We present our experimental investigation of the interspecies Feshbach spectrum in a mixture of ${}^{167}$Er($F = 19/2, m_F = -19/2$)-${}^6$Li($F = 1/2, m_F = 1/2$) atoms in the microkelvin temperature regime. These temperatures are achieved by means of sympathetic cooling with ${}^{174}$Yb as a third species. Interspecies Feshbach resonances are then identified by investigation of the Er-Li inelastic collisional properties for magnetic fields up to 800 G. Numerous narrow resonances as well as six resonances with widths above 1 G could be identified. It is these broader resonances that hold much promise for interesting future investigations of, for exmample, novel superfluid states and Efimov states in large mass-imbalanced, all-fermionic two-component systems.
We perform Feshbach spectroscopy in an ultracold mixture of $^{23}$Na and $^{40}$K with different spin-state combinations. We have observed 24 new interspecies Feshbach resonances at magnetic field up to 350 G. A full coupled-channel calculation is performed to assign these resonances. Among them, 12 resonances are identified as d-wave Feshbach resonances. These d-wave Feshbach resonances are about 5 G systematically smaller than the predications based on previous model potential. Taking into account these new experimental results, we improve the Born-Oppenheimer potentials between Na and K, a…
We report on the experimental observation of Feshbach resonances in large mass-imbalance mixtures of Erbium (Er) and Lithium (Li). All combinations between ${}^{168}$Er, ${}^{166}$Er and ${}^7$Li, ${}^6$Li are cooled to temperatures of a few microkelvin, partially by means of sympathetic cooling together with Ytterbium (Yb) as a third mixture component. The Er-Li inelastic interspecies collisional properties are studied for magnetic fields up to 680 G. In all cases resonant interspecies loss features, indicative of Feshbach resonances, have been observed. While most resonances have sub-Gauss w…
We present a detailed study of interspecies Feshbach resonances of the bosonic $^{23}\mathrm{Na}+$$^{39}\mathrm{K}$ mixture for magnetic fields up to $750 \, \mathrm{G}$ in various collision channels. A total of fourteen Feshbach resonances are reported, as well as four zero crossings of the scattering length and three inelastic two-body loss features. We use the observed magnetic field locations of the resonant features together with the known data on $^{23}\mathrm{Na}+$$^{40}\mathrm{K}$ to refine the singlet and triplet ground state potentials of NaK and achieve a consistent description of F…
We present investigations of the formation rate and collisional stability of lithium Feshbach molecules in an ultracold three-component mixture composed of two resonantly interacting fermionic 6-Li spin states and bosonic 174-Yb. We observe long molecule lifetimes (> 100 ms) even in the presence of a large ytterbium bath and extract reaction rate coefficients of the system. We find good collisional stability of the mixture in the unitary regime, opening new possibilities for studies and probes of strongly interacting quantum gases in contact with a bath species.
In this Letter we have studied dressed bound states in Fermi-Bose mixtures near broad interspecies resonance, and implications on many-body correlations. We present the evidence for a first order phase transition between a mixture of Fermi gas and condensate, and a fully paired mixture where extended fermionic molecules occupy a single pairing channel instead of forming a molecular Fermi surface. We have further investigated the effect of Fermi surface dynamics, pair fluctuations and discussed the validity of our results.
