Ground-state scattering lengths for potassium isotopes determined by double-resonance photoassociative spectroscopy of ultracold K-39 - art. no. 052704

We use double-resonance photoassociative spectroscopy of ultracold K-39 ato ms to precisely determine the triplet a (3)Sigma (t)(u) scattering length f or the various isotopes of potassium. Photoassociation of free K-39 atoms t o the pure long-range 0(g)(-) (v' = 0, J' = 2) level is followed by stimula ted emission to high-lying levels of the a (3)Sigma (t)(u) potential. The b inding energies of levels within 5 GHz below the lowest ground-state 4s(1/2 )(f(a) = 1) +4s(1/2)(f(b) = 1) hyperfine asymptote are measured by both tra p loss and ionization detection. The locations of these near-threshold hype rfine-coupled molecular levels allow us to constrain the triplet potential and thereby determine the triplet scattering length. The result for K-39, a (t) = -33 +/- 5a(0) (1a(0) = 0.0529177 nm), is a factor of similar to5 impr ovement over previous determinations and establishes that a large K-39 Bose -Einstein condensate will not be stable.