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arXiv:1801.06489 · Physical Review Letters

Three-Body Recombination near a Narrow Feshbach Resonance in Li6

Jiaming Li, Ji Liu, Le Luo, Bo Gao

Published May 10, 2018• 26 citations
arXivHTMLPDF

Abstract

We experimentally measure and theoretically analyze the three-atom recombination rate, L_{3}, around a narrow s-wave magnetic Feshbach resonance of ^{6}Li-^{6}Li at 543.3 G. By examining both the magnetic field dependence and, especially, the temperature dependence of L_{3} over a wide range of temperatures from a few μK to above 200 μK, we show that three-atom recombination through a narrow resonance follows a universal behavior determined by the long-range van der Waals potential and can be described by a set of rate equations in which three-body recombination proceeds via successive pairwise interactions. We expect the underlying physical picture to be applicable not only to narrow s wave resonances, but also to resonances in nonzero partial waves, and not only at ultracold temperatures, but also at much higher temperatures.

DOI
10.1103/physrevlett.120.193402

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We experimentally measure and theoretically analyze the three-atom recombination rate, L_{3}, around a narrow s-wave magnetic Feshbach resonance of ^{6}Li-^{6}Li at 543.3 G. By examining both the magnetic field dependence and, especially, the temperature dependence of L_{3} over a wide range of temperatures from a few μK to above 200 μK, we show that three-atom recombination through a narrow resonance follows a universal behavior determined by the long-range van der Waals potential and can be described by a set of rate equations in which three-body recombination proceeds via successive pairwise interactions. We expect the underlying physical picture to be applicable not only to narrow s wave resonances, but also to resonances in nonzero partial waves, and not only at ultracold temperatures, but also at much higher temperatures.
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.
Orbital-resolved three-body recombination across a p-wave Feshbach resonance in ultracold 6^66Li
We report precision, orbital-resolved measurements of three-body recombination near the 159~G ppp-wave Feshbach resonance in an ultracold gas of 6^{6}6Li atoms prepared in their lowest hyperfine state. Using a radio-frequency gated protocol that suppresses magnetic-field transients below the milligauss level, we resolve loss features associated with the ∣mℓ∣=1|m_\ell|=1∣mℓ​∣=1 and mℓ=0m_\ell=0mℓ​=0 orbital projections. The measured three-body loss coefficient L3L_3L3​ is well captured by a thermally averaged cascade-recombination model, enabling extraction of the resonance splitting δBδBδB and effective-range parameter kek_eke​. At the lowest temperature, we obtain δB=7.6(3)δB = 7.6(3)δB=7.6(3)~mG and ke=0.151(6) a0−1k_e = 0.151(6)\,a_0^{-1}ke​=0.151(6)a0−1​, both in quantitative agreement with coupled-channel theory. These results establish orbital-resolved three-body spectroscopy as a precision probe of ppp-wave scattering and provide a benchmark for microscopic models of resonant few-body loss.
The narrow sss-wave Feshbach resonance of a 6Li^{6}\mathrm{Li}6Li Fermi gas shows strong three-body loss, which is proposed to be used to measure the minute change of a magnetic field around the resonance. However, the eddy effect will cause ultracold atom experiencing a magnetic field delay to the desired magnetic field from the current of the magnetic coils. The elimination of the eddy effect will play a key role in any experiments that are motivated to measure the magnetic field to the precision of a parts per million stability. Here, we apply a method to correct the eddy effect for precision measurement of the magnetic field. We first record the three-body loss influenced by the induced eddy effect, then we use a first-order decay model to obtain the time constant of the actual magnetic field by fitting the atom loss. This precisely determines the actual magnetic field according to the time response of the three-body loss. After that, we implement the desired magnetic field to the atoms so that we can analyze the three-body loss across the narrow Feshbach resonance. The measured magnetic-field-dependent rate of three-body loss at an ultralow temperature shows that the three-body recombination is the dominated loss mechanism near the resonance. We expect this practical method of correcting the eddy effect error of the magnetic field can be further applied to future studies of quantum few- and many-body physics near a narrow Feshbach resonance.
We study three-body recombination of fully spin-polarized 6Li^{6}\mathrm{Li}6Li atoms that are interacting resonantly in relative ppp waves. Motivated by a recent experiment, we focus on negative scattering volumes where three atoms recombine into a deep dimer and another atom. We calculate the three-body recombination rate using a Faddeev equation derived from effective field theory. In particular, we study the magnetic field and temperature dependences of the loss rate and use the recombination data to determine the effective range of the ppp-wave atom-atom interaction. We also predict the existence of a shallow three-body resonance state that manifests itself as a prominent feature in the energy-dependent three-body recombination rate.
Abstract We report precision, orbital-resolved measurements of three-body recombination near the 159 G p -wave Feshbach resonance in an ultracold gas of 6 Li atoms prepared in their lowest hyperfine state. Using a radio-frequency gated protocol that suppresses magnetic-field transients below the milligauss level, we resolve loss features associated with the | m ℓ | = 1 and m ℓ = 0 orbital projections. The measured three-body loss coefficient L 3 is well captured by a thermally averaged cascade-recombination model, enabling extraction of the resonance splitting δ B and effective-range parameter k e . At the lowest temperature, we obtain δ B = 7.6 ( 3 ) mG and k e = 0.151 ( 6 ) a 0 − 1 , both in quantitative agreement with coupled-channel theory. These results establish orbital-resolved three-body spectroscopy as a precision probe of p -wave scattering and provide a benchmark for microscopic models of resonant few-body loss.
We have measured the interaction energy and three-body recombination rate for a two-component Fermi gas near a narrow Feshbach resonance and found both to be strongly energy dependent. Even for de Broglie wavelengths greatly exceeding the van der Waals length scale, the behavior of the interaction energy as a function of temperature cannot be described by atoms interacting via a contact potential. Rather, energy-dependent corrections beyond the scattering length approximation are required, indicating a resonance with an anomalously large effective range. For fields where the molecular state is above threshold, the rate of three-body recombination is enhanced by a sharp, two-body resonance arising from the closed-channel molecular state which can be magnetically tuned through the continuum. This narrow resonance can be used to study strongly correlated Fermi gases that simultaneously have a sizable effective range and a large scattering length.