Feshbach Resonances In Collisions Research Articles

Spin–spin interaction and magnetic Feshbach resonances in collisions of high-spin atoms with closed-shell atoms

Spin–spin interaction and magnetic Feshbach resonances in collisions of high-spin atoms with closed-shell atoms

Long-range states and Feshbach resonances in collisions between ultracold alkali-metal diatomic molecules and atoms

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 $^{40}\mathrm{K}^{87}\mathrm{Rb}+^{87}\mathrm{Rb}$. We show multiple types of resonance due to long-range states with rotational and/or hyperfine excitation, and consider the likelihood of them existing at low to moderate magnetic fields.

A Feshbach resonance in collisions between triplet ground-state molecules

Collisional resonances are important tools that have been used to modify interactions in ultracold gases, for realizing previously unknown Hamiltonians in quantum simulations1, for creating molecules from atomic gases2 and for controlling chemical reactions. So far, such resonances have been observed for atom-atom collisions, atom-molecule collisions3-7 and collisions between Feshbach molecules, which are very weakly bound8-10. Whether such resonances exist for ultracold ground-state molecules has been debated owing to the possibly high density of states and/or rapid decay of the resonant complex11-15. Here we report a very pronounced and narrow (25 mG) Feshbach resonance in collisions between two triplet ground-state NaLi molecules. This molecular Feshbach resonance has two special characteristics. First, the collisional loss rate is enhanced by more than two orders of magnitude above the background loss rate, which is saturated at the p-wave universal value, owing to strong chemical reactivity. Second, the resonance is located at a magnetic field where two open channels become nearly degenerate. This implies that the intermediate complex predominantly decays to the second open channel. We describe the resonant loss feature using a model with coupled modes that is analogous to a Fabry-Pérot cavity. Our observations provide strong evidence for the existence of long-lived coherent intermediate complexes even in systems without reaction barriers and open up the possibility of coherent control of chemical reactions.

High-partial-wave separable potential method for investigating Feshbach resonances of ultracold atoms

We present a high-partial-wave (non-zero partial-wave) separable potential method (SPM) for investigating magnetically induced Feshbach resonances in collisions of ultracold atoms, then derive the Lippmann–Schwinger equation for two ultracold alkali-metal atoms in an external magnetic field and calculate the generalized scattering length and weakly bound state energy. We apply this method to the 6Li system and calculate the weakly bound state energy and the scattering volume near three typical p-wave Feshbach resonances. The calculated results by using the SPM agree well with those by using the coupled channel method and with experimental measurements. The SPM is expected to simplify computation of the three-body collision Faddeev equation in the vicinity of two-body high partial-wave Feshbach resonances.

Magnetic Feshbach resonances in collisions of 23Na40K with 40K

We present measurements of more than 80 magnetic Feshbach resonances in collisions of ultracold 23Na40K with 40K. We assign quantum numbers to a group of low-field resonances and show that they are probably due to long-range states of the triatomic complex in which the quantum numbers of the separated atom and molecule are approximately preserved. The resonant states are not members of chaotic bath of short-range states. Similar resonances are expected to be a common feature of alkali-metal diatom + atom systems.

Prospects of Forming High-Spin Polar Molecules from Ultracold Atoms

We have investigated Feshbach resonances in collisions of high-spin atoms such as Er and Dy with closed-shell atoms such as Sr and Yb, using coupled-channel scattering and bound-state calculations. We consider both low-anisotropy and high-anisotropy limits. In both regimes we find many resonances with a wide variety of widths. The wider resonances are suitable for tuning interatomic interactions, while some of the narrower resonances are highly suitable for magnetoassociation to form high-spin molecules. These molecules might be transferred to short-range states, where they would have large magnetic moments and electric dipole moments that can be induced with very low electric fields. The results offer the opportunity to study mixed quantum gases where one species is dipolar and the other is not, and open up important prospects for a new field of ultracold high-spin polar molecules.

Heteroisotopic Feshbach resonances in collisions of cold Ca and Ca+

SynopsisWe investigate ultracold collisions of heteroisotopic pairs of Ca with Ca+ mediated by an external magnetic field. Based on the nuclear spin of Ca, namely I = 7/2 for 43Ca and I = 0 for other isotopes, we identify different scattering dynamics and characterize magnetic Feshbach resonances in 43Ca+43Ca+ and 43Ca+(40,42)Ca+ collisions. Our results suggest that interisotopic Feshbach resonances could be used to control charge-exchange in ultracold atom-ion mixtures of Ca and its ion.

