Magnetic Dipolar Interaction in a Bose-Einstein Condensate Atomic Interferometer

Abstract

We study the role played by the magnetic dipole interaction in an atomic interferometer based on an alkali Bose-Einstein condensate with tunable scattering length. We tune the s-wave interaction to zero using a magnetic Feshbach resonance and measure the decoherence of the interferometer induced by the weak residual interaction between the magnetic dipoles of the atoms. We prove that with a proper choice of the scattering length it is possible to compensate for the dipolar interaction and extend the coherence time of the interferometer. We put in evidence the anisotropic character of the dipolar interaction by working with two different experimental configurations for which the minima of decoherence are achieved for a positive and a negative value of the scattering length, respectively. Our results are supported by a theoretical model we develop. This model indicates that the magnetic dipole interaction should not represent a serious source of decoherence in atom interferometers based on Bose-Einstein condensates. Atom-atom interactions represent a fundamental limit to the performance of atomic Bose Einstein condensate (BEC) interferometers [1,2,3,4]. Atomic collisions lead to density-dependent shifts in the interferometric signal, severely compromising its visibility. In two recent works [5,6], the possibility to strongly reduce the interactioninduced decoherence in a trapped BEC interferometer has been demonstrated by tuning the s-wave scattering length a almost to zero via a magnetic Feshbach resonance. The tunability of a by magnetic means is possible for atoms with a non-vanishing magnetic dipole moment. Therefore, once the s-wave contact interaction is canceled by applying a proper external magnetic field, the magnetic dipole-dipole interaction (MDI) between the atoms remains as a possible source of decoherence for the interferometer. This aspect has been pointed out in [5,6], but both a theoretical analysis and an experimental study of the problem are still missing. The MDI generally does not play a role in experiments with ultra-cold quantum degenerate alkali atoms, where the small magnetic dipole moment µ is on the order of the Bohr magneton µ B and leads to a dipolar interaction energy E d < 0.01 · E s , with E s the s-wave contact interaction energy. So far, studies of the MDI in an ultra-cold gas have been possible mainly with Cr atoms [7], characterized by a large magnetic dipole moment µ = 6µ B that leads to interaction energies E d 36 times larger than for alkali atoms. Evidence of MDI in a spinorial alkali BEC has been only recently reported in [8].In this Letter we study the role played by the MDI in an interferometer where a BEC with weak tunable contact interaction is implemented [5]. We get evidence of the effect of dipolar interaction on the dephasing of the interferometric signal. The MDI is anisotropic and therefore the sign of its contribution to the interaction energy depends on the geometry of the system. We study in particular two different geometries for which the minimum of decoheren...

Matter-wave solitons supported by field-induced dipole-dipole repulsion with spatially modulated strength

“…Unlike the usual contact nonlinearity, which represents effects of collisions between atoms, dipole-dipole interactions (DDIs) give rise to long-range anisotropic forces. The DDIs account for a number of remarkable phenomena in ultracold Bose gases [9]- [11], such as various pattern-formation scenarios [12][13][14][15][16], fractional domain walls [17], d -wave collapse [18,19], specific possibilities for precision measurements [20][21][22], stabilization of the dipolar BEC by optical lattices [23,24], the Einstein -de Haas effect [25], etc. Dipolar BECs can be also used as matter-wave simulators [26], to emulate, in particular, the creation of multi-dimensional solitons via the nonlocal nonlinearity-a subject which has also drawn much attention in optics, where nonlocal interactions of other types (with different interaction kernels) occur too [27][28][29].…”

Direct evaporative cooling of39K atoms to Bose-Einstein condensation

“…Tuning the two body interactions, many collective phenomena have been explored using degenerate quantum gases loaded in optical lattices [5,6]. The almost complete cancellation of the interactions between the atoms has allowed the sensitivity of BEC based atom interferometers to be enhanced [7][8][9]. A fine control of the collisional properties of a gas has offered new possibilities in the study of the interplay between disorder and interaction in matter waves [10][11][12][13].…”

Rotational properties of dipolar Bose-Einstein condensates confined in anisotropic harmonic potentials

“…Initially dipolar effects were investigated experimentally in 52 Cr atoms [17]. More recently dipolar effects have also been investigated experimentally in condensates of 39 K and 7 Li [18] atoms, in spinor condensates [19], in ultracold gases of Dy atoms [20], and in ultracold polar molecules [21,22]. These studies have focused on different aspects of the dipolar interaction such as, e.g., its anisotropy [18], or on its attractive character and the consequent possible collapse of the gas [23].…”