Recent studies demonstrated anomalous temperature shifts for some Fano-Feshbach resonances of thulium atoms. These anomalies were explained by the variation in light intensity in the optical dipole trap, which accompanied changes in temperature. In addition, a temperature-related transformation of the statistics of the interresonance spacing was demonstrated [1]. Here, we analyze the shifts of isolated s- and d-type Fano-Feshbach resonances of ultracold thulium atoms with temperature for a fixed depth of an optical dipole trap. The measurements are consistent with the 3-body recombination-based theory of the temperature-related resonance shift and enable the extraction of the resonance parameters, particularly the magnetic moments of closed channel states. This parameter and the known polarizability of the open channel enable us to separate the contributions of the temperature and Stark shift to the overall shift of the resonances and show the dominant role of the Stark effect in the overall shift.
Here, we report on the observation of a random to chaotic temperature transition in the spacing of Fano-Feshbach resonances in the ultracold polarized gas of thulium atoms. This transition is due to the appearance of so-called d-resonances, which are not accessible at low temperatures, in the spectra at high temperatures, which drastically changes thulium's overall resonance statistic. In addition to this statistical change, it has been observed that s- and d-resonances experience quite different temperature shifts: s-resonances experience almost no shift with the temperature, while d-resonanc…
Recently, transformation from random to chaotic behavior in the statistics of Fano-Feshbach resonances was observed in thulium atoms with rising ensemble temperature. We performed random matrix theory simulations of such spectra and analyzed the resulting statistics. Our simulations show that, when evaluated in terms of the Brody parameter, resonance statistics do not change or change insignificantly with rising temperature if temperature is the only changing parameter. In the experiments evaluated, temperature was changed simultaneously with optical dipole trap depth. Thus, simulations includ…
We consider photoassociation from a state of two free atoms when the continuum state is close to a magnetic field induced Feshbach resonance and analyze Fano interference in photoassociation. We show that the minimum in photoassociation profiles characterized by the Fano asymmetry parameter $q$ is independent of laser intensity, while the maximum explicitly depends on laser intensity. We further discuss the possibility of nonlinear Fano effect in photoassociation near a Feshbach resonance.
We report the observation of resonance-like loss in the trap population of ultracold dysprosium as a function of magnetic field, which we attribute to anisotropy-induced Fano-Feshbach resonances arising from Dy's large magnetic dipole moment and nonzero electronic orbital angular momentum. We recorded these resonances for four different isotopes, three bosonic and one fermionic, over a field range of 0-6 G and show that the number of resonances changes significantly as a function of temperature, even in the nK regime. Most of the observed resonances are of very narrow width. The fermionic isot…
Decay of bound states due to coupling with free particle states is a general phenomenon occurring at energy scales from MeV in nuclear physics to peV in ultracold atomic gases. Such a coupling gives rise to Fano-Feshbach resonances (FFR) that have become key to understanding and controlling interactions - in ultracold atomic gases, but also between quasiparticles such as microcavity polaritons. The energy positions of FFR were shown to follow quantum chaotic statistics. In contrast, lifetimes which are the fundamental property of a decaying state, have so far escaped a similarly comprehensive …
This paper investigates the Fano-Feshbach resonance with a two-channel coupled-square-well model in both the frequency and time domains. This systems is shown to exhibit Fano lineshape profiles in the energy absorption spectrum. The associated time-dependent dipole response has a phase shift that has recently been understood to be related to the Fano lineshape asymmetric $q$ parameter by $ϕ=2arg(q-i)$. The present study demonstrates that the phase-$q$ correspondence is general for any Fano resonance in the weak coupling regime, independent of the transition mechanism.