Multi-channel modelling of the formation of vibrationally cold polar KRb molecules

We describe the theoretical advances that influenced the experimental creation of vibrationally and translationally cold polar 40K87Rb molecules [1, 2]. Cold molecules were created from very-weakly bound molecules formed by magnetic field sweeps near a Feshbach resonance in collisions of ultra-cold 40K and 87Rb atoms. Our analysis include the multi-channel bound-state calculations of the hyperfine and Zeeman mixed X1Σ+ and a3Σ+ vibrational levels. We find excellent agreement with the hyperfine structure observed in experimental data. In addition, we studied the spin–orbit mixing in the intermediate state of the Raman transition. This allowed us to investigate its effect on the vibrationally averaged transition dipole moment to the lowest rovibrational level of the X1Σ+ state. Finally, we obtained an estimate of the polarizability of the initial and final rovibrational states of the Raman transition near frequencies relevant for optical trapping of the molecules.

Feshbach resonances in an ultracoldLi7andRb87mixture

We report on the observation of five Feshbach resonances in collisions between ultracold $^{7}\mathrm{Li}$ and $^{87}\mathrm{Rb}$ atoms in the absolute ground-state mixture where both species are in their $\ensuremath{\mid}f,{m}_{f}⟩=\ensuremath{\mid}1,1⟩$ hyperfine states. The resonances appear as trap losses for the $^{7}\mathrm{Li}$ cloud induced by inelastic heteronuclear three-body collisions. The magnetic field values where they occur are important quantities for an accurate determination of the interspecies interaction potentials. Results of coupled channels calculations based on the observed resonances are presented and refined potential parameters are given. A very broad Feshbach resonance centered around $649\phantom{\rule{0.3em}{0ex}}\mathrm{G}$ should allow for fine-tuning of the interaction strength in future experiments.

Dynamics of OH(2Π)–He collisions in combined electric and magnetic fields

We use accurate quantum mechanical calculations to analyze the effects of parallel electric and magnetic fields on collision dynamics of OH(2Pi) molecules. It is demonstrated that spin relaxation in 3He-OH collisions at temperatures below 0.01 K can be effectively suppressed by moderate electric fields of order 10 kV/cm. We show that electric fields can be used to manipulate Feshbach resonances in collisions of cold molecules. Our results can be verified in experiments with OH molecules in Stark decelerated molecular beams and electromagnetic traps.

Feshbach resonances in mixtures of ultracoldLi6andRb87gases

We report on the observation of two Feshbach resonances in collisions between ultracold $^{6}\mathrm{Li}$ and $^{87}\mathrm{Rb}$ atoms in their respective hyperfine ground states $\ensuremath{\mid}F,{m}_{F}⟩=\ensuremath{\mid}1∕2,1∕2⟩$ and \ensuremath{\mid}1,1⟩. The resonances show up as trap losses for the $^{6}\mathrm{Li}$ cloud induced by inelastic Li-Rb-Rb three-body collisions. The magnetic field values where they occur represent important benchmarks for an accurate determination of the interspecies interaction potentials. A broad Feshbach resonance located at $1066.92\phantom{\rule{0.3em}{0ex}}\mathrm{G}$ opens interesting prospects for the creation of ultracold heteronuclear molecules. We furthermore observe a strong enhancement of the narrow $p$-wave Feshbach resonance in collisions of $^{6}\mathrm{Li}$ atoms at $158.55\phantom{\rule{0.3em}{0ex}}\mathrm{G}$ in the presence of a dense $^{87}\mathrm{Rb}$ cloud. The effect of the $^{87}\mathrm{Rb}$ cloud is to introduce Li-Li-Rb three-body collisions occurring at a higher rate than Li-Li-Li collisions.

Feshbach resonances in ultracold 39K

We discover several magnetic Feshbach resonances in collisions of ultracold 39K atoms, by studying atom losses and molecule formation. Accurate determination of the magnetic-field resonance locations allows us to optimize a quantum collision model for potassium isotopes. We employ the model to predict the magnetic-field dependence of scattering lengths and of near-threshold molecular levels. Our findings will be useful to plan future experiments on ultracold 39K atoms and molecules.

Observation of Feshbach Resonances between Two Different Atomic Species

We have observed three Feshbach resonances in collisions between 6Li and 23Na atoms. The resonances were identified as narrow loss features when the magnetic field was varied. The molecular states causing these resonances have been identified, and additional 6Li-23Na resonances are predicted. These resonances will allow the study of degenerate Bose-Fermi mixtures with adjustable interactions and could be used to generate ultracold heteronuclear molecules.

