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Item Open Access ANALOG PARTICLE PRODUCTION MODEL FOR GENERAL CLASSES OF TAUB-NUT BLACK HOLES(Universe, 2021-09-20) Foo, Joshua; Good, Michael R. R.; Mann, Robert B.Show more We derive a correspondence between the Hawking radiation spectra emitted from general classes of Taub-NUT black holes with that induced by the relativistic motion of an accelerated Dirichlet boundary condition (i.e., a perfectly reflecting mirror) in (1+1)-dimensional flat spacetime. We demonstrate that the particle and energy spectra is thermal at late times and that particle production is suppressed by the NUT parameter. We also compute the radiation spectrum in the rotating, electrically charged (Kerr–Newman) Taub-NUT scenario, and the extremal case, showing, explicitly, how these parameters affect the outgoing particle and energy fluxesShow more Item Open Access GRAVITY WITH SCALAR FIELD VISCOUS FLUID(Journal of Physics: Conference Series, 2021) Myrzakul, S R; Imankul, M; Arzimbetova, M; Myrzakul, T RShow more We focus on a viable teleparallel cosmological model with a scalar field in a flat Friedman-Robertson-Walker universe. The Lagrangian and equations of motion are obtained. The case of an inhomogeneous viscous dark energy is considered and the cosmological parameters associated with the viscosity parameter are determined. It is shown that when considering constant viscosity and state parameter, the Universe expands exponentiallyShow more Item Open Access MOVING MIRROR MODEL FOR QUASITHERMAL RADIATION FIELDS(PHYSICAL REVIEW D, 2020-01-30) Good, Michael R. R.; Linder, Eric V.; Wilczek, FrankShow more We analyze the flow of energy and entropy emitted by a class of moving mirror trajectories which provide models for important aspects of the radiation fields produced by black hole evaporation. The mirror radiation fields provide natural, concrete examples of processes that follow thermal distributions for long periods, accompanied by transients which are brief and carry little net energy, yet ultimately represent pure quantum states. A burst of negative energy flux is a generic feature of these fields, but it need not be prominent.Show more Item Open Access RELATIVISTIC CORRECTIONS TO PHOTONIC ENTANGLED STATES FOR THE SPACE-BASED QUANTUM NETWORK(PHYSICAL REVIEW A, 2020-02-15) Ilo-Okeke, Ebubechukwu O.; Ilyas, Batyr; Tessler, Louis; Takeoka, Masahiro; Jambulingam, Segar; Dowling, Jonathan P.; Byrnes, TimShow more In recent years there has been a great deal of focus on a globe-spanning quantum network, including linked satellites for applications ranging from quantum key distribution to distributed sensors and clocks. In many of these schemes, relativistic transformations may have deleterious effects on the purity of the distributed entangled pairs. In this paper, we make a comparison of several entanglement distribution schemes in the context of special relativity. We consider three types of entangled photons states: polarization, single photon, and Laguerre-Gauss mode entangled states. All three types of entangled states suffer relativistic corrections, albeit in different ways. These relativistic effects become important in the context of applications such as quantum clock synchronization where high fidelity entanglement distribution are requiredShow more Item Open Access RADIATION FROM AN INERTIAL MIRROR HORIZON(Universe, 2020-08) Good, Michael; Abdikamalov, ErnazarShow more The purpose of this study is to investigate radiation from asymptotic zero acceleration motion where a horizon is formed and subsequently detected by an outside witness. A perfectly reflecting moving mirror is used to model such a system and compute the energy and spectrum. The trajectory is asymptotically inertial (zero proper acceleration)—ensuring negative energy flux (NEF), yet approaches light-speed with a null ray horizon at a finite advanced time. We compute the spectrum and energy analytically.Show more Item Open Access Neutrino-driven Convection in Core-collapse Supernovae: High-resolution Simulations(American Astronomical Society, 2016-03) Radice, David; Ott, Christian D.; Abdikamalov, Ernazar; Couch, Sean M.; Haas, Roland; Schnetter, ErikShow more We present results from high-resolution semiglobal simulations of neutrino-driven convection in core-collapse supernovae. We employ an idealized setup with parameterized neutrino heating/cooling and nuclear dissociation at the shock front. We study the internal dynamics of neutrino-driven convection and its role in redistributing energy and momentum through the gain region. We find that even if buoyant plumes are able to locally transfer heat up to the shock, convection is not able to create a net positive energy flux and overcome the downward transport of energy from the accretion flow. Turbulent convection does, however, provide a significant effective pressure support to the accretion flow as it favors the accumulation of energy, mass, and momentum in the gain region. We derive an approximate equation that is able to explain and predict the shock evolution in terms of integrals of quantities such as the turbulent pressure in the gain region or the effects of nonradial motion of