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/9812350 · Physical Review Letters

Measurement of p -Wave Threshold Law Using Evaporatively Cooled Fermionic Atoms

Brian DeMarco, John L. Bohn, J. P. Burke, M. Holland, D. S. Jin

Published May 24, 1999• 169 citations
arXivHTMLPDF

Abstract

We have measured independently both $s$-wave and $p$-wave cross-dimensional thermalization rates for ultracold ${}^{40}\mathrm{K}$ atoms held in a magnetic trap. These measurements reveal that this fermionic isotope has a large positive $s$-wave triplet scattering length in addition to a low temperature $p$-wave shape resonance. We have measured directly the $p$-wave threshold law which, combined with the Fermi statistics, dramatically suppresses elastic collision rates at low temperatures. In addition, we present initial evaporative cooling results that make possible these collision measurements and are a precursor to achieving quantum degeneracy in this neutral, low-density Fermi system.

DOI
10.1103/physrevlett.82.4208

Related papers

Collisional properties of ultracold potassium: Consequences for degenerate Bose and Fermi gases

John L. Bohn, James P. Burke, Chris H. Greene +3 more

The hyperfine-state-selected scattering properties of potassium atoms at ultralow temperatures are calculated using interaction potentials gleaned from an analysis of recent photoassociation data. We predict that the small, probably negative value of the ${}^{39}\mathrm{K}$ triplet scattering length will hamper efforts to produce a Bose-Einstein condensate, unless experiments utilize a broad, accessible magnetic Feshbach resonance. The large positive value calculated for the ${}^{41}\mathrm{K}$ triplet scattering length makes it a better candidate for condensation at zero magnetic field. The fermionic isotope ${}^{40}\mathrm{K}$ is also predicted to have a large, positive scattering length for elastic collisions between spin states of experimental interest, implying that it can be efficiently evaporatively cooled to the quantum degenerate regime. In addition, certain spin states possess Feshbach resonances that may enable tuning of its interatomic interactions, possibly leading to the formation of Cooper pairs.

Physical Review A•May 1, 1999•53 citations

Quantum degeneracy in a fermionic atom gas

Brian DeMarco, D. S. Jin

Summary form only given. Magnetic trapping and evaporative cooling have been employed to cool a million /sup 40/K atoms to below the Fermi temperature, T/sub P/. Simultaneous evaporation of spin-mixed samples is used to overcome the lack of s-wave collisions between spin-polarized fermionic atoms at these ultralow temperatures. By releasing the gas from the magnetic trap and allowing it to expand, the energy and momentum distributions of this quantum degenerate gas were measured. Consistent with Fermi-Dirac (FD) quantum statistics, the total energy in the gas is higher than the classical expectation at the same temperature. Further, the momentum distribution was shown to be non-Gaussian (non-classical) and also congruent with FD statistics.

•May 12, 2000•0 citations

Collisional Properties of Ultracold K-Rb Mixtures

G. Ferrari, M. Inguscio, W. Jastrzȩbski +3 more

We determine the interspecies $s$-wave triplet scattering length ${a}_{3}$ for all K-Rb isotopic mixtures by measuring the elastic cross section for collisions between $^{\mathrm{41}}\mathrm{K}$ and $^{87}\mathrm{R}\mathrm{b}$ in different temperature regimes. The positive value ${a}_{3}=+{163}_{\ensuremath{-}12}^{+57}{a}_{0}$ ensures the stability against collapse of binary $^{41}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$ Bose-Einstein condensates. For the fermion-boson mixture $^{40}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$, we obtain a large and negative scattering length which implies an efficient sympathetic cooling of the fermionic species down to the degenerate regime.

arXiv:cond-mat/0202290•Physical Review Letters•Jul 15, 2002•140 citations

Degenerate Fermi Gases of Ytterbium

Takeshi Fukuhara, Yosuke Takasu, M. Kumakura +1 more

Evaporative cooling was performed to cool fermionic 173Yb atoms in a crossed optical dipole trap. The large elastic collision rate leads to efficient evaporation and we have successfully cooled the atoms to 0.37+/-0.06 of the Fermi temperature, that is to say, to a quantum degenerate regime. In this regime, a plunge of evaporation efficiency was observed as a result of Fermi degeneracy.

