Efimov Resonances Research Articles

Three Resonant Ultracold Bosons: Off-Resonance Effects

We solve a finite range two-channel model for three resonant identical bosons. The model provides a minimal description of the various magnetic Feshbach resonances in single species ultracold bosonic systems, including off-resonant scattering. We obtain important insights into the interpretation of seminal experiments: the three-body recombination rate measured in sodium and the Efimov resonances observed in cesium. This approach quantifies nonuniversal effects appearing for a finite magnetic field detuning.

Observation of Heteronuclear Atomic Efimov Resonances

Building on the recent experimental observation with ultracold atoms, we report the first experimental evidence of Efimov physics in a heteronuclear system. A mixture of ;{41}K and ;{87}Rb atoms was cooled to few hundred nanokelvins and stored in an optical dipole trap. Exploiting a broad interspecies Feshbach resonance, the losses due to three-body collisions were studied as a function of the interspecies scattering length. We observe an enhancement of the three-body collisions for three distinct values of the interspecies scattering lengths, both positive and negative, where no Feshbach resonances are expected. We attribute the two features at negative scattering length to the existence of two kinds of Efimov trimers, KKRb and KRbRb.

Confinement-induced Efimov resonances in Fermi-Fermi mixtures

A Fermi-Fermi mixture of $^{40}\text{K}$ and $^{6}\text{L}\text{i}$ does not exhibit the Efimov effect in a free space, but the Efimov effect can be induced by confining only $^{40}\text{K}$ in one dimension. Here the Efimov's three-body parameter is controlled by the confinement length. We show that the three-body recombination rate in such a system in the dilute limit has a characteristic logarithmic-periodic dependence on the effective scattering length with the scaling factor 22.0 and can be expressed by formulas similar to those for identical bosons in three dimensions. The ultracold mixture of $^{40}\text{K}$ and $^{6}\text{L}\text{i}$ in the one-dimensional--three-dimensional mixed dimensions is thus a promising candidate to observe the Efimov physics in fermions.

Efimov states near a Feshbach resonance

We describe three-body collisions close to a Feshbach resonance by taking into account two-body scattering processes involving both the open and the closed channel. We extract the atom-dimer scattering length and the three-body recombination rate, predicting the existence at negative scattering length of a sharp minimum in the recombination losses due to the presence of a shallow bound level. We obtain very good agreement with the experimental results in atomic 133Cs of Kraemer et al. [Nature 440, 315 (2006)], and predict the position of Efimov resonances in a gas of 39K atoms.

Efimov states embedded in the three-body continuum

We present analytical solutions for the three-body problem with multichannel interactions and identify a class of quasibound Efimov states that can be viewed as three-body Fano-Feshbach resonances. Our method employs a multichannel generalization of the Fermi pseudopotential to model low-energy atom-atom interactions near a magnetically tunable Fano-Feshbach resonance. We discuss the conditions under which quasibound Efimov states may be supported and identify the interaction parameters that limit the lifetimes of these states. We speculate that it may be possible to observe these states using spectroscopic methods, perhaps allowing for the measurement of multiple Efimov resonances.

Calculation of three-body resonances using slow-variable discretization coupled with a complex absorbing potential

We developed a method to calculate positions and widths of three-body resonances. The method combines the hyperspherical adiabatic approach, slow variable discretization method (Tolstikhin et al., J. Phys. B: At. Mol. Opt. Phys. 29, L389 (1996)), and a complex absorbing potential. The method can be used to obtain resonances having short-range or long-range wave functions. In particular, we applied the method to obtain very shallow three-body Efimov resonances for a model system (Nielsen et al., Phys. Rev. A 66, 012705 (2002)).

Efimov resonances in atomic three-body systems

In a recent work [Phys. Rev. Lett. 94, 143201 (2005)], we reported an accumulation of three-body resonant states attached to n=2 and higher two-body thresholds. A more careful investigation revealed that there are resonances of the same kind above the n=1 threshold as well. This suggests that the resonances attached to the thresholds are Efimov resonances.

Evidence for Efimov quantum states in an ultracold gas of caesium atoms

Systems of three interacting particles are notorious for their complex physical behaviour. A landmark theoretical result in few-body quantum physics is Efimov's prediction of a universal set of bound trimer states appearing for three identical bosons with a resonant two-body interaction. Counterintuitively, these states even exist in the absence of a corresponding two-body bound state. Since the formulation of Efimov's problem in the context of nuclear physics 35 years ago, it has attracted great interest in many areas of physics. However, the observation of Efimov quantum states has remained an elusive goal. Here we report the observation of an Efimov resonance in an ultracold gas of caesium atoms. The resonance occurs in the range of large negative two-body scattering lengths, arising from the coupling of three free atoms to an Efimov trimer. Experimentally, we observe its signature as a giant three-body recombination loss when the strength of the two-body interaction is varied. We also detect a minimum in the recombination loss for positive scattering lengths, indicating destructive interference of decay pathways. Our results confirm central theoretical predictions of Efimov physics and represent a starting point with which to explore the universal properties of resonantly interacting few-body systems. While Feshbach resonances have provided the key to control quantum-mechanical interactions on the two-body level, Efimov resonances connect ultracold matter to the world of few-body quantum phenomena.

Efimov resonances in atom-diatom scattering

We have investigated three identical bosons with very large pairwise scattering lengths. Normally such a situation is associated with Efimov states, where the three-body system has a set of very loosely bound states close to the three-body threshold. In the limit of infinite scattering length, the three-body system has infinitely many bound states. If, however, the two-body subsystems have deep lying two-body bound states, the Efimov states lie over the corresponding thresholds for breakup. We have calculated the positions and widths of these Feshbach resonances for some simple potentials numerically and have extracted the systematics. We explore the possibility of observing such Efimov resonances in atom-diatom scattering experiments with alkali atoms.