Classical and quantum interference in multiband optical Bloch oscillations

Classical and quantum interference of light propagating in arrays of coupled waveguides and undergoing multiband optical Bloch oscillations (BOs) with negligible Zener tunneling is theoretically investigated. In particular, it is shown that Mach-Zehnder-like interference effects spontaneously arise in multiband BOs owing to beam splitting and subsequent beam recombination occurring in one BO cycle. As a noteworthy example of quantum interference, we discuss the doubling of interference fringes in photon counting rates for a correlated photon pair undergoing two-band BOs, a phenomenon analogous to the manifestation of the de Broglie wavelength of an entangled biphoton state observed in quantum Mach-Zehnder interferometry.Comment: 11 pages, 4 figure

Experimental petrology and origin of Fra Mauro rocks and soil

Melting experiments over the pressure range 0 to 20 kilobars were conducted on Apollo 14 igneous rocks 14310 and 14072 and on comprehensive fines 14259. The mineralogy and textures of rocks 14310 and 14072 are presumed to be the result of near-surface crystallization. The chemical compositions of the samples show special relationships to multiply-saturated liquids in the system: anorthite-forsterite-fayalite-silica at low pressure. Partial melting of a lunar crust consisting largely of plagioclase, low calcium pyroxene, and olivine, followed by crystal fractionation at the lunar surface is proposed as a mechanism for the production of the igneous rocks and soil glasses sampled by Apollo 14

Invisibility in non-Hermitian tight-binding lattices

Reflectionless defects in Hermitian tight-binding lattices, synthesized by the intertwining operator technique of supersymmetric quantum mechanics, are generally not invisible and time-of-flight measurements could reveal the existence of the defects. Here it is shown that, in a certain class of non-Hermitian tight-binding lattices with complex hopping amplitudes, defects in the lattice can appear fully invisible to an outside observer. The synthesized non-Hermitian lattices with invisible defects possess a real-valued energy spectrum, however they lack of parity-time (PT) symmetry, which does not play any role in the present work.Comment: to appear in Phys. Rev.

Optical analogue of spontaneous symmetry breaking induced by tachyon condensation in amplifying plasmonic arrays

We study analytically and numerically an optical analogue of tachyon condensation in amplifying plasmonic arrays. Optical propagation is modeled through coupled-mode equations, which in the continuous limit can be converted into a nonlinear one-dimensional Dirac-like equation for fermionic particles with imaginary mass, i.e. fermionic tachyons. We demonstrate that the vacuum state is unstable and acquires an expectation value with broken chiral symmetry, corresponding to the homogeneous nonlinear stationary solution of the system. The quantum field theory analogue of this process is the condensation of unstable fermionic tachyons into massive particles. This paves the way for using amplifying plasmonic arrays as a classical laboratory for spontaneous symmetry breaking effects in quantum field theory.Comment: 5 pages, 5 figure

Nonlinearity-induced broadening of resonances in dynamically modulated couplers

We report the observation of nonlinearity-induced broadening of resonances in dynamically modulated directional couplers. When the refractive index of the guiding channels in the coupler is harmonically modulated along the propagation direction and out-of-phase in two channels, coupling can be completely inhibited at resonant modulation frequencies. We observe that nonlinearity broadens such resonances and that localization can be achieved even in detuned systems at power levels well below those required in unmodulated couplers.Comment: 14 pages, 4 figures, to appear in Optics Letter

A folding inhibitor of the HIV-1 Protease

Being the HIV-1 Protease (HIV-1-PR) an essential enzyme in the viral life cycle, its inhibition can control AIDS. The folding of single domain proteins, like each of the monomers forming the HIV-1-PR homodimer, is controlled by local elementary structures (LES, folding units stabilized by strongly interacting, highly conserved, as a rule hydrophobic, amino acids). These LES have evolved over myriad of generations to recognize and strongly attract each other, so as to make the protein fold fast and be stable in its native conformation. Consequently, peptides displaying a sequence identical to those segments of the monomers associated with LES are expected to act as competitive inhibitors and thus destabilize the native structure of the enzyme. These inhibitors are unlikely to lead to escape mutants as they bind to the protease monomers through highly conserved amino acids which play an essential role in the folding process. The properties of one of the most promising inhibitors of the folding of the HIV-1-PR monomers found among these peptides is demonstrated with the help of spectrophotometric assays and CD spectroscopy

Discrete diffraction and shape-invariant beams in optical waveguide arrays

General properties of linear propagation of discretized light in homogeneous and curved waveguide arrays are comprehensively investigated and compared to those of paraxial diffraction in continuous media. In particular, general laws describing beam spreading, beam decay and discrete far-field patterns in homogeneous arrays are derived using the method of moments and the steepest descend method. In curved arrays, the method of moments is extended to describe evolution of global beam parameters. A family of beams which propagate in curved arrays maintaining their functional shape -referred to as discrete Bessel beams- is also introduced. Propagation of discrete Bessel beams in waveguide arrays is simply described by the evolution of a complex $q$ parameter similar to the complex $q$ parameter used for Gaussian beams in continuous lensguide media. A few applications of the $q$ parameter formalism are discussed, including beam collimation and polygonal optical Bloch oscillations. \Comment: 14 pages, 5 figure

Photonic realization of the relativistic Kronig-Penney model and relativistic Tamm surface states

Photonic analogues of the relativistic Kronig-Penney model and of relativistic surface Tamm states are proposed for light propagation in fibre Bragg gratings (FBGs) with phase defects. A periodic sequence of phase slips in the FBG realizes the relativistic Kronig-Penney model, the band structure of which being mapped into the spectral response of the FBG. For the semi-infinite FBG Tamm surface states can appear and can be visualized as narrow resonance peaks in the transmission spectrum of the grating

Classical realization of two-site Fermi-Hubbard systems

A classical wave optics realization of the two-site Hubbard model, describing the dynamics of interacting fermions in a double-well potential, is proposed based on light transport in evanescently-coupled optical waveguides.Comment: 4 page