the fluid. We use this relation as a way to quantify the role of turbulence in the dynamics of the accretion shock. Finally, we investigate the effects of grid resolution, which we change by a factor of 20 between the lowest and highest resolution. Our results show that the shallow slopes of the turbulent kinetic energy spectra reported in previous studies are a numerical artifact. Kolmogorov scaling is progressively recovered as the resolution is increased.Show more Item Open Access Turbulent chimeras in large semiconductor laser array(Nature Research, 2017-02) Shena, J.; Hizanidis, J.; Kovanis, V.; Tsironis, G.P.Show more Semiconductor laser arrays have been investigated experimentally and theoretically from the viewpoint of temporal and spatial coherence for the past forty years. In this work, we are focusing on a rather novel complex collective behavior, namely chimera states, where synchronized clusters of emitters coexist with unsynchronized ones. For the first time, we find such states exist in large diode arrays based on quantum well gain media with nearest-neighbor interactions. The crucial parameters are the evanescent coupling strength and the relative optical frequency detuning between the emitters of the array. By employing a recently proposed figure of merit for classifying chimera states, we provide quantitative and qualitative evidence for the observed dynamics. The corresponding chimeras are identified as turbulent according to the irregular temporal behavior of the classification measure.Show more Item Open Access Qubit lattice coherence induced by electromagnetic pulses in superconducting metamaterials(Nature Research, 2016) Ivić, Z.; Lazarides, N.; Tsironis, G.P.Show more Quantum bits (qubits) are at the heart of quantum information processing schemes. Currently, solid-state qubits, and in particular the superconducting ones, seem to satisfy the requirements for being the building blocks of viable quantum computers, since they exhibit relatively long coherence times, extremely low dissipation, and scalability. The possibility of achieving quantum coherence in macroscopic circuits comprising Josephson junctions, envisioned by Legett in the 1980’s, was demonstrated for the first time in a charge qubit; since then, the exploitation of macroscopic quantum effects in low-capacitance Josephson junction circuits allowed for the realization of several kinds of superconducting qubits. Furthermore, coupling between qubits has been successfully achieved that was followed by the construction of multiple-qubit logic gates and the implementation of several algorithms. Here it is demonstrated that induced qubit lattice coherence as well as two remarkable quantum coherent optical phenomena, i.e., self-induced transparency and Dicke-type superradiance, may occur during light-pulse propagation in quantum metamaterials comprising superconducting charge qubits. The generated qubit lattice pulse forms a compound ”quantum breather” that propagates in synchrony with the electromagnetic pulse. The experimental confirmation of such effects in superconducting quantum metamaterials may open a new pathway to potentially powerful quantum computing.Show more Item Open Access Chaotic properties of spin lattices near second-order phase transitions(American Physical Society, 2015-12-30) de Wijn, A. S.; Hess, B.; Fine, B. V.Show more We perform a numerical investigation of the Lyapunov spectra of chaotic dynamics in lattices of classical spins in the vicinity of second-order ferromagnetic and antiferromagnetic phase transitions. On the basis of this investigation, we identify a characteristic of the shape of the Lyapunov spectra, the “ G-index,” which exhibits a sharp peak as a function of temperature at the phase transition, provided the order parameter is capable of sufficiently strong dynamic fluctuations. As part of this work, we also propose a general numerical algorithm for determining the temperature in many-particle systems, where kinetic energy is not defined.Show more Item Open Access The impact of vorticity waves on the shock dynamics in core-collapse supernovae(Monthly Notices of the Royal Astronomical Society, 2018-04) Huete, Cesar; Abdikamalov, Ernazar; Radice, DavidShow more Convective perturbations arising from nuclear shell burning can play an important role in propelling neutrino-driven core-collapse supernova explosions. In this work, we analyse the impact of vorticity waves on the shock dynamics, and subsequently on the post-shock flow, using the solution of the linear hydrodynamics equations. As a result of the interaction with the shock wave, vorticity waves increase their kinetic energy, and a new set of entropic and acoustic waves is deposited in the post-shock region....Show more Item Open Access Mid-infrared tunable, narrow-linewidth difference-frequency laser based on orientation-patterned gallium phosphide(IOP Publishing, 2017-01-01) Insero, G.; Clivati, C.; D'Ambrosio, D.; De Natale, P.; Santambrogio, G.; Schunemann, P, G.; Borri, S.; Zondy, Jean-JacquesShow more We report on the first characterization of orientation-patterned gallium phosphide (OP-GaP) crystals used to generate narrow-linewidth, coherent mid-infrared (MIR) radiation at 5.85 μm by difference frequency generation (DFG) of continuous-wave (cw) Nd:YAG laser at 1064nm and diode-laser at 1301nm. By comparison of the experimental absolute MIR efficiency versus focusing to Gaussian beam DFG theory, we derive an effective nonlinear coefficient for first-order quasi-phase-matched OP-GaP at the generated DFG wavelength. Using d = (2/π)d 14 and taking into account Miller's delta rule, we retrieve an absolute value of the d 14 quadratic nonlinear susceptibility coefficient of GaP of d 14 = 27.2(3) pm/V at 5.85 μm, in good agreement with the latest absolute measurement of this nonlinear coefficient from non-phase-matched second-harmonic generation (1.32 μm → 0.66 μm) taking into account multiple reflection effects [Shoji et al 1997 J. Opt. Soc. Am. B 14 2268]. The temperature and signal-wave tuning curves are also in qualitative agreement with a recently proposed temperature-dependent Sellmeier equation for OP-GaP when focusing effects are taken into account.Show more Item Open Access Widely tunable (2.6–10.4 μm) BaGa4Se7 optical parametric oscillator pumped by a Q-switched Nd:YLiF4 laser(IOP Publishing, 2018) Kolker, Dmitri; Kostyukova, N.; Boyko, A.; Badikov, V.; Badikov, D.; Shadrintseva, A.; Tretyakova, N.; Zenov, K.; Karapuzikov, A.; Zondy, Jean-JacquesShow more We report on the first BaGa4Se7 nanosecond optical parametric oscillator pumped by Q-switched Nd:YLiF4 laser at 1053 nm. The oscillator exhibits a pump threshold energy as low as 0.25 mJ. Mid-infrared (MIR) idler wave tuning from 2.6 μm to 10.4 μm is demonstrated with an angle-tuned type-I (o-ee) y-cut sample, highlighting the superior performance of this novel large bandgap chalcogenide nonlinear crystal to generate tunable coherent radiation over its full MIR transparency range (0.47–18 μm). The phase-matching data are used to identify the most accurate dispersion relations of this compound among three recently published Sellmeier equations. Damage threshold measurements yielded values as high as 2.04 J cm−2 at 100 Hz pulse repetition rate, one of the largest among existing MIR χ (2)nonlinear materials.Show more Item Open Access Black Hole Bounces on the Road to Quantum Gravity(MDPI, 2018-08-28) Malafarina, DanieleShow more Quantum resolutions of the space-time singularity at the end of gravitational collapse may provide hints towards the properties of a final theory of Quantum-Gravity. The mechanism by which the singularity is avoided and replaced by a bounce depends on the specific behaviour of gravity in the strong field and may have implications for the geometry of the space-time also in the weak field. In the last few decades, several scenarios for black hole bounces have been proposed and I shall argue that the times are now mature to ask the question of whether such bounces can be observed in astrophysical phenomenaShow more Item Open Access Photonic Inverse Design of Simple Particles with Realistic Losses in the Visible Frequency Range †(MDPI, 2019-02-28) Valagiannopoulos, ConstantinosShow more Billions of U.S. dollars of basic and applied research funding have been invested during the last few years in ideas proposing inverse concepts. The photonics market could not make an exception to this global trend, and thus, several agenda-setting research groups have already started providing sophisticated tools, constrained optimization algorithms, and selective evolution techniques towards this direction. Here, we present an approach of inverse design based on the exhaustive trial-and-testing of the available media and changing the physical dimensions’ range according to the operational wavelength. The proposed technique is applied to the case of an optimal radiation-enhancing cylindrical particle fed by a line source of visible light and gives a two-order increase in the magnitude of the produced signal.Show more Item Open Access Optimized Operation of Photonic Devices With Use of Ordinary Bulk Materials(Metamaterials, 2018) Valagiannopoulos, ConstantinosShow more Structural boundaries, materials and feeding sources are the three fundamental segments defining photonic devices. Since excitation is usually dictated by the application and there are infinite ways to select the spatial configuration of the component, an optimization with respect to the used media is both doable and useful. We provide several combinations of elements and compounds making high-performing electromagnetic devices in terms of absorption, scattering and unusual refraction with simple structures like bilayers, two- and three- dimensional core-shell particles or binary metasurfaces. Such large sets of potential candidates for the employed media can be deployed by experimentalists after applying a secondary sweep by imposing additional constraints concerning ease of fabrication.Show more Item Open Access Achieving Anomalous Refraction with Metasurfaces Composed by Two Ordinary Dielectric Materials(Metamaterials, 2018) Tsitsas, N. L.; Valagiannopoulos, ConstantinosShow more The optimal parameters of a dielectric metasurface, composed of two alternating rectangular rods, are investigated so that it exhibits significant enhancement in the −1- diffracted order in