I. Cirac (Max Planck Institute, Garching
Quantum field theory constrains traversable wormhole geometries
SciTech Connect
Ford, L.H. ; Roman, T.A. 
19960501
Recently a bound on negative energy densities in fourdimensional Minkowski spacetime was derived for a minimally coupled, quantized, massless, scalar field in an arbitrary quantum state. The bound has the form of an uncertaintyprincipletype constraint on the magnitude and duration of the negative energy density seen by a timelike geodesic observer. When spacetime is curved and/or has boundaries, we argue that the bound should hold in regions small compared to the minimum local characteristic radius of curvature or the distance to any boundaries, since spacetime can be considered approximately Minkowski on these scales. We apply the bound to the stressenergy of static traversable wormhole spacetimes. Our analysis implies that either the wormhole must be only a little larger than Planck size or that there is a large discrepancy in the length scales which characterize the wormhole. In the latter case, the negative energy must typically be concentrated in a thin band many orders of magnitude smaller than the throat size. These results would seem to make the existence of macroscopic traversable wormholes very improbable. {copyright} {ital 1996 The American Physical Society.}
Continuum regularization of quantum field theory
SciTech Connect
Bern, Z.
19860401
Possible nonperturbative continuum regularization schemes for quantum field theory are discussed which are based upon the Langevin equation of Parisi and Wu. Breit, Gupta and Zaks made the first proposal for new gauge invariant nonperturbative regularization. The scheme is based on smearing in the ''fifthtime'' of the Langevin equation. An analysis of their stochastic regularization scheme for the case of scalar electrodynamics with the standard covariant gauge fixing is given. Their scheme is shown to preserve the masslessness of the photon and the tensor structure of the photon vacuum polarization at the oneloop level. Although stochastic regularization is viable in oneloop electrodynamics, two difficulties arise which, in general, ruins the scheme. One problem is that the superficial quadratic divergences force a bottomless action for the noise. Another difficulty is that stochastic regularization by fifthtime smearing is incompatible with Zwanziger's gauge fixing, which is the only known nonperturbaive covariant gauge fixing for nonabelian gauge theories. Finally, a successful covariant derivative scheme is discussed which avoids the difficulties encountered with the earlier stochastic regularization by fifthtime smearing. For QCD the regularized formulation is manifestly Lorentz invariant, gauge invariant, ghost free and finite to all orders. A vanishing gluon mass is explicitly verified at one loop. The method is designed to respect relevant symmetries, and is expected to provide suitable regularization for any theory of interest. Hopefully, the scheme will lend itself to nonperturbative analysis. 44 refs., 16 figs.
Field theoretical approach for biomembrane coupled with flow field
NASA Astrophysics Data System (ADS)
Oya, Y.; Kawakatsu, T.
20130201
Shape deformation of biomembranes in flow field is well known phenomenon in biological systems, for example red blood cell in blood vessel. To simulate such deformation with use of field theoretical approach, we derived the dynamical equation of phase field for shape of membrane and coupled the equation with NavierStokes equation for flow field. In 2dimensional simulations, we found that a biomembrane in a Poiseuille flow takes a parachute shape similar to the red blood cells.
Quantum states of neutrons in the Earth's gravitational field.
PubMed
Nesvizhevsky, Valery V; Börner, Hans G; Petukhov, Alexander K; Abele, Hartmut; Baessler, Stefan; Ruess, Frank J; Stöferle, Thilo; Westphal, Alexander; Gagarski, Alexei M; Petrov, Guennady A; Strelkov, Alexander V
20020117
The discrete quantum properties of matter are manifest in a variety of phenomena. Any particle that is trapped in a sufficiently deep and wide potential well is settled in quantum bound states. For example, the existence of quantum states of electrons in an electromagnetic field is responsible for the structure of atoms, and quantum states of nucleons in a strong nuclear field give rise to the structure of atomic nuclei. In an analogous way, the gravitational field should lead to the formation of quantum states. But the gravitational force is extremely weak compared to the electromagnetic and nuclear force, so the observation of quantum states of matter in a gravitational field is extremely challenging. Because of their charge neutrality and long lifetime, neutrons are promising candidates with which to observe such an effect. Here we report experimental evidence for gravitational quantum bound states of neutrons. The particles are allowed to fall towards a horizontal mirror which, together with the Earth's gravitational field, provides the necessary confining potential well. Under such conditions, the falling neutrons do not move continuously along the vertical direction, but rather jump from one height to another, as predicted by quantum theory.
Quantum analysis applied to thermo field dynamics on dissipative systems
SciTech Connect
Hashizume, Yoichiro; Okamura, Soichiro; Suzuki, Masuo
20150310
Thermo field dynamics is one of formulations useful to treat statistical mechanics in the scheme of field theory. In the present study, we discuss dissipative thermo field dynamics of quantum damped harmonic oscillators. To treat the effective renormalization of quantum dissipation, we use the SuzukiTakano approximation. Finally, we derive a dissipative von Neumann equation in the Lindbrad form. In the present treatment, we can easily obtain the initial damping shown previously by Kubo.
Electricfield correlation in quantum charged fluids coupled to the radiation field.
PubMed
Jancovici, B
20061101
In a recent paper [S. El Boustani, P. R. Buenzli, and P. A. Martin, Phys. Rev. E 73, 036113 (2006)] about quantum charges in equilibrium with radiation, among other things the asymptotic form of the electricfield correlation has been obtained by a microscopic calculation. It has been found that this correlation has a longrange algebraic decay of the form 1/r3 (except in the classical limit). The macroscopic approach, in the Course of Theoretical Physics of Landau and Lifshitz, gives no such decay. In this Brief Report we revisit and complete the macroscopic approach of Landau and Lifshitz and suggest that, perhaps, the use of a classical electromagnetic field by El Boustani was not justified.
Field theoretical prediction of a property of the tropical cyclone
NASA Astrophysics Data System (ADS)
Spineanu, F.; Vlad, M.
20140101
The large scale atmospheric vortices (tropical cyclones, tornadoes) are complex physical systems combining thermodynamics and fluidmechanical processes. The late phase of the evolution towards stationarity consists of the vorticity concentration, a well known tendency to selforganization , an universal property of the twodimensional fluids. It may then be expected that the stationary state of the tropical cyclone has the same nature as the vortices of many other systems in nature: ideal (Euler) fluids, superconductors, BoseEinsetin condensate, cosmic strings, etc. Indeed it was found that there is a description of the atmospheric vortex in terms of a classical field theory. It is compatible with the more conventional treatment based on conservation laws, but the field theoretical model reveals properties that are almost inaccessible to the conventional formulation: it identifies the stationary states as being close to selfduality. This is of highest importance: the selfduality is known to be the origin of all coherent structures known in natural systems. Therefore the field theoretical (FT) formulation finds that the cuasicoherent form of the atmospheric vortex (tropical cyclone) at stationarity is an expression of this particular property. In the present work we examine a strong property of the tropical cyclone, which arises in the FT formulation in a natural way: the equality of the masses of the particles associated to the matter field and respectively to the gauge field in the FT model is translated into the equality between the maximum radial extension of the tropical cyclone and the Rossby radius. For the cases where the FT model is a good approximation we calculate characteristic quantities of the tropical cyclone and find good comparison with observational data.
Theoretical study of phosphorene tunneling field effect transistors
NASA Astrophysics Data System (ADS)
Chang, Jiwon; Hobbs, Chris
20150201
