Quantum theory of optical-pulse propagation through an amplifying slab

7 págs.; 6 figs.; PACS number: 42.50.2pWe calculate the effects of normal transmission through an amplifying dielectric slab on the properties of an incident pulse of light. The transmitted pulse shows shifts in peak position and additional lengthening or shortening with respect to the unamplified incident pulse. The magnitudes of these effects are generally larger than those of the corresponding changes that occur in transparent or attenuating slabs. They are interpreted in terms of the interference of multiply reflected contributions to the transmitted pulse. The theory is valid for pulses of nonclassical light, but the same reshaping occurs for appropriate pulses of classical light. ©1998 American Physical SocietyWe thank the European Community Human Capital and Mobility Programme and the Ministerio de Educacion y Cultura of Spain for financial support.Peer Reviewe

Optically Tunable Photonic Stop Bands in Homogeneous Absorbing Media.

Resonantly absorbing media supporting electromagnetically induced transparency may give rise to specific periodic patterns where a light probe is found to experience a fully developed photonic band gap yet with negligible absorption everywhere. In ultracold atomic samples the gap is found to arise from spatial regions where Autler-Townes splitting and electromagnetically induced transparency alternate with one another and detailed calculations show that accurate and efficient coherent optical control of the gap can be accomplished. The remarkable experimental simplicity of the control scheme would ease quantum nonlinear optics applications

Photons on a leash

Quantum coherence and interference can be used to control the light-matter interaction and the propagation of light in multilevel systems. Effects of electromagnetically induced transparency based on exciton and biexciton levels or on impurity levels in solid-state media are here reviewed. New photonic crystal structures created via coherent optical nonlinearities in such solid media are also considered and discusse

Nonclassical phase of the electromagnetic field in a nonstationary dielectric

4 págs.; 2 figs.; PACS number~s!: 42.50.Lc, 12.20.2mThe quantum state of the electromagnetic field propagating in a nonstationary dielectric can acquire a phase shift that arises from modifications in the quantum fluctuations of the field. The shift could be observed, even for quite weak modifications, as a fringe displacement in an interference experiment. © 1998 The American Physical SocietyMinisterio de Educación y Cultura of Spain for partial support.Peer Reviewe

Atomic recoil effects in slow light propagation

We theoretically investigate the effect of atomic recoil on the propagation of ultraslow light pulses through a coherently driven Bose-Einstein condensed gas. For a sample at rest, the group velocity of the light pulse is the sum of the group velocity that one would observe in the absence of mechanical effects (infinite mass limit) and the velocity of the recoiling atoms (light-dragging effect). We predict that atomic recoil may give rise to a lower bound for the observable group velocities, as well as to pulse propagation at negative group velocities without appreciable absorption

Polarization qubit phase gate in driven atomic media

We present here an all--optical scheme for the experimental realization of a quantum phase gate. It is based on the polarization degree of freedom of two travelling single photon wave-packets and exploits giant Kerr nonlinearities that can be attained in coherently driven ultracold atomic media.Comment: 4 pages, 1 figure, in press on PR

Perfect absorption and no reflection in disordered photonic crystals

Understanding the effects of disorder on the light propagation in photonic devices is of major importance from both fundamental and applied points of view. Unidirectional reflectionless and coherent perfect absorption of optical signals are unusual yet fascinating phenomena that have recently sparked an extensive research effort in photonics. These two phenomena, which arise from topological deformations of the scattering matrix S parameters space, behave differently in the presence of different types of disorder, as we show here for a lossy photonic crystal prototype with a parity-time antisymmetric susceptibility or a more general non-Hermitian one

Physics of excitonic quasiparticles: beyond conventional polaritons

Some aspects of post-conventional polariton physics are discussed. In the framework of quantum statistical properties we demonstrate that polaritons are intrinsically squeezed. The polariton squeezing is frequency tunable, and can be larger than that in usual atomic systems. The new phonoriton excitation, which gives rise to spectrum reconstruction, is reexamined on the basis of a simple model: threshold behavior, new gap structure and related properties are discussed

Effects of atomic interactions on the resonant tunneling of sodium condensates

4noWe investigate the influence of atomic interactions on the tunnelling of sodium condensates across a spatially oscillating optical barrier. In the limit of very fast barrier oscillations, in which resonant tunnelling via a metastable state takes place, the interactions affect the position and lineshape of the transmission peak. We anticipate that the possibility of modulating the interactions in a tunnelling condensate can be exploited to achieve nonlinear effects such as optical limiting and bistability.openopenD. EMBRIACO; M. L. CHIOFALO; M. ARTONI; AND G. C. LA ROCCAD., Embriaco; M. L., Chiofalo; Artoni, Maurizio; AND G. C., LA ROCC

A polymorphism in the human serotonin 5-HT2A receptor gene may protect against systemic sclerosis by reducing platelet aggregation

Introduction: Platelet aggregation may contribute to the pathogenesis of systemic sclerosis: following activation, platelets release significant amounts of serotonin - which promotes vasoconstriction and fibrosis, and further enhances aggregation. The C+1354T polymorphism in the exonic region of the serotonin 2A receptor gene determining the His452Tyr substitution was associated with blunted intracellular responses after serotonin stimulation, and may have a role in susceptibility to scleroderma. Methods: One hundred and fifteen consecutive systemic sclerosis patients and 140 well-matched healthy control individuals were genotyped by sequence-specific primer-PCR for the His452Tyr substitution of the serotonin 2A receptor gene, and associations were sought with scleroderma and its main clinical features. The functional relevance of the His452Tyr substitution was also assessed by evaluating the aggregation of platelet-rich plasma from His452/ His452 and His452/Tyr452 healthy individuals after stimulation with adenosine diphosphate ± serotonin. Results: The T allele of the C+1354T polymorphism was underrepresented in scleroderma patients compared with control individuals (5.2% versus 12.4%, P < 0.001, chi-square test and 1,000-fold permutation test) and its carriage reduced the risk for systemic sclerosis (odds ratio = 0.39, 95% confidence interval = 0.19 to 0.85, P < 0.01). Platelets from His452/Tyr452 healthy subjects more weakly responded to serotonin stimulation compared with platelets from His452/His452 individuals (3.2 ± 2.6-fold versus 9.6 ± 8.6-fold increase in aggregation, P = 0.017 by Kolmogorov-Smirnov test and P = 0.003 after correction for baseline adenosine diphosphate-induced aggregation values). Conclusion: The His452Tyr substitution may influence susceptibility to systemic sclerosis by altering platelet aggregation in response to serotonin