We present a study of interspecies Feshbach resonances in ultracold $^{7}$Li-$^{133}$Cs Bose-Bose mixtures. We locate ten interspecies resonances in three different spin-state combinations. By comparing to coupled-channel calculations, we assign six of the resonances to $s$-wave channels and the rest to $p$-wave channels. We use the $s$-wave resonances to refine the ground-state potentials of LiCs in the coupled-channel calculations and then obtain an accurate characterization of the scattering and bound-state properties of the mixtures. Our results will be useful for future experiments with u…
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 inte…
We investigate ultracold collisions in a novel mixture of $^6$Li and $^{53}$Cr fermionic atoms, discovering more than 50 interspecies Feshbach resonances via loss spectroscopy. Building a full coupled-channel model, we unambiguously characterize the $^{6}$Li-$^{53}$Cr scattering properties and yield predictions for other isotopic pairs. In particular, we identify various Feshbach resonances that enable the controlled tuning of elastic $s$- and $p$-wave $^{6}$Li-$^{53}$Cr interactions. Our studies thus make lithium-chromium mixtures emerge as optimally-suited platforms for the experimental sear…
We observe new Feshbach resonances in ultracold mixtures of $^{85}$Rb and $^{87}$Rb atoms in the $^{85}$Rb$|2, +2\rangle$+$^{87}$Rb$|1, +1\rangle$ and $^{85}$Rb$|2, -2\rangle$+$^{87}$Rb$|1, -1\rangle$ scattering channels. The positions and properties of the resonances are predicted and characterized using the semi-analytic multichannel quantum-defect theory by Gao. Of particular interest, a number of broad entrance-channel dominated p-wave resonances are identified, implicating exciting opportunities for studying a variety of p-wave interaction dominated physics.
We measure higher partial wave Feshbach resonances in an ultracold mixture of fermionic $^6$Li and bosonic $^{133}$Cs by magnetic field dependent atom-loss spectroscopy. For the $p$-wave Feshbach resonances we observe triplet structures corresponding to different projections of the pair rotation angular momentum onto the external magnetic field axis. We attribute the splittings to the spin-spin and spin-rotation couplings by modelling the observation using a full coupled-channel calculation. Comparison with an oversimplified model, estimating the spin-rotation coupling by describing the weakly…
Motivated by the prospect of observing Efimov and Bose polaron physics in ultracold mixtures of bosonic atoms with large mass imbalance, this work investigates the magnetic Feshbach resonances between $^{7}\text{Li}$ and $^{133}\text{Cs}$. The resonances are predicted at the 1 gauss level using the model of Pires et al. [Phys. Rev. A, 90, 012710] obtained from experimental observations of resonances between $^{6}\text{Li}$ and $^{133}\text{Cs}$. It is found that a few resonances in a practical range of magnetic field intensity could be used to tune the scattering length between $^{7}\text{Li}$…
We observe interspecies Feshbach resonances due to s-wave bound states in ultracold $^{39}$K-$^{133}$Cs scattering for three different spin mixtures. The resonances are observed as joint atom loss and heating of the K sample. We perform least-squares fits to obtain improved K-Cs interaction potentials that reproduce the observed resonances, and carry out coupled-channel calculations to characterize the scattering and bound-state properties for $^{39}$K-Cs, $^{40}$K-Cs and $^{41}$K-Cs. Our results open up the possibilities of tuning interactions in K-Cs atomic mixtures and of producing ultracol…
We have observed 69 $^{41}$K-$^6$Li interspecies Feshbach resonances including 13 elastic p-wave resonances and 6 broad d-wave resonances of $^{41}$K atoms in different spin-state combinations at fields up to 600~G. Multi-channel quantum defect theory calculation is performed to assign these resonances and the results show perfect agreement with experimental values after improving input parameters. The observed broad p- and d- wave resonances display a full resolved multiplet structure. They may serve as important simulators to nonzero partial wave dominated physics.
