Magnetic Feshbach Resonances Research Articles

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

We investigate interactions and ultracold collisions of high-spin but spherical atoms with closed-shell atoms, focusing on the example of Cr with Yb. Such a combination has only one potential energy curve but gives rise to a substantial intra-atomic spin–spin interaction, which causes Feshbach resonances due to rotationally excited states. We find such resonances are guaranteed below 250 G and can reach widths of tens of G in favorable circumstances. We study the effect of hyperfine structure, which can create additional wide resonances at low fields. Finally, we consider isotopic substitution and show that for any realistic potential it is very likely that at least one combination of commonly used isotopes will have resonances with experimentally favorable properties. Thus, this is a promising system for both molecule formation and studying quantum mixtures including dipolar species. Published by the American Physical Society 2024

Observing S-Matrix Pole Flow in Resonance Interplay

We provide an overview of experiments exploring resonances in the collision of ultracold clouds of atoms. Using a laser-based accelerator that capitalises on the energy resolution provided by the ultracold atomic setting, we unveil resonance phenomena such as Feshbach and shape resonances in their quintessential form by literally photographing the halo of outgoing scattered atoms. We exploit the tunability of magnetic Feshbach resonances to instigate an interplay between scattering resonances. By experimentally recording the scattering in a parameter space spanned by collision energy and magnetic field, we capture the imprint of the S-matrix pole flow in the complex energy plane. After revisiting experiments that place a Feshbach resonance in the proximity of a shape resonance and an anti-bound state, respectively, we discuss the possibility of using S-matrix pole interplay between two Feshbach resonances to create a bound-state-in-the-continuum.

Two-component dimers of ultracold atoms with center-of-mass-momentum dependent interactions

In a previous paper [Phys. Rev. A 95, 060 701(R) (2017)], we demonstrated that a new type of two-body interaction, which depends on the center of mass (CoM) momentum, can be realized for ultracold atoms via laser-modulated magnetic Feshbach resonance (MFR). Further studies (e.g. L He et al, Phys. Rev. Lett. 120, 045 302 (2018)) show that various interesting phenomena, such as Fulde–Ferrell superfluids, can be induced by scattering between ultracold atoms with this interaction. In this work we investigate the shallow bound states of two ultracold atoms with this type of interaction. We show that when the magnetic field B is below the MFR point B 0, two shallow bound states can appear in this system. Namely, a ‘two-component dimer’ or a dimer with pseudo-spin 1/2 can be formed by two atoms. Furthermore, the dispersion curve of the dimer may have either single or double minimums in the CoM momentum space. The latter case can be explained as a result from significant pseudo-spin-orbital coupling (SOC) effects. Our results show that the ultracold gases with CoM momentum dependent interaction may be a candidate for quantum simulations with ultracold two-component molecules, especially the molecule gases with SOC.

High-flux source system for matter-wave interferometry exploiting tunable interactions

Atom interferometers allow determining inertial effects to high accuracy. Quantum-projection noise as well as systematic effects impose demands on large atomic flux as well as ultralow expansion rates. Here we report on a high-flux source of ultracold atoms with free expansion rates near the Heisenberg limit directly upon release from the trap. Our results are achieved in a time-averaged optical dipole trap and enabled through dynamic tuning of the atomic scattering length across two orders of magnitude interaction strength via magnetic Feshbach resonances. We demonstrate Bose-Einstein condensates with more than 6×104 particles after evaporative cooling for 170 ms and their subsequent release with a minimal expansion energy of 4.5 nK in one direction. Based on our results we estimate the performance of an atom interferometer and compare our source system to a high performance chip trap, as readily available for ultraprecise measurements in microgravity environments. Published by the American Physical Society 2024

The two-body collision controlled by the magnetic field and laser field near magnetic Feshbach resonance

It is crucial to control the collision between ultracold atoms by applying external fields. We developed a theoretical model for investigating the s-wave scattering of ultracold atoms controlled by the magnetic field and laser field. The calculation is performed by using the close-coupling method and mapped Fourier grid method. Due to the interference between the photoassociation and bound-to-bound transitions, the bound state in the continuum, which is a resonance with a vanishing width, occurs at the magnetic field position near the magnetic Feshbach resonance. The widths of resonances in the neighborhood of the bound state in the continuum are narrow. Changing the laser intensity can shift the magnetic field position where the bound state in the continuum occurs through modifying the ground molecular state to induce wide resonances at desired magnetic field positions. By increasing the resonance width, the tunability of the real part of the scattering length at resonances can be significantly improved. Changing the laser intensity can also adjust the coupling between the ground and excited molecular states. When the coupling between the ground and excited molecular states approaches zero, a resonance is induced, and the photoassociation and bound-to-bound transitions are both significantly suppressed at this resonance. Therefore, the atomic loss peak due to spontaneous emission does not appear at this resonance. The magnetic field position of this resonance is stable against the change in laser frequency.