the transmission region. An efficient integral-equation methodology is used for the numerical computations. Representative results of initial optimizations are presentedShow more Item Open Access Zeeman gyrotropic scatterers: Resonance splitting, anomalous scattering, and embedded eigenstates(Nanomaterials and Nanotechnology, 2018-09) Gangaraj, S Ali Hassani; Monticone, Francesco; Valagiannopoulos, ConstantinosShow more Anomalous scattering effects (invisibility, superscattering, Fano resonances, etc) enabled by complex media and metamaterials have been the subject of intense efforts in the past couple of decades. In this article, we present a full analysis of the unusual and extreme scattering properties of an important class of complex scatterers, namely, gyrotropic cylindrical bodies, including both homogeneous and core–shell configurations. Our study unveils a number of interesting effects, including Zeeman splitting of plasmonic scattering resonances, tunable gyrotropy-induced rotation of dipolar radiation patterns as well as extreme Fano resonances and non-radiating eigenmodes (embedded eigenstates) of the gyrotropic scatterer. We believe that these theoretical findings may enable new opportunities to control and tailor scattered fields beyond what is achievable with isotropic reciprocal objects, being of large significance for different applications, from tunable directive nano-antennas to selective chiral sensors and scattering switches, as well as in the context of nonreciprocal and topological metamaterialsShow more Item Open Access Lateral radiative forces exerted by evanescent fields along a hyperbolic metamaterial slab(Journal of Physics, 2018) Nefedov, I. S.; Shalin, A. S.; Valagiannopoulos, ConstantinosShow more We show and investigate the optical forces acting on a particle in the vicinity of a planar waveguide which is lled with hyperbolic material and supports propagation across its plane (two-dimensional). The anisotropy axis of its medium lies in plane of the waveguide. In contrast to commonly considered pushing or pulling forces, acting in one-dimensional guiding structures, in the case of two-dimensional wave propagation, the angles between the momentum and the total energy ow may take any value around the circle. Accordingly, evanescent elds out of the slab exert lateral radiative forces on a nanoparticle oriented parallel to momentum being controllably di erent from the total energy ow direction. This provides a exibility in manipulation by nanoparticles by employing suitably engineered hyperbolic structures.Show more Item Open Access Highly selective transmission and absorption from metasurfaces of periodically corrugated cylindrical particles(Physical review B, 2018-09-25) Tagay, Zhenisbek; Valagiannopoulos, ConstantinosShow more Gratings of infinite wires make, perhaps, the simplest class of metasurfaces, which, however, are utilized for a variety of different objectives in wave manipulation. Importantly, due to their analytical solvability, they can be fully optimized in a fast and direct way. In this study, a lattice of periodically corrugated cylindrical particles under oblique plane-wave excitation is considered and treated rigorously. Several cases of particle radii, distances between two consecutive cylinders, and angles of illumination are examined; as a result, very high selectivity of the metasurface response in terms of line-of-sight transmission and absorption is reported. That abrupt change in the device output becomes even more dramatic in the parametric vicinity of the emergence of new refractive orders, which makes the proposed metasurface exceptionally fitting for switching, filtering, and sensing applicationsShow more Item Open Access Brillouin spectroscopy and radiography for assessment of viscoelastic and regenerative properties of mammalian bones(Journal of Biomedical Optics, 2018-09-27) Akilbekova, Dana; Ogay, Vyacheslav; Yakupov, Talgat; Sarsenova, Madina; Umbayev, Bauyrzhan; Nurakhmetov, Asset; Tazhin, Kairat; Yakovlev, Vladislav V.; Utegulov, Zhandos N.Show more Biomechanical properties of mammalian bones, such as strength, toughness, and plasticity, are essential for understanding how microscopic-scale mechanical features can link to macroscale bones’ strength and fracture resistance. We employ Brillouin light scattering (BLS) microspectroscopy for local assessment of elastic properties of bones under compression and the efficacy of the tissue engineering approach based on heparin-conjugated fibrin (HCF) hydrogels, bone morphogenic proteins, and osteogenic stem cells in the regeneration of the bone tissues. BLS is noninvasive and label-free modality for probing viscoelastic properties of tissues that can give information on structure-function properties of normal and pathological tissues. Results showed that MCS and BPMs are critically important for regeneration of elastic and viscous properties, respectively, HCF gels containing combination of all factors had the best effect with complete defect regeneration at week nine after the implantation of bone grafts and that the bones with fully consolidated fractures have higher values of elastic moduli compared with defective bonesShow more