Photoassociation (PA) spectrum in the presence of a magnetic Feshbach resonance is analyzed. Nonperturbative solution of the problem yields analytical expressions for PA linewidth and shift which are applicable for arbitrary PA laser intensity and magnetic field tuning of Feshbach Resonance. We show that by tuning magnetic field close to Fano minimum, it is possible to suppress power broadening at increased laser intensities. This occurs due to quantum interference of PA transitions from unperturbed and perturbed continuum. Line narrowing at high laser intensities is accompanied by large spect…
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…
Compared to purely atomic collisions, ultracold collisions involving molecules have the potential to support a much larger number of Fano-Feshbach resonances due to the huge amount of ro-vibrational states available. In order to handle such ultracold atom-molecule collisions, we formulate a theory that incorporates the ro-vibrational Fano-Feshbach resonances in a statistical manner while treating the physics of the long-range scattering, which is sensitive to such things as hyperfine states, collision energy and any applied electromagnetic fields, exactly within multichannel quantum defect the…
The multichannel quantum defect theory (MQDT) in combination with the frame transformation (FT) approach is applied to model the Fano-Feshbach resonances measured for $^{7}$Li$^{87}$Rb and $^{6}$Li$^{87}$Rb [Marzok {\it et al.} Phys. Rev. A {\bf 79} 012717 (2009)]. The MQDT results show a level of accuracy comparable to that of previous models based on direct, fully numerical solutions of the the coupled channel Schrödinger equations (CC). Here, energy levels deduced from 2-photon photoassociation spectra for $^{7}$Li$^{85}$Rb are assigned by applying the MQDT approach, obtaining the bound sta…
Emergent Fano-Feshbach resonance in two-band superconductors with an incipient quasi-flat band: Enhanced critical temperature evading particle-hole fluctuations
该研究针对两带超导中粒子-空穴涨落抑制配对的问题，通过GMB形式体系研究准平带体系，发现涌现的Fano-Feshbach共振可规避涨落抑制、提升$T_{\ m c}$，揭示多带超导的普适特征。
We propose a new type of Feshbach resonance occurring when two different ultracold atoms in their ground state undergo an s-wave collision in the presence of a continuous-wave laser light. The atoms collide in the dissociation continuum of the molecular electronic ground state which is coupled by the light to a rovibrational level of the same electronic ground state: we name this a Laser-Assisted Self-Induced Feshbach Resonance (LASIFR). This mechanism, valid for all polar molecules, is analyzed on the example of ultracold 87Rb and 84Sr atoms, for which the laser frequency falls in the THz ran…
We have demonstrated the resonant control of the elastic scattering cross sections in the vicinity of Feshbach resonances between $^{23}$Na$^{40}$K molecules and $^{40}$K atoms by studying the thermalization between them. The elastic scattering cross sections vary by more than two orders of magnitude close to the resonance, and can be well described by an asymmetric Fano profile. The parameters that characterize the magnetically tunable s-wave scattering length are determined from the elastic scattering cross sections. The observation of resonantly controlled elastic scattering cross sections …
Compared to purely atomic collisions, ultracold molecular collisions potentially support a much larger number of Fano-Feshbach resonances due to the enormous number of ro-vibrational states available. In fact, for alkali-metal dimers we find that the resulting density of resonances cannot be resolved at all, even on the sub-$μ$K temperature scale of ultracold experiments. As a result, all observables become averaged over many resonances and can effectively be described by simpler, non-resonant scattering calculations. Two particular examples are discussed: non-chemically reactive RbCs and chem…
We study a polarized Fermi gas and demonstrate that Fano-Feshbach (FF) resonances lead to the pairing of fermions and holes into long living massive bosonic modes (bifermions and biholes), which can be viewed as signatures of a first order quantum phase transition. These modes, which are neither conventional Cooper pairs nor closed channel bosonic dimers, have a peculiar dispersion relation and appear already in the weak coupling limit, i.e. for large FF detunings. Our result is in accord with claims of Schunck \emph{et al.} [cond-mat/0702066] that by stabilizing the normal state the populatio…
The collision dynamics of $^{17}O_2(^3Σ_g^-) +^{17}O_2(^3Σ_g^-)$ in the presence of a magnetic field is studied within the close-coupling formalism in the range between 10 nK and 50 mK. A recent global {\em ab initio} potential energy surface (PES) is employed and its effect on the dynamics is analyzed and compared with previous calculations where an experimentally derived PES was used [New J. Phys {\bf 11}, 055021 (2009)]. In contrast to the results using the older PES, magnetic field dependence of the low-field-seeking state in the ultracold regime is characterized by quite a large backgroun…
Exact and asymptotic lineshape expressions are derived from the semi-classical density matrix representation describing a set of closed three-level atomic or molecular states including decoherences, relaxation rates and light-shifts. An accurate analysis of the exact steady-state Dark Resonance profile describing the Autler-Townes doublet, the Electromagnetically Induced Transparency or Coherent Population Trapping resonance and the Fano-Feshbach lineshape, leads to the linewidth expression of the two-photon Raman transition and frequency-shifts associated to the clock transition. From an adia…
Atomic and molecular samples reduced to temperatures below 1 microkelvin, yet still in the gas phase, afford unprecedented energy resolution in probing and manipulating how their constituent particles interact with one another. For simple atoms, such as alkalis, scattering resonances are extremely well-characterized. However, ultracold physics is now poised to enter a new regime, where far more complex species can be cooled and studied, including magnetic lanthanide atoms and even molecules. For molecules, it has been speculated that a dense forest of resonances in ultracold collision cross se…
