Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:cond-mat/0410167 · AIP conference proceedings

Expansion of a lithium gas in the BEC-BCS crossover

J. Zhang

Published Jan 1, 2005• 9 citations
arXivHTMLPDF

Abstract

We report on experiments in 6Li Fermi gases near Feshbach resonances. A broad s‐wave resonance is used to form a Bose‐Einstein condensate of weakly bound 6Li2 molecules in a crossed optical trap. The measured molecule‐molecule scattering length of 170−60+100 nm at 770 G is found in good agreement with theory. The expansion energy of the cloud in the BEC‐BCS crossover region is measured. Finally we discuss the properties of p‐wave Feshbach resonances observed near 200 Gauss and new s‐wave resonances in the heteronuclear 6Li‐ 7Li mixture.

DOI
10.1063/1.1928857

Related papers

Experimental Study of the BEC-BCS Crossover Region in Lithium 6

Thomas Bourdel, Lev Khaykovich, J. Cubizolles +6 more

We report Bose-Einstein condensation of weakly bound $^{6}\mathrm{L}\mathrm{i}_{2}$ molecules in a crossed optical trap near a Feshbach resonance. We measure a molecule-molecule scattering length of ${170}_{\ensuremath{-}60}^{+100}\text{ }\mathrm{n}\mathrm{m}$ at $770\text{ }\mathrm{G}$, in good agreement with theory. We study the 2D expansion of the cloud and show deviation from hydrodynamic behavior in the BEC-BCS crossover region.

arXiv:cond-mat/0403091•Physical Review Letters•Jul 27, 2004•815 citations

Exploring the BEC-BCS Crossover with an Ultracold Gas of 6Li Atoms

M. Bartenstein

We present an overview of our recent measurements on the crossover from a Bose‐Einstein condensate of molecules to a Bardeen‐Cooper‐Schrieffer superfluid. The experiments are performed on a two‐component spin‐mixture of 6Li atoms, where a Feshbach resonance serves as the experimental key to tune the s‐wave scattering length and thus to explore the various interaction regimes. In the BEC‐BCS crossover, we have characterized the interaction energy by measuring the size of the trapped gas, we have studied collective excitation modes, and we have observed the pairing gap. Our observations provide strong evidence for superfluidity in the strongly interacting Fermi gas.

arXiv:cond-mat/0412712•AIP conference proceedings•Jan 1, 2005•2 citations

Conversion of a Degenerate Fermi Gas of 6Li Atoms to a Molecular BEC

Kevin E. Strecker

Atomic Feshbach resonances have recently been used to produce a strongly interacting Fermi gas, where the BCS/BEC crossover can be explored. We have used both narrow and broad Feshbach resonances to convert a quantum degenerate Fermi gas of 6Li atoms into an ultracold gas of Li2 molecules. For the narrow resonances, the molecules are formed by coherent adiabatic passage through the resonance. We find that 50% of the atoms are converted to molecules. Furthermore, the lifetime of these molecules was measured to be surprisingly long, 1 s. We will discuss these measurements in the context of the present theoretical understanding. Molecules can also be formed using static fields near the broad Feshbach resonance. The lifetime of these molecules is again long, and sufficient to enable their evaporation to a Bose‐Einstein condensate. Phase contrast images of the molecular condensate are presented. The BCS/BEC crossover may be explored by starting with a pure molecular condensate on the low‐field side of the Feshbach resonance, and adiabatically changing the field to any final value around resonance. We combine this ability with optical spectroscopy on a bound‐bound molecular transition to probe the nature of the many‐body wavefunction in the crossover regime.