In this work, device performances of tunneling field effect transistors (TFETs) based on phosphorene are explored via selfconsistent atomistic quantum transport simulations. Phosphorene is an ultrathin twodimensional (2D) material with a direct band gap suitable for TFETs applications. Our simulation shows that phosphorene TFETs exhibit subthreshold slope below 60 mV/dec and a wide range of oncurrent depending on the transport direction due to highly anisotropic band structures of phosphorene. By benchmarking with monolayer MoTe2 TFETs, we predict that phosphorene TFETs oriented in the small effective mass direction can yield much larger oncurrent at the same oncurrent/offcurrent ratio than monolayer MoTe2 TFETs. It is also observed that a gate underlap structure is required for scaling down phosphorene TFETs in the small effective mass direction to suppress the sourcetodrain direct tunneling leakage current.
Theoretical study of phosphorene tunneling field effect transistors
SciTech Connect
Chang, Jiwon; Hobbs, Chris
20150223
In this work, device performances of tunneling field effect transistors (TFETs) based on phosphorene are explored via selfconsistent atomistic quantum transport simulations. Phosphorene is an ultrathin twodimensional (2D) material with a direct band gap suitable for TFETs applications. Our simulation shows that phosphorene TFETs exhibit subthreshold slope below 60 mV/dec and a wide range of oncurrent depending on the transport direction due to highly anisotropic band structures of phosphorene. By benchmarking with monolayer MoTe{sub 2} TFETs, we predict that phosphorene TFETs oriented in the small effective mass direction can yield much larger oncurrent at the same oncurrent/offcurrent ratio than monolayer MoTe{sub 2} TFETs. It is also observed that a gate underlap structure is required for scaling down phosphorene TFETs in the small effective mass direction to suppress the sourcetodrain direct tunneling leakage current.
An implementation problem for boson fields and quantum Girsanov transform
NASA Astrophysics Data System (ADS)
Ji, Un Cig; Obata, Nobuaki
20160801
We study an implementation problem for quadratic functions of annihilation and creation operators on a boson field in terms of quantum white noise calculus. The implementation problem is shown to be equivalent to a linear differential equation for white noise operators containing quantum white noise derivatives. The solution is explicitly obtained and turns out to form a class of white noise operators including generalized FourierGauss and FourierMehler transforms, Bogoliubov transform, and a quantum extension of the Girsanov transform.
Modern Quantum Field Theory II  Proceeeings of the International Colloquium
NASA Astrophysics Data System (ADS)
Das, S. R.; Mandal, G.; Mukhi, S.; Wadia, S. R.
19950801
The Table of Contents for the book is as follows: * Foreword * 1. Black Holes and Quantum Gravity * Quantum Black Holes and the Problem of Time * Black Hole Entropy and the Semiclassical Approximation * Entropy and Information Loss in Two Dimensions * Strings on a Cone and Black Hole Entropy (Abstract) * Boundary Dynamics, Black Holes and Spacetime Fluctuations in Dilation Gravity (Abstract) * Pair Creation of Black Holes (Abstract) * A Brief View of 2Dim. String Theory and Black Holes (Abstract) * 2. String Theory * NonAbelian Duality in WZW Models * Operators and Correlation Functions in c ≤ 1 String Theory * New Symmetries in String Theory * A Look at the Discretized Superstring Using Random Matrices * The Nested BRST Structure of WnSymmetries * LandauGinzburg Model for a Critical Topological String (Abstract) * On the Geometry of Wn Gravity (Abstract) * O(d, d) Tranformations, Marginal Deformations and the Coset Construction in WZNW Models (Abstract) * Nonperturbative Effects and Multicritical Behaviour of c = 1 Matrix Model (Abstract) * Singular Limits and String Solutions (Abstract) * BV Algebra on the Moduli Spaces of Riemann Surfaces and String Field Theory (Abstract) * 3. Condensed Matter and Statistical Mechanics * Stochastic Dynamics in a DepositionEvaporation Model on a Line * Models with InverseSquare Interactions: Conjectured Dynamical Correlation Functions of the CalogeroSutherland Model at Rational Couplings * Turbulence and Generic Scale Invariance * Singular Perturbation Approach to Phase Ordering Dynamics * Kinetics of DiffusionControlled and BallisticallyControlled Reactions * Field Theory of a Frustrated Heisenberg Spin Chain * FQHE Physics in Relativistic Field Theories * Importance of Initial Conditions in Determining the Dynamical Class of Cellular Automata (Abstract) * Do HardCore Bosons Exhibit Quantum Hall Effect? (Abstract) * Hysteresis in Ferromagnets * 4. Fundamental Aspects of Quantum Mechanics and Quantum Field Theory
No resonant tunneling in standard scalar quantum field theory
NASA Astrophysics Data System (ADS)
Copeland, Edmund J.; Padilla, Antonio; Saffin, Paul M.
20080101
We investigate the nature of resonant tunneling in standard scalar Quantum Field Theory. Following the pioneering work of Banks, Bender and Wu we describe the quantum field theory in terms of infinite dimensional quantum mechanics and utilize the ``Most probable escape path'' (MPEP) as the class of paths which dominate the path integral in the classically forbidden region. Considering a 1+1 dimensional field theory example we show that there are five conditions that any associated bound state in the classically allowed region must satisfy if resonant tunnelling is to occur, and we then proceed to show that it is impossible to satisfy all five conditions simultaneously.
Potential theoretic methods for far field sound radiation calculations
NASA Technical Reports Server (NTRS)
Hariharan, S. I.; Stenger, Edward J.; Scott, J. R.
19950101
In the area of computational acoustics, procedures which accurately predict the farfield sound radiation are much sought after. A systematic development of such procedures are found in a sequence of papers by Atassi. The method presented here is an alternate approach to predicting far field sound based on simple layer potential theoretic methods. The main advantages of this method are: it requires only a simple free space Green's function, it can accommodate arbitrary shapes of Kirchoff surfaces, and is readily extendable to threedimensional problems. Moreover, the procedure presented here, though tested for unsteady lifting airfoil problems, can easily be adapted to other areas of interest, such as jet noise radiation problems. Results are presented for lifting airfoil problems and comparisons are made with the results reported by Atassi. Direct comparisons are also made for the flat plate case.
Decoherence of quantum fields: Pointer states and predictability
SciTech Connect
Anglin, J.R.; Zurek, W.H.
19960601
We study environmentally induced decoherence of an electromagnetic field in a homogeneous, linear, dielectric medium. We derive an independent oscillator model for such an environment, which is sufficiently realistic to encompass essentially all linear physical optics. Applying the {open_quote}{open_quote}predictability sieve{close_quote}{close_quote} to the quantum field, and introducing the concept of a {open_quote}{open_quote}quantum halo,{close_quote}{close_quote} we recover the familiar dichotomy between background field configurations and photon excitations around them. We are then able to explain why a typical linear environment for the electromagnetic field will effectively render the former classically distinct, but leave the latter fully quantum mechanical. Finally, we suggest how and why quantum matter fields should suffer a very different form of decoherence. {copyright} {ital 1996 The American Physical Society.}
Matter coupling to strong electromagnetic fields in twolevel quantum systems with broken inversion symmetry.
PubMed
Kibis, O V; Slepyan, G Ya; Maksimenko, S A; Hoffmann, A
20090116
We demonstrate theoretically the parametric oscillator behavior of a twolevel quantum system with broken inversion symmetry exposed to a strong electromagnetic field. A multitude of resonance frequencies and additional harmonics in the scattered light spectrum as well as an altered Rabi frequency are predicted to be inherent to such systems. In particular, dipole radiation at the Rabi frequency appears to be possible. Since the Rabi frequency is controlled by the strength of the coupling electromagnetic field, the effect can serve for the frequencytuned parametric amplification and generation of electromagnetic waves. Manifestation of the effect is discussed for IIInitride quantum dots with strong builtin electric field breaking the inversion symmetry. Terahertz emission from arrays of such quantum dots is shown to be experimentally observable. PMID:19257272