We present a detailed study of the scattering properties of ultracold mixtures of bosonic potassium atoms. We locate 20 previously unobserved Feshbach resonances in isotopic 39K-41K mixtures. These are assigned to s-wave molecular channels by comparison to an asymptotic bound state model and coupled channels calculations. Additional Feshbach resonances are studied in spin mixtures of a single potassium isotope, both in 39K and 41K. In particular, we characterize the parameters of a selected 39K Feshbach resonance by radio-frequency association of Feshbach molecules. Our results could be exploi…
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 …
We investigate magnetoassociation of ultracold fermionic Feshbach molecules in a mixture of $^{40}$K and $^{87}$Rb atoms, where we can create as many as $7\times 10^4$ $^{40}$K$^{87}$Rb molecules with a conversion efficiency as high as 45%. In the perturbative regime, we find that the conversion efficiency depends linearly on the density overlap of the two gases, with a slope that matches a parameter-free model that uses only the atom masses and the known Feshbach resonance parameters. In the saturated regime, we find that the maximum number of Feshbach molecules depends on the atoms' phase-sp…
We discuss the stability of homonuclear and heteronuclear mixtures of 3He and 4He atoms in the metastable 2^3S_1 state (He*) and predict positions and widths of Feshbach resonances by using the Asymptotic Bound-state Model (ABM). All calculations are performed without fit parameters, using \emph{ab-initio} calculations of molecular potentials. One promising very broad Feshbach resonance (ΔB=72.9^{+18.3}_{-19.3} mT) is found that allows for tuning of the inter-isotope scattering length.
We report on the observation of Feshbach resonances at low magnetic field strength (below 10 G) in the Fermi-Fermi mixture of $^{161}$Dy and $^{40}$K. We characterize five resonances by measurements of interspecies thermalization rates and molecular binding energies. As a case of particular interest for applications, we consider a resonance near 7.29 G, which combines accurate magnetic tunability and access to the universal regime of interactions with experimental simplicity. We show that lifetimes of a few 100 ms can be achieved for the optically trapped, resonantly interacting mixture. We al…
We have observed 26 interspecies Feshbach resonances at fields up to 2050 G in ultracold $^6$Li+$^{23}$Na mixtures for different spin-state combinations. Applying the asymptotic bound-state model to assign the resonances, we have found that most resonances have d-wave character. This analysis serves as guidance for a coupled-channel calculation, which uses modified interaction potentials to describe the positions of the Feshbach resonances well within the experimental uncertainty and to calculate their widths. The scattering length derived from the improved interaction potentials is experiment…
The spectrum of two bosons and two fermions in a trap is calculated using a correlated-Gaussian basis throughout the range of a broad Fano-Feshbach resonance. The calculations provide a few-body solution to the magneto-association of fermionic Feshbach molecules. This solution is used to study the time evolution of the system as the scattering length changes, mimicking experiments with Bose-Fermi mixtures near Fano-Feshbach resonances. The structure of avoided crossings in the few-body spectrum enables an interpretation of the dynamics of the system as a sequence of Landau-Zener transitions. T…
Magnetically-tunable Feshbach resonances are an indispensable tool for experiments with atomic quantum gases. We report on twenty thus far unpublished Feshbach resonances and twenty one further probable Feshbach resonances in spin mixtures of ultracold fermionic 40 K with temperatures well below 100 nK. In particular, we locate a broad resonance at B=389.6 G with a magnetic width of 26.4 G. Here 1 G=10^-4 T. Furthermore, by exciting low-energy spin waves, we demonstrate a novel means to precisely determine the zero crossing of the scattering length for this broad Feshbach resonance. Our findin…
We examine the density profiles of the quantum degenerate Bose-Fermi mixture of $^{174}$Yb-$^{173}$Yb, experimental observed recently, in the mean field regime. In this mixture there is a possibility of tuning the Bose-Bose and Bose-Fermi interactions simultaneously using two well separated optical Feshbach resonances, and it is a good candidate to explore phase separation in Bose-Fermi mixtures. Depending on the Bose-Bose scattering length $a_\BB$, as the Bose-Fermi interaction is tuned the density of the fermions is pinched or swapping with bosons occurs.
We study the widths of interspecies Feshbach resonances in a mixture of the fermionic quantum gases 6Li and 40K. We develop a model to calculate the width and position of all available Feshbach resonances for a system. Using the model we select the optimal resonance to study the 6Li/40K mixture. Experimentally, we obtain the asymmetric Fano lineshape of the interspecies elastic cross section by measuring the distillation rate of 6Li atoms from a potassium-rich 6Li/40K mixture as a function of magnetic field. This provides us with the first experimental determination of the width of a resonance…
We describe the formation of fermionic NaLi Feshbach molecules from an ultracold mixture of bosonic 23Na and fermionic 6Li. Precise magnetic field sweeps across a narrow Feshbach resonance at 745 G result in a molecule conversion fraction of 5% for our experimental densities and temperatures, corresponding to a molecule number of 5*10^4. The observed molecular decay ifetime is 1.3 ms after removing free Li and Na atoms from the trap.
