548 research outputs found
Collective excitations and instability of an optical lattice due to unbalanced pumping
We solve self-consistently the coupled equations of motion for trapped
particles and the field of a one-dimensional optical lattice. Optomechanical
coupling creates long-range interaction between the particles, whose nature
depends crucially on the relative power of the pump beams. For asymmetric
pumping, traveling density wave-like collective oscillations arise in the
lattice, even in the overdamped limit. Increasing the lattice size or pump
asymmetry these waves can destabilize the lattice.Comment: 5 pages, minor changes (SI units, new references
Geometric resonance cooling of polarizable particles in an optical waveguide
In the radiation field of an optical waveguide, the Rayleigh scattering of
photons is shown to result in a strongly velocity-dependent force on atoms. The
pump field, which is injected in the fundamental branch of the waveguide, is
favorably scattered by a moving atom into one of the transversely excited
branches of propagating modes. All fields involved are far detuned from any
resonances of the atom. For a simple polarizable particle, a linear friction
force coefficient comparable to that of cavity cooling can be achieved.Comment: 4 page
Damping of quasiparticles in a Bose-Einstein condensate coupled to an optical cavity
We present a general theory for calculating the damping rate of elementary
density wave excitations in a Bose-Einstein condensate strongly coupled to a
single radiation field mode of an optical cavity. Thereby we give a detailed
derivation of the huge resonant enhancement in the Beliaev damping of a density
wave mode, predicted recently by K\'onya et al., Phys.~Rev.~A 89, 051601(R)
(2014). The given density-wave mode constitutes the polariton-like soft mode of
the self-organization phase transition. The resonant enhancement takes place,
both in the normal and ordered phases, outside the critical region. We show
that the large damping rate is accompanied by a significant frequency shift of
this polariton mode. Going beyond the Born-Markov approximation and determining
the poles of the retarded Green's function of the polariton, we reveal a strong
coupling between the polariton and a collective mode in the phonon bath formed
by the other density wave modes
Fundamental limitation of ultrastrong coupling between light and atoms
In a recent work of ours [Phys. Rev. Lett. 112, 073601 (2014)], we
generalized the Power-Zineau-Woolley gauge to describe the electrodynamics of
atoms in an arbitrary confined geometry. Here we complement the theory by
proposing a tractable form of the polarization field to represent atomic
material with well-defined intra-atomic potential. The direct electrostatic
dipole-dipole interaction between the atoms is canceled. This theory yields a
suitable framework to determine limitations on the light-matter coupling in
quantum optical models with discernible atoms. We find that the superradiant
criticality is at the border of covalent molecule formation and
crystallization.Comment: 6 page
Selecting molecules in the vibrational and rotational ground state by deflection
A beam of diatomic molecules scattered off a standing wave laser mode splits
according to the rovibrational quantum state of the molecules. Our numerical
calculation shows that single state resolution can be achieved by properly
tuned, monochromatic light. The proposed scheme allows for selecting
non-vibrating and non-rotating molecules from a thermal beam, implementing a
laser Maxwell's demon to prepare a rovibrationally cold molecular ensemble.Comment: 11 pages, LaTeX. To appear in the European Physical Journal
Cold atom dynamics in a quantum optical lattice potential
We study a generalized cold atom Bose Hubbard model, where the periodic
optical potential is formed by a cavity field with quantum properties. On the
one hand the common coupling of all atoms to the same mode introduces cavity
mediated long range atom-atom interactions and on the other hand atomic
backaction on the field introduces atom-field entanglement. This modifies the
properties of the associated quantum phase transitions and allows for new
correlated atom-field states including superposition of different atomic
quantum phases. After deriving an approximative Hamiltonian including the new
long range interaction terms we exhibit central physical phenomena at generic
configurations of few atoms in few wells. We find strong modifications of
population fluctuations and next-nearest neighbor correlations near the phase
transition point.Comment: 4 pages, 5 figures, corrected typo
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