38,995 research outputs found
Study of Objectives
Focal length, chromatic and spherical aberration, and astigmatism testing for astronomical telescop
Neural-Network Approach to Dissipative Quantum Many-Body Dynamics
In experimentally realistic situations, quantum systems are never perfectly
isolated and the coupling to their environment needs to be taken into account.
Often, the effect of the environment can be well approximated by a Markovian
master equation. However, solving this master equation for quantum many-body
systems, becomes exceedingly hard due to the high dimension of the Hilbert
space. Here we present an approach to the effective simulation of the dynamics
of open quantum many-body systems based on machine learning techniques. We
represent the mixed many-body quantum states with neural networks in the form
of restricted Boltzmann machines and derive a variational Monte-Carlo algorithm
for their time evolution and stationary states. We document the accuracy of the
approach with numerical examples for a dissipative spin lattice system
Synchronized Switching in a Josephson Junction Crystal
We consider a superconducting coplanar waveguide resonator where the central
conductor is interrupted by a series of uniformly spaced Josephson junctions.
The device forms an extended medium that is optically nonlinear on the single
photon level with normal modes that inherit the full nonlinearity of the
junctions but are nonetheless accessible via the resonator ports. For specific
plasma frequencies of the junctions a set of normal modes clusters in a narrow
band and eventually become entirely degenerate. Upon increasing the intensity
of a red detuned drive on these modes, we observe a sharp and synchronized
switching from low occupation quantum states to high occupation classical
fields, accompanied by a pronounced jump from low to high output intensity.Comment: 13 pages, 5 figure
Entangling the motion of two optically trapped objects via time-modulated driving fields
We study entanglement of the motional degrees of freedom of two tethered and
optically trapped microdisks inside a single cavity. By properly choosing the
position of the trapped objects in the optical cavity and driving proper modes
of the cavity it is possible to equip the system with linear and quadratic
optomechanical couplings. We show that a parametric coupling between the
fundamental vibrational modes of two tethered mircodiscs can be generated via a
time modulated input laser. For a proper choice of the modulation frequency,
this mechanism can drive the motion of the microdisks into an inseparable state
in the long time limit via a two-mode squeezing process. We numerically confirm
the performance of our scheme for current technology and briefly discuss an
experimental setup which can be employed for detecting this entanglement by
employing the quadratic coupling. We also comment on the perspectives for
generating such entanglement between the oscillations of optically levitated
nanospheres.Comment: 9 pages, 3 figure
Floquet engineering in superconducting circuits: from arbitrary spin-spin interactions to the Kitaev honeycomb model
We derive a theory for the generation of arbitrary spin-spin interactions in
superconducting circuits via periodic time modulation of the individual qubits
or the qubit-qubit interactions. The modulation frequencies in our approach are
in the microwave or radio frequency regime so that the required fields can be
generated with standard generators. Among others, our approach is suitable for
generating spin lattices that exhibit quantum spin liquid behavior such as
Kitaev's honeycomb model.Comment: 21 pages, 9 figure
Many Body Physics with Coupled Transmission Line Resonators
We present the Josephson junction intersected superconducting transmission
line resonator. In contrast to the Josephson parametric amplifier, Josephson
bifurcation amplifier and Josephson parametric converter we consider the regime
of few microwave photons. We review the derivation of eigenmode frequencies and
zero point fluctuations of the nonlinear transmission line resonator and the
derivation of the eigenmode Kerr nonlinearities. Remarkably these
nonlinearities can reach values comparable to Transmon qubits rendering the
device ideal for accessing the strongly correlated regime. This is particularly
interesting for investigation of quantum many-body dynamics of interacting
particles under the influence of drive and dissipation. We provide current
profiles for the device modes and investigate the coupling between resonators
in a network of nonlinear transmission line resonators.Comment: submitted to the proceedings of the CEWQO 2012 conferenc
The Circuit Quantum Electrodynamical Josephson Interferometer
Arrays of circuit cavities offer fascinating perspectives for exploring
quantum many-body systems in a driven dissipative regime where excitation
losses are continuously compensated by coherent input drives. Here we
investigate a system consisting of three transmission line resonators, where
the two outer ones are driven by coherent input sources and the central
resonator interacts with a superconducting qubit. Whereas a low excitation
number regime of such a device has been considered previously with a numerical
integration, we here specifically address the high excitation density regime.
We present analytical approximations to these regimes in the form of two
methods. The first method is a Bogoliubov or linear expansion in quantum
fluctuations which can be understood as an approximation for weak
nonlinearities. As the second method we introduce a combination of mean-field
decoupling for the photon tunneling with an exact approach to a driven Kerr
nonlinearity which can be understood as an approximation for low tunneling
rates. In contrast to the low excitation regime we find that for high
excitation numbers the anti-bunching of output photons from the central cavity
does not monotonously disappear as the tunnel coupling between the resonators
is increased.Comment: revised, comparison of numerics and mean-field adde
Master equation approach for interacting slow- and stationary-light polaritons
A master equation approach for the description of dark-state polaritons in
coherently driven atomic media is presented. This technique provides a
description of light-matter interactions under conditions of
electromagnetically induced transparency (EIT) that is well suited for the
treatment of polariton losses. The master equation approach allows us to
describe general polariton-polariton interactions that may be conservative,
dissipative or a mixture of both. In particular, it enables us to study
dissipation-induced correlations as a means for the creation of strongly
correlated polariton systems. Our technique reveals a loss mechanism for
stationary-light polaritons that has not been discussed so far. We find that
polariton losses in level configurations with non-degenerate ground states can
be a multiple of those in level schemes with degenerate ground states
The Bose-Hubbard model with localized particle losses
We consider the Bose-Hubbard model with particle losses at one lattice site.
For the non-interacting case, we find that half of the bosons of an initially
homogeneous particle distribution, are not affected by dissipation that only
acts on one lattice site in the center of the lattice. A physical
interpretation of this result is that the surviving particles interfere
destructively when they tunnel to the location of the dissipative defect and
therefore never reach it. Furthermore we find for a one-dimensional model that
a fraction of the particles can propagate across the dissipative defect even if
the rate of tunneling between adjacent lattice sites is much slower than the
loss rate at the defect. In the interacting case, the phase coherence is
destroyed and all particles eventually decay. We thus analyze the effect of
small interactions and small deviations from the perfectly symmetric setting on
the protection of the particles against the localized losses. A possible
experimental realization of our setup is provided by ultracold bosonic atoms in
an optical lattice, where an electron beam on a single lattice site ionizes
atoms that are then extracted by an electrostatic field.Comment: 10 pages, 5 figures, minor revisions to previous versio
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