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

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

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

π\piNN coupling and two-pion photoproduction on the nucleon

Effects of non-resonant photoproductions arising from two different $\pi NN$ couplings are investigated in the $\gamma N\to\pi\pi N$ reaction. We find that the pseudoscalar (PS) $\pi NN$ coupling is generally preferable to the pseudovector (PV) $\pi NN$ coupling and particularly the total cross sections are successfully described by the model with the PS $\pi NN$ coupling. In order to see the difference between the two couplings, we also show the results of invariant mass spectra and helicity-dependent cross sections in various isospin channels calculated with the PS and PV couplings.Comment: 35 pages, 11 figures, minor changes and version to be published in Phys.Rev.

Penicillium aureocephalum Munt.-Cvetk., Hoyo et Gómez-Bolea, un interessant ascomicet anamòrfic amb aspecte de mixomicet : distribució, ecologia i fenologia

Cinc anys després de la descripció de Penicillium aureocephalum per Muntañola-Cvetkovic, Hoyo i GórnezBolea, els autors del present treball han anat afegint Inés dades de camp a les ja existents, que comencen a subministrar una imatge més viva d'aquest curiós anamorf saprotrófic dins de les comunitats naturals on esporula. El present treball és un resum d'aquestes dades corológiques, ecológiques i fenológiques, acompanyat de comentaris. La principal conclu sió és que I'espécie se' ns presenta com un fong termófil que colonit za preferentm ent fulles caigudes de surera (Quercus suber), que han mort a l' arbre per la calor produída per incendis, pero que també pot créixer, menys sovint, sobre altres substrats, com ara fulles o fruits de Cistus salviifolius, C. ladanifer, Quercus coccifera, etc. que han estat descarre gats per les plantes com a resposta a un fort estrés hídric. El treball inclou un mapa de la distribuci ó de I'espécie en el Pare Natural del Cap de Creus, fins ara I' área óptima de creixement, i un altre mapa amb la distribució coneguda actualment en els Paisos Catalans, on apareix provisionahnent endémica. S'ofereix un estudi macrofotográfic de l'especie, útil per ajudar els mic ólegs a trobar noves localitat s d'aquest curiosa especie d'anamorf, tan diferent de les més conegudes de Penicillium , ja que té aspect e de mixomic et, que es comporta COIll a term ófila i saprotrófica sobre fulles riques en nutrients.Five years after the description of Penicillium aureocephalum by Muntañola-C vetkovic, Hoyo and G ómez-Bolea, an increasing wealth of field data has been gathered by the authors, which provide a vivid image of the anamorph of this curious saprotrophic species. Chorological, ecological and phenological data are here summarized and discussed. The species appears to be thermophilou s, preferentially colonizing fallen leaves of cork trees (Quercus suber) killed by wildfires, but also growing sometimes on other substrata, such as dead leaves of Cistus salviifolius,C. ladanifer, Quercus coccifera, etc. which may have dropped as a response to severe water stress. A distribution map of the species in the Natural Park of Cap de Creus, which apparently is its natural habitat and another nowith showing the currently known distribution in the Catalan Countries, are given. A macrophotographic survey ofthe species is also included in order to aid in the recognition of this curious myxomycete-looking thermophilou s, anamorphic species, saprotrophic on nutrient-rich substrata, and so different from the usual Penicillium taxa

Entanglement of two qubits mediated by one-dimensional plasmonic waveguides

We investigate qubit-qubit entanglement mediated by plasmons supported by one-dimensional waveguides. We explore both the situation of spontaneous formation of entanglement from an unentangled state and the emergence of driven steady-state entanglement under continuous pumping. In both cases, we show that large values for the concurrence are attainable for qubit-qubit distances larger than the operating wavelength by using plasmonic waveguides that are currently available.Comment: 4 pages, 4 figures. Minor Changes. Journal Reference added. Highlighted in Physic

Dynamics of the excitations of a quantum dot in a microcavity

We study the dynamics of a quantum dot embedded in a three-dimensional microcavity in the strong coupling regime in which the quantum dot exciton has an energy close to the frequency of a confined cavity mode. Under the continuous pumping of the system, confined electron and hole can recombine either by spontaneous emission through a leaky mode or by stimulated emission of a cavity mode that can escape from the cavity. The numerical integration of a master equation including all these effects gives the dynamics of the density matrix. By using the quantum regression theorem, we compute the first and second order coherence functions required to calculate the photon statistics and the spectrum of the emitted light. Our main result is the determination of a range of parameters in which a state of cavity modes with poissonian or sub-poissonian (non-classical) statistics can be built up within the microcavity. Depending on the relative values of pumping and rate of stimulated emission, either one or two peaks close to the excitation energy of the dot and/or to the natural frequency of the cavity are observed in the emission spectrum. The physics behind these results is discussed