We observe two consecutive heteronuclear Efimov resonances in an ultracold Li-Cs mixture by measuring three-body loss coefficients as a function of magnetic field near a Feshbach resonance. The first resonance is detected at a scattering length of a (0) − = −320(10) a0 corresponding to ∼ 7(∼ 3) times the Li-Cs (Cs-Cs) van der Waals range. The second resonance appears at 5.8(1.0) a (0) − close to the unitarity-limited regime at the sample temperature of 450 nK. Indication of a third resonance is found in the atom loss spectra. The scaling of the resonance positions is close to the predicted universal scaling value of 4.9 for zero temperature. Deviations from universality might be caused by finite-range and temperature effects, as well as magnetic field dependent Cs-Cs interactions.The control of interactions in ultracold atomic systems via magnetically tunable Feshbach resonances opens up new pathways for the investigation of few-and manybody physics [1]. One intriguing example is the access to the universal regime, which is characterized by a magnitude of the scattering length a exceeding all other length scales of the system. In the limit of at least two resonant pairwise interactions, an infinite series of three-body bound-states, the so called Efimov states, exists [2][3][4]. Counterintuitively, these trimers persist even for a < 0, where the two body potential does not support a boundstate. The ratio between two subsequent trimer energies follows a discrete scale invariance with a universal scaling factor of exp(−2π/s 0 ). Here, s 0 only depends on the quantum statistics of the constituent atoms, their mass ratio, and the number of resonant interactions [3, 5]. This scale invariance is also reflected in those values of a where the energy of the bound-states coincides with the threshold of three free atoms for a < 0, resulting in enhanced three-body loss. When the position of the first resonance is given by a − only depends on the characteristic range r 0 of the interatomic van der Waals potential [6][7][8][9][10][11]. The universal scaling factor acquires a value of 22.7 for equal mass constituents and features a drastic reduction in heteronuclear massimbalanced systems of two heavy and one light particle [3, 5], resulting e.g. in a factor of 4.9 for a 6 Li-133 Cs mixture.In ultracold atom experiments, Efimov resonances become evident in the three-body loss coefficient L 3 in the rate equation for atom lossṅ = −L 3 n 3 . Here, n denotes the number density of atoms, and L 3 ∝ C(a)a 4 . The Efimov physics are contained in the dimensionless, logperiodic function C(a). Thus far, Efimov resonances have been studied in several equal mass systems [6,7,[12][13][14][15][16][17][18], where the scaling between different resonances is predicted to follow C(a) = C(22.7a). This large scaling factor demands a level of temperature and magnetic field control which makes the observation of an excited Efimov states highly involved. There had been indication of such an excited state in a three-component Fermi gas of 6 Li atoms ...
We show that short-range pair correlations in a strongly interacting Fermi gas follow a simple universal law described by Tan's relations. This is achieved through measurements of the static structure factor which displays a universal scaling proportional to the ratio of Tan's contact to the momentum C/q. Bragg spectroscopy of ultracold 6Li atoms from a periodic optical potential is used to measure the structure factor for a wide range of momenta and interaction strengths, providing broad confirmation of this universal law. We calibrate our Bragg spectra using the f-sum rule, which is found to improve the accuracy of the structure factor measurement.
We have studied the transition from two to three dimensions in a low temperature weakly interacting 6Li Fermi gas. Below a critical atom number N(2D) only the lowest transverse vibrational state of a highly anisotropic oblate trapping potential is occupied and the gas is two dimensional. Above N(2D) the Fermi gas enters the quasi-2D regime where shell structure associated with the filling of individual transverse oscillator states is apparent. This dimensional crossover is demonstrated through measurements of the cloud size and aspect ratio versus atom number.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.