Three-dimensional localization of ultracold atoms in an optical disordered potential (1108.0137v4)

Abstract: We report a study of three-dimensional (3D) localization of ultracold atoms suspended against gravity, and released in a 3D optical disordered potential with short correlation lengths in all directions. We observe density profiles composed of a steady localized part and a diffusive part. Our observations are compatible with the self-consistent theory of Anderson localization, taking into account the specific features of the experiment, and in particular the broad energy distribution of the atoms placed in the disordered potential. The localization we observe cannot be interpreted as trapping of particles with energy below the classical percolation threshold.

• The paper demonstrates Anderson Localization by showing that up to 22% of atoms become localized at a disorder amplitude of V_R/h ∼ 400 Hz.
• The experiment uses a dilute Bose-Einstein condensate in a 3D laser-induced optical disorder to distinguish between localized and diffusive atom fractions.
• Results reveal that increasing disorder reduces diffusion coefficients, underscoring the potential of disordered optical systems for quantum simulations.

Three-Dimensional Localization of Ultracold Atoms in an Optical Disordered Potential

The paper investigates the three-dimensional (3D) localization of ultracold atoms within a disordered optical potential and scrutinizes the applicability of the self-consistent theory of Anderson Localization (AL) in such a setting. The paper utilized a dilute Bose-Einstein condensate (BEC) of $^{87}$Rb atoms, initially confined in a near-isotropic Gaussian optical trap before being exposed to a 3D laser-induced optical disorder. The potential is characterized by short correlation lengths in all directions, and the atoms are magnetically suspended to negate gravitational effects.

The experimental findings reveal that the density profiles of the atoms comprise two parts: a localized portion and a diffusive component. The steady localized fraction signifies regions where atoms remain trapped, indicative of AL, whereas the diffusive section corresponds to atoms not trapped by the disorder. The presence of both parts provides compelling evidence that the behavior aligns well with the theory of AL as it applies to the experiment's configuration, particularly considering the energy distribution breadth of the atoms that experienced the optical disorder.

Significant quantitative results from the paper include the observation that the localized fraction of atoms increases with the disorder amplitude up to a certain limit, reaching approximately 22% at a disorder amplitude of $V_R/h \sim 400$ Hz. Meanwhile, diffusion coefficients fall noticeably with increasing disorder, reaching plateau values at substantial amplitudes. The experiment's focused approach ensures that the disorder characteristics remain in the quantum regime, ruling out possible classical trapping interpretations.

The paper positions AL within optical lattices as a platform for further exploration of quantum behaviors in disordered systems and highlights the considerable intricacy in properly modeling energy distributions once disorders influence such distributions.

Potential future directions of this research involve honing methods for more controlled energy distributions in experimental settings and refining interaction models where atom-atom interplays could shed light on AL's robustness in such complex conditions. The insights from these investigations are likely to have substantial implications in condensed matter physics and quantum computing, especially where disorder is used intentionally to explore quantum phenomena.

In conclusion, this research underscores the necessity for a coherent understanding of disorder's quantum mechanical effects on ultracold gases, providing a considerable step forward in experimental and theoretical treatments of 3D AL.