magnetization found experimentally and for the apparent constancy of the Curie point with changes of shape. Below the critical value the theory implies a pure ferromagnetic state, which is not in agreement with experiment. Probable reasons for the discrepancy are given.
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