A quasi-monomode guided atom-laser from an all-optical Bose-Einstein condensate

We report the achievement of an optically guided and quasi-monomode atom laser, in all spin projection states (mF = −1, 0 and +1) of F = 1 in rubidium 87. The atom laser source is a Bose-Einstein condensate (BEC) in a crossed dipole trap, purified to any one spin projection state by a spin-distillation process applied during the evaporation to BEC. The atom laser is outcoupled by an inhomogenous magnetic field, applied along the waveguide axis. The mean excitation number in the transverse modes is 〈n〉 = 0.65 ± 0.05 for mF = 0 and 〈n〉 = 0.8 ± 0.3 for the low field seeker mF = −1. Using a simple thermodynamical model, we infer from our data the population in each excited mode. When atoms are coherently extracted from a BoseEinstein condensate (BEC) they form an atom laser, a coherent matter wave in which many atoms occupy a single quantum mode. Atom lasers are orders of magnitude brighter than thermal atom beams, and are first and second order coherent [1, 2]. They are of fundamental interest, for example, for studies of atom-light entanglement, quantum correlations of massive particles [3] and quantum transport phenomena [4–10]. They are of practical interest for matter-wave holography through the engineering of their phase [11], and for atom interferometry because of their sensitivity to inertial fields [12]. Many prospects for atom lasers depend upon a high degree of control over the internal and external degrees of freedom and over the flux. The control of the output flux in a pulsed or continuous manner has been investigated using different outcoupling schemes: short and intense radiofrequency pulses [13], gravity induced tunneling [14], optical Raman pulses [15], long and weak radiofrequency fields [16], and by decreasing the trap depth [17]. The control of their internal state is intimately related to the outcoupling strategy. Atoms are either outcoupled in the magnetically insensitive (to first order) Zeeman state mF = 0 or another Zeeman state, each offering different advantages. Atom lasers in mF = 0 are ideal for precision measurement [18] because of their low magnetic sensitivity. Atoms in other Zeeman states, however, are ideal for measurements of magnetic fields because of their high magnetic sensitivity [19]. The control of the external degrees of freedom has been investigated through the atom laser beam divergence while propagating downwards due to gravity [20,21]. Inhomogeneous magnetic field have been used to realize atom optical elements [22]. Recently, a guided and quasi-continuous atom laser from a magnetically trapped BEC has been reported [23]. In this Letter, we report on a new approach to generate guided atom laser. This method can produce an atom laser in any Zeeman state. In addition, our nonstate changing outcoupling scheme leads to an intrinsically good transverse mode-matching, that enables the production of a quasi-monomode guided atom laser. Therefore, we achieve simultaneously a high degree of control of the internal and external degrees of freedom. The atom laser is extracted from a Bose Einstein condensate produced in a dipole trap. The trap is made from a Ytterbium fiber laser (IPG LASER, model YLR300-LP) with a central wavelength of 1072 nm and a