We present measurements and a theoretical model for the interplay of spin-dependent interactions and external magnetic fields in atomic spinor condensates. We highlight general features such as quadratic Zeeman dephasing and its influence on coherent spin mixing processes by focusing on a specific coherent superposition state in a
F=1 87Rb Bose-Einstein condensate. In particular, we observe the transition from coherent spinor oscillations to the thermal equilibration.
We study the nonequilibrium coherent spin-mixing dynamics in ferromagnetic spin-1 and antiferromagnetic spin-2 thermal gases of ultracold
87Rb atoms. Long-lasting spin population oscillations with magnetic-field-dependent resonances are observed in both cases. Our observations are well reproduced by Boltzmann equations of the Wigner distribution function. Compared to the equation of motion of spinor Bose-Einstein condensates, the only difference here is a factor-of-2 increase in the spin-dependent interaction, which is confirmed directly in the spin-2 case by measuring the relation between the oscillation amplitude and the sample's density.
We report the observation of coherent heteronuclear spin dynamics driven by interspecies spin-spin interaction in an ultracold spinor mixture, which manifests as periodical and well-correlated spin oscillations between two atomic species. In particular, we investigate the magnetic field dependence of the oscillations and find a resonance behavior which depends on both the linear and quadratic Zeeman effects and the spin-dependent interaction. We also demonstrate a unique knob for controlling the spin dynamics in the spinor mixture with species-dependent vector light shifts.
The single-mode approximation (SMA) has been widely employed in ultracold spinor gases, where all spin components share the same spatial mode. By adopting generalized Van Vleck (GVV) perturbation theory, we achieve a relative error of
10−6 in the ground-state energy with a reduced effective Hilbert space dimension of
∼103 for two spin-1 bosons confined in a one-dimensional hard-wall trap. With the accurate GVV method, we explore the validity of the SMA across ground-state properties and quench spin dynamics for two
7Li,
87Rb, or
23Na atoms. Numerical results show that the quadratic Zeeman energy
q provides a powerful control knob: by increasing
∣q∣, the fidelity between the spin components in the ground state gradually decreases, leading eventually to the breakdown of the SMA (due to the competition between the kinetic energy and the quadratic Zeeman energy). Quench spin dynamics with abruptly increased
q further reveals multiple resonances, where the SMA-predicted micromotion and beyond-SMA macromotion appear simultaneously. These results point to a direction to investigate the quantum spin-mixing dynamics beyond the SMA, particularly in recent experiments of strongly interacting spin-1 atomic gases.
We discuss the static and dynamic magnetic properties of cold quantum gas systems. In particular, we investigate and analyze the ground state properties and dynamics of F = 2 spinor Bose-Einstein condensates of 87Rb. The rich physics of these systems is governed by an interplay between mean-field-driven spin dynamics and hyperfine-changing losses in addition to interactions with atoms in the thermal cloud. We find conversion rates on the order of 10-12 cm3 s-1 for spin-changing collisions within the F = 2 manifold and spin-dependent loss rates on the order of 10-13 cm3 s-1 for hyperfine-changing collisions. Our data leads to the conclusion that the F = 2 ground state of 87Rb is polar, while we measure the F = 1 ground state to be ferromagnetic. As remarkable features in the spin dynamics we observe spinor oscillations and a delayed formation of new mF-condensate components.
We experimentally study spin dynamics in a sodium antiferromagnetic spinor condensate as a result of spin-dependent interactions
c and microwave dressing field interactions characterized by the net quadratic Zeeman effect
qnet. In contrast to magnetic fields, microwave dressing fields enable us to access both negative and positive values of
qnet. We find an experimental signature to determine the sign of
qnet and observe harmonic spin population oscillations at every
qnet except near each separatrix in phase space where spin oscillation period diverges. No spin domains and spatial modes are observed in our system. Our data in the negative
qnet region exactly resembles what is predicted to occur in a ferromagnetic spinor condensate in the positive
qnet region. This observation agrees with an important prediction derived from the mean-field theory: spin dynamics in spin-1 condensates substantially depends on the sign of
qnet/c. This work uses only one atomic species to reveal mean-field spin dynamics, especially the remarkably different relationship between each separatrix and the magnetization, of spin-1 antiferromagnetic and ferromagnetic spinor condensates.