100 research outputs found
Band-gap solitons in nonlinear optically-induced lattices
We introduce novel optical solitons that consist of a periodic and a
spatially localized components coupled nonlinearly via cross-phase modulation.
The spatially localized optical field can be treated as a gap soliton supported
by the optically-induced nonlinear grating. We find different types of these
band-gap composite solitons and demonstrate their dynamical stability.Comment: 4 pages, 5 figure
Dark-Bright Solitons in Inhomogeneous Bose-Einstein Condensates
We investigate dark-bright vector solitary wave solutions to the coupled
non-linear Schr\"odinger equations which describe an inhomogeneous two-species
Bose-Einstein condensate. While these structures are well known in non-linear
fiber optics, we show that spatial inhomogeneity strongly affects their motion,
stability, and interaction, and that current technology suffices for their
creation and control in ultracold trapped gases. The effects of controllably
different interparticle scattering lengths, and stability against
three-dimensional deformations, are also examined.Comment: 5 pages, 5 figure
Modulational instability of spinor condensates
We demonstrate, analytically and numerically, that the ferromagnetic phase of
the spinor Bose-Einstein condenstate may experience modulational instability of
the ground state leading to a fragmentation of the spin domains. Together with
other nonlinear effects in the atomic optics of ultra-cold gases (such as
coherent photoassociation and four-wave mixing) this effect provides one more
analogy between coherent matter waves and light waves in nonlinear optics.Comment: 4 pages, 4 figures. Accepted for Phys. Rev. A Rapid Communication
Direct measurement of polariton-polariton interaction strength in the Thomas-Fermi regime of exciton-polariton condensation
Bosonic condensates of exciton polaritons (light-matter quasiparticles in a
semiconductor) provide a solid-state platform for studies of non-equilibrium
quantum systems with a spontaneous macroscopic coherence. These driven,
dissipative condensates typically coexist and interact with an incoherent
reservoir, which undermines measurements of key parameters of the condensate.
Here, we overcome this limitation by creating a high-density exciton-polariton
condensate in an optically-induced "box" trap. In this so-called Thomas-Fermi
regime, the condensate is fully separated from the reservoir and its behaviour
is dominated by interparticle interactions. We use this regime to directly
measure the polariton-polariton interaction strength, and reduce the existing
uncertainty in its value from four orders of magnitude to within three times
the theoretical prediction. The Thomas-Fermi regime has previously been
demonstrated only in ultracold atomic gases in thermal equilibrium. In a
non-equilibrium exciton-polariton system, this regime offers a novel
opportunity to study interaction-driven effects unmasked by an incoherent
reservoir.Comment: 11 pages, 5 figure
Topological phase transition in an all-optical exciton-polariton lattice
Topological insulators are a class of electronic materials exhibiting robust
edge states immune to perturbations and disorder. This concept has been
successfully adapted in photonics, where topologically nontrivial waveguides
and topological lasers were developed. However, the exploration of topological
properties in a given photonic system is limited to a fabricated sample,
without the flexibility to reconfigure the structure in-situ. Here, we
demonstrate an all-optical realization of the orbital Su-Schrieffer-Heeger
(SSH) model in a microcavity exciton-polariton system, whereby a cavity photon
is hybridized with an exciton in a GaAs quantum well. We induce a zigzag
potential for exciton polaritons all-optically, by shaping the nonresonant
laser excitation, and measure directly the eigenspectrum and topological edge
states of a polariton lattice in a nonlinear regime of bosonic condensation.
Furthermore, taking advantage of the tunability of the optically induced
lattice we modify the intersite tunneling to realize a topological phase
transition to a trivial state. Our results open the way to study topological
phase transitions on-demand in fully reconfigurable hybrid photonic systems
that do not require sophisticated sample engineering.Comment: 7 pages, 4 figure
Macroscopic superposition states of ultracold bosons in a double-well potential
We present a thorough description of the physical regimes for ultracold
bosons in double wells, with special attention paid to macroscopic
superpositions (MSs). We use a generalization of the Lipkin-Meshkov-Glick
Hamiltonian of up to eight single particle modes to study these MSs, solving
the Hamiltonian with a combination of numerical exact diagonalization and
high-order perturbation theory. The MS is between left and right potential
wells; the extreme case with all atoms simultaneously located in both wells and
in only two modes is the famous NOON state, but our approach encompasses much
more general MSs. Use of more single particle modes brings dimensionality into
the problem, allows us to set hard limits on the use of the original two-mode
LMG model commonly treated in the literature, and also introduces a new mixed
Josephson-Fock regime. Higher modes introduce angular degrees of freedom and MS
states with different angular properties.Comment: 15 pages, 8 figures, 1 table. Mini-review prepared for the special
issue of Frontiers of Physics "Recent Progresses on Quantum Dynamics of
Ultracold Atoms and Future Quantum Technologies", edited by Profs. Lee, Ueda,
and Drummon
Symmetry-breaking Effects for Polariton Condensates in Double-Well Potentials
We study the existence, stability, and dynamics of symmetric and anti-symmetric states of quasi-one-dimensional polariton condensates in double-well potentials, in the presence of nonresonant pumping and nonlinear damping. Some prototypical features of the system, such as the bifurcation of asymmetric solutions, are similar to the Hamiltonian analog of the double-well system considered in the realm of atomic condensates. Nevertheless, there are also some nontrivial differences including, e.g., the unstable nature of both the parent and the daughter branch emerging in the relevant pitchfork bifurcation for slightly larger values of atom numbers. Another interesting feature that does not appear in the atomic condensate case is that the bifurcation for attractive interactions is slightly sub-critical instead of supercritical. These conclusions of the bifurcation analysis are corroborated by direct numerical simulations examining the dynamics of the system in the unstable regime.MICINN (Spain) project FIS2008- 0484
Structure and stability of two-dimensional Bose-Einstein condensates under both harmonic and lattice confinement
In this work, we study pancake-shaped Bose-Einstein condensates confined by
both a cylindrically symmetric harmonic potential and an optical lattice with
equal periodicity in two orthogonal directions. We first identify the spectrum
of the underlying two-dimensional linear problem through multiple-scale
techniques. Then, we use the results obtained in the linear limit as a starting
point for a nonlinear existence and stability analysis of the lowest energy
states, emanating from the linear ones, in the nonlinear problem. Two-parameter
continuations of these states are performed for increasing nonlinearity and
optical lattice strengths, and their instabilities and temporal evolution are
investigated. It is found that the ground state as well as one of the excited
states are either stable or weakly unstable for both attractive and repulsive
interatomic interactions
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