90 research outputs found
Quantum operational measurement of amplitude and phase parameters for SU(3)-symmetry optical field
We consider a new approach to describe a quantum optical Bose-system with
internal Gell-Mann symmetry by the SU(3)-symmetry polarization map in Hilbert
space. The operational measurement in density (or coherency) matrix elements
for the three mode optical field is discussed for the first time. We have
introduced a set of operators that describes the quantum measurement procedure
and the behavior of fluctuations for the amplitude and phase characteristics of
three level system. The original twelve-port interferometer for parallel
measurements of the Gell-Mann parameters is proposed. The quantum properties of
W-qutrit states under the measurement procedure are examined.Comment: 11 pages, 2 eps-figures, uses iopart.cl
Lasing and high temperature phase transitions in atomic systems with dressed state polaritons
We consider the fundamental problem of high temperature phase transitions in
the system of high density two-level atoms off-resonantly interacting with a
pump field in the presence of optical collisions (OCs) and placed in the
cavity. OCs are considered in the framework of thermalization of atomic dressed
state (DS) population. For the case of a strong atom-field coupling condition
we analyze the problem of thermodynamically equilibrium superradiant phase
transition for the order parameter representing a real amplitude of cavity mode
and taking place as a result of atomic DSs thermalization process. Such
transition is also connected with condensed (coherent) properties of low branch
(LB) DS-polaritons occurring in the cavity. For describing non-equilibrium
phase transitions we derive Maxwell-Bloch like equations which account for
cavity decay rate, collisional decay rate and spontaneous emission. Various
aspects of transitions to laser field formation by using atomic DS levels for
both positive and negative detuning of a pump field from atomic transition
frequency are studied in detail. It is revealed, that for positive atom-light
detuning DS lasing can be obtained in the presence of quasi-equilibrium DS
population that corresponds to a true two-level atomic system with the
inversion in nonresonant limit.Comment: 12 pages, 8 figure
Nonlinear Bloch-waves and current states of exciton-polariton condensates
The formation of nonlinear Bloch states in open driven-dissipative system of
exciton-polaritons loaded into a weak-contrast 1D periodic lattice is studied
numerically and analytically. The condensate is described within the framework
of mean-field theory by the coupled equations for the order parameter and for
the density of incoherent excitons. The stationary nonlinear solutions having
the structure of Bloch waves are studied in detail. It is shown that there is a
bifurcation leading to the appearance of a family of essentially nonlinear
states. The special feature of these solutions is that its current does not
vanish when the quasi-momentum of the state approaches the values equal to the
half of the lattice constant. To explain the bifurcations found in numerical
simulations a simple perturbative approach is developed. The stability of the
nonlinear states is examined by linear spectral analysis and by direct
numerical simulations. An experimental scheme allowing the observation of the
discussed nonlinear current states is suggested and studied by numerical
simulations.Comment: 12 pages, 7 figure
Oscillatory dynamics of non-equilibrium dissipative exciton-polariton condensates in weak-contrast lattices
We study nonlinear dynamics of exciton-polaritons in an incoherently pumped
semiconductor microcavity with embedded weak-contrast lattice and coupled to an
exciton reservoir. We elucidate fundamental features of non-equilibrium
exciton-polariton condensate trapped in one-dimensional periodical potential
close to zero momentum (so-called "Zero-state") and to the state at the
boundary of Brillouin zone ("-state"). Within the framework of the
mean-field theory, we identify different regimes of both relaxation and
oscillatory dynamics of coherent exciton-polaritons governed by superpositions
of Bloch eigenstates within the periodic lattice. In particular, we
theoretically demonstrate stable macroscopical oscillations, akin to nonlinear
Josephson oscillations, between different spectral components of a polariton
condensate in the momenta-space. We elucidate a strong influence of the
dissipative effects and the feedback induced by the inhomogeneity of incoherent
reservoir on the dynamics of the coherent polaritons.Comment: 9 pages, 5 figure
Topological spin Meissner effect in exciton-polariton spinor condensate: constant amplitude solutions, half-vortices and symmetry breaking
We generalize the spin Meissner effect for exciton-polariton condensate
confined in annular geometries to the case of non-trivial topology of the
condensate wavefunction. In contrast to the conventional spin Meissner state,
topological spin Meissner states can in principle be observed at arbitrary high
magnetic field not limited by the critical magnetic field value for the
condensate in a simply-connected geometry. One special example of the
topological Meissner states are half-vortices. We show that in the absence of
magnetic field half-vortices in a ring exist in a form of superposition of
elementary half-vortex states which resolves recent experimental results where
such puzzling superposition was observed. Furthermore, we show that if a pure
