Feasibility of studying vortex noise in two-dimensional superconductors with cold atoms

We investigate the feasibility of using ultracold neutral atoms trapped near a thin superconductor to study vortex noise close to the Kosterlitz-Thouless-Berezinskii transition temperature. Alkali atoms such as rubidium probe the magnetic field produced by the vortices. We show that the relaxation time $T_1$ of the Zeeman sublevel populations can be conveniently adjusted to provide long observation times. We also show that the transverse relaxation times $T_2$ for Zeeman coherences are ideal for studying the vortex noise. We briefly consider the motion of atom clouds held close to the surface as a method for monitoring the vortex motion.

Figure 1

Reproduced from Ref. 14. Spectral density of magnetic flux noise, $S_{\Phi }\left(f\right)$, versus frequency $f=\omega ∕2\pi$ for 15 temperatures above the Kosterlitz-Thouless-Berezinskii transition. Scatter at higher temperatures is due to subtraction of SQUID noise. Dashed lines have slope $-1$ and $0$. Inset shows $dV∕dI$ versus T.