Search

Fully understanding a chemical reaction on the quantum level is a long-standing goal in physics and chemistry. Experimental investigation of such state-to-state chemistry requires both the preparation of the reactants and the detection of the products in a quantum state resolved way, which has been a long term challenge. Using the high level control in the ultracold domain, we prepare a few-body quantum state of reactants and demonstrate state-to-state chemistry with unprecedented resolution. We present measurements and accompanying theoretical analysis for the recombination of three spin-polarized ultracold Rb atoms forming a weakly bound Rb$_2$ dimer. Detailed insights of the reaction process are obtained that suggest propensity rules for the distribution of reaction products. The scheme can readily be adapted to other species and opens a door to detailed investigations of inelastic or reactive processes in domains never before accessible., Comment: 27 pages, 11 figures, including Supplementary Information

The multichannel Efimov physics is investigated in ultracold heteronuclear admixtures of K and Rb atoms. We observe a shift in the scattering length where the first atom-dimer resonance appears in the $^{41}$K-$^{87}$Rb system relative to the position of the previously observed atom-dimer resonance in the $^{40}$K-$^{87}$Rb system. This shift is well explained by our calculations with a three-body model including the van der Waals interactions, and, more importantly, the multichannel spinor physics. With only minor difference in the atomic masses of the admixtures, the shift in the atom-dimer resonance positions can be cleanly ascribed to the isolated and overlapping Feshbach resonances in the $^{40}$K-$^{87}$Rb and $^{41}$K-$^{87}$Rb systems, respectively. Our study demonstrates the role of the multichannel Feshbach physics in determining Efimov resonances in heteronuclear three-body systems., Comment: 8 pages, 4 figures, several refferences are corrected

We investigate theoretically and experimentally the heteronuclear Efimov scenario for a three-body system that consists of two bosons and one distinguishable particle with positive intraspecies scattering lengths. The three-body parameter at the three-body scattering threshold and the scaling factor between consecutive Efimov resonances are found to be controlled by the scattering length between the two bosons, approximately independent of short-range physics. We observe two excited-state Efimov resonances in the three-body recombination spectra of an ultracold mixture of fermionic $^6 $Li and bosonic $^{133} $Cs atoms close to a Li-Cs Feshbach resonance, where the Cs-Cs interaction is positive. Deviation of the obtained scaling factor of 4.0(3) from the universal prediction of 4.9 and the absence of the ground state Efimov resonance shed new light on the interpretation of the universality and the discrete scaling behavior of heteronuclear Efimov physics., Comment: 6 pages, 3 figures, additional supplemental material

The quantum mechanical few-body problem at ultracold energies poses severe challenges to theoretical techniques, particularly when long-range interactions are present that decay only as a power-law potential. In this paper we review the techniques and progress in studies of universal few-body physics for ultracold atoms, particularly those related to long-range interactions.

Experimental studies with ultracold atoms have enabled major breakthroughs in understanding three-body physics, historically a fundamental yet challenging problem. This is because the interactions among ultracold atoms can be precisely varied using magnetically tunable scattering resonances known as Feshbach resonances. The collisions of ultracold atoms have been discovered to have many universal aspects near the unitarity limit. Away from this limit, many quantum states are expected to be active during a three-body collision, making the collisional observables practically unpredictable. Here we report a major development in predicting three-body ultracold scattering rates by properly building in the pairwise van der Waals interactions plus the multi-spin properties of a tunable Feshbach resonance state characterized by two known dimensionless two-body parameters. Numerical solution of the Schr{\"o}dinger equation then predicts the three-atom collisional rates without adjustable fitting parameters needed to fit data. Our calculations show quantitative agreement in magnitude and feature position and shape across the full range of tuning of measured rate coefficients for three-body recombination and atom-dimer collisions involving ultracold Cs atoms., Comment: 3 figures

We report the experimental and theoretical study of two-body interactions in a $^{6}$Li-$^{133}$Cs Fermi- Bose mixture. Using a translatable dipole trap setup, we have successfully trapped the two species in the same trap with temperatures of a few microkelvins. By monitoring atom number loss and inter-species thermalization, we identify five s-wave interspecies Feshbach resonances in the lowest two scattering channels. We construct a coupled channels model using molecular potentials to fit and characterize these resonances. Two of the resonances are as wide as 60 G and thus should be suitable for creating Feshbach molecules and searching for universal few-body scaling.

