Many-body effects on adiabatic passage through Feshbach resonances

Abstract

We theoretically study the dynamics of an adiabatic sweep through a Feshbach resonance, thereby converting a degenerate quantum gas of fermionic atoms into a degenerate quantum gas of bosonic dimers. Our analysis relies on a zero temperature mean-field theory which accurately accounts for initial molecular quantum fluctuations, triggering the association process. The structure of the resulting semiclassical phase space is investigated, highlighting the dynamical instability of the system towards association, for sufficiently small detuning from resonance. It is shown that this instability significantly modifies the finite-rate efficiency of the sweep, transforming the single-pair exponential Landau-Zener behavior of the remnant fraction of atoms Gamma on sweep rate alpha, into a power-law dependence as the number of atoms increases. The obtained nonadiabaticity is determined from the interplay of characteristic time scales for the motion of adiabatic eigenstates and for fast periodic motion around them. Critical slowing-down of these precessions near the instability leads to the power-law dependence. A linear power law $Gamma\propto alpha$ is obtained when the initial molecular fraction is smaller than the 1/N quantum fluctuations, and a cubic-root power law $Gamma\propto alph{a}^{1/3}$ is attained when it is larger. Our mean-field analysis is confirmed by exact calculations, using Fock-space expansions. Finally, we fit experimental low temperature Feshbach sweep data with a power-law dependence. While the agreement with the experimental data is well within experimental error bars, similar accuracy can be obtained with an exponential fit, making additional data highly desirable.

9 pages, 9 figures

References in corpus (6)

• Observation of Bose-Einstein Condensation of Molecules
• Weakly bound dimers of fermionic atoms
• Observation of molecules produced from a Bose-Einstein condensate
• Nonequilibrium dynamics and thermodynamics of a degenerate Fermi gas across a Feshbach resonance
• Adiabatic association of ultracold molecules via magnetic field tunable interactions
• Molecular production in two-component atomic Fermi gases

Cited by in corpus (9)

• Non-adiabacity and large flucutations in a many particle Landau Zener problem
• Many body generalization of the Landau Zener problem
• Dynamics of a many-particle Landau-Zener model: inverse sweep
• Universality in nonadiabatic behaviour of classical actions in nonlinear models with separatrix crossings
• Many-Body Effects on Nonadiabatic Feshbach Conversion in Bosonic Systems
• Role of Particle Interactions in the Feshbach Conversion of Fermion Atoms to Bosonic Molecules
• Matter-wave squeezing and the generation of SU(1,1) and SU(2) coherent-states via Feshbach resonances
• Variational ansatz for the nonlinear Landau-Zener problem for cold atom association
• Molecular production at a wide Feshbach resonance in Fermi-gas of cooled atoms