122 research outputs found
Branch-entangled polariton pairs in planar microcavities and photonic wires
A scheme is proposed for the generation of branch-entangled pairs of
microcavity polaritons through spontaneous inter-branch parametric scattering.
Branch-entanglement is achievable when there are two twin processes, where the
role of signal and idler can be exchanged between two different polariton
branches. Branch-entanglement of polariton pairs can lead to the emission of
frequency-entangled photon pairs out of the microcavity. In planar
microcavities, the necessary phase-matching conditions are fulfilled for
pumping of the upper polariton branch at an arbitrary in-plane wave-vector. The
important role of nonlinear losses due to pair scattering into high-momentum
exciton states is evaluated. The results show that the lack of protection of
the pump polaritons in the upper branch is critical. In photonic wires,
branch-entanglement of one-dimensional polaritons is achievable when the pump
excites a lower polariton sub-branch at normal incidence, providing protection
from the exciton reservoir.Comment: Under review at PR
Probing microcavity polariton superfluidity through resonant Rayleigh scattering
We investigate the two-dimensional motion of polaritons injected into a
planar microcavity by a continuous wave optical pump in presence of a static
perturbation, e.g. a point defect. By finding the stationary solutions of the
nonlinear mean-field equations (away from any parametric instability), we show
how the spectrum of the polariton Bogoliubov-like excitations reflects onto the
shape and intensity of the resonant Rayleigh scattering emission pattern in
both momentum and real space. We find a superfluid regime in the sense of the
Landau criterion, in which the Rayleigh scattering ring in momentum space
collapses as well as its normalized intensity. More generally, we show how
collective excitation spectra having no analog in equilibrium systems can be
observed by tuning the excitation angle and frequency. Predictions with
realistic semiconductor microcavity parameters are given
Controlling discrete and continuous symmetries in 'superradiant' phase transitions
We explore theoretically the physics of a collection of two-level systems
coupled to a single-mode bosonic field in the non-standard configuration where
each (artificial) atom is coupled to both field quadratures of the boson mode.
We determine the rich phase diagram showing 'superradiant' phases with
different symmetries. We demonstrate that it is possible to pass from a
discrete, parity-like symmetry to a continuous U(1) symmetry
even in the ultrastrong coupling regime where the rotating wave approximation
for the interaction between field and two-level systems is no longer
applicable. By applying this general paradigm, we propose a scheme for the
experimental implementation of such continuous U(1) symmetry in circuit QED
systems, with the appearance of photonic Goldstone and amplitude modes above a
critical point
Comment on "Superradiant Phase Transitions and the Standard Description of Circuit QED"
A Comment on the Letter by O. Viehmann, J. von Delft, and F. Marquardt [Phys.
Rev. Lett. {\bf 107}, 113602 (2011)]
Counter-polarized single-photon generation from the auxiliary cavity of a weakly nonlinear photonic molecule
We propose a scheme for the resonant generation of counter-polarized single
photons in double asymmetric cavities with a small Kerr optical nonlinearity
(as that created by a semiconductor quantum well) compared to the mode
broadening. Due to the interplay between spatial intercavity tunneling and
polarization coupling, by weakly exciting with circularly polarized light one
of the cavities, we predict strong antibunching of counter-polarized light
emission from the non-pumped auxiliary cavity. This scheme due to quantum
interference is robust against surface scattering of pumping light, which can
be suppressed both by spatial and polarization filters
Spontaneous microcavity-polariton coherence across the parametric threshold: Quantum Monte Carlo studies
We investigate the appearance of spontaneous coherence in the parametric
emission from planar semiconductor microcavities in the strong coupling regime.
Calculations are performed by means of a Quantum Monte Carlo technique based on
the Wigner representation of the coupled exciton and cavity-photon fields. The
numerical results are interpreted in terms of a non-equilibrium phase
transition occurring at the parametric oscillation threshold: below the
threshold, the signal emission is incoherent, and both the first and the
second-order coherence functions have a finite correlation length which becomes
macroscopic as the threshold is approached. Above the threshold, the emission
is instead phase-coherent over the whole two-dimensional sample and intensity
fluctuations are suppressed. Similar calculations for quasi-one-dimensional
microcavities show that in this case the phase-coherence of the signal emission
has a finite extension even above the threshold, while intensity fluctuations
are suppressed
Input-output theory of cavities in the ultra-strong coupling regime: the case of a time-independent vacuum Rabi frequency
We present a full quantum theory for the dissipative dynamics of an optical
cavity in the ultra-strong light-matter coupling regime, in which the vacuum
Rabi frequency is comparable to the electronic transition frequency and the
anti-resonant terms of the light-matter coupling play an important role. In
particular, our model can be applied to the case of intersubband transitions in
doped semiconductor quantum wells embedded in a microcavity. The coupling of
the intracavity photonic mode and of the electronic polarization to the
external, frequency-dependent, dissipation baths is taken into account by means
of quantum Langevin equations in the input-output formalism. Observable spectra
(reflection, absorption, transmission and electroluminescence) are calculated
analytically in the case of a time-independent vacuum Rabi frequency
On the robustness of strongly correlated multi-photon states in frustrated driven-dissipative cavity lattices
We present a theoretical study on the robustness of multi-photon states in a
frustrated lattice of coupled nonlinear optical cavities, which are described
by a driven-dissipative Bose-Hubbard model. In particular, we focus here on a
Lieb lattice with two elementary cells and periodic boundary conditions. Due to
the geometric frustration of the lattice, the non-equilibrium steady state can
exhibit dark sites with low photon density and strong correlations, ascribable
to the population of multi-photon modes. We explore the sensitivity of such
strong correlations on the random inhomogeneity of the lattice parameters. We
show that the correlations are more sensitive to the inhomogeneity of the
cavity frequencies than to the random fluctuations of the hopping strength.Comment: Accepted for publication on EPJ-Special Topics "Quantum gases and
quantum coherence": 10 pages, 5 figure
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