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

Quantum Electronics and Laser Science Conference

Sympathetic evaporative cooling of /sup 6/Li by /sup 7/Li

Andrew G. Truscott, Kevin E. Strecker, Randall G. Hulet

Published Nov 13, 2002• 0 citations
Publisher

Abstract

Summary form only given. The last five years has seen an explosive growth in activity in the field of quantum degenerate gases, and there are now many realizations of Bose-Einstein condensation (BEC) of trapped atomic gasses. However, only one experiment has produced a quantum degenerate Fermi gas. The ultimate goal of the experiment discussed here is to achieve a BCS phase transition in a trapped gas of fermionic /sup 6/Li atoms. This requires a phase-space density that is much higher than that needed for BEC, as the temperature must be made much less than the Fermi temperature.BEC in trapped gases has only been achieved using forced evaporative cooling. Since this method depends on elastic collisions, however, it fails for an ultracold Fermi gas, as the Pauli principle forbids s-wave collisions between identical fermions. To circumvent this obstacle, we simultaneously trap a /sup 7/Li-/sup 6/Li mixture, and use rf-induced evaporation to cool /sup 7/Li. /sup 6/Li is then cooled via thermalizing elastic collisions with the /sup 7/Li. The clover-leaf-type magnetic trap is loaded from a two-species magneto-optical trap (MOT).

DOI
10.1109/qels.2001.962226

Related papers

Experiments with Ultracold Quantum-degenerate Fermionic Lithium Atoms

Wolfgang Ketterle

Experimental methods of laser and evaporative cooling, used in the production of atomic Bose-Einstein condensates have recently been extended to realize quantum degeneracy in trapped Fermi gases. Fermi gases are a new rich system to explore the implications of Pauli exclusion on scattering properties of the system, and ultimately fermionic superfluidity. We have produced a new macroscopic quantum system, in which a degenerate Li-6 Fermi gas coexists with a large and stable Na-23 BEC. This was accomplished using inter-species sympathetic cooling of fermionic 6Li in a thermal bath of bosonic Na-23. We have achieved high numbers of both fermions (less than 10(exp 5) and bosons (less than 10(exp 6), and Li-6 quantum degeneracy corresponding to one half of the Fermi temperature. This is the first time that a Fermi sea was produced with a condensate as a "refrigerator".

•Jan 1, 2003•0 citations

Mixtures of ultracold gases: Fermi sea and Bose-Einstein condensate of lithium isotopes

Florian Schreck

This thesis presents studies of quantum degenerate atomic gases of fermionic 6Li and bosonic 7Li. Degeneracy is reached by evaporative cooling of 7Li in a strongly confining magnetic trap. Since at low temperatures direct evaporative cooling is not possible for a polarized fermionic gas, 6Li is sympathetically cooled by thermal contact with 7Li. In a first series of experiments both isotopes are trapped in their low-field seeking higher hyperfine states. A Fermi degeneracy of is achieved for 105 fermions. For more than ~300 atoms, the 7Li condensate collapses, due to the attractive interatomic interaction in this state. This limits the degeneracy reached for both species. To overcome this limit, in a second series of experiments 7Li and 6Li atoms are transferred to their low field seeking lower hyperfine states, where the boson-boson interaction is repulsive but weak. The inter-isotope collisions are used to thermalize the mixture. A 7Li Bose-Einstein condensate (BEC) of 104 atoms immersed in a Fermi sea is produced. The BEC is quasi-one-dimensional and the thermal fraction can be negligible. The measured degeneracies are . The temperature is measured using the bosonic thermal fraction, which vanishes at the lowest temperatures, limiting our measurement sensitivity. In a third series of experiments, the bosons are transferred into an optical trap and their internal state is changed to , the lowest energy state. A Feshbach resonance is detected and used to produce a BEC with tunable atomic interactions. When the effective interaction between atoms is tuned to be small and attractive, we observe the formation of a matter-wave bright soliton. Propagation of the soliton without spreading over a macroscopic distance of 1.1~mm is observed.

Annales de Physique•Mar 1, 2003•11 citations

Sympathetic cooling of a Bose/Fermi mixture of lithium to quantum degeneracy

Kevin E. Strecker

A dual species electromagnetic trap has been developed for the purpose of studying quantum degeneracy and the BCS phase transition in 6Li. Since the symmetry requirements of quantum mechanics forbid collisions between identical ultra-cold fermions, the standard method of cooling atoms in a magnetic trap, evaporative cooling, will not work. To circumvent this obstacle we evaporatively cool 7Li, the boson, and allow sympathetic collisions between the bosons and fermions to cool the 6Li to quantum degeneracy. This thesis will cover the experimental details pertaining to capturing, cooling, and probing a mixture of atomic 7Li and 6Li.

