Feshbach resonances in ultracold atomic and molecular collisions: threshold behaviour and suppression of poles in scattering lengths
Jeremy M. Hutson
备注：
10 pages, 2 figures. Version 4 has slightly revised content to reflect the realisation that the resonant scattering length a_res can be complex, which will sometimes produce a reduction in inealastic scattering near a resonance
In the absence of inelastic scattering, Feshbach resonances produce poles in scattering lengths and very large peaks in elastic cross sections. However, inelastic scattering removes the poles. Whenever the resonant state is coupled comparably to the elastic and inelastic channels, the scattering length exhibits only a small oscillation and peaks in cross sections are dramatically suppressed. A resonant scattering length is defined to characterize the amplitude of the oscillation, and is shown to be small for many collisions of ultracold molecules. The results suggest that cross sections for ultracold molecular inelastic collisions are much less sensitive to details of the potential than has been believed.
Feshbach-optimized photoassociation of ultracold $^6$Li$^{87}$Rb molecules with short pulses
本文研究了在磁费什巴赫共振附近短脉冲作用下，基态$^6$ Li $^{87}$ Rb分子通过$\mathrm{B}^1Π$电子态的双色光缔合.施加近共振磁场以混合初始波函数的超精细单重态和三重态分量并增强光缔合速率，然后通过第二脉冲将群体转移到基态。我们表明，产生的分子的绝对数量的增加高达三个数量级是可以实现的深绑定的振动水平。这种技术可以推广到具有可接近的磁费什巴赫共振的其他分子。
We investigate magnetically tunable Feshbach resonances in ultracold collisions between ground-state Yb and Cs atoms, using coupled-channel calculations based on an interaction potential recently determined from photoassociation spectroscopy. We predict resonance positions and widths for all stable isotopes of Yb, together with resonance decay parameters where appropriate. The resonance patterns are richer and more complicated for fermionic Yb than for spin-zero isotopes, because there are additional level splittings and couplings due to scalar and tensorial Yb hyperfine interactions. We exami…
我们报道了超冷玻色子$^{23}$ Na $^{87}$ Rb Feshbach分子通过磁缔合的产生。通过斜变跨物种间费什巴赫共振的磁场，可以从近简并的超冷混合物中产生至少4000个分子。由于非弹性原子-分子碰撞的快速损失被观察到，这限制了纯分子数，在去除残留原子后，到1700。纯分子样品可以在光阱中存活21.8（8）ms，足够长的时间用于将来的分子光谱学研究，以相干地转移到单重态振转基态，其中这些分子对化学反应是稳定的，并且具有3.3德拜的永久电偶极矩。我们还用振荡磁场方法测量了Feshbach分子在费什巴赫共振附近的结合能，发现这些分子有很大的闭通道分数。
Charge transfer in ultracold gases via Feshbach resonances
我们研究了在同元素原子和离子的异源同位素组合的超冷碰撞中控制电荷交换的前景。这种处理方法很容易应用于碱金属或链烷烃-土金属，如过程$^9$ Be $^{+}$ + $^{10}$ Be $\leftrightarrow$ $^{9}$ Be + $^{10}$ Be $^{+}$所示，它具有良好的电子、核和超精细结构。费什巴赫共振得到的量子散射计算在一个标准的耦合通道形式主义与非BO条款起源于核动力学运营商。在322 G处预测的窄共振附近，我们发现电荷交换速率系数从几乎为零上升到大于$10^{-12}$ cm $^3$ /s的值。我们的研究结果表明，可控的电荷交换反应之间的不同同位素的合适的原子-离子对与潜在的应用量子系统工程研究电荷扩散被困冷原子-离子混合物和模拟多体物理。
Ultracold Fermionic Feshbach Molecules of $^{23}$Na$^{40}$K
我们报告的超冷费米子Feshbach分子的形成$^{23}$ Na $^{40}$ K，第一个费米子分子，是化学稳定的基态。在费什巴赫共振附近，近简并分子气体的寿命超过100 ms。所测得的分子结合能对磁场的依赖性证明了在宽的场范围内的分子的开放通道的字符，并意味着显着的单重混合。这将使得能够有效地转移到单重振动基态，导致具有强偶极相互作用的稳定分子费米气体。
We report the observation of a dimer-dimer inelastic collision resonance for ultracold Feshbach molecules made of bosonic sodium and rubidium atoms. This resonance, which we attribute to the crossing of the dimer-dimer threshold with a heteronuclear tetramer state, manifests itself as a pronounced inelastic loss peak of dimers when the interspecies scattering length between the constituent atoms is tuned. Near this resonance, a strong modification of the temperature dependence of the dimer-dimer scattering is observed. Our result provides insight into the heteronuclear four-body system consist…
We present a study of interspecies Feshbach resonances in ultracold $^{7}$Li-$^{133}$Cs Bose-Bose mixtures. We locate ten interspecies resonances in three different spin-state combinations. By comparing to coupled-channel calculations, we assign six of the resonances to $s$-wave channels and the rest to $p$-wave channels. We use the $s$-wave resonances to refine the ground-state potentials of LiCs in the coupled-channel calculations and then obtain an accurate characterization of the scattering and bound-state properties of the mixtures. Our results will be useful for future experiments with u…
We investigate ultracold collisions in a novel mixture of $^6$Li and $^{53}$Cr fermionic atoms, discovering more than 50 interspecies Feshbach resonances via loss spectroscopy. Building a full coupled-channel model, we unambiguously characterize the $^{6}$Li-$^{53}$Cr scattering properties and yield predictions for other isotopic pairs. In particular, we identify various Feshbach resonances that enable the controlled tuning of elastic $s$- and $p$-wave $^{6}$Li-$^{53}$Cr interactions. Our studies thus make lithium-chromium mixtures emerge as optimally-suited platforms for the experimental sear…