AIP conference proceedings•Jan 1, 2005•0 citations

Observation of Bose-Einstein Condensation of Molecules

Martin W. Zwierlein, Claudiu A. Stan, Christian H. Schunck +4 more

We have observed Bose-Einstein condensation of molecules. When a spin mixture of fermionic 6Li atoms was evaporatively cooled in an optical dipole trap near a Feshbach resonance, the atomic gas was converted into 6Li2 molecules. Below 600 nK, a Bose-Einstein condensate of up to 900 000 molecules was identified by the sudden onset of a bimodal density distribution. This condensate realizes the limit of tightly bound fermion pairs in the crossover between BCS superfluidity and Bose-Einstein condensation.

arXiv:cond-mat/0311617•Physical Review Letters•Dec 15, 2003•938 citations

Molecular Bose-Einstein condensates and p-wave Feshbach molecules of 6Li2

Fuchs, Jurgen

This thesis describes the production of molecular Bose-Einstein condensates (BEC) of 6Li2 dimers and binding energy measurements of p-wave Feshbach molecules. A σ− Zeeman slower is used to produce a continuous beam of isotopically enriched 6Li atoms at speeds low enough to load a magneto-optical trap (MOT). We currently have a flux of slowed atoms of ~ 5 · 106 atoms/s loading the MOT with more than 108 atoms. We then transfer up to 106 atoms in an almost equal spin mixture of the two lowest hyperfine states into an optical dipole trap. We achieved condensates in three different crossed optical dipole trap geometries. The initial low power optical dipole trap was formed using light from a 25WVersaDisk Yb:YAG laser at 1030 nm. It consisted of a 15 W beam crossed with a 13 W beam at about 80 degrees with a waist of approximately 30 μm in each beam. By translating the focus of the second beam we could change the trap geometry from near symmetric to elongated. Nowadays, we produce condensates in a crossed dipole trap formed by a 100 W fibre laser. Both arms are focussed to a waist of 40 μm, cross each other at 14 degrees and have laser powers of ~80 W and ~70 W, respectively. Evaporative cooling is achieved by reducing the laser power near the broad s-wave Feshbach resonance at 834 G. By tuning to the low magnetic field side (770 G) of the Feshbach resonance molecules are formed through three-body recombination at sufficiently low temperatures. Further evaporation leads to the creation of a molecular BEC. After reducing the laser power by a factor of about 1000 in approximately 3 s we have observed more than 30 000 condensed molecules. During the evaporation the temperature decreases from about 100 μK to below 100 nK. We present measurements of the binding energies of 6Li p-wave Feshbach molecules formed in combinations of the |F = 1/2,mF = +1/2i (|1i) and |F = 1/2,mF = −1/2i (|2i) states. The binding energies scale linearly with magnetic field detuning for all three resonances. The relative molecular magnetic moments are found to be 113 ± 7 μK/G, 111 ± 6 μK/G and 118 ± 8 μK/G for the |1i − |1i, |1i − |2i and |2i − |2i resonances, respectively, in good agreement with theoretical predictions.

•Jan 1, 2009•0 citations

Pairing of fermionic lithium-6 throughout the BEC-BCS crossover

Guthrie B. Partridge

The pairing of fermionic particles is an essential ingredient of superconductivity and of the superfluidity of 3He. While such phenomena are accurately described by BCS theory in the limit of weak pairing strength, a complete understanding remains elusive when pairing strength is increased, such as in high temperature superconductors. We create ultracold gases of trapped fermionic 6Li atoms, through which we directly observe fermionic pairing. In our system, there are no impurities whatsoever, and parameters such as the number and temperature of the trapped atoms are precisely and independently controlled. In addition, a Feshbach resonance enables the continuous tuning of interaction strength and sign between the paired atoms. This control allows us to observe the smooth crossover of a molecular Bose Einstein condensate (MBEC) to a superfluid of weakly interacting Cooper pairs. With these tools, we have performed several fundamental measurements of pairing in fermionic systems.\nWe use optical molecular spectroscopy to precisely measure the closed-channel contribution to the many body state of paired 6Li atoms within a broad Feshbach resonance. The magnitude of this contribution is small, and supports the concept of universality for the description of broad Feshbach resonances. Moreover, the dynamics of the excitation provide clear evidence for pairing across the BEC-BCS crossover, and for the first time, into the weakly interacting BCS regime.\nWe also prepare a polarized Fermi gas with unequal numbers of two spin states of 6Li atoms. The real-space densities of the polarized, strongly-interacting, two-component Fermi gas reveal two low temperature regimes. At the lowest temperatures, the gas separates into a phase with a uniformly paired superfluid core surrounded by a shell of normal, unpaired atoms. This phase separation is accompanied by a spatial deformation of the core. At higher temperatures, the uniformly paired core persists, though it does not deform. This temperature dependence is consistent with a tri-critical point in the phase diagram. These measurements of pairing in a polarized Fermi gas are relevant to predictions of exotic phases of quark matter and magnetized superconductors.