Matter coupling to strong electromagnetic fields in twolevel quantum systems with broken inversion symmetry.
PubMed
Kibis, O V; Slepyan, G Ya; Maksimenko, S A; Hoffmann, A
20090116
We demonstrate theoretically the parametric oscillator behavior of a twolevel quantum system with broken inversion symmetry exposed to a strong electromagnetic field. A multitude of resonance frequencies and additional harmonics in the scattered light spectrum as well as an altered Rabi frequency are predicted to be inherent to such systems. In particular, dipole radiation at the Rabi frequency appears to be possible. Since the Rabi frequency is controlled by the strength of the coupling electromagnetic field, the effect can serve for the frequencytuned parametric amplification and generation of electromagnetic waves. Manifestation of the effect is discussed for IIInitride quantum dots with strong builtin electric field breaking the inversion symmetry. Terahertz emission from arrays of such quantum dots is shown to be experimentally observable.

Is there a "most perfect fluid" consistent with quantum field theory?
PubMed
Cohen, Thomas D
20070713
It was recently conjectured that the ratio of the shear viscosity to entropy density eta/s for any fluid always exceeds [formula: see text]. A theoretical counterexample to this bound can be constructed from a nonrelativistic gas by increasing the number of species in the fluid while keeping the dynamics essentially independent of the species type. The question of whether the underlying structure of relativistic quantum field theory generically inhibits the realization of such a system and thereby preserves the possibility of a universal bound is considered here. Using rather conservative assumptions, it is shown here that a metastable gas of heavy mesons in a particular controlled regime of QCD provides a realization of the counterexample and is consistent with a welldefined underlying relativistic quantum field theory. Thus, quantum field theory appears to impose no lower bound on eta/s, at least for metastable fluids.

Numerical and theoretical study of Bernstein modes in a magnetized quantum plasma
NASA Astrophysics Data System (ADS)
Eliasson, Bengt; Shukla, Padma K.
20081001
A numerical and theoretical study is presented for the propagation of electron Bernstein modes in a magnetized quantum plasma. The dispersion relation for electrostatic waves is derived, using a semiclassical Vlasov model for FermiDirac distributed electrons. The dispersion relation is checked numerically with direct Vlasov simulations, where the wave energy is concentrated to the Bernstein modes as well as to the zerofrequency convective mode. Dispersion relations in the long wavelength limit are derived, including the upper hybrid dispersion relation for a degenerate quantum plasma.

Numerical and theoretical study of Bernstein modes in a magnetized quantum plasma
SciTech Connect
Eliasson, Bengt; Shukla, Padma K.
20081015
A numerical and theoretical study is presented for the propagation of electron Bernstein modes in a magnetized quantum plasma. The dispersion relation for electrostatic waves is derived, using a semiclassical Vlasov model for FermiDirac distributed electrons. The dispersion relation is checked numerically with direct Vlasov simulations, where the wave energy is concentrated to the Bernstein modes as well as to the zerofrequency convective mode. Dispersion relations in the long wavelength limit are derived, including the upper hybrid dispersion relation for a degenerate quantum plasma.

Advancements in the Field of Quantum Dots
NASA Astrophysics Data System (ADS)
Mishra, Sambeet; Tripathy, Pratyasha; Sinha, Swami Prasad.
20120801
Quantum dots are defined as very small semiconductor crystals of size varying from nanometer scale to a few micron i.e. so small that they are considered dimensionless and are capable of showing many chemical properties by virtue of which they tend to be lead at one minute and gold at the second minute.Quantum dots house the electrons just the way the electrons would have been present in an atom, by applying a voltage. And therefore they are very judiciously given the name of being called as the artificial atoms. This application of voltage may also lead to the modification of the chemical nature of the material anytime it is desired, resulting in lead at one minute to gold at the other minute. But this method is quite beyond our reach. A quantum dot is basically a semiconductor of very tiny size and this special phenomenon of quantum dot, causes the band of energies to change into discrete energy levels. Band gaps and the related energy depend on the relationship between the size of the crystal and the exciton radius. The height and energy between different energy levels varies inversely with the size of the quantum dot. The smaller the quantum dot, the higher is the energy possessed by it.There are many applications of the quantum dots e.g. they are very wisely applied to:Light emitting diodes: LEDs eg. White LEDs, Photovoltaic devices: solar cells, Memory elements, Biology : =biosensors, imaging, Lasers, Quantum computation, Flatpanel displays, Photodetectors, Life sciences and so on and so forth.The nanometer sized particles are able to display any chosen colour in the entire ultraviolet visible spectrum through a small change in their size or composition.

Enhanced upconversion of entangled photons and quantum interference under a localized field in nanostructures.
PubMed
Osaka, Yoshiki; Yokoshi, Nobuhiko; Nakatani, Masatoshi; Ishihara, Hajime
20140401
We theoretically investigate the upconversion process of two entangled photons on a molecule, which is coupled by a cavity or nanoscale metallic structure. Within onedimensional inputoutput theory, the propagators of the photons are derived analytically and the upconversion probability is calculated numerically. It is shown that the coupling with the nanostructure clearly enhances the process. We also find that the enhancement becomes further pronounced for some balanced system parameters, such as the quantum correlation between photons, radiation decay, and coupling between the nanostructure and molecule. The nonmonotonic dependencies are reasonably explained in view of quantum interference between the coupled modes of the whole system. This result indicates that controlling quantum interference and correlation is crucial for fewphoton nonlinearity, and provides a new guidance to wide variety of fields, e.g., quantum electronics and photochemistry.