arXiv:cond-mat/0607228•Physical Review Letters•Jan 17, 2007•312 citations

Evaporative cooling of unitary Fermi gas mixtures in optical traps

Le Luo, Bason E. Clancy, J Joseph +3 more

We measure the scaling laws for the number of atoms and the cloud size as a function of trap depth for evaporative cooling of a unitary Fermi gas in an optical trap. A unitary Fermi gas comprises a trapped mixture of atoms in two hyperfine states which is tuned to a collisional (Feshbach) resonance using a bias magnetic field. Near resonance, the zero energy s-wave scattering length diverges, and the s-wave scattering cross-section is limited by unitarity to be 4π/ k 2 , where k is the relative wavevector of the colliding particles. In this case, the collision cross-section for evaporation scales inversely with the trap depth, enabling runaway evaporation under certain conditions. We demonstrate high evaporation efficiency, which is achieved by maintaining a high ratio η of trap depth to thermal energy as the trap depth is lowered. We derive and demonstrate a trap lowering curve which maintains η constant for a unitary gas. This evaporation curve yields a quantum degenerate sample from a classical gas in a fraction of a second, with only a factor of three loss in atom number.

New Journal of Physics•Sep 27, 2006•49 citations

Magnetic field control of ultracold atom-molecule collision

Musie Beyene

In this work we investigate the potential of controlling cold (O(K)−mK) and ultracold (mK-μK) atom-molecule collisions by tuning scattering states across Feshbach resonances using magnetic fields. We are interested in particular in the prospect of suppressing the often undesirable inelastic collisions. The He-O_2 system provides the vehicle for our study. We calculate bound and quasi-bound states of several isotopic combinations, including their Zeeman structure, to reveal the underlaying pattern for easier characterization of quasi-bound states in terms of rigorous and approximately good quantum numbers. These calculations also help us locate the fields at which zero-energy resonances will occur. Scattering calculations are then performed for collisions of 3^He and 4^He with {16}^O_2 at fixed (1 μK) energy but varying magnetic field. The field is varied to sweep the scattering state across resonance. At low and ultralow energies we enter the Wigner threshold regime where the S-partial wave dominates the wavefunction. The cross sections, and the real and imaginary parts of the scattering length, vary dramatically across resonance. Their profiles are used to analyze the resonances. In a highlight of our results we show that dramatic suppression of inelastic cross sections occur for 4^He-{16}^O_2 . The resonances are relatively wide (of order 100 Gauss), with suppression of inelastic scattering over a similarly wide range of fields and for temperatures ranging from 10 mK down to 1 μK. We conclude that under certain conditions it is possible to almost completely eliminate inelastic collisions. This is potentially very important for cooling techniques, such as evaporative and sympathetic cooling, that require efficient elastic cross sections. Suppression of inelastic collisions can not only increase thermalization efficiency but it can also result in longer trap-lifetimes by reducing transitions to untrapable states.