•Jan 1, 2002•1 citation

This Week in Science

Evaporative cooling of an atom gas of bosons, whereby the hottest atoms are progressively removed, is an effective and widely used method for forming Bose-Einstein condensates. For Fermi gases, however, collisions between identical fermions are forbidden, and new tricks, such as mixing two Fermi gases with different spin states, have been used to form Fermi condensates. Truscott et al. (p. 2570; see the Perspective by O'Hara and Thomas) now create quantum-degenerate Bose and Fermi condensates simultaneously from a boson-fermion mixture. Heat is removed from the fermions through elastic collisions with the bosons, a process called sympathetic cooling. They show that different statistics associated with the two types of gases can actually be visualized.

Science•Mar 30, 2001•0 citations

Optically-trapped Fermi gas

Michael E. Gehm, S. R. Granade, M.-S. Chang +2 more

Summary form only given. Cold, dense gases of fermions offer exciting new opportunities for fundamental studies of quantum degeneracy, collective behavior, and superfluidity. Fermionic /sup 6/Li has been the subject of numerous theoretical treatments. This is due in part to its anomalously large and negative triplet scattering length, a/sub T/=-2160 a/sub O/, which arises from a near zero energy resonance. The large scattering length leads to two-state mixtures which are predicted to undergo a transition to a superfluid state at a relatively high temperature. To increase our well depth, we retroreflect the CO/sub 2/ beam which forms our optical trap, nearly doubling the intensity of the trapping field and thus the well depth. We will discuss this technique and its effect on evaporative cooling, and report our progress towards producing a degenerate gas of /sup 6/Li.

Quantum Electronics and Laser Science Conference•Nov 13, 2002•2 citations

A quantum degenerate Bose–Fermi mixture of 41 K and 6 Li

Yu-Ping Wu, Xing-Can Yao, Hao-Ze Chen +4 more

Abstract We report a new apparatus for the study of two-species quantum degenerate mixture of 41 K and 6 Li atoms. We develop and combine several advanced cooling techniques to achieve both a large atom number and high phase space density of the two-species atom clouds. Furthermore, we build a high efficiency two-species magnetic transport system to transfer atom clouds from the 3D magneto-optical-trap chamber to a full glass science chamber of an extreme high vacuum environment and good optical access. We perform a forced radio-frequency evaporative cooling for 41 K atoms while the 6 Li atoms are sympathetically cooled in an optically plugged magnetic trap. Finally, we achieve the simultaneous quantum degeneracy for the 41 K and 6 Li atoms. The Bose–Einstein condensate of 41 K has 1.4 × 10 5 atoms with a condensate fraction of about 62%, while the degenerate Fermi gas of 6 Li has a total atom number of 5.4 × 10 5 at 0.25 Fermi temperature.