Strongfield ionization in classical and quantum dynamics
SciTech Connect
Ritchie, B. ); Bowden, C.M.; Sung, C.C.; Li, Y.Q. )
19900601
Classical and quantum results for the strongelectromagneticfield ionization of the ground state of a generic model are compared. Quantum results are also presented for the strongfield ionization of the hydrogen atom. These results demonstrate that ionization depends strongly on the phase of the field in such a way that the interaction potential acts as a barrier or well at large distances from the binding region, producing effectively a closed or open gate'' to the region of space outside the atom. The open gate is analogous to a strong, static electric field applied to an atom such that the atom ionizes classically. Quantum and classical ensemble results for the ionization probability are found to show close qualitative agreement. Other comparisons are made for classical versus quantum wavepacket trajectories.

Illustrating the quantum approach with an Earth magnetic field MRI
NASA Astrophysics Data System (ADS)
Pars Benli, Kami; Dillmann, Baudouin; Louelh, Ryma; PoirierQuinot, Marie; Darrasse, Luc
20150501
Teaching imaging of magnetic resonance (MR) today is still as challenging as it has always been, because it requires admitting that we cannot express fundamental questions of quantum mechanics with straightforward language or without using extensive theory. Here we allow students to face a real MR setup based on the Earth's magnetic field. We address the applied side of teaching MR using a device that is affordable and that proves to be sufficiently robust, at universities in Orsay, France, and San Sebastian, Spain, in experimental practicals at undergraduate and graduate levels. We specifically present some of the advantages of low field for measuring R2 relaxation rates, reaching a power of separation of 1.5 μmol on Mn(II) ions between two water bottles each of half a liter. Finally we propose key approaches for the lecturers to adopt when they are asked to pass from theoretical knowledge to teachable knowhow. The outcomes are fast calibration and the MR acquisition protocols, demonstrating the reproducibility of energy transfer during the saturation pulses, and the quantitative nature of MR, with water protons and a helium3 sample.

Quantum Gravity from the Point of View of Locally Covariant Quantum Field Theory
NASA Astrophysics Data System (ADS)
Brunetti, Romeo; Fredenhagen, Klaus; Rejzner, Katarzyna
20160801
We construct perturbative quantum gravity in a generally covariant way. In particular our construction is background independent. It is based on the locally covariant approach to quantum field theory and the renormalized BatalinVilkovisky formalism. We do not touch the problem of nonrenormalizability and interpret the theory as an effective theory at large length scales.

Field theoretic simulations of the interfacial properties of complex coacervates
NASA Astrophysics Data System (ADS)
Riggleman, Robert; Fredrickson, Glenn
20110301
Many biological processes and emerging technologies, such as wet adhesives and biosensors, rely on the association between oppositely charged polyelectrolytes. Such association is driven not only by the electrostatic interactions between the polyelectrolytes, but there is also a substantial entropy gain associated with counterion release upon complexation. In some cases, the association between oppositely charged polymers can lead to a solid precipitate while others can result in a fluid phase rich in polyelectrolytes (coacervate phase) coexisting with a polyelectrolytedilute solvent phase. For many of the applications seeking to exploit coacervation, characterization of the interface between the solvent phase and the coacervate is of paramount importance. In this talk, we will present the results of fieldtheoretic simulations for a coarsegrained polyelectrolyte model that exhibits complex coacervation. Our simulations sample the fullyfluctuating fields in threedimensions and provide a detailed characterization of the interface between the solvent and the coacervate phase for symmetric polyelectrolytes (where both the polycations and the polyanions carry identical charge densities) as a function of salt concentration and strength of the electrostatic fields. Finally, we characterize the interfacial properties for a select set of asymmetric conditions.

Monte Carlo fieldtheoretic simulations of a homopolymer blend
NASA Astrophysics Data System (ADS)
Spencer, Russell; Matsen, Mark
Fluctuation corrections to the macrophase segregation transition (MST) in a symmetric homopolymer blend are examined using Monte Carlo fieldtheoretic simulations (MCFTS). This technique involves treating interactions between unlike monomers using standard MonteCarlo techniques, while enforcing incompressibility as is done in meanfield theory. When using MCFTS, we need to account for a UV divergence. This is done by renormalizing the FloryHuggins interaction parameter to incorporate the divergent part of the Hamiltonian. We compare different ways of calculating this effective interaction parameter. Near the MST, the length scale of compositional fluctuations becomes large, however, the high computational requirements of MCFTS restrict us to small system sizes. We account for these finite size effects using the method of Binder cumulants, allowing us to locate the MST with high precision. We examine fluctuation corrections to the mean field MST, χN = 2 , as they vary with the invariant degree of polymerization, N =ρ2a6 N . These results are compared with particlebased simulations as well as analytical calculations using the renormalized one loop theory. This research was funded by the Center for Sustainable Polymers.

Charge fractionalization in oxide heterostructures: A fieldtheoretical model
NASA Astrophysics Data System (ADS)
Karthick Selvan, M.; Panigrahi, Prasanta K.
20160601
LaAlO3/SrTiO3 heterostructure with polar and nonpolar constituents has been shown to exhibit interface metallic conductivity due to fractional charge transfer to the interface. The interface reconstruction by electron redistribution along the (001) orientation, in which half of an electron is transferred per twodimensional unit cell to the adjacent planes, resulting in a net transfer of half of the charge to both the interface and topmost atomic planes, has been ascribed to a polar discontinuity at the interface in the polar catastrophe model. This avoids the divergence of the electrostatic potential, as the number of layers are increased, producing an oscillatory electric field and finite potential. Akin to the description of charge fractionalization in quasionedimensional polyacetylene by the fieldtheoretic JackiwRebbi model with fermions interacting with a topologically nontrivial background field, we show an analogous connection between the polar catastrophe model and the BellRajaraman model, where the charge fractionalization occurs in the soliton free sector as an end effect.

Quantum electrodynamics with an external field disturbing vacuum stability
NASA Astrophysics Data System (ADS)
Gitman, D. M.; Fradkin, E. S.; Shvartsman, Sh. M.
The problems of quantum field theory with unstable vacuum are examined using quantum electrodynamics with an external field as an example. The instability manifests itself as the possibility of electronpositron pair generation from vacuum due to external electric fields. A perturbation theory for the matrix elements of the transition process is developed which allows, in an exact manner, for interaction with the external field generating the pairs. It is shown that the development of a special perturbation theory, in which propagators have a matrix structure, is required for calculating the mean values of the operators of physical quantities in quantum field theory. Calculations of various processes in pairgenerating fields are presented.