Collective excitation of Bose–Einstein condensate of 23Na via high-partial wave Feshbach resonance

We experimentally observe the collective excitation (called surface-mode excitation) of Bose–Einstein condensate of 23Na by ramping the external magnetic field across the high-partial wave magnetic Feshbach resonance corresponding to vary the atomic interaction. We check the collective surface mode excitation of state for the three d-wave and three g-wave Feshbach resonances below 600 G and find that only two d-wave resonances present the strong excitation, another d-wave resonance only creates a weak excitation, and all g-wave resonances do not, which reflects the strength of these magnetic Feshbach resonances. For the collective excitation, the excitation of surface modes along the axial weak-confinement and radial strong-confinement of optical dipole trap shows different characteristics. We also study the lifetime of the collective oscillation by measuring the damping rate of the oscillation amplitude, which is caused by the mechanisms of dephasing effect and collisional relaxation. This excitation method gives us a new tool for investigating the properties of ultracold quantum gases without changing the trap frequencies.

Unitary p-wave interactions between fermions in an optical lattice.

Exchange-antisymmetric pair wavefunctions in fermionic systems can give rise to unconventional superconductors and superfluids1-3. The realization of these states in controllable quantum systems, such as ultracold gases, could enable new types of quantum simulations4-8, topological quantum gates9-11 and exotic few-body states12-15. However, p-wave and other antisymmetric interactions are weak in naturally occurring systems16,17, and their enhancement via Feshbach resonances in ultracold systems has been limited by three-body loss18-24. Here we create isolated pairs of spin-polarized fermionic atoms in a multiorbital three-dimensional optical lattice. We spectroscopically measure elastic p-wave interaction energies of strongly interacting pairs of atoms near a magnetic Feshbach resonance. The interaction strengths are widely tunable by the magnetic field and confinement strength, and yet collapse onto a universal curve when rescaled by the harmonic energy and length scales of a single lattice site. The absence of three-body processes enables the observation of elastic unitary p-wave interactions, as well as coherent oscillations between free-atom and interacting-pair states. All observations are compared both to an exact solution using a p-wave pseudopotential and to numerical solutions using an ab initio interaction potential. The understanding and control of on-site p-wave interactions provides a necessary component for the assembly of multiorbital lattice models25,26 and a starting point for investigations of how to protect such systems from three-body recombination in the presence of tunnelling, for instance using Pauli blocking and lattice engineering27,28.

Strongly Interacting Bose Polarons in Two-Dimensional Atomic Gases and Quantum Fluids of Polaritons

Polarons are quasiparticles relevant across many fields in physics: from condensed matter to atomic physics. Here, we study the quasiparticle properties of two-dimensional strongly interacting Bose polarons in atomic Bose–Einstein condensates and polariton gases. Our studies are based on the non-self consistent T-matrix approximation adapted to these physical systems. For the atomic case, we study the spectral and quasiparticle properties of the polaron in the presence of a magnetic Feshbach resonance. We show the presence of two polaron branches: an attractive polaron, a low-lying state that appears as a well-defined quasiparticle for weak attractive interactions, and a repulsive polaron, a metastable state that becomes the dominant branch at weak repulsive interactions. In addition, we study a polaron arising from the dressing of a single itinerant electron by a quantum fluid of polaritons in a semiconductor microcavity. We demonstrate the persistence of the two polaron branches whose properties can be controlled over a wide range of parameters by tuning the cavity mode.

Observation of magnetic Feshbach resonances between Cs and Yb173

We report the observation of magnetic Feshbach resonances between $^{173}\mathrm{Yb}$ and $^{133}\mathrm{Cs}$. In a mixture of Cs atoms prepared in the $(f=3,{m}_{f}=3)$ state and unpolarized fermionic $^{173}\mathrm{Yb}$, we observe resonant atom loss due to two sets of magnetic Feshbach resonances around 622 and 702 G. Resonances for individual Yb nuclear spin components ${m}_{i,\mathrm{Yb}}$ are split by its interaction with the Cs electronic spin, which also provides the main coupling mechanism for the observed resonances. The observed splittings and relative resonance strengths are in good agreement with theoretical predictions from coupled-channel calculations.

