Why measured cold-atom mobility edges in 3D speckle disagree with numerics
In plain words
Atoms released into a random pattern of laser light (speckle) can be trapped by disorder if their energy is below a threshold, the mobility edge. The measured thresholds lie well above the values computed for the same disorder.
Precise statement
Noninteracting atoms (spin-polarized K-40 fermions, K-39 at zero scattering length, dilute Rb-87 BEC) in a 3D laser speckle potential of strength $V_R$ and correlation length $\sigma$, with correlation energy $E_\sigma = \hbar^2/(m \sigma^2)$. Measured mobility edges $E_c(V_R)$ (Kondov 2011, Jendrzejewski 2012, Semeghini 2015) disagree with transfer-matrix and scaling numerics (Delande and Orso 2014), the measured values lying higher by large factors. An answer is either an energy-resolved measurement (narrow energy distribution, calibrated energy shift from loading) agreeing with numerics, or the identified missing physics (energy distribution after loading, residual interactions, finite observation time).
What would settle it
A measurement of $E_{c}$ with atoms prepared in a narrow, independently calibrated energy band in the speckle, compared with numerics for the exact speckle geometry.
Status in the literature
Pasek, Orso and Delande (PRL 2017) showed that speckle anisotropy cannot explain the gap and that $E_{c}$ obeys universal scaling; no later measurement closing the gap is known to this compilation.
Related problems
- More general than Critical exponent of the real-space 3D Anderson transition for atoms