We study the properties of dilute bosons immersed in a single component Fermi sea across a broad boson-fermion Feshbach resonance. The stability of the mixture requires that the bare interaction between bosons exceeds a critical value, which is a universal function of the boson-fermion scattering length, and exhibits a maximum in the unitary region. We calculate the quantum depletion, momentum distribution and the boson contact parameter across the resonance. The transition from condensate to molecular Fermi gas is also discussed.
Ultracold gases of interacting spin-orbit coupled fermions are predicted to display exotic phenomena such as topological superfluidity and its associated Majorana fermions. Here, we experimentally demonstrate a route to strongly-interacting single-component atomic Fermi gases by combining an s-wave Feshbach resonance (giving strong interactions) and spin-orbit coupling (creating an effective p-wave channel). We identify the Feshbach resonance by its associated atomic loss feature and show that, in agreement with our single-channel scattering model, this feature is preserved and shifted as a fu…
In the vicinity of a narrow Feshbach resonances Efimov features are expected to be characterized by the resonance's properties rather than the van der Waals length of the interatomic potential. Although this theoretical prediction is well-established by now, it still lacks experimental confirmation. Here, we apply our recently developed three-channel model [Yudkin and Khaykovich, Phys. Rev. A 103, 063303 (2021)] to the experimental result obtained in a mass-imbalanced $^6$Li-$^{133}$Cs mixture in the vicinity of the narrowest resonance explored to date [Johansen at. al. Nat. Phys. 13, 731 (201…
We theoretically evaluate the feasibility to form magnetically-tunable Feshbach molecules in collisions between fermionic $^6$Li atoms and bosonic metastable $^{174}$Yb($^3$P$_2$) atoms. In contrast to the well-studied alkali-metal atom collisions, collisions with meta-stable atoms are highly anisotropic. Our first-principle coupled-channel calculation of these collisions reveals the existence of broad Feshbach resonances due to the combined effect of anisotropic-molecular and atomic-hyperfine interactions. In order to fit our predictions to the specific positions of experimentally-observed br…
We present a joint experimental and theoretical investigation of the lifetime of weakly bound dimers formed near narrow interspecies Feshbach resonances in mass-imbalanced Fermi-Fermi systems, considering the specific example of a mixture of $^6$Li and $^{40}$K atoms. Our work addresses the central question of the increase in the stability of the dimers resulting from Pauli suppression of collisional losses, which is a well-known effect in mass-balanced fermionic systems near broad resonances. We present measurements of the spontaneous dissociation of dimers in dilute samples, and of the colli…
We report on the observation of nineteen interspecies Feshbach resonances in an optically trapped ultracold Bose-Fermi mixture of ^{133}Cs and ^{6}Li in the two energetically lowest spin states. We assign the resonances to s- and p-wave molecular channels by a coupled-channels calculation, resulting in an accurate determination of LiCs ground state potentials. Fits of the resonance position based on the undressed Asymptotic Bound State model do not provide the same level of accuracy as the coupled-channels calculation. Several broad s-wave resonances provide prospects to create fermionic LiCs …
In a recent Letter (Phys. Rev. lett. 105, 195301 (2010)), Song et al. introduced a new variational approach to treat strong attractive boson-fermion (BF) correlations in BF atomic mixtures. The proposed theory predicts a first order phase transition to a condensate of composite BF pairs with center of mass momentum Q=0 as opposed to a composite fermionic molecular Fermi gas. We show in this comment that their approach is incorrect and moreover, by resorting to an exactly solvable model we demonstrate that there cannot be more than one correlated Q=0 BF pair in complete contradiction with their…
We study the three-fermion problem within a 1D model of a Feshbach resonance in order to gain insight into how the FFLO-like state at small negative scattering lengths evolves into a Bose-Fermi mixture at small positive scattering lengths. The FFLO state possesses an oscillating superfluid correlation function, while in a Bose-Fermi mixture correlations are monotonic. We find that this behavior is is already present at the 3-body level. We present an exact study of the 3-body problem, and gain extra insights by considering worldlines of a path integral Monte-Carlo calculation.