Photocurrent Control in a Magnetic Field through Quantum Interference
NASA Astrophysics Data System (ADS)
Rao, Kiran Murti
Quantummechanical interference between excitation pathways can be used to inject photocurrents optically in semiconductors, the properties of which can be coherently controlled through the phases and polarizations of the optical pulses. In this thesis, coherent photocurrent control is investigated theoretically for twodimensional semiconductor systems in a perpendicular magnetic field. The semiconductor systems are subjected to optical pulses with centre frequencies o 0 and 2o0, which excite interband transitions through one and twophoton processes, selection rules for which are determined from envelope wave functions. It is shown using timedependent perturbation theory that the interference between one and twophoton pathways connecting a particular valence Landau level to two different but adjacent conduction Landau levels manifests itself as electron currents that rotate counterclockwise, while interference between pathways connecting two adjacent valence Landau levels to a particular conduction Landau level manifests itself as hole currents that rotate clockwise. The initial directions of the currents can be controlled by adjusting the polarizations and a relative phase parameter of the pulses. The analysis is performed for a GaAs quantum well, monolayer graphene and bilayer graphene. For GaAs, the equally spaced Landau levels in each band lead to electron currents rotating at a single frequency and hole currents rotating at a different frequency. Monolayer and bilayer graphene allow currents with multiple frequency components as well as other peculiarities resulting from additional interference processes not present for GaAs. The photocurrents in all of these systems radiate in the terahertz regime. This radiation is calculated for realistic experimental conditions, with scattering and relaxation processes accounted for phenomenologically. Finally, the effect of Coulomb interactions on the coherent control process is considered for an undoped Ga

Black hole state counting in loop quantum gravity: a numbertheoretical approach.
PubMed
Agulló, Iván; Barbero G, J Fernando; DíazPolo, Jacobo; FernándezBorja, Enrique; Villaseñor, Eduardo J S
20080530
We give an efficient method, combining numbertheoretic and combinatorial ideas, to exactly compute black hole entropy in the framework of loop quantum gravity. Along the way we provide a complete characterization of the relevant sector of the spectrum of the area operator, including degeneracies, and explicitly determine the number of solutions to the projection constraint. We use a computer implementation of the proposed algorithm to confirm and extend previous results on the detailed structure of the black hole degeneracy spectrum.

Theoretical and experimental examination of nearfield acoustic levitation.
PubMed
Nomura, Hideyuki; Kamakura, Tomoo; Matsuda, Kazuhisa
20020401
A planar object can be levitated stably close to a piston sound source by making use of acoustic radiation pressure. This phenomenon is called nearfield acoustic levitation [Y. Hashimoto et al., J. Acoust. Soc. Am. 100, 20572061 (1996)]. In the present article, the levitation distance is predicted theoretically by numerically solving basic equations in a compressible viscous fluid subject to the appropriate initial and boundary conditions. Additionally, experiments are carried out using a 19.5kHz piston source with a 40mm aperture and various aluminum disks of different sizes. The measured levitation distance agrees well with the theory, which is different from a conventional theory, and the levitation distance is not inversely proportional to the square root of the surface density of the levitated disk in a strict sense. PMID:12002842

Theoretical performance of solar cell based on minibands quantum dots
SciTech Connect
Aly, Abou ElMaaty M. Email: ashraf.nasr@gmail.com; Nasr, A. Email: ashraf.nasr@gmail.com
20140321
The tremendous amount of research in solar energy is directed toward intermediate band solar cell for its advantages compared with the conventional solar cell. The latter has lower efficiency because the photons have lower energy than the bandgap energy and cannot excite mobile carriers from the valence band to the conduction band. On the other hand, if mini intermediate band is introduced between the valence and conduction bands, then the smaller energy photons can be used to promote charge carriers transfer to the conduction band and thereby the total current increases while maintaining a large open circuit voltage. In this article, the influence of the new band on the power conversion efficiency for structure of quantum dots intermediate band solar cell is theoretically investigated and studied. The timeindependent Schrödinger equation is used to determine the optimum width and location of the intermediate band. Accordingly, achievement of a maximum efficiency by changing the width of quantum dots and barrier distances is studied. Theoretical determination of the power conversion efficiency under the two different ranges of QD width is presented. From the obtained results, the maximum power conversion efficiency is about 70.42%. It is carried out for simple cubic quantum dot crystal under fully concentrated light. It is strongly dependent on the width of quantum dots and barrier distances.

Quantum perceptron over a field and neural network architecture selection in a quantum computer.
PubMed
da Silva, Adenilton José; Ludermir, Teresa Bernarda; de Oliveira, Wilson Rosa
20160401
In this work, we propose a quantum neural network named quantum perceptron over a field (QPF). Quantum computers are not yet a reality and the models and algorithms proposed in this work cannot be simulated in actual (or classical) computers. QPF is a direct generalization of a classical perceptron and solves some drawbacks found in previous models of quantum perceptrons. We also present a learning algorithm named Superposition based Architecture Learning algorithm (SAL) that optimizes the neural network weights and architectures. SAL searches for the best architecture in a finite set of neural network architectures with linear time over the number of patterns in the training set. SAL is the first learning algorithm to determine neural network architectures in polynomial time. This speedup is obtained by the use of quantum parallelism and a nonlinear quantum operator. PMID:26878722

Quantum perceptron over a field and neural network architecture selection in a quantum computer.
PubMed
da Silva, Adenilton José; Ludermir, Teresa Bernarda; de Oliveira, Wilson Rosa
20160401
In this work, we propose a quantum neural network named quantum perceptron over a field (QPF). Quantum computers are not yet a reality and the models and algorithms proposed in this work cannot be simulated in actual (or classical) computers. QPF is a direct generalization of a classical perceptron and solves some drawbacks found in previous models of quantum perceptrons. We also present a learning algorithm named Superposition based Architecture Learning algorithm (SAL) that optimizes the neural network weights and architectures. SAL searches for the best architecture in a finite set of neural network architectures with linear time over the number of patterns in the training set. SAL is the first learning algorithm to determine neural network architectures in polynomial time. This speedup is obtained by the use of quantum parallelism and a nonlinear quantum operator.

Finite fielddependent symmetries in perturbative quantum gravity
SciTech Connect
Upadhyay, Sudhaker
20140115
In this paper we discuss the absolutely anticommuting nilpotent symmetries for perturbative quantum gravity in general curved spacetime in linear and nonlinear gauges. Further, we analyze the finite fielddependent BRST (FFBRST) transformation for perturbative quantum gravity in general curved spacetime. The FFBRST transformation changes the gaugefixing and ghost parts of the perturbative quantum gravity within functional integration. However, the operation of such symmetry transformation on the generating functional of perturbative quantum gravity does not affect the theory on physical ground. The FFBRST transformation with appropriate choices of finite BRST parameter connects nonlinear Curci–Ferrari and Landau gauges of perturbative quantum gravity. The validity of the results is also established at quantum level using Batalin–Vilkovisky (BV) formulation.  Highlights: •The perturbative quantum gravity is treated as gauge theory. •BRST and antiBRST transformations are developed in linear and nonlinear gauges. •BRST transformation is generalized by making it finite and field dependent. •Connection between linear and nonlinear gauges is established. •Using BV formulation the results are established at quantum level also.

