845 research outputs found
Cavity-induced phase stability to decelerate a fast molecular beam via feedback-controlled time-varying optical pumps
We have identified a novel phase stability mechanism from the intracavity
field-induced self-organization of a fast-moving molecular beam into travelling
molecular packets in the bad cavity regime, which is then used to decelerate
the molecular packets by feedback-controlled time-varying laser pumps to the
cavity. We first applied the linear stability analysis to derive an expression
for this self-organization in the adiabatic limit and show that the
self-organization of the beam leads to the formation of travelling molecular
packets, which in turn function as a dynamic Bragg grating, thus modulating
periodically the intracavity field by superradiant scattering of the pump
photons. The modulation encodes the position information of the molecular
packets into the output of the intracavity field instantaneously. We then
applied time-varying laser pumps that are automatically switched by the output
of the intracavity field to slow down the molecular packets via a feedback
mechanism and found that most of the molecules in the molecular packets are
decelerated to zero central velocity after tens of stages. Our cavity-based
deceleration proposal works well in the bad cavity regime, which is very
different from the conventional cavity- based cooling strategies where a good
cavity is preferred. Practical issues in realizing the proposal are also
discussed.Comment: 24 pages, 7 figure
Quantum phases of strongly interacting Rydberg atoms in triangular lattices
We present a theoretical study on the system of laser-driven strongly
interacting Rydberg atoms trapped in a two-dimensional triangular lattice, in
which the dipole-dipole interactions between Rydberg states result in exotic
quantum phases. By using the mean-field theory, we investigate the steady state
solutions and analyze their dynamical stabilities. We find that in the
strong-interaction limit, the dynamics of the system is chaotic and exhibits
random oscillations under appropriate laser detunings. Lyapunov exponent
criterion is introduced to confirm the existence of this chaotic behavior. In
addition, we present a full quantum calculation based on a six-atom model, and
find that the system exhibits some bi-antiferromagnetic properties in every
triangular cell when the one-photon detuning is exactly resonant or
blue-shifted.Comment: 5 pages, 4 figure
Anderson Localization of cold atomic gases with effective spin-orbit interaction in a quasiperiodic optical lattice
We theoretically investigate the localization properties of a spin-orbit
coupled spin-1/2 particle moving in a one-dimensional quasiperiodic potential,
which can be experimentally implemented using cold atoms trapped in a
quasiperiodic optical lattice potential and external laser fields. We present
the phase diagram in the parameter space of the disorder strength and those
related to the spin-orbit coupling. The phase diagram is verified via
multifractal analysis of the atomic wavefunctions and the numerical simulation
of diffusion dynamics. We found that spin-orbit coupling can lead to the
spectra mixing (coexistence of extended and localized states) and the
appearance of mobility edges.Comment: 8 pages, 7 figures, to be published in Phys. Rev.
Dynamical phases in a one-dimensional chain of Heterospecies Rydberg atoms with next-nearest neighbor interactions
We theoretically investigate the dynamical phase diagram of a one-dimensional
chain of laser-excited two-species Rydberg atoms. The existence of a variety of
unique dynamical phases in the experimentally-achievable parameter region is
predicted under the mean-field approximation, and the change of those phases
when the effect of the next-nearest neighbor interaction is included is further
discussed. In particular we find the competition of the strong Rydberg-Rydberg
interactions and the optical excitation imbalance can lead to the presence of
complex multiple chaotic phases, which are highly sensitive to the initial
Rydberg-state population and the strength of the next-nearest neighbor
interactions.Comment: 8 pages, 6 figures, accepted by Physical Review
Bloch oscillations of spin-orbit-coupled cold atoms in an optical lattice and spin current generation
We study the Bloch oscillation dynamics of a spin-orbit-coupled cold atomic
gas trapped inside a one-dimensioanl optical lattice. The eigenspectra of the
system is identified as two interpenetrating Wannier-Stark ladder. Based on
that, we carefully analyzed the Bloch oscillation dynamics and found out that
intraladder coupling between neighboring rungs of Wannier-Stark ladder give
rise to ordinary Bloch oscillation while interladder coupling lead to small
amplitude high frequency oscillation superimposed on it. Specifically
spin-orbit interaction breaks Galilean invariance, which can be reflected by
out-of-phase oscillation of the two spin components in the accelerated frame.