Helium atoms in the metastable $2^3{S_{1}}$ state (He$^*$) have unique advantages for ultracold atomic experiments. However, there is no known accessible Feshbach resonance in He$^*$, which could be used to manipulate the scattering length and hence unlock several new experimental possiblities. Previous experimental and theoretical studies for He$^*$ have produced contradictory results. We aimed to resolve this discrepancy with a theoretical search for Feshbach resonances, using a new close-coupled model of He$^*$ collisions in the presence of an external magnetic field. Several resonances wer…
Recent studies demonstrated anomalous temperature shifts for some Fano-Feshbach resonances of thulium atoms. These anomalies were explained by the variation in light intensity in the optical dipole trap, which accompanied changes in temperature. In addition, a temperature-related transformation of the statistics of the interresonance spacing was demonstrated [1]. Here, we analyze the shifts of isolated s- and d-type Fano-Feshbach resonances of ultracold thulium atoms with temperature for a fixed depth of an optical dipole trap. The measurements are consistent with the 3-body recombination-base…
We consider the long-range states expected for complexes formed from an alkali-metal diatomic molecule in a singlet state and an alkali-metal atom. We explore the structure of the Hamiltonian for such systems, and the couplings between the six angular momenta that are present. We consider the patterns and densities of the long-range states, and the terms in the Hamiltonian that can cause Feshbach resonances when the states cross threshold as a function of magnetic field. We present a case study of $^{40}$K$^{87}$Rb+$^{87}$Rb. We show multiple types of resonance due to long-range states with ro…
We measure higher partial wave Feshbach resonances in an ultracold mixture of fermionic $^6$Li and bosonic $^{133}$Cs by magnetic field dependent atom-loss spectroscopy. For the $p$-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…
We have observed 69 $^{41}$K-$^6$Li interspecies Feshbach resonances including 13 elastic p-wave resonances and 6 broad d-wave resonances of $^{41}$K atoms in different spin-state combinations at fields up to 600~G. Multi-channel quantum defect theory calculation is performed to assign these resonances and the results show perfect agreement with experimental values after improving input parameters. The observed broad p- and d- wave resonances display a full resolved multiplet structure. They may serve as important simulators to nonzero partial wave dominated physics.
We propose a new type of Feshbach resonance occurring when two different ultracold atoms in their ground state undergo an s-wave collision in the presence of a continuous-wave laser light. The atoms collide in the dissociation continuum of the molecular electronic ground state which is coupled by the light to a rovibrational level of the same electronic ground state: we name this a Laser-Assisted Self-Induced Feshbach Resonance (LASIFR). This mechanism, valid for all polar molecules, is analyzed on the example of ultracold 87Rb and 84Sr atoms, for which the laser frequency falls in the THz ran…
Ultracold assembly of diatomic molecules has enabled great advances in controlled chemistry, ultracold chemical physics, and quantum simulation with molecules. Extending the ultracold association to triatomic molecules will offer many new research opportunities and challenges in these fields. A possible approach is to form triatomic molecules in the ultracold atom and diatomic molecule mixture by employing the Feshbach resonance between them. Although the ultracold atom-diatomic-molecule Feshbach resonances have been observed recently, utilizing these resonances to form triatomic molecules rem…
We measure chemical reactions between a single trapped $^{174}$Yb$^+$ ion immersed in an ultracold bath of $^6$Li atoms containing trace amounts of Li$_2$ dimers. This produces LiYb$^+$ molecular ions that we detect via mass spectrometry. We explain the reaction rates by modelling the dimer density as a function of the magnetic field and obtain excellent agreement when we assume the reaction to follow the Langevin rate. Our results present a novel approach towards the creation of cold molecular ions and point to the exploration of ultracold chemistry in ion molecule collisions. What is more, w…
We have investigated magnetically tunable Feshbach resonances in ultracold collisions of Rb with Yb in its metastable $^3$P$_2$ and $^3$P$_0$ states, using coupled-channel scattering and bound-state calculations. For the $^3$P$_2$ state, we find sharp resonances when both atoms are in their lowest Zeeman sublevels. However, these resonances are decayed by inelastic processes that produce Yb atoms in $^3$P$_1$ and $^3$P$_0$ states. The molecules that might be produced by magnetoassociation at the $^3$P$_2$ thresholds can decay by similar pathways and would have lifetimes no more than a few micr…