BOOK REVIEW: Quantum Field Theory in a Nutshell (2nd edn) Quantum Field Theory in a Nutshell (2nd edn)
NASA Astrophysics Data System (ADS)
Peskin, Michael E.
20110401
Anthony Zee is not only a leading theoretical physicist but also an author of popular books on both physics and nonphysics topics. I recommend especially `Swallowing Clouds', on Chinese cooking and its folklore. Thus, it is not surprising that his textbook has a unique flavor. Derivations end, not with `QED' but with exclamation points. At the end of one argument, we read `Vive Cauchy!', in another `the theorem practically exudes generality'. This is quantum field theory taught at the knee of an eccentric uncle; one who loves the grandeur of his subject, has a keen eye for a slick argument, and is eager to share his repertoire of anecdotes about Feynman, Fermi, and all of his heroes. A onepage section entitled `Electric Charge' illustrates the depth and tone of the book. In the previous section, Zee has computed the Feynman diagram responsible for vacuum polarization, in which a photon converts briefly to a virtual electronpositron pair. In the first paragraph, he evaluates this expression, giving a concrete formula for the momentumdependence of the electric charge, an important effect of quantum field theory. Next, he dismisses other possible diagrams that could affect the value of the electric charge. Most authors would give an explicit argument that these diagrams cancel, but for Zee it is more important to make the point that this result is expected and, from the right point of view, obvious. Finally, he discusses the implications for the relative size of the charges of the electron and the proton. If the magnitudes of charges are affected by interactions, and the proton has strong interactions but the electron does not, can it make sense that the charges of the proton and the electron are exactly equal and opposite? The answer is yes, and also that this was the real point of the whole derivation. The book takes on the full range of topics covered in typical graduate course in quantum field theory, and many additional topics: magnetic monopoles, solitons

BOOK REVIEW: Quantum Field Theory in a Nutshell (2nd edn) Quantum Field Theory in a Nutshell (2nd edn)
NASA Astrophysics Data System (ADS)
Peskin, Michael E.
20110401
Anthony Zee is not only a leading theoretical physicist but also an author of popular books on both physics and nonphysics topics. I recommend especially `Swallowing Clouds', on Chinese cooking and its folklore. Thus, it is not surprising that his textbook has a unique flavor. Derivations end, not with `QED' but with exclamation points. At the end of one argument, we read `Vive Cauchy!', in another `the theorem practically exudes generality'. This is quantum field theory taught at the knee of an eccentric uncle; one who loves the grandeur of his subject, has a keen eye for a slick argument, and is eager to share his repertoire of anecdotes about Feynman, Fermi, and all of his heroes. A onepage section entitled `Electric Charge' illustrates the depth and tone of the book. In the previous section, Zee has computed the Feynman diagram responsible for vacuum polarization, in which a photon converts briefly to a virtual electronpositron pair. In the first paragraph, he evaluates this expression, giving a concrete formula for the momentumdependence of the electric charge, an important effect of quantum field theory. Next, he dismisses other possible diagrams that could affect the value of the electric charge. Most authors would give an explicit argument that these diagrams cancel, but for Zee it is more important to make the point that this result is expected and, from the right point of view, obvious. Finally, he discusses the implications for the relative size of the charges of the electron and the proton. If the magnitudes of charges are affected by interactions, and the proton has strong interactions but the electron does not, can it make sense that the charges of the proton and the electron are exactly equal and opposite? The answer is yes, and also that this was the real point of the whole derivation. The book takes on the full range of topics covered in typical graduate course in quantum field theory, and many additional topics: magnetic monopoles, solitons

Theoretical analysis of magnetic field interactions with aortic blood flow
SciTech Connect
Kinouchi, Y.; Yamaguchi, H.; Tenforde, T.S.
19960401
The flow of blood in the presence of a magnetic field gives rise to induced voltages in the major arteries of the central circulatory system. Under certain simplifying conditions, such as the assumption that the length of major arteries (e.g., the aorta) is infinite and that the vessel walls are not electrically conductive, the distribution of induced voltages and currents within these blood vessels can be calculated with reasonable precision. However, the propagation of magnetically induced voltages and currents from the aorta into neighboring tissue structures such as the sinuatrial node of the heart has not been previously determined by any experimental or theoretical technique. In the analysis presented in this paper, a solution of the complete NavierStokes equation was obtained by the finite element technique for blood flow through the ascending and descending aortic vessels in the presence of a uniform static magnetic field. Spatial distributions of the magnetically induced voltage and current were obtained for the aortic vessel and surrounding tissues under the assumption that the wall of the aorta is electrically conductive. Results are presented for the calculated values of magnetically induced voltages and current densities in the aorta and surrounding tissue structures, including the sinuatrial node, and for their fieldstrength dependence. In addition, an analysis is presented of magnetohydrodynamic interactions that lead to a small reduction of blood volume flow at high field levels above approximately 10 tesla (T). Quantitative results are presented on the offsetting effects of oppositely directed blood flows in the ascending and descending aortic segments, and a quantitative estimate is made of the effects of assuming an infinite vs. a finite length of the aortic vessel in calculating the magnetically induced voltage and current density distribution in tissue.

Entanglement negativity in extended systems: a field theoretical approach
NASA Astrophysics Data System (ADS)
Calabrese, Pasquale; Cardy, John; Tonni, Erik
20130201
We report on a systematic approach for the calculation of the negativity in the ground state of a onedimensional quantum field theory. The partial transpose {\\rho }_{A}^{{T}_{2}} of the reduced density matrix of a subsystem A = A1∪A2 is explicitly constructed as an imaginarytime path integral and from this the replicated traces {Tr}({\\rho }_{A}^{{T}_{2}})^{n} are obtained. The logarithmic negativity E=log \\Vert {\\rho }_{A}^{{T}_{2}}\\Vert is then the continuation to n → 1 of the traces of the even powers. For pure states, this procedure reproduces the known results. We then apply this method to conformally invariant field theories (CFTs) in several different physical situations for infinite and finite systems and without or with boundaries. In particular, in the case of two adjacent intervals of lengths ℓ1,ℓ2 in an infinite system, we derive the result ℰ ∼ (c/4)ln(ℓ1ℓ2/(ℓ1 + ℓ2)), where c is the central charge. For the more complicated case of two disjoint intervals, we show that the negativity depends only on the harmonic ratio of the four end points and so is manifestly scale invariant. We explicitly calculate the scale invariant functions for the replicated traces in the case of the CFT for the free compactified boson, but we have not so far been able to obtain the n → 1 continuation for the negativity even in the limit of large compactification radius. We have checked all our findings against exact numerical results for the harmonic chain which is described by a noncompactified free boson.

Quantum entanglement of identical particles by standard informationtheoretic notions.
PubMed
Lo Franco, Rosario; Compagno, Giuseppe
20160209
Quantum entanglement of identical particles is essential in quantum information theory. Yet, its correct determination remains an open issue hindering the general understanding and exploitation of manyparticle systems. Operatorbased methods have been developed that attempt to overcome the issue. Here we introduce a statebased method which, as second quantization, does not label identical particles and presents conceptual and technical advances compared to the previous ones. It establishes the quantitative role played by arbitrary wave function overlaps, local measurements and particle nature (bosons or fermions) in assessing entanglement by notions commonly used in quantum information theory for distinguishable particles, like partial trace. Our approach furthermore shows that bringing identical particles into the same spatial location functions as an entangling gate, providing fundamental theoretical support to recent experimental observations with ultracold atoms. These results pave the way to set and interpret experiments for utilizing quantum correlations in realistic scenarios where overlap of particles can count, as in BoseEinstein condensates, quantum dots and biological molecular aggregates.

