Accurate Determination of the Scattering Length of Metastable Helium Atoms Using Dark Resonances between Atoms and Exotic Molecules

Abstract

We present a new measurement of the s-wave scattering length a of spin-polarized helium atoms in the 2(3)S1 metastable state. Using two-photon photoassociation spectroscopy and dark resonances, we measure the energy E(nu)=14= -91.35+/- 0.06 MHz of the least-bound state nu = 14 in the interaction potential of the two atoms. We deduce a value of a=7.512+/-0.005 nm, which is at least 100 times more precise than the best previous determinations and is in disagreement with some of them. This experiment also demonstrates the possibility to create exotic molecules binding two metastable atoms with a lifetime of the order of 1 micros.

Feshbach resonances inHe3*-Goosen1, Tiecke2, Vassen3 et al. 2010Phys. Rev. A142320View full textAdd to dashboardCite

“…From the binding energy of the ν = 14 ro-vibrational state in the quintet potential, which is only slightly below the dissociation threshold, a large positive scattering length a = 7.567(24) nm was deduced [4,10,17], in very good agreement with experimental findings [18]. For collisions between atoms which are not in the fully stretched spin states, Penning ionization (PI) losses will strongly compromise the stability of trapped He * atoms in experiments.…”

“…The former ones are usually described as complex potentials to incorporate the effect of PI and have been described to a certain degree of accuracy by Müller et al [1]. The latter potential (S = 2) does not exhibit PI and can therefore be accurately described by a purely real potential, which has been measured and calculated with very high accuracy [4,18].…”

“…For 4 He * -4 He * they predicted a binding energy of the least bound state (ν = 14) equal to −89.6(8) MHz. Using two-photon photoassociation spectroscopy, Moal et al [18] measured the binding energy of this least bound state to be 44 2 /h = −91.35(6) MHz. We use this measurement as input parameter for 4 He * -4 He * ABM calculations, and we use Eq.…”

Ultracold metastable helium: Ramsey fringes and atom interferometry

“…[30] we extract scattering lengths if we ignore the imaginary part related to Penning ionization or degenerate collisions (0, 0 → −1, +1 or vice versa): a 0,0 ≈ 120 a 0 , a 1,1 = a −1,−1 = a 0,1 = a 0,−1 ≈ 140 a 0 , a 1,−1 ≈ 60 a 0 (with a 0 the Bohr radius). Of these three scattering lengths, only a 1,1 is known from experiments to be 142.0(1) a 0 [14,15]. As the interaction strengths g i,j scale linearly with the scattering lengths, we find g 0,0 ≈ 6 7 g 1,1 ≈ 2g 1,−1 .…”

“…Also molecular potentials for two metastable helium atoms can be calculated very accurately in some cases. This has allowed a stringent test of quantum chemistry calculations from a measurement of the s-wave scattering length a between two m = +1 atoms in the metastable 2 3 S 1 state, a theory = 7.567 (24) nm [12,13], while a exp = 7.512 (5) nm [14]. Examples of other confrontations between experiment and theory for cold collisions between metastable helium atoms can be found in Ref.…”