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arXiv:1810.11201 · Physical Review A

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

Lauriane Fouché, Amaudric Boissé, Guillaume Berthet, S. Lepoutre, Andrea Simoni, Thomas Bourdel

Published Feb 6, 2019• 12 citations
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Abstract

We study atom losses associated to a previously unreported magnetic Feshbach resonance in $^{39}\mathrm{K}$. This resonance is peculiar in that it presents $d$-wave character both in the open and 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 us to reproduce the observed dependance of the loss rate as a function of temperature and magnetic field.

DOI
10.1103/physreva.99.022701

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We study atom losses associated to a previously unreported magnetic Feshbach resonance in potassium 39. This resonance is peculiar in that it presents ddd-wave character both in the open and in the closed channels, directly coupled by the dominant spin-exchange interaction. The losses associated to a ddd-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.
We analyze a narrow Feshbach resonance with ultracold chromium atoms colliding in ddd wave. The resonance is made possible by dipole-dipole interactions, which couple an incoming l=2l=2l=2 collision channel with a bound molecular state with l=0l=0l=0. We find that three-body losses associated with this resonance increase with temperature, and that the loss feature width as a function of magnetic field also increases linearly with temperature. The analysis of our experimental data shows that the Feshbach coupling is small compared both to the temperature and to the density limited lifetime of the resonant bound molecular state. One consequence is that the three-body loss rate is proportional to the square of the number of atoms, and that we can directly relate the amplitude of the losses to the Feshbach coupling parameter. We compare our measurement to a calculation of the coupling between the collisional channel and the molecular bound state by dipole-dipole interactions, and find a good agreement, with no adjustable parameter. An analysis of the loss line shape is also performed, which enables to precisely measure the position of the resonance.
We report on the observation of magnetic Feshbach resonances in a Fermi-Fermi mixture of ultracold atoms with extreme mass imbalance and on their unique p-wave dominated three-body recombination processes.Our system consists of open-shell alkali-metal 6 Li and closed-shell 173 Yb atoms, both spin polarized and held at various temperatures between 1 and 20 μK.We confirm that Feshbach resonances in this system are solely the result of a weak separation-dependent hyperfine coupling between the electronic spin of 6 Li and the nuclear spin of 173 Yb.Our analysis also shows that three-body recombination rates are controlled by the identical fermion nature of the mixture, even in the presence of s-wave collisions between the two species and with recombination rate coefficients outside the Wigner threshold regime at our lowest temperature.Specifically, a comparison of experimental and theoretical line shapes of the recombination process indicates that the characteristic asymmetric line shape as a function of applied magnetic field and a maximum recombination rate coefficient that is independent of temperature can only be explained by triatomic collisions with nonzero, p-wave total orbital angular momentum.The resonances can be used to form ultracold doublet ground-state molecules and to simulate quantum superfluidity in mass-imbalanced mixtures.
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High partial-wave Feshbach resonances in an ultracold 6^66Li-133^{133}133Cs mixture
We measure higher partial wave Feshbach resonances in an ultracold mixture of fermionic 6^66Li and bosonic 133^{133}133Cs by magnetic field dependent atom-loss spectroscopy. For the ppp-wave Feshbach resonances we observe triplet structures corresponding to different projections of the pair rotation angular momentum onto the external magnetic field axis. We attribute the splittings to the spin-spin and spin-rotation couplings by modelling the observation using a full coupled-channel calculation. Comparison with an oversimplified model, estimating the spin-rotation coupling by describing the weakly bound close-channel molecular state with the perturbative multipole expansion, reveals the significant contribution of the molecular wavefunction at short internuclear distances. Our findings highlight the potential of Feshbach resonances in providing precise information on short- and intermediate-range molecular couplings and wavefunctions. The observed ddd-wave Feshbach resonances allow us to refine the LiCs singlet and triplet ground-state molecular potential curves at large internuclear separations.
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