Magnetic Dipolar Interaction in a Bose-Einstein Condensate Atomic Interferometer

We study the role played by the magnetic dipole interaction in the decoherence of a lattice-based interferometer that employs an alkali Bose-Einstein condensate with a tunable scattering length. The different behavior we observe for two different orientations of the dipoles gives us evidence of the anisotropic character of the interaction. The experiment is correctly reproduced by a model we develop only if the long-range interaction between different lattice sites is taken into account. Our model indicates that dipolar interaction can be compensated by a proper choice of the scattering length and that the magnetic dipole interaction should not represent an obstacle for atom interferometry with Bose-Einstein condensates with a tunable interaction.

Figure 1

Schematic representation of the character of the magnetic dipolar interaction in the two different experimental configurations. (a) For dipoles parallel to the lattice direction, the on-site MDI is repulsive, while the weaker intersite MDI is attractive. (b) For dipoles orthogonal to the lattice direction, the on-site MDI is attractive, while the intersite MDI is repulsive.

Figure 2

Decoherence rate of the interferometer as a function of the external magnetic field applied during Bloch oscillations for a lattice parallel (circles, left vertical scale) and orthogonal (squares, right vertical scale) to $\overrightarrow{B}$. Each point is the result of the average of five measurements. The error bars are the standard deviation of the average. Solid lines are parabolic fits to the data.

Figure 3

(a) On-site dipolar interaction energy (solid line) and intersite dipolar interaction energy (dashed line) as a function of the lattice site $j$ for the $\mathrm{OL}\parallel \overrightarrow{B}$ configuration. (b) Total interaction energy for $a=0$ (dotted line), $a=-0.52a_0$ (dashed line), i.e., the value that cancels the on-site MDI and for $a=-0.32a_0$ (solid line), i.e., the value that minimizes the decoherence.