Interferometric measurement of interhyperfine scattering lengths in ${}^{87}$Rb

Abstract

We present interferometeric measurements of the $f=1$ to $f=2$ inter-hyperfine scattering lengths in a single-domain spinor Bose-Einstein condensate of ${}^{87}$Rb. The inter-hyperfine interaction leads to a strong and state-dependent modification of the spin-mixing dynamics with respect to a non-interacting description. We employ hyperfine-specific Faraday-rotation probing to reveal the evolution of the transverse magnetization in each hyperfine manifold for different state preparations, and a comagnetometer strategy to cancel laboratory magnetic noise. The method allows precise determination of inter-hyperfine scattering length differences, calibrated to intra-hyperfine scattering length differences. We report $(a_3^{(12)}-a_2^{(12)})/(a_2^{(1)}-a_0^{(1)})=-1.27(15)$ and $(a_1^{(12)}-a_2^{(12)})/(a_2^{(1)}-a_0^{(1)})=-1.31(13)$, limited by atom number uncertainty. With achievable control of atom number, we estimate precisions of $\approx 0.3\%$ should be possible with this technique.