The ultracold mixture of \Na and \Rb atoms has become an important system for investigating physics in Bose-Bose atomic mixtures and for forming ultracold ground-state polar molecules. In this work, we provide an improved characterization of the most commonly used Feshbach resonance near 347.64 G between \Na and \Rb in their absolute ground states. We form Feshbach molecules using this resonance and measure their binding energies by dissociating them via magnetic field modulation. We use the binding energies to refine the singlet and triplet potential energy curves, using coupled-channel bound…
We develop a diagrammatic approach for solving few-body problems in heteronuclear fermionic mixtures near a narrow interspecies Feshbach resonance. We calculate s-, p-, and d-wave phaseshifts for the scattering of an atom by a weakly-bound dimer. The fermionic statistics of atoms and the composite nature of the dimer lead to a strong angular momentum dependence of the atom-dimer interaction, which manifests itself in a peculiar interference of the scattered s- and p-waves. This effect strengthens with the mass ratio and is remarkably pronounced in 40K-(40K-6Li) atom-dimer collisions. We calcul…
We present a detailed theoretical and experimental study of Feshbach resonances in the 6Li-40K mixture. Particular attention is given to the inelastic scattering properties, which have not been considered before. As an important example, we thoroughly investigate both elastic and inelastic scattering properties of a resonance that occurs near 155 G. Our theoretical predictions based on a coupled channels calculation are found in excellent agreement with the experimental results. We also present theoretical results on the molecular state that underlies the 155G resonance, in particular concerni…
We theoretically investigate normal-state properties of a gas mixture of single-component bosons and fermions with a hetero-nuclear Feshbach resonance. Including strong hetero-pairing fluctuations associated with the Feshbach resonance, we calculate single-particle density of states, as well as the spectral weight at various interaction strengths. For this purpose, we employ an improved T-matrix approximation (TMA), where the bare Bose Green's function in the non-selfconsistent TMA self-energy is modified so as to satisfy the Hugenholtz-Pines relation at the Bose-Einstein condensation (BEC) te…
We present measurements of interspecies Feshbach resonances and subsequent creation of dual-species Bose-Einstein condensates of $^{23}\mathrm{Na}$ and $^{39}\mathrm{K}$. We prepare both optically trapped ensembles in the spin state $\left|f = 1,m_{f}=-1\right\rangle$ and perform atom loss spectroscopy in a magnetic field range from 0 to $700 \, \mathrm{G}$. The observed features include several s-wave poles and a zero crossing of the interspecies scattering length as well as inelastic two-body contributions in the $\mathcal{M} = m_{\mathrm{Na}}+m_{\mathrm{K}} = -2$ submanifold. We identify an…
We report on the experimental observation of a strongly interacting gas of ultracold two-electron fermions with orbital degree of freedom and magnetically tunable interactions. This realization has been enabled by the demonstration of a novel kind of Feshbach resonance occurring in the scattering of two 173Yb atoms in different nuclear and electronic states. The strongly interacting regime at resonance is evidenced by the observation of anisotropic hydrodynamic expansion of the two-orbital Fermi gas. These results pave the way towards the realization of new quantum states of matter with strong…
We study the dissociation of Feshbach molecules in ultracold Fermi gases with spin-orbit (SO) coupling. Since SO coupling can induce quantum transition between the Feshbach molecules and the fully polarized Fermi gas, the Feshbach molecules can be dissociated by the SO coupling. We experimentally realized this new type of dissociation in ultracold gases of 40K atoms with SO coupling created by Raman beams, and observed that the dissociation rate is highly non-monotonic on both the positive and negative Raman-detuning sides. Our results show that the dissociation of Feshbach molecules can be co…
We study inelastic two-body relaxation in a spin-polarized ultracold Fermi gas in the presence of a p-wave Feshbach resonance. It is shown that in reduced dimensionalities, especially in the quasi-one-dimensional case, the enhancement of the inelastic rate constant on approach to the resonance is strongly suppressed compared to three dimensions. This may open promising paths for obtaining novel many-body states.
