Quantitative analysis of losses close to a d -wave open-channel Feshbach resonance in K39

Abstract

We study atom losses associated to a previously unreported magnetic Feshbach resonance in potassium 39. This resonance is peculiar in that it presents d-wave character both in the open and in the closed channels, directly coupled by the dominant spin-exchange interaction. The losses associated to a d-wave open-channel resonance present specific signatures such as strong temperature dependance and anisotropic line shapes. The resonance strength and position depend on the axial projection of the orbital angular momentum of the system and are extracted from rigorous multichannel calculations. A two-step model, with an intermediate collision complex being ejected from the trap after collisions with free atoms, permits to reproduce the observed dependance of the loss rate as a function of temperature and magnetic field. PACS numbers: 34.50.Cx, Ultra-cold atoms are many-body quantum systems that offer great control and versatility [1]. Feshbach resonances allow in particular the interatomic interaction to be accurately controlled [2]. Such resonances occur when the kinetic energy of two colliding particles in an open channel becomes close to the energy of a bound state in a closed channel potential. Experimentally, Feshbach resonances in atomic collisions are typically induced and controlled using a variable magnetic field, relying on the different magnetic moment of two free atoms and of the resonant molecular state. The main parameter characterizing the interations at ultra-low temperatures (typically below 1µK), the s-wave scattering length a, can thus be made to vary and accurately controlled. These features have permitted the production of weakly bound molecules for large and positive a [3-8], the study of the BEC-BCS crossover with fermions [10][11][12], and the study of resonantly interacting Bose gases [13][14][15].In the case of spin-exchange interactions between open and closed collision channels, the coupling is isotropic and the orbital angular momentum is conserved. However, other types of coupling such as the dipolar spin-spin interaction are anisotropic and the orbital momentum can change. For example, d-wave or g-wave resonances, where d and g refer to the symmetry of the bound state have been reported for collisions in the s-wave [2,16,17]. Higher partial wave collisions in the entrance channel can also become resonant at higher energies. These resonances then have specific features and signatures as the collision rates strongly depends on the collision energy due to the centrifugal barrier that needs to be overcome. Feshbach resonances with higher partial waves in the entrance channel have been reported in p-waves [18-20] and also in d-waves [21-23]. A d-wave shape resonance was also discovered in 41 K [24]. Close to these resonances for fermions, high-order-wave pairing is expected, while p-wave and d-wave pairing plays a key role in superfluid liquid 3 He [25] or in d-wave Hi-Tc superconductors [26].For bosons, molecular condensates of rotating molecules are predicted [27]. Progresses in these direc...

Beyond Born-Oppenheimer approximation in ultracold atomic collisions

“…We identify the Feshbach resonance position by the maximum scattering rate coefficient at the kinetic energy given by the experimental conditions. We base our analysis on Feshbach resonance data for the isotope combinations 39 K-39 K from D'Errico et al [11] and [14,21], 40 K-40 K from Regal et al [22,25], 39 K-41 K from Tanzi et al [14], 41 K-41 K from Chen et al [24] and Tanzi et al [14], and 40 K-41 K from Wu et al [12]. We summarize the data in Tab.…”

Feshbach Resonances in p -Wave Three-Body Recombination within Fermi-Fermi Mixtures of Open-Shell Li6 and Closed-Shell Green1, Li2, Toh3 et al. 2020Phys. Rev. X541270View full textAdd to dashboardCite

“…In our fermionic system, recombination is dominated by trimer p-wave collisions and, as we show, has an asymmetric line shape and a temperature-independent maximum loss rate coefficient. Previously, such temperature-dependent studies have only been performed in bosonic systems [30][31][32][33][34] where the rate coefficients are controlled by either s-or d-wave trimer collisions and p-wave collisions do not play a role.…”

Exploring ultracold collisions in $^6$Li-$^{53}$Cr Fermi mixtures: Feshbach resonances and scattering properties of a novel alkali-transition metal system

“…2(a) and (b), respectively. Both features are highly asymmetric and they sensitively widen for increasing temperature, a behavior typical of l > 0wave FRs [58,59,62]. Without aiming at a quantitative lineshape analysis, we remark that the observed trends are well reproduced (see solid lines in Fig.…”