150 research outputs found
An effective quasi-one-dimensional description of a spin-1 atomic condensate
Within the mean field theory we extend the effective quasi-1D non-polynomial
Schr\"{o}dinger equation (NPSE) approach to the description of a spin-1 atomic
condensate in a tight radial confinement geometry for both weak and strong
atom-atom interactions. Detailed comparisons with full time dependent 3D
numerical simulations show excellent agreement as in the case of a single
component scalar condensate, demonstrating our result as an efficient and
effective tool for the understanding of spin-1 condensate dynamics observed in
several recent experiments.Comment: 5 pages, 3 eps figures, to appear in Phys. Rev. A. Small typoes
corrections. Updated Reference
Localization of spin mixing dynamics in a spin-1 Bose-Einstein condensate
We propose to localize spin mixing dynamics in a spin-1 Bose-Einstein
condensate by a temporal modulation of spin exchange interaction, which is
tunable with optical Feshbach resonance. Adopting techniques from coherent
control, we demonstrate the localization/freezing of spin mixing dynamics, and
the suppression of the intrinsic dynamic instability and spontaneous spin
domain formation in a ferromagnetically interacting condensate of Rb
atoms. This work points to a promising scheme for investigating the weak
magnetic spin dipole interaction, which is usually masked by the more dominant
spin exchange interaction.Comment: 4 pages, 5 eps figures, published in Phys. Rev. A
Coherent spin mixing dynamics in a spin-1 atomic condensate
We study the coherent off-equilibrium spin mixing inside an atomic
condensate. Using mean field theory and adopting the single spatial mode
approximation (SMA), the condensate spin dynamics is found to be well described
by that of a nonrigid pendulum, and displays a variety of periodic oscillations
in an external magnetic field. Our results illuminate several recent
experimental observations and provide critical insights into the observation of
coherent interaction-driven oscillations in a spin-1 condensate.Comment: 6 pages, 5 eps figures, update the discussion of the experimental
result
Bose-Einstein condensation of trapped interacting spin-1 atoms
We investigate Bose-Einstein condensation of trapped spin-1 atoms with
ferromagnetic or antiferromagnetic two-body contact interactions. We adopt the
mean field theory and develop a Hartree-Fock-Popov type approximation in terms
of a semiclassical two-fluid model. For antiferromagnetic interactions, our
study reveals double condensations as atoms in the state never seem
to condense under the constraints of both the conservation of total atom number
and magnetization . For ferromagnetic interactions, however, triple
condensations can occur. Our results can be conveniently understood in terms of
the interplay of three factors: (anti) ferromagnetic atom-atom interactions,
conservation, and the miscibilities between and among different condensed
components.Comment: RevTex 4, 9 pages, 5 eps figures, to appear in Phys. Rev. A, vol 70,
p
Effective size of a trapped atomic Bose gas
We investigate the temperature-dependent effective size of a trapped
interacting atomic Bose gas within a mean field theory approximation. The
sudden shrinking of the average length, as observed in an earlier experiment by
Wang {\it et al.} [Chin. Phys. Lett. {\bf 20}, 799 (2003)], is shown to be a
good indication for Bose-Einstein condensation (BEC). Our study also supports
the use of the average width of a trapped Bose gas for a nondestructive
calibration of its temperature.Comment: RevTex4, 6 pages, 4 eps figures, to appear in Phys. Rev.
Dynamical instability and domain formation in a spin-1 Bose condensate
We interpret the recently observed spatial domain formation in spin-1 atomic
condensates as a result of dynamical instability. Within the mean field theory,
a homogeneous condensate is dynamically unstable (stable) for ferromagnetic
(antiferromagnetic) atomic interactions. We find this dynamical instability
naturally leads to spontaneous domain formation as observed in several recent
experiments for condensates with rather small numbers of atoms. For trapped
condensates, our numerical simulations compare quantitatively to the
experimental results, thus largely confirming the physical insight from our
analysis of the homogeneous case.Comment: RevTex4, 4 pages with 3 color eps figure, to appear in Phys. Rev.
Let
Dynamical control of two-level system's decay and long time freezing
We investigate with exact numerical calculation coherent control of a
two-level quantum system's decay by subjecting the two-level system to many
periodic ideal phase modulation pulses. For three spectrum intensities
(Gaussian, Lorentzian, and exponential), we find both suppression and
acceleration of the decay of the two-level system, depending on difference
between the spectrum peak position and the eigen frequency of the two-level
system. Most interestingly, the decay of the two-level system freezes after
many control pulses if the pulse delay is short. The decay freezing value is
half of the decay in the first pulse delay.Comment: 6 pages, 6 figures, published in Phys. Rev.
Solitons in a trapped spin-1 atomic condensate
We numerically investigate a particular type of spin solitons inside a
trapped atomic spin-1 Bose-Einstein condensate (BEC) with ferromagnetic
interactions. Within the mean field theory approximation, our study of the
solitonic dynamics shows that the solitonic wave function, its center of mass
motion, and the local spin evolutions are stable and are intimately related to
the domain structures studied recently in spin-1 Rb condensates. We
discuss a rotating reference frame wherein the dynamics of the solitonic local
spatial spin distribution become time independent.Comment: 8 pages, 8 color eps figure
Long-time electron spin storage via dynamical suppression of hyperfine-induced decoherence in a quantum dot
The coherence time of an electron spin decohered by the nuclear spin
environment in a quantum dot can be substantially increased by subjecting the
electron to suitable dynamical decoupling sequences. We analyze the performance
of high-level decoupling protocols by using a combination of analytical and
exact numerical methods, and by paying special attention to the regimes of
large inter-pulse delays and long-time dynamics, which are outside the reach of
standard average Hamiltonian theory descriptions. We demonstrate that dynamical
decoupling can remain efficient far beyond its formal domain of applicability,
and find that a protocol exploiting concatenated design provides best
performance for this system in the relevant parameter range. In situations
where the initial electron state is known, protocols able to completely freeze
decoherence at long times are constructed and characterized. The impact of
system and control non-idealities is also assessed, including the effect of
intra-bath dipolar interaction, magnetic field bias and bath polarization, as
well as systematic pulse imperfections. While small bias field and small bath
polarization degrade the decoupling fidelity, enhanced performance and temporal
modulation result from strong applied fields and high polarizations. Overall,
we find that if the relative errors of the control parameters do not exceed 5%,
decoupling protocols can still prolong the coherence time by up to two orders
of magnitude.Comment: 16 pages, 10 figures, submitted to Phys. Rev.
Mean field ground state of a spin-1 condensate in a magnetic field
We revisit the topic of the mean field ground state of a spin-1 atomic
condensate inside a uniform magnetic field () under the constraints that
both the total number of atoms () and the magnetization () are
conserved. In the presence of an internal state (spin component) independent
trap, we also investigate the dependence of the so-called single spatial mode
approximation (SMA) on the magnitude of the magnetic field and . Our
result indicate that the quadratic Zeeman effect is an important factor in
balancing the mean field energy from elastic atom-atom collisions that are
known to conserve both and .Comment: 13 pages, 9 figures, to be published in New J. Phys.
(http://www.njp.org/
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