half-vortex state is to be observed, a non-zero magnetic field of a specific
magnitude needs to be applied. Studying exciton-polariton in a ring in presence
of TE-TM splitting, we observe spin Meissner states which break rotational
symmetry of the system by developing inhomogeneous density distributions. We
classify various states arising in presence of non-zero TE-TM splitting based
on what states they can be continued from by increasing the TE-TM splitting
parameter from zero. With further increasing TE-TM splitting, states with
broken symmetry may transform into stable half-dark solitons and therefore may
serve as a useful tool to generate various non-trivial states of a spinor
condensate
Quantum metrology beyond Heisenberg limit with entangled matter wave solitons
By considering matter wave bright solitons from weakly coupled Bose-Einstein
condensates trapped in a double-well potential, we study the formation of
macroscopic non-classical states, including Schr\"odinger-cat superposition
states and maximally path entangled -states. With these macroscopic
states, we examine Mach-Zehnder interferometer in the context of parity
measurements, in order to obtain Heisenberg limit accuracy for linear phase
shift measurement. We reveal that the ratio between two-body scattering length
and intra-well hopping parameter can be measured with the scaling beyond this
limit by using nonlinear phase shift with interacting quantum solitons.Comment: 7 pages, 4 figure
Qubits based on Polariton Rabi Oscillators
We propose a novel physical mechanism for creation of long lived macroscopic
exciton-photon qubits in semiconductor microcavities with embedded quantum
wells in the strong couping regime. We argue that the coherence time of Rabi
oscillations can be dramatically enhanced due to their stimulated pumping from
a permanent thermal reservoir of polaritons. The polariton qubit is a
superposition of lower branch (LP) and upper branch (UP) exciton-polariton
states. We discuss applications of such qubits for quantum information
processing, cloning and storage purposes
Quantum storage and cloning of light states in EIT-like medium
In the paper we consider a new approach for storage and cloning of quantum information by three level atomic (molecular) systems in the presence of the electromagnetically induced transparency (EIT) effect. For that, the various schemes of transformation into the bright and dark polaritons for quantum states of optical field in the medium are proposed. Physical conditions of realization of quantum nondemolition (QND) storage of quantum optical state are formulated for the first time. We have shown that the best storage and cloning of can be achieved with the atomic ensemble in the Bose-Einstein condensation state. We discuss stimulated Raman two-color photoassociation for experimental realization of the schemes under consideration
Hyperbolic Metamaterials with Bragg Polaritons
We propose a novel mechanism for designing quantum hyperbolic metamaterials
with use of semi-conductor Bragg mirrors containing periodically
arrangedquantum wells. The hyperbolic dispersion of exciton-polariton modes is
realized near the top of the first allowed photonic miniband in such structure
which leads to formation of exciton-polariton X-waves. Exciton-light coupling
provides a resonant non-linearity which leads to non-trivial topologic
solutions. We predict formation of low amplitude spatially localized
oscillatory structures: oscillons described by kink shaped solutions of the
effective Ginzburg-Landau-Higgs equation. The oscillons have direct analogies
in the gravita-tional theory. We discuss implementation of exciton-polariton
Higgs fields for the Schrodinger cat state generation
Predicting quantum advantage by quantum walk with convolutional neural networks
Quantum walks are at the heart of modern quantum technologies. They allow to
deal with quantum transport phenomena and are an advanced tool for constructing
novel quantum algorithms. Quantum walks on graphs are fundamentally different
from classical random walks analogs, in particular, they walk faster than
classical ones on certain graphs, enabling in these cases quantum algorithmic
applications and quantum-enhanced energy transfer. However, little is known
about the possible advantages on arbitrary graphs not having explicit
symmetries. For these graphs one would need to perform simulations of classical
and quantum walk dynamics to check if the speedup occurs, which could take a
long computational time. Here we present a new approach for the solution of the
quantum speedup problem, which is based on a machine learning algorithm that
predicts the quantum advantage by just looking at a graph. The convolutional
neural network, which we designed specifically to learn from graphs, observes
simulated examples and learns complex features of graphs that lead to a quantum
advantage, allowing to identify graphs that exhibit quantum advantage without
performing any quantum walk or random walk simulations. The performance of our
approach is evaluated for line and random graphs, where classification was
always better than random guess even for the most challenging cases. Our
findings pave the way to an automated elaboration of novel large-scale quantum
circuits utilizing quantum walk based algorithms, and to simulating
high-efficiency energy transfer in biophotonics and material science.Comment: 10 pages, 5 figure
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