arXiv:1702.08630•Journal of Physics B Atomic Molecular and Optical Physics•Mar 9, 2017•19 citations
Summary form only given. The last five years has seen an explosive growth in activity in the field of quantum degenerate gases, and there are now many realizations of Bose-Einstein condensation (BEC) of trapped atomic gasses. However, only one experiment has produced a quantum degenerate Fermi gas. The ultimate goal of the experiment discussed here is to achieve a BCS phase transition in a trapped gas of fermionic /sup 6/Li atoms. This requires a phase-space density that is much higher than that needed for BEC, as the temperature must be made much less than the Fermi temperature.BEC in trapped gases has only been achieved using forced evaporative cooling. Since this method depends on elastic collisions, however, it fails for an ultracold Fermi gas, as the Pauli principle forbids s-wave collisions between identical fermions. To circumvent this obstacle, we simultaneously trap a /sup 7/Li-/sup 6/Li mixture, and use rf-induced evaporation to cool /sup 7/Li. /sup 6/Li is then cooled via thermalizing elastic collisions with the /sup 7/Li. The clover-leaf-type magnetic trap is loaded from a two-species magneto-optical trap (MOT).
Experimental methods of laser and evaporative cooling, used in the production of atomic Bose-Einstein condensates have recently been extended to realize quantum degeneracy in trapped Fermi gases. Fermi gases are a new rich system to explore the implications of Pauli exclusion on scattering properties of the system, and ultimately fermionic superfluidity. We have produced a new macroscopic quantum system, in which a degenerate Li-6 Fermi gas coexists with a large and stable Na-23 BEC. This was accomplished using inter-species sympathetic cooling of fermionic 6Li in a thermal bath of bosonic Na-23. We have achieved high numbers of both fermions (less than 10(exp 5) and bosons (less than 10(exp 6), and Li-6 quantum degeneracy corresponding to one half of the Fermi temperature. This is the first time that a Fermi sea was produced with a condensate as a "refrigerator".
This thesis presents studies of quantum degenerate atomic gases of fermionic 6Li and bosonic 7Li. Degeneracy is reached by evaporative cooling of 7Li in a strongly confining magnetic trap. Since at low temperatures direct evaporative cooling is not possible for a polarized fermionic gas, 6Li is sympathetically cooled by thermal contact with 7Li. In a first series of experiments both isotopes are trapped in their low-field seeking higher hyperfine states. A Fermi degeneracy of is achieved for 105 fermions. For more than ~300 atoms, the 7Li condensate collapses, due to the attractive interatomic interaction in this state. This limits the degeneracy reached for both species. To overcome this limit, in a second series of experiments 7Li and 6Li atoms are transferred to their low field seeking lower hyperfine states, where the boson-boson interaction is repulsive but weak. The inter-isotope collisions are used to thermalize the mixture. A 7Li Bose-Einstein condensate (BEC) of 104 atoms immersed in a Fermi sea is produced. The BEC is quasi-one-dimensional and the thermal fraction can be negligible. The measured degeneracies are . The temperature is measured using the bosonic thermal fraction, which vanishes at the lowest temperatures, limiting our measurement sensitivity. In a third series of experiments, the bosons are transferred into an optical trap and their internal state is changed to , the lowest energy state. A Feshbach resonance is detected and used to produce a BEC with tunable atomic interactions. When the effective interaction between atoms is tuned to be small and attractive, we observe the formation of a matter-wave bright soliton. Propagation of the soliton without spreading over a macroscopic distance of 1.1~mm is observed.
A dual species electromagnetic trap has been developed for the purpose of studying quantum degeneracy and the BCS phase transition in 6Li. Since the symmetry requirements of quantum mechanics forbid collisions between identical ultra-cold fermions, the standard method of cooling atoms in a magnetic trap, evaporative cooling, will not work. To circumvent this obstacle we evaporatively cool 7Li, the boson, and allow sympathetic collisions between the bosons and fermions to cool the 6Li to quantum degeneracy. This thesis will cover the experimental details pertaining to capturing, cooling, and probing a mixture of atomic 7Li and 6Li.
Evaporative cooling of an atom gas of bosons, whereby the hottest atoms are progressively removed, is an effective and widely used method for forming Bose-Einstein condensates. For Fermi gases, however, collisions between identical fermions are forbidden, and new tricks, such as mixing two Fermi gases with different spin states, have been used to form Fermi condensates. Truscott et al. (p. 2570; see the Perspective by O'Hara and Thomas) now create quantum-degenerate Bose and Fermi condensates simultaneously from a boson-fermion mixture. Heat is removed from the fermions through elastic collisions with the bosons, a process called sympathetic cooling. They show that different statistics associated with the two types of gases can actually be visualized.
Summary form only given. Cold, dense gases of fermions offer exciting new opportunities for fundamental studies of quantum degeneracy, collective behavior, and superfluidity. Fermionic /sup 6/Li has been the subject of numerous theoretical treatments. This is due in part to its anomalously large and negative triplet scattering length, a/sub T/=-2160 a/sub O/, which arises from a near zero energy resonance. The large scattering length leads to two-state mixtures which are predicted to undergo a transition to a superfluid state at a relatively high temperature. To increase our well depth, we retroreflect the CO/sub 2/ beam which forms our optical trap, nearly doubling the intensity of the trapping field and thus the well depth. We will discuss this technique and its effect on evaporative cooling, and report our progress towards producing a degenerate gas of /sup 6/Li.
Abstract We report a new apparatus for the study of two-species quantum degenerate mixture of 41 K and 6 Li atoms. We develop and combine several advanced cooling techniques to achieve both a large atom number and high phase space density of the two-species atom clouds. Furthermore, we build a high efficiency two-species magnetic transport system to transfer atom clouds from the 3D magneto-optical-trap chamber to a full glass science chamber of an extreme high vacuum environment and good optical access. We perform a forced radio-frequency evaporative cooling for 41 K atoms while the 6 Li atoms are sympathetically cooled in an optically plugged magnetic trap. Finally, we achieve the simultaneous quantum degeneracy for the 41 K and 6 Li atoms. The Bose–Einstein condensate of 41 K has 1.4 × 10 5 atoms with a condensate fraction of about 62%, while the degenerate Fermi gas of 6 Li has a total atom number of 5.4 × 10 5 at 0.25 Fermi temperature.