The electro production of d* dibaryon

$d^*$ dibaryon study is a critical test of hadron interaction models. The electro production cross sections of $ed\to ed^*$ have been calculated based on the meson exchange current model and the cross section around 30 degree of 1 GeV electron in the laboratory frame is about 10 nb. The implication of this result for the $d^*$ dibaryon search has been discussed.Comment: 12 pages, 12 figures, Late

Quantum Phase Transitions detected by a local probe using Time Correlations and Violations of Leggett-Garg Inequalities

In the present paper we introduce a way of identifying quantum phase transitions of many-body systems by means of local time correlations and Leggett-Garg inequalities. This procedure allows to experimentally determine the quantum critical points not only of finite-order transitions but also those of infinite order, as the Kosterlitz-Thouless transition that is not always easy to detect with current methods. By means of simple analytical arguments for a general spin-$1 / 2$ Hamiltonian, and matrix product simulations of one-dimensional $X X Z$ and anisotropic $X Y$ models, we argue that finite-order quantum phase transitions can be determined by singularities of the time correlations or their derivatives at criticality. The same features are exhibited by corresponding Leggett-Garg functions, which noticeably indicate violation of the Leggett-Garg inequalities for early times and all the Hamiltonian parameters considered. In addition, we find that the infinite-order transition of the $X X Z$ model at the isotropic point can be revealed by the maximal violation of the Leggett-Garg inequalities. We thus show that quantum phase transitions can be identified by purely local measurements, and that many-body systems constitute important candidates to observe experimentally the violation of Leggett-Garg inequalities.Comment: Minor changes, 11 pages, 11 figures. Final version published in Phys. Rev.

Restrictions on the coherence of the ultrafast optical emission from an electron-hole pairs condensate

We report on the transfer of coherence from a quantum-well electron-hole condensate to the light it emits. As a function of density, the coherence of the electron-hole pair system evolves from being full for the low density Bose-Einstein condensate to a chaotic behavior for a high density BCS-like state. This degree of coherence is transfered to the light emitted in a damped oscillatory way in the ultrafast regime. Additionally, the photon field exhibits squeezing properties during the transfer time. We analyze the effect of light frequency and separation between electron and hole layers on the optical coherence. Our results suggest new type of ultrafast experiments for detecting electron-hole pair condensation.Comment: 4 pages,3 figures, to be published in Physical Review Letters. Minor change

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

Emitters of NN-photon bundles

We propose a scheme based on the coherent excitation of a two-level system in a cavity to generate an ultrabright CW and focused source of quantum light that comes in groups (bundles) of $N$ photons, for an integer $N$ tunable with the frequency of the exciting laser. We define a new quantity, the \emph{purity} of $N$-photon emission, to describe the percentage of photons emitted in bundles, thus bypassing the limitations of Glauber correlation functions. We focus on the case $1\le N\le3$ and show that close to 100% of two-photon emission and 90% of three-photon emission is within reach of state of the art cavity QED samples. The statistics of the bundles emission shows that various regimes---from $N$-photon lasing to $N$-photon guns---can be realized. This is evidenced through generalized correlation functions that extend the standard definitions to the multi-photon level.Comment: Introduce the n-th order N-photon correlation functions. Reorganized to emphasize the N-photon emitter, now extended to the antibunching regime, rather than only coherent emission as previsoul