613 research outputs found
Reproducing spin lattice models in strongly coupled atom-cavity systems
In an array of coupled cavities where the cavities are doped with an atomic
V-system, and the two excited levels couple to cavity photons of different
polarizations, we show how to construct various spin models employed in
characterizing phenomena in condensed matter physics, such as the spin-1/2
Ising, XX, Heisenberg, and XXZ models. The ability to construct networks of
arbitrary geometry also allows for the simulation of topological effects. By
tuning the number of excitations present, the dimension of the spin to be
simulated can be controlled, and mixtures of different spin types produced. The
facility of single-site addressing, the use of only the natural hopping photon
dynamics without external fields, and the recent experimental advances towards
strong coupling, makes the prospect of using these arrays as efficient quantum
simulators promising.Comment: 4 pages, 3 figures. v3: References adde
Simulation of high-spin Heisenberg models in coupled cavities
We propose a scheme to realize the Heisenberg model of any spin in an
arbitrary array of coupled cavities. Our scheme is based on a fixed number of
atoms confined in each cavity and collectively applied constant laser fields,
and is in a regime where both atomic and cavity excitations are suppressed. It
is shown that as well as optically controlling the effective spin Hamiltonian,
it is also possible to engineer the magnitude of the spin. Our scheme would
open up an unprecedented way to simulate otherwise intractable high-spin
problems in many-body physics.Comment: 4 pages, 2 figure
Beyond mean-field bistability in driven-dissipative lattices: bunching-antibunching transition and quantum simulation
In the present work we investigate the existence of multiple nonequilibrium
steady states in a coherently driven XY lattice of dissipative two-level
systems. A commonly used mean-field ansatz, in which spatial correlations are
neglected, predicts a bistable behavior with a sharp shift between low- and
high-density states. In contrast one-dimensional matrix product methods reveal
these effects to be artifacts of the mean-field approach, with both
disappearing once correlations are taken fully into account. Instead, a
bunching-antibunching transition emerges. This indicates that alternative
approaches should be considered for higher spatial dimensions, where classical
simulations are currently infeasible. Thus we propose a circuit QED quantum
simulator implementable with current technology to enable an experimental
investigation of the model considered
Spinons and Holons with Polarized Photons in a Nonlinear Waveguide
We show that the spin-charge separation predicted for correlated fermions in
one dimension, could be observed using polarized photons propagating in a
nonlinear optical waveguide. Using coherent control techniques and employing a
cold atom ensemble interacting with the photons, large nonlinearities in the
single photon level can be achieved. We show that the latter can allow for the
simulation of a strongly interacting gas, which is made of stationary
dark-state polaritons of two species and then shown to form a Luttinger liquid
of effective fermions for the right regime of interactions. The system can be
tuned optically to the relevant regime where the spin-charge separation is
expected to occur. The characteristic features of the separation as
demonstrated in the different spin and charge densities and velocities can be
efficiently detected via optical measurements of the emitted photons with
current optical technologies.Comment: To appear in New Journal of Physic
F-GAMMA: On the phenomenological classification of continuum radio spectra variability patterns of Fermi blazars
The F-GAMMA program is a coordinated effort to investigate the physics of
Active Galactic Nuclei (AGNs) via multi-frequency monitoring of Fermi blazars.
In the current study we show and discuss the evolution of broad-band radio
spectra, which are measured at ten frequencies between 2.64 and 142 GHz using
the Effelsberg 100-m and the IRAM 30-m telescopes. It is shown that any of the
78 sources studied can be classified in terms of their variability
characteristics in merely 5 types of variability. It is argued that these can
be attributed to only two classes of variability mechanisms. The first four
types are dominated by spectral evolution and can be described by a simple
two-component system composed of: (a) a steep quiescent spectral component from
a large scale jet and (b) a time evolving flare component following the
"Shock-in-Jet" evolutionary path. The fifth type is characterised by an
achromatic change of the broad band spectrum, which could be attributed to a
different mechanism, likely involving differential Doppler boosting caused by
geometrical effects. Here we present the classification, the assumed physical
scenario and the results of calculations that have been performed for the
spectral evolution of flares.Comment: Proceedings of the conference: "The Central Kiloparsec in Galactic
Nucleic: Astronomy at High Angular Resolution 2011", August 29 - September 2,
2011, Bad Honnef, German
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