The stability and structure of the(mZ+,e−,e−,e+)system

The stability and structure of the $({m}^{Z+},{e}^{\ensuremath{-}},{e}^{\ensuremath{-}},{e}^{+})$ system is studied as a function of the mass of the ${m}^{Z+}$ particle and for $Z=1$, 2, 3, and 10. The $Z=1$ system can be regarded as an analog of the $A\mathrm{Ps}$ system (where $A$ is a group I or IB atom of the periodic table) and was found to be stable for all values of ${m}^{+}$. This is supportive of the idea that all the group I and IB atoms can bind Ps. The $({m}^{2+},{e}^{\ensuremath{-}},{e}^{\ensuremath{-}},{e}^{+})$ system is stable for all ${m}^{2+}∕{m}_{e}\ensuremath{\leqslant}0.68$ and evolves into a configuration best described as $({m}^{2+},{\mathrm{Ps}}^{\ensuremath{-}})$ when ${m}^{2+}∕{m}_{e}\ensuremath{\rightarrow}0$. The $({m}^{3+},{e}^{\ensuremath{-}},{e}^{\ensuremath{-}},{e}^{+})$ system was stable for a mass range given by ${m}^{3+}∕{m}_{e}\ensuremath{\leqslant}0.066\phantom{\rule{0.2em}{0ex}}32$, which suggests that positrons could form Feshbach resonances in collisions with positive ions which are isolectronic with the group II and IIB columns of the periodic table. The $({m}^{3+},{e}^{\ensuremath{-}},{e}^{\ensuremath{-}},{e}^{+})$ system has the unusual property that it has a mass range where it becomes more compact while its binding energy simultaneously decreases. The $({m}^{10+},{e}^{\ensuremath{-}},{e}^{\ensuremath{-}},{e}^{+})$ system is also stable at ${m}^{10+}∕{m}_{e}=0.002\phantom{\rule{0.2em}{0ex}}54$, which implies stability for all mass ratios less than 0.002 54. In total, the calculations suggest that the $({m}^{Z+},{e}^{\ensuremath{-}},{e}^{\ensuremath{-}},{e}^{+})$ system is stable whenever the ${m}^{Z+}+{\mathrm{Ps}}^{\ensuremath{-}}$ or $({m}^{Z+},{e}^{\ensuremath{-}})+\mathrm{Ps}$ breakups represent the lowest energy dissociation channel. As part of the analysis some improved estimates of the properties of the KPs ground state are reported.

Observation of optically induced feshbach resonances in collisions of cold atoms

We have observed optically induced Feshbach resonances in a cold ( <1 mK) sodium vapor. The optical coupling of the ground and excited-state potentials changes the scattering properties of an ultracold gas in much the same way as recently observed magnetically induced Feshbach resonances, but allows for some experimental conveniences associated with using lasers. The scattering properties can be varied by changing either the intensity or the detuning of a laser tuned near a photoassociation transition to a molecular state in the dimer. In principle this method allows the scattering length of any atomic species to be altered. A simple model is used to fit the dispersive resonance line shapes.

Observation of Low-Field Feshbach Resonances in Collisions of Cesium Atoms

We observe several Feshbach resonances in magnetic fields below 40 G for Cs atoms trapped in a 1D optical lattice. One resonance occurs in the lowest-energy ground state $F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3$, ${m}_{F}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3$ which is stable against inelastic binary collisions. This opens new possibilities for Bose condensation of Cs. When the elastic collision rate far exceeds the radial vibration frequency, we enter a 2D hydrodynamic regime where the thermalization rate is independent of density and temperature. Other resonances are also observed in the $F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3$, ${m}_{F}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}3$ state through a dramatic increase in the dipolar relaxation rate.

Prediction of Feshbach resonances in collisions of ultracold rubidium atoms

The observation of Bose-Einstein condensation ~BEC! in dilute ultracold gas samples of rubidium @1#, lithium @2#, and sodium atoms @3# has made it possible to study this macroscopic quantum phenomenon in its pure form without complicated modifications due to strong interactions. A variety of experiments has been proposed or already carried out, fascinating examples being the observation of collective shape oscillations and the observation of the relative phase of two Bose-Einstein condensates @4,5#. A rich variety of other experiments would come into reach if one could alter arbitrarily, possibly even in real time, the sign and magnitude of the atom-atom scattering length a. The scattering length occurs as the coefficient of the condensate self-interaction term in the condensate wave equation and has a profound effect on the stability and other properties of the condensate. An opportunity to change this parameter would arise if it were possible to tune the scattering length by means of external fields, i.e., either a static magnetic field @6# or a timedependent optical @7# or rf field @8#.