Proposal for a Magneto-optical Beam Splitter for Atoms

Abstract

PACS. 32.80 -Photon interactions with atoms. P ACS. 42.50 -Quantum optics.Abstract. -In this letter we present a theoretical study of the coherent diffraction of three-level atoms from a light field with a polarization gradient (counterpropagating crossed linearly polarized beams) and a static magnetic field applied parallel to the laser propagation direction. We show that for a particular ratio of the laser field intensity and the magnetic-field strength, there occurs a resonance between the Larmor precession of the magnetic alignment and the Rabi oscillations. On resonance the atomic wave function is diffracted by an approximately triangular optical potential which leads to a very efficient coherent splitting of the atomic beam. The proposed configuration is particularly interesting in relation to atom interferometry, when efficient coherent beam splitters for atoms are required.Introduction. -Atom interferometry has a considerable potential both as a technique for precision measurement and as a means to perfonn fundamental tests of our understanding of quantum theory [1]. For many applications the sensitivity of an interferometer is proportional to the area enclosed by the two paths. Consequently, an important consideration in atom interferometry is a large spatial splitting of the atomic wave function. In previous experiments coherent atomic-beam splitters were realized by diffraction from microstructures [2,3] or an optical standing wave [4], ;-:/2 laser pulses [5], stimulated Raman transitions [6] and the optical Stern-Gerlach effect [7].For microstructures the splitting is inversely proportional to the grating period and therefore limited by microfabrication techniques. The momentum distribution produced by coherent diffraction from a standing light wave has an envelope given by a Bessel function distribution. For this reason, standing-wave diffraction is not an efficient technique for producing a coherent splitting into high-transverse-momentum states. In the case of single-photon excitation or stimulated Raman transitions, the maximum momentum kick imparted to the atom per process is limited to one or two photon momenta (flk), respectively. A larger splitting of order 8ftk was achieved using the optical Stern-Gerlach effect [7]. Another proposed method for an effective beam splitting is based on the adiabatic passage between Zeeman sublevels for multilevel atoms [8].In this paper we report on a new approach to coherently split an atomic beam. We consider the diffraction of atoms in a polarization gradient light field (counterpropagating crossed linearly polarized beams) and a static magnetic field applied parallel to the laser propagation direction (fig. la»). For a particular ratio of the laser intensity and magnetic-field strength, one of the eigenstates of the interaction experiences an approximately triangular potential in the transverse direction resulting in a large, clearly two-peaked splitting in momentum space. The total splitting is proportional to the light-and

Interaction of atoms with a magneto-optical potential

“…ReI E(r)e (4) where d is the electric dipole operator and the laser amplitude E(r) is where p= -gjpBJ is the magnetic moment. The magnetic field is parallel to the quantization axis, therefore HB has only diagonal elements corresponding to the Zeeman shift.…”

“…In this paper we show that by introducing a further degree of freedom in the light-atom interaction (namely, polarization-selective absorption and emission), it is pos-sible to gain more control of the momentum-transfer process, and for example create an effective scheme for an atomic beam splitter [4]. Two extensions of the normal standing-wave interaction are proposed.…”

Atomic beam splitters based on light

“…This would mean that once the atom has absorbed a photon from one direction, it always absorbs from that direction and emits into the other. This turns out to be possible for three level atoms interacting with a magneto-optical potential formed by counter-propagating, orthogonal linearly polarized beams and a static magnetic field applied parallel to the laser propagation direction [23].…”

“…As an example a splitting of ±40lik was predicted for metastable helium under experimentalIy realistic conditions [23].…”

Bichromatic beam splitter for three-level atoms

“…Such a system is given by the magneto-optical beam splitter suggested by Pfau et aL [10] and Ovchinnikov et al [11], which passes the atomic beam through a potential which is closely triangular in form. It has been successfully experimentally demonstrated by Pfau et al [12].…”