Steerable optical tweezers as a laser based collider for ultracold atoms

Niels Kjærgaard
Department of Physics, QSO – Centre for Quantum Science, and Dodd-Walls Centre, University of Otago

Resonances are a paradigm of quantum mechanical scattering. Their manifestation become particularly clear for ultracold atoms due to the pristine nature of these systems. In the past, we have observed the striking anisotropic scattering halos resulting from shape resonances that are set up by centrifugal barriers in the cold collisions between nanokelvin atomic clouds. Examples include a p-wave resonance for fermionic potassium [1] and a d-wave resonance for bosonic rubidium [2]. More recently we have employed an optical collider [3] based on steerable tweezer beams [4] to investigate scattering at magnetic Feshbach resonances. While experiments on ultracold gases so far almost exclusively have been conducted at threshold (in the zero-energy limit) our scheme allows us to operate above threshold and to map out the resonance in a parameter space spanned by both energy and magnetic field. We will present the case of measurements on a narrow, highly inelastic interstate resonance of rubidium [5]. This will be contrasted to our results for a broad interspecies elastic scattering resonance between potassium and rubidium displaying the tell-tale asymmetric Beutler-Fano line shape.

1.     R. Thomas, K.O. Roberts, E. Tiesinga, A.C.J. Wade, P.B. Blakie, A.B Deb, N. Kjærgaard, Multiple scattering dynamics of fermions at an isolated p-wave resonance, Nature Communications 7, 12069 (2016).

2.     N. R. Thomas, N. Kjærgaard, P. S. Julienne, and A. C. Wilson, Imaging of s and d partial-wave interference in quantum scattering of identical bosonic atom, Physical Review Letters 93, 173201 (2004).

3.     A. Rakonjac, A. B. Deb, S. Hoinka, D. Hudson, B. J. Sawyer, and N. Kjærgaard, Laser based accelerator for ultracold atoms, Optics Letters 37, 1085-1087 (2012).

4.     K. O. Roberts, T. McKellar, J. Fekete, A. Rakonjac, A. B. Deb, N. Kjærgaard, Steerable optical tweezers for ultracold atom studies Optics Letters 39, 2012-2015 (2014).

5.     M.S.J Horvath, R. Thomas, E. Tiesinga, A.B. Deb, N. Kjærgaard, Above-threshold scattering about a Feshbach resonance for ultracold atoms in an optical collider Nature Communications 8, 452 (2017).