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中国物理B：英文版

Radio-frequency spectroscopy of weakly bound molecules in ultracold Fermi gasRadio-frequency spectroscopy of weakly bound molecules in ultracold Fermi gasRadio-frequency spectroscopy of weakly bound molecules in ultracold Fermi gas

黄良辉, 王鹏军, 付正坤, 张婧

Published Jan 1, 2014• 0 citations
OpenAlex

Abstract

We create weakly bound Feshbach molecules in ultracold Fermi gas 4~K by sweeping a magnetic field across a broad Feshbach resonance point 202.2 G with a rate of 20 ms/G and perform the dissociation process using radio-frequency （RF） technology. From RF spectroscopy, we obtain the binding energy of the weakly bound molecules in the vicinity of Feshbach resonance. Our measurement also shows that the number of atoms generated from the dissociation process is different at various magnetic fields with the same RF amplitude, which gives us a deeper understanding of weakly bound Feshbach molecules.

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We create weakly bound Feshbach molecules in ultracold Fermi gas 4~K by sweeping a magnetic field across a broad Feshbach resonance point 202.2 G with a rate of 20 ms/G and perform the dissociation process using radio-frequency （RF） technology. From RF spectroscopy, we obtain the binding energy of the weakly bound molecules in the vicinity of Feshbach resonance. Our measurement also shows that the number of atoms generated from the dissociation process is different at various magnetic fields with the same RF amplitude, which gives us a deeper understanding of weakly bound Feshbach molecules.
We create weakly bound Feshbach molecules in ultracold Fermi gas 40 K by sweeping a magnetic field across a broad Feshbach resonance point 202.2 G with a rate of 20 ms/G and perform the dissociation process using radio-frequency (RF) technology. From RF spectroscopy, we obtain the binding energy of the weakly bound molecules in the vicinity of Feshbach resonance. Our measurement also shows that the number of atoms generated from the dissociation process is different at various magnetic fields with the same RF amplitude, which gives us a deeper understanding of weakly bound Feshbach molecules.
We perform radio-frequency dissociation spectroscopy of weakly bound 6Li2 Feshbach molecules using low-density samples of about 30 molecules in an optical dipole trap. Combined with a high magnetic field stability, this allows us to resolve the discrete trap levels in the radio-frequency dissociation spectra. This novel technique allows the binding energy of Feshbach molecules to be determined with unprecedented precision. We use these measurements as an input for a fit to the 6Li scattering potential using coupled-channel calculations. From this new potential, we determine the pole positions of the broad 6Li Feshbach resonances with an accuracy better than 7×10(-4) of the resonance widths. This eliminates the dominant uncertainty for current precision measurements of the equation of state of strongly interacting Fermi gases. As an important consequence, our results imply a corrected value for the Bertsch parameter ξ measured by Ku et al. [Science 335, 563 (2012)], which is ξ=0.370(5)(8).
Ultracold 39K gases provide an ideal platform to study quantum few- and many-body systems, due to the high degree of control present in these systems. In particular, Feshbach resonances facilitate a magnetically tunable interaction strength between the atoms in the gas, and allow the formation of two- and three-body bound states, called Feshbach molecules and Efimov trimers respectively. Radio-frequency dissociation spectroscopy of weakly bound Feshbach molecules is one of the most precise ways to characterize the properties of a Feshbach resonance. We apply a numerical method to our Feshbach molecule binding energy data to compute the shift in the molecule’s binding energy due to the presence of a confining potential. These simulations are first used to replicate the confinement shift found for 6Li Feshbach molecules by another group, and then to correct our measurement results for the binding energy of 39K Feshbach molecules. The correction of these measurements is necessary for our determination of the Feshbach resonance location with unprecedented accuracy.
The binding energy of Feshbach molecules from a two-component Fermi gas of 40{}^{40}40K atoms has been experimentally measured with the momentum-resolved Raman spectroscopy. Comparing with the radio-frequency spectroscopy, in the present experiment the signal of unpaired (free atoms) and the bound molecules can be directly observed and the binding energy can be simultaneously determined in a single running experiment. The energy-momentum dispersion spectra of the ultracold Fermi gas in the BEC side are also measured and reconstructed. The present experimental technology of the momentum-resolved Raman spectroscopy can be easily extended to perform spatially momentum-resolved Raman spectroscopy and to obtain the response spectra of a homogeneous system in the local density approximation.
We report on the formation of ultracold weakly bound Feshbach molecules of 23Na40K, the first fermionic molecule that is chemically stable in its absolute ground state. The lifetime of the nearly degenerate molecular gas exceeds 100 ms in the vicinity of the Feshbach resonance. The measured dependence of the molecular binding energy on the magnetic field demonstrates the open-channel character of the molecules over a wide field range and implies significant singlet admixture. This will enable efficient transfer into the singlet vibrational ground state, resulting in a stable molecular Fermi gas with strong dipolar interactions.
We employ radio-frequency spectroscopy on weakly bound (6)Li(2) molecules to precisely determine the molecular binding energies and the energy splittings between molecular states for different magnetic fields. These measurements allow us to extract the interaction parameters of ultracold (6)Li atoms based on a multichannel quantum scattering model. We determine the singlet and triplet scattering lengths to be a(s) = 45.167(8)a(0) and a(t) = -2140(18)a(0) (1a(0) = 0.052 917 7 nm), and the positions of the broad Feshbach resonances in the energetically lowest three s-wave scattering channels to be 83.41(15), 69.04(5), and 81.12(10) mT.