Yujun Wang

Universal three-body parameter in heteronuclear atomic systems.

In Efimov physics, a three-body parameter (3BP), previously regarded as nonuniversal, uniquely defines bound and scattering properties of three particles. A universal 3BP, however, has been recently shown in experiments and theory in ultracold homonuclear gases. Our present study further predicts a universal 3BP for heteronuclear atomic systems near broad Feshbach resonances and provides physical interpretations for its origin. We show that for a system composed of two light and one heavy atom, the physical origin of the universal 3BP is similar to the homonuclear case, while for systems composed by one light and two heavy atoms, the universality of the 3BP is now mostly controlled by the heavy-heavy interatomic properties. This new universality is explained by the universal properties of the van der Waals interactions in a simple Born-Oppenheimer picture. Finally, we show the numerically determined 3BPs for some combinations of alkali atoms used in ultracold experiments.

Ultracold Few-Body Systems

Abstract Recent advances in controlling interatomic interactions, coupled with new techniques for producing and interrogating exotic regimes in ultracold quantum gases, have resulted in the emergence of ultracold systems as a natural and inspiring playground for few-body physics, feeding the robust and interdisciplinary growth of this field. Both theory and experiment have benefitted from this interplay and have pushed the study of fundamental, universal few-body physics forward more rapidly than at any time during the previous few decades. The non-pertubative nature of these strongly correlated few-body systems makes them extremely challenging, but at the same time is responsible for interesting and counterintuitive phenomena—the Efimov effect being one of the most prominent examples. In this paper, we review the fundamentals of strongly correlated few-body physics for ultracold systems, much of which is related to three-body Efimov physics, and we survey the current state of experimental achievement. We do not, however, restrict our exploration to the three-body Efimov effect and analyze several few-body systems that fall outside this now-canonical Efimov scenario. We discuss systems with more than three particles—a natural extension of Efimov physics—and we discuss systems in which the interactions are not short-ranged, therefore violating a fundamental condition for Efimov physics, but with equally universal properties.

Efimov Effect for Three Interacting Bosonic Dipoles

Three oriented bosonic dipoles are treated by using the hyperspherical adiabatic representation, providing numerical evidence that the Efimov effect persists near a two-dipole resonance and in a system where angular momentum is not conserved. Our results further show that the Efimov features in scattering observables become universal, with a known three-body parameter; i.e., the resonance energies depend only on the two-body physics, which also has implications for the universal spectrum of the four-dipole problem. Moreover, the Efimov states should be long-lived, which is favorable for their creation and manipulation in ultracold dipolar gases. Finally, deeply bound two-dipole states are shown to be relatively stable against collisions with a third dipole, owing to the emergence of a repulsive interaction originating in the angular momentum nonconservation for this system.

Ultracold three-body collisions near narrow Feshbach resonances

We study ultracold three-body collisions of bosons and fermions when the interatomic interaction is tuned near a narrow Feshbach resonance. We show that the width of the resonance has a substantial impact on the collisional properties of ultracold gases in the strongly interacting regime. From our numerical and analytical analyses, we identify universal features dependent on the resonance width. Remarkably, we find that all inelastic processes near narrow resonances leading to deeply bound states in bosonic systems are suppressed, while those for fermionic systems are enhanced. As a result, narrow resonances present a scenario that is the reverse of that found for broad resonances, opening up the possibility of creating stable samples of ultracold bosonic gases with large scattering lengths.

Efimov Trimer Formation via Ultracold Four-Body Recombination

We discuss the collisional formation of Efimov trimers via ultracold four-body recombination. In particular, we consider the reaction A+A+A+B-->A_{3}+B with A and B ultracold atoms. We obtain expressions for the four-body recombination rate up to an overall constant and show that it reflects the three-body Efimov physics either as a function of collision energy or as a function of the two-body s-wave scattering length between A atoms. In addition, we briefly discuss issues important for experimentally observing this interesting and unexplored process.

Universal three-body recombination via resonant d-wave interactions

For a system of three identical bosons interacting via short-range forces, when two of the atoms are about to form a two-body s-wave dimer, there exists an infinite number of three-body bound states. This effect is the well-known Efimov effect. These three-body states (Efimov states) are found to be universal for ultracold atomic gases and the lowest Efimov state crosses the three-body break-up threshold when the s-wave two-body scattering length is

Universal Three-Body Physics for Fermionic Dipoles

a \approx -9.73 r_{\rm vdW}

Heteronuclear Efimov Scenario with Positive Intraspecies Scattering Length.

,

Conditions for Efimov physics for finite-range potentials

r_{\rm vdW}

Cold three-body collisions in hydrogen-hydrogen-alkali-metal atomic systems

being the van der Waals length. This article focuses on a generalized version of this Efimov scenario, where two of the atoms are about to form a two-body d-wave dimer, which leads to strong d-wave interactions. In a recent paper [B. Gao, Phys. Rev. A. {\bf 62}, 050702(R) (2000)], Bo Gao has predicted that for broad resonances the d-wave dimer is always formed near