1,140 research outputs found
Spontaneous patterns in coherently driven polariton microcavities
We consider a polariton microcavity resonantly driven by two external lasers
which simultaneously pump both lower and upper polariton branches at normal
incidence. In this setup, we study the occurrence of instabilities of the
pump-only solutions towards the spontaneous formation of patterns. Their
appearance is a consequence of the spontaneous symmetry breaking of
translational and rotational invariance due to interaction induced parametric
scattering. We observe the evolution between diverse patterns which can be
classified as single-pump, where parametric scattering occurs at the same
energy as one of the pumps, and as two-pump, where scattering occurs at a
different energy. For two-pump instabilities, stripe and chequerboard patterns
become the dominant steady-state solutions because cubic parametric scattering
processes are forbidden. This contrasts with the single-pump case, where
hexagonal patterns are the most common arrangements. We study the possibility
of controlling the evolution between different patterns. Our results are
obtained within a linear stability analysis and are confirmed by finite size
full numerical calculations.Comment: 15 pages, 9 figure
All-optical non-demolition measurement of single-hole spin in a quantum-dot molecule
We propose an all-optical scheme to perform a non-demolition measurement of a
single hole spin localized in a quantum-dot molecule. The latter is embedded in
a microcavity and driven by two lasers. This allows to induce Raman transitions
which entangle the spin state with the polarization of the emitted photons. We
find that the measurement can be completed with high fidelity on a timescale of
100 ps, shorter than the typical T2. Furthermore, we show that the scheme can
be used to induce and observe spin oscillations without the need of
time-dependent magnetic fields
Silicon purification using a Cu-Si alloy source
Production of 99.9999% pure silicon from 98% pure metallurgical grade (MG) silicon by a vapor transport filtration process (VTP) is described. The VTF process is a cold wall version of an HCl chemical vapor transport technique using a Si:Cu3Si alloy as the silicon source. The concentration, origin, and behavior of the various impurities involved in the process were determined by chemically analyzing alloys of different purity, the slag formed during the alloying process, and the purified silicon. Atomic absorption, emission spectrometry, inductively coupled plasma, spark source mass spectrometry, and secondary ion mass spectroscopy were used for these analyses. The influence of the Cl/H ratio and the deposition temperature on the transport rate was also investigated
Spin Information from Vector-Meson Decay in Photoproduction
For the photoproduction of vector mesons, all single and double spin
observables involving vector meson two-body decays are defined consistently in
the center of mass. These definitions yield a procedure for
extracting physically meaningful single and double spin observables that are
subject to known rules concerning their angle and energy evolution. As part of
this analysis, we show that measuring the two-meson decay of a photoproduced
or does not determine the vector meson's vector polarization, but
only its tensor polarization. The vector meson decay into lepton pairs is also
insensitive to the vector meson's vector polarization, unless one measures the
spin of one of the leptons. Similar results are found for all double spin
observables which involve observation of vector meson decay. To access the
vector meson's vector polarization, one therefore needs to either measure the
spin of the decay leptons, make an analysis of the background interference
effects or relate the vector meson's vector polarization to other accessible
spin observables.Comment: 22 pages, 3 figure
Optimizing photon indistinguishability in the emission from incoherently-excited semiconductor quantum dots
Most optical quantum devices require deterministic single-photon emitters.
Schemes so far demonstrated in the solid state imply an energy relaxation which
tends to spoil the coherent nature of the time evolution, and with it the
photon indistinguishability. We focus our theoretical investigation on
semiconductor quantum dots embedded in microcavities. Simple and general
relations are identified between the photon indistinguishability and the
collection efficiency. The identification of the key parameters and of their
interplay provides clear indications for the device optimization
Two-photon spectra of quantum emitters
We apply our recently developed theory of frequency-filtered and
time-resolved N-photon correlations to study the two-photon spectra of a
variety of systems of increasing complexity: single mode emitters with two
limiting statistics (one harmonic oscillator or a two-level system) and the
various combinations that arise from their coupling. We consider both the
linear and nonlinear regimes under incoherent excitation. We find that even the
simplest systems display a rich dynamics of emission, not accessible by simple
single photon spectroscopy. In the strong coupling regime, novel two-photon
emission processes involving virtual states are revealed. Furthermore, two
general results are unraveled by two-photon correlations with narrow linewidth
detectors: i) filtering induced bunching and ii) breakdown of the
semi-classical theory. We show how to overcome this shortcoming in a
fully-quantized picture.Comment: 27 pages, 8 figure
Band Offsets at Semiconductor-Oxide Interfaces from Hybrid Density Functional Calculations
Band offsets at semiconductor-oxide interfaces are determined through a
scheme based on hybrid density functionals, which incorporate a fraction
of Hartree-Fock exchange. For each bulk component, the fraction
is tuned to reproduce the experimental band gap, and the conduction
and valence band edges are then located with respect to a reference level. The
lineup of the bulk reference levels is determined through an interface
calculation, and shown to be almost independent of the fraction .
Application of this scheme to the Si-SiO, SiC-SiO, and Si-HfO
interfaces yields excellent agreement with experiment.Comment: 4 pages, 4 figure
Polarization entanglement visibility of photon pairs emitted by a quantum dot embedded in a microcavity
We study the photon emission from a quantum dot embedded in a microcavity.
Incoherent pumping of its excitons and biexciton provokes the emission of leaky
and cavity modes. By solving a master equation we obtain the correlation
functions required to compute the spectrum and the relative efficiency among
the emission of pairs and single photons. A quantum regime appears for low
pumping and large rate of emission. By means of a post-selection process, a two
beams experiment with different linear polarizations could be performed
producing a large polarization entanglement visibility precisely in the quantum
regime.Comment: 13 pages and 6 figure
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