Entangled coherent states by mixing squeezed vacuum and coherent light

Entangled coherent states are shown to emerge, with high fidelity, when mixing coherent and squeezed vacuum states of light on a beam-splitter. These maximally entangled states, where photons bunch at the exit of a beamsplitter, are measured experimentally by Fock-state projections. Entanglement is examined theoretically using a Bell-type nonlocality test and compared with ideal entangled coherent states. We experimentally show nearly perfect similarity with entangled coherent states for an optimal ratio of coherent and squeezed vacuum light. In our scheme, entangled coherent states are generated deterministically with small amplitudes, which could be beneficial, for example, in deterministic distribution of entanglement over long distances.Comment: 6 pages, 6 figures, comments are welcom

Parametric Self-Oscillation via Resonantly Enhanced Multiwave Mixing

We demonstrate an efficient nonlinear process in which Stokes and anti-Stokes components are generated spontaneously in a Raman-like, near resonant media driven by low power counter-propagating fields. Oscillation of this kind does not require optical cavity and can be viewed as a spontaneous formation of atomic coherence grating

Spontaneously generated X-shaped light bullets

We observe the formation of an intense optical wavepacket fully localized in all dimensions, i.e. both longitudinally (in time) and in the transverse plane, with an extension of a few tens of fsec and microns, respectively. Our measurements show that the self-trapped wave is a X-shaped light bullet spontaneously generated from a standard laser wavepacket via the nonlinear material response (i.e., second-harmonic generation), which extend the soliton concept to a new realm, where the main hump coexists with conical tails which reflect the symmetry of linear dispersion relationship.Comment: 5 pages, 4 figures, submitted for publicatio

Neutrino Spin Transitions and the Violation of the Equivalence Principle

The violation of the equivalence principle (VEP) causing neutrino oscillations is of current interest. We study here the possibility of not only flavor oscillation but spin flavor oscillation of ultra high energy ($\sim$ 1 PeV) neutrinos emanating from AGN due to VEP and due to the presence of a large magnetic field ($\sim$ 1 Tesla) in AGN. In particular we look at the resonance spin flavor conversion driven by the AGN potential. Interesting bounds on the transition magnetic moment of neutrinos may therefore be obtained.Comment: Latex, 12 pages, no figures. To appear in Journal of Physics G: Nuclear and Particle Physics. Two references adde

Standoff Detection of Solid Traces by Single-Beam Nonlinear Raman Spectroscopy Using Shaped Femtosecond Pulses

We demonstrate a single-beam, standoff (>10m) coherent anti-Stokes Raman scattering spectroscopy (CARS) of various materials, including trace amounts of explosives and nitrate samples, under ambient light conditions. The multiplex measurement of characteristic molecular vibrations with <20cm-1 spectral resolution is carried out using a single broadband (>550cm-1) phase-shaped femtosecond laser pulse. We exploit the strong nonresonant background signal for amplification of the weak backscattered resonant CARS signal by using a homodyne detection scheme. This facilitates a simple, highly sensitive single-beam spectroscopic technique, with a potential for hazardous materials standoff detection applications

Azimuthally polarized spatial dark solitons: exact solutions of Maxwell's equations in a Kerr medium

Spatial Kerr solitons, typically associated with the standard paraxial nonlinear Schroedinger equation, are shown to exist to all nonparaxial orders, as exact solutions of Maxwell's equations in the presence of vectorial Kerr effect. More precisely, we prove the existence of azimuthally polarized, spatial, dark soliton solutions of Maxwell's equations, while exact linearly polarized (2+1)-D solitons do not exist. Our ab initio approach predicts the existence of dark solitons up to an upper value of the maximum field amplitude, corresponding to a minimum soliton width of about one fourth of the wavelength.Comment: 4 pages, 4 figure

Slow-light optical bullets in arrays of nonlinear Bragg-grating waveguides

We demonstrate how to control independently both spatial and temporal dynamics of slow light. We reveal that specially designed nonlinear waveguide arrays with phase-shifted Bragg gratings demonstrate the frequency-independent spatial diffraction near the edge of the photonic bandgap, where the group velocity of light can be strongly reduced. We show in numerical simulations that such structures allow a great flexibility in designing and controlling dispersion characteristics, and open a way for efficient spatiotemporal self-trapping and the formation of slow-light optical bullets.Comment: 4 pages, 4 figures; available from http://link.aps.org/abstract/PRL/v97/e23390

Influence of damping on the vanishing of the electro-optic effect in chiral isotropic media

Using first principles, it is demonstrated that radiative damping alone cannot lead to a nonvanishing electro-optic effect in a chiral isotropic medium. This conclusion is in contrast with that obtained by a calculation in which damping effects are included using the standard phenomenological model. We show that these predictions differ because the phenomenological damping equations are valid only in regions where the frequencies of the applied electromagnetic fields are nearly resonant with the atomic transitions. We also show that collisional damping can lead to a nonvanishing electrooptic effect, but with a strength sufficiently weak that it is unlikely to be observable under realistic laboratory conditions

Cavity Light Bullets: 3D Localized Structures in a Nonlinear Optical Resonator

We consider the paraxial model for a nonlinear resonator with a saturable absorber beyond the mean-field limit and develop a method to study the modulational instabilities leading to pattern formation in all three spatial dimensions. For achievable parametric domains we observe total radiation confinement and the formation of 3D localised bright structures. At difference from freely propagating light bullets, here the self-organization proceeds from the resonator feedback, combined with diffraction and nonlinearity. Such "cavity" light bullets can be independently excited and erased by appropriate pulses, and once created, they endlessly travel the cavity roundtrip. Also, the pulses can shift in the transverse direction, following external field gradients.Comment: 4 pages, 3 figures, simulations files available at http://www.ba.infn.it/~maggipin/PRLmovies.htm, submitted to Physical Review Letters on 24 March 200