•Jan 1, 2007•0 citations
We report on experiments in 6Li Fermi gases near Feshbach resonances. A broad s‐wave resonance is used to form a Bose‐Einstein condensate of weakly bound 6Li2 molecules in a crossed optical trap. The measured molecule‐molecule scattering length of 170−60+100 nm at 770 G is found in good agreement with theory. The expansion energy of the cloud in the BEC‐BCS crossover region is measured. Finally we discuss the properties of p‐wave Feshbach resonances observed near 200 Gauss and new s‐wave resonances in the heteronuclear 6Li‐ 7Li mixture.
We report Bose-Einstein condensation of weakly bound 6Li2^{6}\mathrm{L}\mathrm{i}_{2}6Li2​ molecules in a crossed optical trap near a Feshbach resonance. We measure a molecule-molecule scattering length of ${170}_{\ensuremath{-}60}^{+100}\text{ }\mathrm{n}\mathrm{m}$ at 770 G770\text{ }\mathrm{G}770 G, in good agreement with theory. We study the 2D expansion of the cloud and show deviation from hydrodynamic behavior in the BEC-BCS crossover region.
We present an overview of our recent measurements on the crossover from a Bose‐Einstein condensate of molecules to a Bardeen‐Cooper‐Schrieffer superfluid. The experiments are performed on a two‐component spin‐mixture of 6Li atoms, where a Feshbach resonance serves as the experimental key to tune the s‐wave scattering length and thus to explore the various interaction regimes. In the BEC‐BCS crossover, we have characterized the interaction energy by measuring the size of the trapped gas, we have studied collective excitation modes, and we have observed the pairing gap. Our observations provide strong evidence for superfluidity in the strongly interacting Fermi gas.
Atomic Feshbach resonances have recently been used to produce a strongly interacting Fermi gas, where the BCS/BEC crossover can be explored. We have used both narrow and broad Feshbach resonances to convert a quantum degenerate Fermi gas of 6Li atoms into an ultracold gas of Li2 molecules. For the narrow resonances, the molecules are formed by coherent adiabatic passage through the resonance. We find that 50% of the atoms are converted to molecules. Furthermore, the lifetime of these molecules was measured to be surprisingly long, 1 s. We will discuss these measurements in the context of the present theoretical understanding. Molecules can also be formed using static fields near the broad Feshbach resonance. The lifetime of these molecules is again long, and sufficient to enable their evaporation to a Bose‐Einstein condensate. Phase contrast images of the molecular condensate are presented. The BCS/BEC crossover may be explored by starting with a pure molecular condensate on the low‐field side of the Feshbach resonance, and adiabatically changing the field to any final value around resonance. We combine this ability with optical spectroscopy on a bound‐bound molecular transition to probe the nature of the many‐body wavefunction in the crossover regime.
We have observed Bose-Einstein condensation of molecules. When a spin mixture of fermionic 6Li atoms was evaporatively cooled in an optical dipole trap near a Feshbach resonance, the atomic gas was converted into 6Li2 molecules. Below 600 nK, a Bose-Einstein condensate of up to 900 000 molecules was identified by the sudden onset of a bimodal density distribution. This condensate realizes the limit of tightly bound fermion pairs in the crossover between BCS superfluidity and Bose-Einstein condensation.