Rapid generation of all-optical K39 Bose-Einstein condensates using a low-field Feshbach resonance

Ultracold potassium is an interesting candidate for quantum technology applications and fundamental research as it allows controlling intra-atomic interactions via low-field magnetic Feshbach resonances. However, the realization of high-flux sources of Bose-Einstein condensates remains challenging due to the necessity of optical trapping to use magnetic fields as free parameter. We investigate the production of all-optical $^{39}$K Bose-Einstein condensates with different scattering lengths using a Feshbach resonance near $33$ G. By tuning the scattering length in a range between $75\, a_0$ and $300\, a_0$ we demonstrate a trade off between evaporation speed and final atom number and decrease our evaporation time by a factor of $5$ while approximately doubling the evaporation flux. To this end, we are able to produce fully condensed ensembles with $5.8\times10^4$ atoms within $850$ ms evaporation time at a scattering length of $232\, a_0$ and $1.6\times10^5$ atoms within $3.9$ s at $158\, a_0$, respectively. We deploy a numerical model to analyse the flux and atom number scaling with respect to scattering length, identify current limitations and simulate the optimal performance of our setup. Based on our findings we describe routes towards high-flux sources of ultra-cold potassium for inertial sensing.

Realization of space-dependent interactions by an optically controlled magnetic p -wave Feshbach resonance in degenerate Fermi gases

We report experimental realization of the space-dependent interaction by optical controlled narrow $p$-wave magnetic Feshbach resonance in a $^{40}\mathrm{K}$ Fermi gas. A space varied optical field at the tune-out wavelength is applied to illuminate the atomic sample, which drives the bound-to-bound molecular transition to shift the energy of a closed-channel molecule state. Due to the position varied atomic interaction induced by the different laser intensity distribution across the entire Fermi atom cloud, the space-dependent atomic loss rate is observed. This scheme provides a control technique to study the Fermi gas with the space-dependent atomic $p$-wave interaction, and has great potential in quantum simulation.

Microscopy of an ultranarrow Feshbach resonance using a laser-based atom collider: A quantum defect theory analysis

We employ a quantum defect theory framework to provide a detailed analysis of the interplay between a magnetic Feshbach resonance and a shape resonance in cold collisions of ultracold $^{87}\mathrm{Rb}$ atoms as captured in recent experiments using a laser-based collider [M. Chilcott et al., Phys. Rev. Research 3, 033209 (2021)]. By exerting control over a parameter space spanned by both collision energy and magnetic field, the width of a Feshbach resonance can be tuned over several orders of magnitude. We apply a quantum defect theory specialized for ultracold atomic collisions to fully describe of the experimental observations. While the width of a Feshbach resonance generally increases with collision energy, its coincidence with a shape resonance leads to a significant additional boost. By conducting experiments at a collision energy matching the shape resonance and using the shape resonance as a magnifying lens, we demonstrate a feature broadening to a magnetic width of 8 G compared to a predicted Feshbach resonance width much less than $0.1$ mG.

Laser manipulation of spin-exchange interaction between alkaline-earth atoms in 1S0 and 3P2 states

Ultracold gases of fermionic alkaline-earth(-like) atoms are hopeful candidates for the quantum simulation of many-body physics induced by magnetic impurities (e.g., the Kondo physics), because there are spin-exchange interactions (SEIs) between two atoms in the electronic ground ($^{1}\mathrm{S}_{0}$) and metastable ($^{3}\mathrm{P}$) state, respectively. Nevertheless, this SEI cannot be tuned via magnetic Feshbach resonance. In this paper, we propose three methods to control the SEI between one atom in the $^{1}\mathrm{S}_{0}$ state and another atom in the $^{3}\mathrm{P}_{2}$ states or $^{3}\mathrm{P}_{2}\text{\ensuremath{-}}^{3}\mathrm{P}_{0}$ dressed states, with one or two laser beams. These methods are based on the spin-dependent ac-Stark shifts of the $^{3}\mathrm{P}_{2}$ states or the $^{3}\mathrm{P}_{2}\text{\ensuremath{-}}^{3}\mathrm{P}_{0}$ Raman coupling. We show that due to the structure of alkaline-earth (like) atoms, the heating effects induced by the laser beams of our methods are very weak. For instance, for ultracold Yb atoms, ac-Stark-shift difference of variant spin states of the $^{3}\mathrm{P}_{2}(F=3/2)$ level, or the strength of the $^{3}\mathrm{P}_{2}\text{\ensuremath{-}}^{3}\mathrm{P}_{0}$ Raman coupling, could be of the order of $(2\ensuremath{\pi})\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$, while the heating rate (photon scattering rate) is only of the order of Hz. As a result, the Feshbach resonances, with which one can efficiently control the SEI by changing the laser intensity, may be induced by the laser beams with a low-enough heating rate, even if the scattering lengths of the bare interatomic interaction are so small that they are comparable with the length scale associated with the van der Waals interaction.

Erratum: Dispersive optical detection of magnetic Feshbach resonances in ultracold gases [Phys. Rev. A 96 , 022705 (2017)

Received 13 February 2022DOI:https://doi.org/10.1103/PhysRevA.105.029901©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAtom & ion trapping & guidingBose gasesLaser spectroscopyScattering of atoms, molecules, clusters & ionsUltracold collisionsAtomic, Molecular & Optical

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.

A compact and fast magnetic coil for the manipulation of quantum gases with Feshbach resonances.