Quantum entanglement of identical particles by standard informationtheoretic notions
NASA Astrophysics Data System (ADS)
Lo Franco, Rosario; Compagno, Giuseppe
20160201
Quantum entanglement of identical particles is essential in quantum information theory. Yet, its correct determination remains an open issue hindering the general understanding and exploitation of manyparticle systems. Operatorbased methods have been developed that attempt to overcome the issue. Here we introduce a statebased method which, as second quantization, does not label identical particles and presents conceptual and technical advances compared to the previous ones. It establishes the quantitative role played by arbitrary wave function overlaps, local measurements and particle nature (bosons or fermions) in assessing entanglement by notions commonly used in quantum information theory for distinguishable particles, like partial trace. Our approach furthermore shows that bringing identical particles into the same spatial location functions as an entangling gate, providing fundamental theoretical support to recent experimental observations with ultracold atoms. These results pave the way to set and interpret experiments for utilizing quantum correlations in realistic scenarios where overlap of particles can count, as in BoseEinstein condensates, quantum dots and biological molecular aggregates.

Quantum entanglement of identical particles by standard informationtheoretic notions
PubMed Central
Lo Franco, Rosario; Compagno, Giuseppe
20160101
Quantum entanglement of identical particles is essential in quantum information theory. Yet, its correct determination remains an open issue hindering the general understanding and exploitation of manyparticle systems. Operatorbased methods have been developed that attempt to overcome the issue. Here we introduce a statebased method which, as second quantization, does not label identical particles and presents conceptual and technical advances compared to the previous ones. It establishes the quantitative role played by arbitrary wave function overlaps, local measurements and particle nature (bosons or fermions) in assessing entanglement by notions commonly used in quantum information theory for distinguishable particles, like partial trace. Our approach furthermore shows that bringing identical particles into the same spatial location functions as an entangling gate, providing fundamental theoretical support to recent experimental observations with ultracold atoms. These results pave the way to set and interpret experiments for utilizing quantum correlations in realistic scenarios where overlap of particles can count, as in BoseEinstein condensates, quantum dots and biological molecular aggregates. PMID:26857475

Localization of firearm projectiles in the human body using a superconducting quantum interference device magnetometer: A theoretical study
NASA Astrophysics Data System (ADS)
Hall Barbosa, C.
20040601
A technique had been previously developed, based on magnetic field measurements using a superconducting quantum interference device sensor, to localize in three dimensions steel needles lost in the human body. In all six cases that were treated until now, the technique allowed easy surgical localization of the needles with high accuracy. The technique decreases, by a large factor, the surgery time for foreign body extraction, and also reduces the generally high odds of failure. The method is accurate, noninvasive, and innocuous, and with clear clinical importance. Despite the importance of needle localization, the most prevalent foreign body in the modern society is the firearm projectile (bullet), generally composed of lead, a paramagnetic material, thus not presenting a remanent magnetic field as steel needles do. On the other hand, since lead is a good conductor, eddy current detection techniques can be employed, by applying an alternating magnetic field with the aid of excitation coils. The primary field induces eddy currents on the lead, which in turn generate a secondary magnetic field that can be detected by a magnetometer, and give information about position and volume of the conducting foreign body. In this article we present a theoretical study for the development of a localization technique for lead bullets inside the human body. Initially, we present a model for the secondary magnetic field generated by the bullet, given a known applied field. After that, we study possible excitation systems, and propose a localization algorithm based on the detected magnetic field.

Polarizationentangled photon generation in a semiconductor quantum dot coupled to a cavity interacting with external fields
NASA Astrophysics Data System (ADS)
Blekos, Kostas; Iliopoulos, Nikos; Stasinou, MariaEftaksia; Vlachos, Evaggelos; Terzis, Andreas F.
20141201
We theoretically investigate polarizationentangled photon generation using a semiconductor quantum dot embedded in a microcavity. The entangled states can be produced by the application of two crosscircularly polarized laser fields. The quantum dot nanostructure is considered as a fourlevel system (ground, two excitons and biexciton states), and the theoretical study relies on the dressed states scheme. The quantum correlations, reported in terms of the entanglement of formation, are extensively studied for several values of the important parameters of the quantum dot system as the biexciton binding energy, the decoherence times of the characteristic transitions, the quality factor of the cavity and the intensities of the applied fields.

Dirac fields in loop quantum gravity and big bang nucleosynthesis
SciTech Connect
Bojowald, Martin; Das, Rupam; Scherrer, Robert J.
20080415
Big bang nucleosynthesis requires a fine balance between equations of state for photons and relativistic fermions. Several corrections to equation of state parameters arise from classical and quantum physics, which are derived here from a canonical perspective. In particular, loop quantum gravity allows one to compute quantum gravity corrections for Maxwell and Dirac fields. Although the classical actions are very different, quantum corrections to the equation of state are remarkably similar. To lowest order, these corrections take the form of an overall expansiondependent multiplicative factor in the total density. We use these results, along with the predictions of big bang nucleosynthesis, to place bounds on these corrections and especially the patch size of discrete quantum gravity states.

Cosmology from group field theory formalism for quantum gravity.
PubMed
Gielen, Steffen; Oriti, Daniele; Sindoni, Lorenzo
20130719
We identify a class of condensate states in the group field theory (GFT) formulation of quantum gravity that can be interpreted as macroscopic homogeneous spatial geometries. We then extract the dynamics of such condensate states directly from the fundamental quantum GFT dynamics, following the procedure used in ordinary quantum fluids. The effective dynamics is a nonlinear and nonlocal extension of quantum cosmology. We also show that any GFT model with a kinetic term of Laplacian type gives rise, in a semiclassical (WKB) approximation and in the isotropic case, to a modified Friedmann equation. This is the first concrete, general procedure for extracting an effective cosmological dynamics directly from a fundamental theory of quantum geometry.

Optical absorption coefficients in GaN/Al(Ga)N double inverse parabolic quantum wells under static external electric field
NASA Astrophysics Data System (ADS)
El Kadadra, A.; Fellaoui, K.; Abouelaoualim, D.; Oueriagli, A.
20160901
In this work, we have investigated theoretically the effects of applied electric field on the linear and nonlinear optical properties in a GaN/AlxGa1xN double inverse parabolic quantum well for different Al concentrations at the well center. Our calculations are based on the potential morphing method in the effective mass approximation. The systematic theoretical investigation contains results with all possible combinations of the involved parameters, such as quantum well width, quantum barrier width, Al concentration at each well center and magnitude of the external electric field. Our results show that the electric fields strengths, the parameter of nanostructure and incident optical intensity have a great effect on the optical characteristics of these nanostructures. Thus, the absorption coefficients which can be suitable for great performance optical modulators and multiple infrared optical device applications can be easily obtained by tuning the external electric field value and the Al concentration at the well center.