The possibility of generating spin current in this system are also explored.Comment: 8 pages, 6 figure
Anisotropic deformation of Rydberg blockade sphere in few-atom systems
Rydberg blockade sphere persists an intriguing picture by which a number of
collective many-body effects caused by the strong Rydberg-Rydberg interactions
can be clearly understood and profoundly investigated. In the present work, we
develop a new definition for the effective two-atom blockade radius and show
that the original spherically shaped blockade surface would be deformed when
the real number of atoms increases from two to three. This deformation of
blockade sphere reveals spatially anisotropic and shrunken properties which
strongly depend on the interatomic distance. In addition, we also study the
optimal conditions for the Rydberg antiblockade effect and make predictions for
improving the antiblockade efficiency in few-atom systems.Comment: 7 pages, 3 figures, submitted to Physical Review
Deceleration of molecules in a supersonic beam by the optical field in a low-finesse cavity
We study the dynamics of a supersonic molecular beam in a low-finesse optical
cavity and demonstrate that most molecules in the beam can be decelerated to
zero central velocity by the intracavity optical field in a process analogous
to electrostatic Stark deceleration. We show that the rapid switching of the
optical field for slowing the molecules is automatically generated by the
cavity-induced dynamics. We further show that of the molecules can be
optically trapped at a few millikelvin in the same cavity.Comment: 6 pages, 6 figure
Efficiency limitation for realizing an atom-molecule adiabatic transfer based on a chainwise system
In a recent work we have developed a robust chainwise atom-molecule adiabatic
passage scheme to produce ultracold ground-state molecules via
photo-associating free atoms [J. Qian {\it et.al.} Phys. Rev. A 81 013632
(2010)]. With the help of intermediate auxiliary levels, the pump laser
intensity requested in the atomic photo-association process can be greatly
reduced. In the present work, we extend the scheme to a more generalized
(2+1)-level system and investigate the efficiency limitation for it. As the
increase of intermediate levels and auxiliary lasers, the atom-molecule
adiabatic passage would be gradually closed, leading to a poor transfer
efficiency. For the purpose of enhancing the efficiency, we present various
optimization approaches to the laser parameters, involving order number ,
relative strength ratio and absolute strength. We show there can remain a limit
on the population transfer efficiency given by a three-level system.
In addition, we illustrate the importance of selecting an appropriate number of
intermediate levels for maintaining a highly efficient transfer under mild
experimental conditions.Comment: 9 pages, 6 figures, accepted by josa
Generating correlated (2+1)-photon in an active Raman gain medium
A scheme of generating controllable (2+1) photons in a double-
atomic system based on active-Raman-gain is presented in this paper. Such (2+1)
photons can be a potential candidate to generate a correlated photon pair as
the photon `1' acts as a trigger. Compared to other schemes of generating
correlated photon pairs, our scheme exhibits a number of advantages due to the
exploit of the stimulated Raman process.Comment: 8 pages, 8 figure
Cavity-induced switching between localized and extended states in a non-interacting Bose-Einstein condensate
We study an ultracold atom-cavity coupling system, which had been implemented
in experiment to display weak light nonlinearity [S. Gupta \textit{et al}.,
Phys. Rev. Lett. \textbf{99}, 213601 (2007)]. The model is described by a
non-interacting Bose-Einstein condensate contained in a Fabry-P\'{e}rot optical
resonator, in which two incommensurate standing-wave modes are excited and thus
form a quasiperiodic optical lattice potential for the atoms. Special emphasis
are paid to the variation of atomic wavefunction induced by the cavity light
field. We show that bistability between the atomic localized and extended
states can be generated under appropriate conditions
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