Cold atom experiments commonly use broad magnetic Feshbach resonances to manipulate the interaction between atoms. In order to induce quantum dynamics by a change in the interaction strength, rapid (∼μs) magnetic field changes over several tens of Gauss are required. Here, we present a compact designof a coil and its control circuit for a change in the magnetic field up to 36G in 3 µs. The setup comprises two concentric solenoids with minimal space requirements, which can be readily added to existing apparatuses. This designmakes the observation of non-equilibrium physics with broad Feshbach resonances accessible.

Quantum Spin State Selectivity and Magnetic Tuning of Ultracold Chemical Reactions of Triplet Alkali-Metal Dimers with Alkali-Metal Atoms.

We demonstrate that it is possible to efficiently control ultracold chemical reactions of alkali-metal atoms colliding with open-shell alkali-metal dimers in their metastable triplet states by choosing the internal hyperfine and rovibrational states of the reactants as well as by inducing magnetic Feshbach resonances with an external magnetic field. We base these conclusions on coupled-channel statistical calculations that include the effects of hyperfine contact and magnetic-field-induced Zeeman interactions on ultracold chemical reactions of hyperfine-resolved ground-state Na and the triplet NaLi(a^{3}Σ^{+}) producing singlet Na_{2}(^{1}Σ_{g}^{+}) and a Li atom. We find that the reaction rates are sensitive to the initial hyperfine states of the reactants. The chemical reaction of fully spin-polarized, high-spin states of rotationless NaLi(a^{3}Σ^{+},v=0,N=0) molecules with fully spin-polarized Na is suppressed by a factor of 10-100 compared to that of unpolarized reactants. We interpret these findings within the adiabatic state model, which treats the reaction as a sequence of nonadiabatic transitions between the initial nonreactive high-spin state and the final low-spin states of the reaction complex. In addition, we show that magnetic Feshbach resonances can similarly change reaction rate coefficients by several orders of magnitude. Some of these resonances are due to resonant trimer bound states dissociating to the N=2 rotational state of NaLi(a^{3}Σ^{+},v=0) and would thus exist in systems without hyperfine interactions.

The effects of Feshbach resonance on spectral shifts in photoassociation of Cs atoms

We study the effects of magnetic Feshbach resonance on the shifts in photoassociation (PA) spectra of ultracold Cs atoms. A series of atom loss spectra show a linear variation of the frequency shift with the PA laser intensity at different magnetic fields near the d-wave Feshbach resonance of optically trapped Cs atoms. The magnetic field-dependence of the slope of the shift on the PA laser intensity exhibits a dispersive change near the Feshbach resonance. The theoretical formula derived from a model based on Fano resonance fits well with the experimental data. Using a model rectangular potential with tunable well depth and applying the Franck-Condon principle, we obtain numerical results, which are found to be largely in disagreement with the experimental findings.

Observation of a strongly ferromagnetic spinor Bose-Einstein condensate

We report the observation of strongly ferromagnetic F=1 spinor Bose-Einstein condensates of Li7 atoms. The condensates are generated in an optical dipole trap without using magnetic Feshbach resonances, so that the condensates have internal spin degrees of freedom. Studying the nonequilibrium spin dynamics, we have measured the ferromagnetic spin interaction energy and determined the s-wave scattering length difference among total spin f channels to be af=2−af=0=−18(3) Bohr radius. This strong collision-channel dependence leads to a large variation in the condensate size with different spin composition. We were able to excite a radial monopole mode after a spin-flip transition between the |mF=0〉 and |mF=1〉 spin states. From the experiments, we estimated the scattering length ratio af=2/af=0=0.27(6), and determined af=2=7(2) and af=0=25(5) Bohr radii, respectively. The results indicate the spin-dependent interaction energy of our system is as large as 46% of the condensate chemical potential.1 MoreReceived 11 June 2020Accepted 28 August 2020DOI:https://doi.org/10.1103/PhysRevResearch.2.033471Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBose-Einstein condensatesUltracold collisionsAtomic, Molecular & Optical

Feshbach resonances in an erbium-dysprosium dipolar mixture

We report on the observation of heteronuclear magnetic Feshbach resonances in several isotope mixtures of the highly magnetic elements erbium and dysprosium. Among many narrow features, we identify two resonances with a width greater than one Gauss. We characterize one of these resonances, in a mixture of $^{168}$Er and $^{164}$Dy, in terms of loss rates and elastic cross section, and observe a temperature dependence of the on-resonance loss rate suggestive of a universal scaling associated with broad resonances. Our observations hold promise for the use of such a resonance for tuning the interspecies scattering properties in a dipolar mixture. We further compare the prevalence of narrow resonances in an $^{168}$Er-$^{164}$Dy mixture to the single-species case, and observe an increased density of resonances in the mixture.