We present an overview of recent developments in species-imbalanced ("polarized") Feshbach-resonant Fermi gases. We summarize the current status of thermodynamics of these systems in terms of a phase diagram as a function of the Feshbach resonance detuning, polarization and temperature. We review instabilities of the s-wave superfluidity across the BEC-BCS crossover to phase separation, FFLO states, polarized molecular superfluidity and the normal state, driven by the species imbalance. We discuss different models and approximations of this system and compare their predictions to current exper…
We investigate magnetically tunable Feshbach resonances between ultracold europium atoms and between europium and alkali-metal atoms using multichannel quantum scattering calculations. For ultracold gases of europium atoms both homonuclear $^{153}$Eu+$^{153}$Eu and heteronuclear $^{151}$Eu+$^{153}$Eu systems are studied. Calculations for mixtures of europium and alkali-metal atoms are carried out for prototype systems of $^{153}$Eu+$^{87}$Rb and $^{153}$Eu+$^7$Li. We analyze the prospects for the control of scattering properties, observation of quantum chaotic behavior, and magnetoassociation …
We have created a quantum degenerate Bose-Fermi mixture of 23Na and 40K with widely tunable interactions via broad interspecies Feshbach resonances. Twenty Feshbach resonances between 23Na and 40K were identified. The large and negative triplet background scattering length between 23Na and 40K causes a sharp enhancement of the fermion density in the presence of a Bose condensate. As explained via the asymptotic bound-state model (ABM), this strong background scattering leads to a series of wide Feshbach resonances observed at low magnetic fields. Our work opens up the prospect to create chemic…
We theoretically investigate the high-temperature thermodynamics of a harmonically trapped Fermi gas across a narrow Feshbach resonance, by using the second-order quantum virial expansion, and point out some new features compared to the broad resonance. The interatomic interaction is modeled by the pseudopotential with an additional parameter, i.e., the effective range, to characterize the narrow resonance width. Deeply inside the width of a narrow Feshbach resonance, we find the second virial coefficient evolves with the effective range from the well-known universal value 1/4 in the broad-res…
In this letter we consider the superradiant phase transition of a two-component Fermi gas in a cavity across a Feshbach resonance. It is known that quantum statistics plays a crucial role for the superradiant phase transition in atomic gases; in contrast to bosons, in a Fermi gas this transition exhibits strong density dependence. We show that across a Feshbach resonance, while the two-component Fermi gas passes through the BEC-BCS crossover, the superradiant phase transition undergoes a corresponding crossover from a fermionic behavior on the weakly interacting BCS side, to a bosonic behavior…
We propose a general method for optical control of magnetic Feshbach resonances in ultracold atomic gases with more than one molecular state in an energetically closed channel. Using two optical frequencies to couple two states in the closed channel, inelastic loss arising from spontaneous emission is greatly suppressed by destructive quantum interference at the two-photon resonance, i.e., dark-state formation, while the scattering length is widely tunable by varying the frequencies and/or intensities of the optical fields. This technique is of particular interest for a two-component atomic Fe…
We study the quench dynamics of a two-component ultracold Fermi gas from the weak into the strong interaction regime, where the short time dynamics are governed by the exponential growth rate of unstable collective modes. We obtain an effective interaction that takes into account both Pauli blocking and the energy dependence of the scattering amplitude near a Feshbach resonance. Using this interaction we analyze the competing instabilities towards Stoner ferromagnetism and pairing.