•Jan 1, 2011•0 citations
We have measured independently both sss-wave and ppp-wave cross-dimensional thermalization rates for ultracold 40K{}^{40}\mathrm{K}40K atoms held in a magnetic trap. These measurements reveal that this fermionic isotope has a large positive sss-wave triplet scattering length in addition to a low temperature ppp-wave shape resonance. We have measured directly the ppp-wave threshold law which, combined with the Fermi statistics, dramatically suppresses elastic collision rates at low temperatures. In addition, we present initial evaporative cooling results that make possible these collision measurements and are a precursor to achieving quantum degeneracy in this neutral, low-density Fermi system.
The hyperfine-state-selected scattering properties of potassium atoms at ultralow temperatures are calculated using interaction potentials gleaned from an analysis of recent photoassociation data. We predict that the small, probably negative value of the 39K{}^{39}\mathrm{K}39K triplet scattering length will hamper efforts to produce a Bose-Einstein condensate, unless experiments utilize a broad, accessible magnetic Feshbach resonance. The large positive value calculated for the 41K{}^{41}\mathrm{K}41K triplet scattering length makes it a better candidate for condensation at zero magnetic field. The fermionic isotope 40K{}^{40}\mathrm{K}40K is also predicted to have a large, positive scattering length for elastic collisions between spin states of experimental interest, implying that it can be efficiently evaporatively cooled to the quantum degenerate regime. In addition, certain spin states possess Feshbach resonances that may enable tuning of its interatomic interactions, possibly leading to the formation of Cooper pairs.
Summary form only given. Magnetic trapping and evaporative cooling have been employed to cool a million /sup 40/K atoms to below the Fermi temperature, T/sub P/. Simultaneous evaporation of spin-mixed samples is used to overcome the lack of s-wave collisions between spin-polarized fermionic atoms at these ultralow temperatures. By releasing the gas from the magnetic trap and allowing it to expand, the energy and momentum distributions of this quantum degenerate gas were measured. Consistent with Fermi-Dirac (FD) quantum statistics, the total energy in the gas is higher than the classical expectation at the same temperature. Further, the momentum distribution was shown to be non-Gaussian (non-classical) and also congruent with FD statistics.
We determine the interspecies sss-wave triplet scattering length a3{a}_{3}a3​ for all K-Rb isotopic mixtures by measuring the elastic cross section for collisions between 41K^{\mathrm{41}}\mathrm{K}41K and 87Rb^{87}\mathrm{R}\mathrm{b}87Rb in different temperature regimes. The positive value ${a}_{3}=+{163}_{\ensuremath{-}12}^{+57}{a}_{0}$ ensures the stability against collapse of binary $^{41}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$ Bose-Einstein condensates. For the fermion-boson mixture $^{40}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$, we obtain a large and negative scattering length which implies an efficient sympathetic cooling of the fermionic species down to the degenerate regime.
We measure the scaling laws for the number of atoms and the cloud size as a function of trap depth for evaporative cooling of a unitary Fermi gas in an optical trap. A unitary Fermi gas comprises a trapped mixture of atoms in two hyperfine states which is tuned to a collisional (Feshbach) resonance using a bias magnetic field. Near resonance, the zero energy s-wave scattering length diverges, and the s-wave scattering cross-section is limited by unitarity to be 4π/ k 2 , where k is the relative wavevector of the colliding particles. In this case, the collision cross-section for evaporation scales inversely with the trap depth, enabling runaway evaporation under certain conditions. We demonstrate high evaporation efficiency, which is achieved by maintaining a high ratio η of trap depth to thermal energy as the trap depth is lowered. We derive and demonstrate a trap lowering curve which maintains η constant for a unitary gas. This evaporation curve yields a quantum degenerate sample from a classical gas in a fraction of a second, with only a factor of three loss in atom number.
In this work we investigate the potential of controlling cold (O(K)−mK) and ultracold (mK-μK) atom-molecule collisions by tuning scattering states across Feshbach resonances using magnetic fields. We are interested in particular in the prospect of suppressing the often undesirable inelastic collisions. The He-O_2 system provides the vehicle for our study. We calculate bound and quasi-bound states of several isotopic combinations, including their Zeeman structure, to reveal the underlaying pattern for easier characterization of quasi-bound states in terms of rigorous and approximately good quantum numbers. These calculations also help us locate the fields at which zero-energy resonances will occur. Scattering calculations are then performed for collisions of 3^He and 4^He with {16}^O_2 at fixed (1 μK) energy but varying magnetic field. The field is varied to sweep the scattering state across resonance. At low and ultralow energies we enter the Wigner threshold regime where the S-partial wave dominates the wavefunction. The cross sections, and the real and imaginary parts of the scattering length, vary dramatically across resonance. Their profiles are used to analyze the resonances. In a highlight of our results we show that dramatic suppression of inelastic cross sections occur for 4^He-{16}^O_2 . The resonances are relatively wide (of order 100 Gauss), with suppression of inelastic scattering over a similarly wide range of fields and for temperatures ranging from 10 mK down to 1 μK. We conclude that under certain conditions it is possible to almost completely eliminate inelastic collisions. This is potentially very important for cooling techniques, such as evaporative and sympathetic cooling, that require efficient elastic cross sections. Suppression of inelastic collisions can not only increase thermalization efficiency but it can also result in longer trap-lifetimes by reducing transitions to untrapable states.