[Show abstract][Hide abstract] ABSTRACT: Atomic matter waves, like electromagnetic waves, can be focused, reflected, guided and split by currently available passive atom-optical elements. However, the key for many applications of electromagnetic waves lies in the availability of amplifiers. These active devices allow small signals to be detected, and led to the development of masers and lasers. Although coherent atomic beams have been produced, matter wave amplification has not been directly observed. Here we report the observation of phase- coherent amplification of atomic matter waves. The active medium is a Bose- Einstein condensate, pumped by light that is far off resonance. An atomic wave packet is split off the condensate by diffraction from an optical standing wave, and then amplified. We verified the phase coherence of the amplifier by observing interference of the output wave with a reference wave packet. This development provides a new tool for atom optics and atom interferometry, and opens the way to the construction of active matter-wave devices.
[Show abstract][Hide abstract] ABSTRACT: Two sets of studies concerning the interaction of off-resonant light with a sodium Bose–Einstein condensate are described.
In the first set, properties of a Bose–Einstein condensate were studied using Bragg spectroscopy. The high momentum and energy
resolution of this method allowed a spectroscopic measurement of the mean-field energy and of the intrinsic momentum distribution
of the condensate. Depending on the momentum transfer, both the phonon regime as well as the free-particle regime could be
explored. In the second set of studies, the cigar-shaped condensate was exposed to a single off-resonant laser beam and highly
directional scattering of light and atoms was observed. This collective light scattering was caused by the long coherence
time of the quasi-particles in the condensate and resulted in a new form of matter wave amplification.
Full-text · Article · Nov 1999 · Applied Physics B
[Show abstract][Hide abstract] ABSTRACT: Rayleigh scattering off a Bose-Einstein condensate was studied. Exposing an elongated condensate to a single off-resonant laser beam resulted in the observation of highly directional scattering of light and atoms. This collective light scattering is caused by the coherent center-of-mass motion of the atoms in the condensate. A directional beam of recoiling atoms was built up by matter wave amplification.
[Show abstract][Hide abstract] ABSTRACT: Stimulated small-angle light scattering was used to measure the structure factor of a Bose-Einstein condensate in the phonon regime. The excitation strength for phonons was found to be significantly reduced from that of free particles, revealing the presence of correlated pair excitations and quantum depletion in the condensate. The Bragg resonance line strength and line shift agreed with predictions of a local density approximation. Comment: 4 pages, 3 figures
Full-text · Article · Jun 1999 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: Quantum tunneling was observed in the decay of metastable spin domains in gaseous Bose-Einstein condensates. A mean-field description of the tunneling was developed and compared with measurement. The tunneling rates are a sensitive probe of the boundary between spin domains, and indicate a spin structure in the boundary between spin domains which is prohibited in the bulk fluid. These experiments were performed with optically trapped F=1 spinor Bose-Einstein condensates of sodium. Comment: 5 pages, 4 figures
Preview · Article · Feb 1999 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: Bose-Einstein condensates of dilute atomic gases, characterized by a macroscopic population of the quantum mechanical ground state, are a new, weakly interacting quantum fluid. In most experiments condensates in a single weak field seeking state are magnetically trapped. These condensates can be described by a scalar order parameter similar to the spinless superfluid 4He. Even though alkali atoms have angular momentum, the spin orientation is not a degree of freedom because spin flips lead to untrapped states and are therefore a loss process. In contrast, the recently realized optical trap for sodium condensates confines atoms independently of their spin orientation. This opens the possibility to study spinor condensates which represent a system with a vector order parameter instead of a scalar. Here we report a study of the equilibrium state of spinor condensates in an optical trap. The freedom of spin orientation leads to the formation of spin domains in an external magnetic field. The structure of these domains are illustrated in spin domain diagrams. Combinations of both miscible and immiscible spin components were realized.
[Show abstract][Hide abstract] ABSTRACT: Properties of a Bose-Einstein condensate were studied by stimulated, two-photon Bragg scattering. The high momentum and energy resolution of this method allowed a spectroscopic measurement of the mean-field energy and of the intrinsic momentum uncertainty of the condensate. The coherence length of the condensate was shown to be equal to its size. Bragg spectroscopy can be used to determine the dynamic structure factor over a wide range of energy and momentum transfers. Comment: 4 pages, 3 figures
Full-text · Article · Jan 1999 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: The properties of Bose-Einstein condensed gases can be strongly altered by tuning the external magnetic field near a Feshbach resonance. Feshbach resonances affect elastic collisions and lead to the observed modification of the scattering length. However, as we report here, this is accompanied by a strong increase in the rate of inelastic collisions. The observed three-body loss rate in a sodium Bose-Einstein condensation increased when the scattering length was tuned to both larger or smaller values than the off-resonant value. This observation and the maximum measured increase of the loss rate by several orders of magnitude are not accounted for by theoretical treatments. The strong losses impose severe limitations for using Feshbach resonances to tune the properties of Bose-Einstein condensates. A new Feshbach resonance in sodium at 1195 G was observed. Comment: 4 pages, 3 figures
Preview · Article · Jan 1999 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: Bose-Einstein condensates have been prepared in long-lived metastable excited states. Two complementary types of metastable states were observed. The first is due to the immiscibility of multiple components in the condensate, and the second to local suppression of spin-relaxation collisions. Relaxation via re-condensation of non-condensed atoms, spin relaxation, and quantum tunneling was observed. These experiments were done with F=1 spinor Bose-Einstein condensates of sodium confined in an optical dipole trap. Comment: 3 figures included in paper, fourth figure separate
Preview · Article · Nov 1998 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: Collective excitations of a dilute Bose gas were probed above and below
the Bose-Einstein condensation temperature. The temperature dependencies
of the frequency and damping rates of condensate oscillations indicate
significant interactions between the condensate and the thermal cloud.