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 $a \approx -9.73 r_{\rm vdW}$, $r_{\rm vdW}$ 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 $a \approx 0.956 r_{\rm vdW}$. Here we find that a single universal three-body state associated with the d-wave dimer is also formed near the three-body break-up threshold at $a \approx 1.09 r_{\rm vdW}$ and its signature can be found through enhancement of the three-body recombination. The three-body effective potential curves that are crucial for understanding the recombination dynamics are also calculated and analyzed. An improved method to calculate the couplings, effective potential curves, and recombination rate coefficients is presented., Comment: 7 figures

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, have 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 atoms, 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 (BO) picture. Finally, we show the numerically determined 3BPs for some combinations of alkali atoms used in ultracold experiments., Comment: 5 pages, 3 figures, 1 table

The bound state and low-energy scattering properties of two oriented dipoles are investigated for both bosonic and fermionic symmetries. Interestingly, a universal scaling emerges for the expectation value of the angular momentum for deeply-bound two-dipole states. This scaling traces to the pendulum motion of two dipoles in strong dipole regime. The low-energy scattering phase shifts of two dipoles also show universal behavior. These universal observations make connections to the scaling laws reported in Refs. [1, 2] for three dipoles. Atomic units are used throughout this work., Comment: 7 pages, 6 figures, 1 table

We study three- and four-body Efimov physics in a heteronuclear atomic system with three identical heavy bosonic atoms and one light atom. We show that exchange of the light atom between the heavy atoms leads to both three- and four-body features in the low-energy inelastic rate constants that trace to the Efimov effect. Further, the effective interaction generated by this exchange can provide an additional mechanism for control in ultracold experiments. Finally, we find that there is no true four-body Efimov effect - that is, no infinite number of four-body states in the absence of two- and three-body bound states - resolving a decades-long controversy., Comment: 5 pages, 4 figures

A study of the universal physics for three oriented fermionic dipoles in the hyperspherical adiabatic representation predicts a single long-lived three-dipole state, which exists in only one three-body symmetry, should form near a two-dipole resonance. Our analysis reveals the spatial configuration of the universal state, and the scaling of its binding energy and lifetime with the strength of the dipolar interaction. In addition, three-body recombination of fermionic dipoles is found to be important even at ultracold energies. An additional finding is that an effective long-range repulsion arises between a dipole and a dipolar dimer that is tunable via dipolar interactions., Comment: 4 pages, 3 figures, 1 table

Three oriented bosonic dipoles are treated 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., Comment: 4 pages, 2 figures, 1 table

We develop an adiabatic Floquet picture in the length gauge to describe the dynamics of a hydrogen atom in an intense laser field. In this picture, we discuss the roles played by frequency and intensity in terms of adiabatic potentials and the couplings between them, which gives a physical and intuitive picture for quantum systems exposed to a laser field. For simplicity, analyze hydrogen and give the adiabatic potential curves as well as some physical quantities that can be readily calculated for the ground state. Both linearly and circularly polarized laser fields are discussed., Comment: 10 pages, 10 figures, and 1 table

We find that universal three-body physics extends beyond the threshold regime to non-zero energies. For ultracold atomic gases with a negative two-body $s$-wave scattering length near a Feshbach resonance, we show the resonant peaks characteristic of Efimov physics persist in three-body recombination to higher collision energies. For this and other inelastic processes, we use the adiabatic hyperspherical representation to derive universal analytical expressions for their dependence on the scattering length, the collision energy, and --- for narrow resonances --- the effective range. These expressions are supported by full numerical solutions of the Schr\"odinger equation and display log-periodic dependence on energy characteristic of Efimov physics. This dependence is robust and might be used to experimentally observe several Efimov features., Comment: 16 pages, 6 figures

We have studied hydrogen-hydrogen-alkali three-body systems in the adiabatic hyperspherical representation. For the spin-stretched case, there exists a single $X$H molecular state when $X$ is one of the bosonic alkali atoms: $^7$Li, $^{23}$Na, $^{39}$K, $^{87}$Rb and $^{133}$Cs. As a result, the {\em only} recombination process is the one that leads to formation of $X$H molecules, H+H+$X$$\rightarrow$$X$H+H, and such molecules will be stable against vibrational relaxation. We have calculated the collision rates for recombination and collision induced dissociation as well as the elastic cross-sections for H+$X$H collisions up to a temperature of 0.5 K, including the partial wave contributions from $J^\Pi$=$0^+$ to $5^-$. We have also found that there is just one three-body bound state for such systems for $J^\Pi$=$0^+$ and no bound states for higher angular momenta., Comment: 10 pages, 5 figures, 4 tables

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. We obtain numerical and analytical results that allow us to identify universal features related to the resonance width. For narrow resonances, we have found a suppression of all inelastic processes in boson systems leading to deeply bound states and an enhancement for fermion systems., Comment: 5 pages, 3 figures