We study theoretically magnetically induced Feshbach resonances and near-threshold bound states in isotopic NaK pairs. Our calculations accurately reproduce Feshbach spectroscopy data on Na$^{40}$K and explain the origin of the observed multiplets in the p-wave [Phys. Rev. A 85, 051602(R) (2012)]. We apply the model to predict scattering and bound state threshold properties of the boson-boson Na$^{39}$K and Na$^{41}$K systems. We find that the Na$^{39}$K isotopic pair presents broad magnetic Feshbach resonances and favorable ground-state features for producing non-reactive polar molecules by t…
We use quantum Monte Carlo, including backflow corrections, to investigate a two-component Fermi gas on the upper branch of a Feshbach resonance and contrast it with the hard sphere gas. We find that, in both cases, the Fermi liquid becomes unstable to ferromagnetism at a $k_F a$ smaller than the mean field result, where $k_F$ is the Fermi wavevector and $a$ the scattering length. Even though the total energies $E(k_F a)$ are similar in the two cases, their pair correlations and kinetic energies are completely different, reflecting the underlying potentials. We discuss the extent to which our …
We study the impurity problem in a gas of $^{173}$Yb atoms near the recently discovered orbital Feshbach resonance. In an orbital Feshbach resonance, atoms in the electronic ground state $^1S_0$ interact with those in the long-lived excited $^3P_0$ state with magnetically tunable interactions. We consider an impurity atom with a given hyperfine spin in the $^3P_0$ state interacting with a single-component Fermi sea of atoms in the ground $^1S_0$ manifold. Close to the orbital Feshbach resonance, the impurity can induce collective particle-hole excitations out of the Fermi sea, which can be reg…
We study the problem of a single impurity of mass $M$ immersed in a Fermi sea of particles of mass $m$. The impurity and the fermions interact through a s-wave narrow Feshbach resonance, so that the Feshbach length $R_*$ naturally appears in the system. We use simple variational ansatz, limited to at most one pair of particle-hole excitations of the Fermi sea and we determine for the polaronic and dimeronic branches the phase diagram between absolute ground state, local minimum, thermodynamically unstable regions (with negative effective mass), and regions of complex energies (with negative im…
Experimental control of magnetic Fano-Feshbach resonances in ultracold $^{40}$K Fermi gases, using radio-frequency (RF) fields, is demonstrated. Spectroscopic measurements are made of three molecular levels within 50 MHz of the atomic continuum, along with their variation with magnetic field. Modifying the scattering properties by an RF field is shown by measuring the loss profile versus magnetic field. This work provides the high accuracy locations of ground molecular states near the s-wave Fano-Feshbach resonance, which can be used to study the crossover regime from a Bose-Einstein condensat…
We directly measured the normalized $\it{s}$-wave scattering cross-section of ultracold $^{40}\rm{K}$ atoms across a magnetic-field Feshbach resonance by colliding pairs of degenerate Fermi gases (DFGs) and imaging the scattered atoms. We extracted the scattered fraction for a range of bias magnetic fields, and measured the resonance location to be $B_0 = 20.206(15)$ mT with width $Δ= 1.0(5)$ mT. To optimize the signal-to-noise ratio of atom number in scattering images, we developed techniques to interpret absorption images in a regime where recoil induced detuning corrections are significant.…
We use laser light near-resonant with a molecular bound-to-bound transition to control a magnetic Feshbach resonance in ultracold Fermi gases of $^{40}$K atoms. The spectrum of excited molecular states is measured by applying a laser field that couples the ground Feshbach molecular state to electronically excited molecular states. Nine strong bound-to-bound resonances are observed below the $^{2}P_{1/2}+^{2}S_{1/2}$ threshold. We use radio-frequency spectroscopy to characterize the laser-dressed bound state near a specific bound-to-bound resonance and show clearly the shift of the magnetic Fes…
