Guided Quasicontinuous Atom Laser

Abstract

We report the first realization of a guided quasicontinuous atom laser by rf outcoupling a BEC, from a hybrid optomagnetic trap into a horizontal atomic waveguide. This configuration allows us to cancel the acceleration due to gravity and keep the de Broglie wavelength constant at 0.5 µm during 0.1 s of propagation. We also show that our configuration, equivalent to pigtailing an optical fiber to a (photon) semiconductor laser, ensures an intrinsically good transverse mode matching.PACS numbers: 03.75. Pp, 39.20.+q, 42.60.Jf,41.85.Ew The Bose-Einstein condensation of atoms in the lowest level of a trap represents the matter-wave analog to the accumulation of photons in a single mode of a laser cavity. In analogy to photonic lasers, atom lasers can be obtained by outcoupling from a trapped Bose-Einstein condensate (BEC) to free space [1,2,3]. However, since atoms are massive particles, gravity plays an important role in the laser properties: in the case of rf outcouplers, it lies at the very heart of the extraction process [4] and in general, the beam is strongly accelerated downwards, causing a rapid decrease of the de Broglie wavelength. With the growing interest in coherent atom sources for atom interferometry [5,6,7] and new studies of quantum transport phenomena [8,9,10,11,12,13,14] where large and well defined de Broglie wavelength are desirable, a better control of the atomic motion during its propagation is needed. One solution is to couple the atom laser into a horizontal waveguide, so that the effect of gravity is canceled, leading to the realization of a coherent matter wave with constant wavelength.We report in this letter on the realization of such a guided quasicontinuous atom laser, where the coherent source, i.e. the trapped BEC, and the guide are merged together in a hybrid combination of a magnetic Ioffe-Pritchard trap and a horizontally elongated far offresonance optical trap constituting an atomic waveguide (see Fig. 1). The BEC, in a state sensitive to both trapping potentials, is submitted to a rf outcoupler yielding atoms in a state sensitive only to the optical potential, resulting in an atom laser propagating along the weak confining axis of the optical trap. In addition to canceling the effect of gravity, this configuration has several advantages. Firstly, coupling into a guide from a BEC rather than from a thermal sample [15] allows us to couple a significant flux into a small number of transverse modes of the guide. Secondly, the weak longitudinal trapping potential of the guide can be compensated by the antitrapping potential due to the second order Zeeman effect acting onto the outcoupled atoms, resulting in an atom laser with a quasiconstant de Broglie wavelength. Thirdly, using an rf outcoupler rather than releasing a BEC into a guide [14,16] results into quasicontinuous operation, thus insuring sharp linewidth, and gives a better control on the beam parameters. Indeed, changing the frequency of the outcoupler allows one to tune the value of the de Broglie wavelength of the atom...

Non-Markovian dynamics in atom-laser outcoupling from a double-well Bose–Einstein condensate

“…Our two-mode trapped condensate model has been motivated by recent experiments on the merging of independently formed BECs [4], and the first realization of a guided quasicontinuous atom laser [27]. For the sake of comparison with earlier work, relying on a single-mode trapped condensate, we have focused on an interaction-free model.…”

“…Indeed, as we discussed earlier, the quadratic atomic dispersion relation is associated with a density of atomic states which diverges for small frequencies (see equation 26). This behavior is also reflected in the spectral response (27) and implies that the continuum under consideration does not vary slowly for all frequencies.…”

“…Formally speaking, the strong transverse confinement allows us to assume that the transverse dynamics of the free atoms adiabatically follow the slowly varying transverse potential of the optical guide V f (r ⊥ ) [27]. For the sake of simplicity, throughout this work we assume that the transverse guide potential is nearly the same with the transverse potential of trap A i.e.,…”

“…In the absence of gravitational or other forces (as in the experimental setup [27]), the longitudinal component of the potential is V f (z) = 0. Thus, the field operator for the free atoms can be expanded aŝ…”

“…In particular, we choose the frequencies of the discrete modes to be ω j = jε, where the mode spacing ε is determined by the upper-limit condition of the discretization, namely ω up = M ε. The corresponding coupling for the j mode, is determined by the spectral response (27) as follows…”