This thesis describes the production of molecular Bose-Einstein condensates (BEC) of 6Li2 dimers and binding energy measurements of p-wave Feshbach molecules. A σ− Zeeman slower is used to produce a continuous beam of isotopically enriched 6Li atoms at speeds low enough to load a magneto-optical trap (MOT). We currently have a flux of slowed atoms of ~ 5 · 106 atoms/s loading the MOT with more than 108 atoms. We then transfer up to 106 atoms in an almost equal spin mixture of the two lowest hyperfine states into an optical dipole trap. We achieved condensates in three different crossed optical dipole trap geometries. The initial low power optical dipole trap was formed using light from a 25WVersaDisk Yb:YAG laser at 1030 nm. It consisted of a 15 W beam crossed with a 13 W beam at about 80 degrees with a waist of approximately 30 μm in each beam. By translating the focus of the second beam we could change the trap geometry from near symmetric to elongated. Nowadays, we produce condensates in a crossed dipole trap formed by a 100 W fibre laser. Both arms are focussed to a waist of 40 μm, cross each other at 14 degrees and have laser powers of ~80 W and ~70 W, respectively. Evaporative cooling is achieved by reducing the laser power near the broad s-wave Feshbach resonance at 834 G. By tuning to the low magnetic field side (770 G) of the Feshbach resonance molecules are formed through three-body recombination at sufficiently low temperatures. Further evaporation leads to the creation of a molecular BEC. After reducing the laser power by a factor of about 1000 in approximately 3 s we have observed more than 30 000 condensed molecules. During the evaporation the temperature decreases from about 100 μK to below 100 nK. We present measurements of the binding energies of 6Li p-wave Feshbach molecules formed in combinations of the |F = 1/2,mF = +1/2i (|1i) and |F = 1/2,mF = −1/2i (|2i) states. The binding energies scale linearly with magnetic field detuning for all three resonances. The relative molecular magnetic moments are found to be 113 ± 7 μK/G, 111 ± 6 μK/G and 118 ± 8 μK/G for the |1i − |1i, |1i − |2i and |2i − |2i resonances, respectively, in good agreement with theoretical predictions.
The pairing of fermionic particles is an essential ingredient of superconductivity and of the superfluidity of 3He. While such phenomena are accurately described by BCS theory in the limit of weak pairing strength, a complete understanding remains elusive when pairing strength is increased, such as in high temperature superconductors. We create ultracold gases of trapped fermionic 6Li atoms, through which we directly observe fermionic pairing. In our system, there are no impurities whatsoever, and parameters such as the number and temperature of the trapped atoms are precisely and independently controlled. In addition, a Feshbach resonance enables the continuous tuning of interaction strength and sign between the paired atoms. This control allows us to observe the smooth crossover of a molecular Bose Einstein condensate (MBEC) to a superfluid of weakly interacting Cooper pairs. With these tools, we have performed several fundamental measurements of pairing in fermionic systems.\nWe use optical molecular spectroscopy to precisely measure the closed-channel contribution to the many body state of paired 6Li atoms within a broad Feshbach resonance. The magnitude of this contribution is small, and supports the concept of universality for the description of broad Feshbach resonances. Moreover, the dynamics of the excitation provide clear evidence for pairing across the BEC-BCS crossover, and for the first time, into the weakly interacting BCS regime.\nWe also prepare a polarized Fermi gas with unequal numbers of two spin states of 6Li atoms. The real-space densities of the polarized, strongly-interacting, two-component Fermi gas reveal two low temperature regimes. At the lowest temperatures, the gas separates into a phase with a uniformly paired superfluid core surrounded by a shell of normal, unpaired atoms. This phase separation is accompanied by a spatial deformation of the core. At higher temperatures, the uniformly paired core persists, though it does not deform. This temperature dependence is consistent with a tri-critical point in the phase diagram. These measurements of pairing in a polarized Fermi gas are relevant to predictions of exotic phases of quark matter and magnetized superconductors.