Hydrodynamic oscillations of the thermal cloud analogous to first sound
were observed. An out-of-phase dipolar oscillation of the thermal cloud
and the condensate was also studied, analogous to second sound. The
excitations were observed in situ using nondestructive imaging
[Show abstract][Hide abstract] ABSTRACT: The study of Bose-Einstein condensation in DC magnetic traps has yielded a rich harvest of researches. By studying the process of condensate formation in a super-cooled atomic gas, one not only verifies theories describing dynamic properties of the condensate, but also discerns the stimulated character of collisions into the condensate from the surrounding vapor. Studies of sound propagation have explored and detailed the connection between Bose-Einstein condensation in dilute vapors and quantum liquids such as superfluid <sup>4</sup>He. Further, the study of low-lying collective excitations, in particular their frequency and damping as a function of temperature have challenged pre-existing theoretical frameworks. These studies make use of repeated, nondestructive, in-situ imaging of Bose-Einstein condensates, and of optical and magnetic tools for manipulating cold atomic gases. Recently, the field of Bose-Einstein condensation has been widened by the successful transfer of a condensate into an optical trap. This trap enables much tighter confinement than that provided by existing magnetic traps, the confinement of arbitrary superpositions of hyperfine states, and tight confinement in the presence of a strong magnetic field. We will present recent results in these and other studies
[Show abstract][Hide abstract] ABSTRACT: We present a method of adiabatically changing the local phase-space density of an ultracold gas, using a combination of magnetic and optical forces. Applying this method, we observe phase-space density increases in a gas of sodium atoms by as much as 50-fold. The transition to Bose-Einstein condensation was crossed reversibly, attaining condensate fractions of up to 30%. Measurements of the condensate fraction reveal its reduction due to interactions. Comment: 4 pages with 4 figures
Preview · Article · May 1998 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: Optical confinement of Bose-Einstein condensates offers a new way of circumventing many limitations of magnetic traps used so far. All hyperfine levels can be optically trapped, allowing for studies of the dynamical and collisional properties of each level. Recent progress will be reported.( Present Address of M.R.A: Bell Laboratories, Lucent Technologies, 600 Mountain Ave., Murray Hill, N.J. 67974)
[Show abstract][Hide abstract] ABSTRACT: We report on the optical confinement of a Bose-Einstein condensate of sodium using a far-detuned infrared laser. This optical trap allowed for tight confinement, resulting in high density condensates and enabling the creation of condensates in an uncondensed gas through adiabatic compression. Recent results will be discussed.( Present Address of M.R.A: Bell Laboratories --- Lucent Technologies, 600 Mountain Ave., Murray Hill, N.J. 67974)
[Show abstract][Hide abstract] ABSTRACT: It has long been predicted that the scattering of ultracold atoms can be altered significantly through a so-called 'Feshbach resonance'. Two such resonances have now been observed in optically trapped Bose–Einstein condensates of sodium atoms by varying an external magnetic field. They gave rise to enhanced inelastic processes and a dispersive variation of the scattering length by a factor of over ten. These resonances open new possibilities for the study and manipulation of Bose–Einstein condensates.
[Show abstract][Hide abstract] ABSTRACT: The formation of a Bose-Einstein condensate of a dilute atomic gas has been studied in situ with a nondestructive, time-resolved imaging technique. Sodium atoms were evaporatively cooled close to the onset of Bose-Einstein condensation and then suddenly quenched to below the transition temperature. The subsequent equilibration and condensate formation showed a slow onset distinctly different from simple relaxation. This behavior provided evidence for the process of bosonic stimulation, or coherent matter-wave amplification, crucial to the concept of an atom laser.
[Show abstract][Hide abstract] ABSTRACT: Collective excitations of a dilute Bose gas were probed above and below the Bose-Einstein condensation temperature. The temperature dependencies of the frequency and damping rates of condensate oscillations indicate significant interactions between the condensate and the thermal cloud. Hydrodynamic oscillations of the thermal cloud were observed, constituting first sound. An antisymmetric dipolar oscillation of the thermal cloud and the condensate was studied, representing the bulk flow of a superfluid through the normal fluid. The excitations were observed in situ using non-destructive imaging techniques.
[Show abstract][Hide abstract] ABSTRACT: With an optical dipole trap it is possible to confine Bose–Einstein condensates in different hyperfine states and in arbitrary magnetic bias fields, thus overcoming two major limitations of magnetic traps. In this review paper we characterize the properties of such a dipole trap and we summarize experiments which made use of the new experimental possibilities, including the reversible formation of a Bose–Einstein condensate, the observation of Feshbach resonances in sodium and the ground state properties of spinor Bose-Einstein condensates. Finally, we present some new results on the shape of magnetically trapped and ballistically expanding condensates.
No preview · Article · Jan 1998 · Journal of Low Temperature Physics
[Show abstract][Hide abstract] ABSTRACT: We review the recent achievements in observing Bose-Einstein condensation (BEC) in dilute atomic gases, and summarize our own studies of BEC in sodium. These include studies of static and dynamic behavior of the condensate and of its coherence properties.
No preview · Article · Dec 1997 · Journal of Low Temperature Physics