PREFACE: Particles and Fields: Classical and Quantum
NASA Astrophysics Data System (ADS)
Asorey, M.; ClementeGallardo, J.; Marmo, G.
20070701
This volume contains some of the contributions to the Conference Particles and Fields: Classical and Quantum, which was held at Jaca (Spain) in September 2006 to honour George Sudarshan on his 75th birthday. Former and current students, associates and friends came to Jaca to share a few wonderful days with George and his family and to present some contributions of their present work as influenced by George's impressive achievements. This book summarizes those scientific contributions which are presented as a modest homage to the master, collaborator and friend. At the social ceremonies various speakers were able to recall instances of his lifelong activity in India, the United States and Europe, adding colourful remarks on the friendly and intense atmosphere which surrounded those collaborations, some of which continued for several decades. This meeting would not have been possible without the financial support of several institutions. We are deeply indebted to Universidad de Zaragoza, Ministerio de Educación y Ciencia de España (CICYT), Departamento de Ciencia, Tecnología y Universidad del Gobierno de Aragón, Universitá di Napoli 'Federico II' and Istituto Nazionale di Fisica Nucleare. Finally, we would like to thank the participants, and particularly George's family, for their contribution to the wonderful atmosphere achieved during the Conference. We would like also to acknowledge the authors of the papers collected in the present volume, the members of the Scientific Committee for their guidance and support and the referees for their generous work. M Asorey, J ClementeGallardo and G Marmo The Local Organizing Committee George Sudarshan International Advisory Committee A. Ashtekhar (Pennsylvania State University, USA)  L. J. Boya (Universidad de Zaragoza, Spain)  I. Cirac (Max Planck Institute, Garching

Families of Particles with Different Masses in PTSymmetric Quantum Field Theory
SciTech Connect
Bender, Carl M.; Klevansky, S. P.
20100716
An elementary fieldtheoretic mechanism is proposed that allows one Lagrangian to describe a family of particles having different masses but otherwise similar physical properties. The mechanism relies on the observation that the DysonSchwinger equations derived from a Lagrangian can have many different but equally valid solutions. Nonunique solutions to the DysonSchwinger equations arise when the functional integral for the Green's functions of the quantum field theory converges in different pairs of Stokes' wedges in complexfield space, and the solutions are physically viable if the pairs of Stokes' wedges are PT symmetric.

Families of particles with different masses in PTsymmetric quantum field theory.
PubMed
Bender, Carl M; Klevansky, S P
20100716
An elementary fieldtheoretic mechanism is proposed that allows one Lagrangian to describe a family of particles having different masses but otherwise similar physical properties. The mechanism relies on the observation that the DysonSchwinger equations derived from a Lagrangian can have many different but equally valid solutions. Nonunique solutions to the DysonSchwinger equations arise when the functional integral for the Green's functions of the quantum field theory converges in different pairs of Stokes' wedges in complexfield space, and the solutions are physically viable if the pairs of Stokes' wedges are PT symmetric.

A novel quantum field approach to photoexcited insulators
NASA Astrophysics Data System (ADS)
Klotins, E.
20160701
In order to predict optical properties of insulating materials under intensive laser excitation, we generalized methods of quantum electrodynamics, allowing us to simulate excitation of electrons and holes, interacting with each other and acoustic phonons. The prototypical model considers a twoband dielectric material characterized by the dispersion relations for electron and hole states. We developed a universal description of excited electrons, holes and acoustic phonons within joint quantum kinetics formalism. Illustrative solutions for the quasiparticle birthannihilation operators, applicable at short laser pulses at 0 K, are obtained by the transition from the macroscopic description to the quantum field formalism.

Quantum field between moving mirrors: A three dimensional example
NASA Technical Reports Server (NTRS)
Hacyan, S.; Jauregui, Roco; Villarreal, Carlos
19950101
The scalar quantum field uniformly moving plates in three dimensional space is studied. Field equations for Dirichlet boundary conditions are solved exactly. Comparison of the resulting wavefunctions with their instantaneous static counterpart is performed via Bogolubov coefficients. Unlike the one dimensional problem, 'particle' creation as well as squeezing may occur. The time dependent Casimir energy is also evaluated.

Quantum simulation
NASA Astrophysics Data System (ADS)
Georgescu, I. M.; Ashhab, S.; Nori, Franco
20140101
Simulating quantum mechanics is known to be a difficult computational problem, especially when dealing with large systems. However, this difficulty may be overcome by using some controllable quantum system to study another less controllable or accessible quantum system, i.e., quantum simulation. Quantum simulation promises to have applications in the study of many problems in, e.g., condensedmatter physics, highenergy physics, atomic physics, quantum chemistry, and cosmology. Quantum simulation could be implemented using quantum computers, but also with simpler, analog devices that would require less control, and therefore, would be easier to construct. A number of quantum systems such as neutral atoms, ions, polar molecules, electrons in semiconductors, superconducting circuits, nuclear spins, and photons have been proposed as quantum simulators. This review outlines the main theoretical and experimental aspects of quantum simulation and emphasizes some of the challenges and promises of this fastgrowing field.

Quantum electrodynamics in finite volume and nonrelativistic effective field theories
NASA Astrophysics Data System (ADS)
Fodor, Z.; Hoelbling, C.; Katz, S. D.; Lellouch, L.; Portelli, A.; Szabo, K. K.; Toth, B. C.
20160401
Electromagnetic effects are increasingly being accounted for in lattice quantum chromodynamics computations. Because of their longrange nature, they lead to large finitesize effects over which it is important to gain analytical control. Nonrelativistic effective field theories provide an efficient tool to describe these effects. Here we argue that some care has to be taken when applying these methods to quantum electrodynamics in a finite volume.

BOOK REVIEW: Classical Solutions in Quantum Field Theory Classical Solutions in Quantum Field Theory
NASA Astrophysics Data System (ADS)
Mann, Robert
20130201
Quantum field theory has evolved from its early beginnings as a tool for understanding the interaction of light with matter into a rather formidable technical paradigm, one that has successfully provided the mathematical underpinnings of all nongravitational interactions. Over the eight decades since it was first contemplated the methods have become increasingly more streamlined and sophisticated, yielding new insights into our understanding of the subatomic world and our abilities to make clear and precise predictions. Some of the more elegant methods have to do with nonperturbative and semiclassical approaches to the subject. The chief players here are solitons, instantons, and anomalies. Over the past three decades there has been a steady rise in our understanding of these objects and of our ability to calculate their effects and implications for the rest of quantum field theory. This book is a welcome contribution to this subject. In 12 chapters it provides a clear synthesis of the key developments in these subjects at a level accessible to graduate students that have had an introductory course to quantum field theory. In the author's own words it provides both 'a survey and an overview of this field'. The first half of the book concentrates on solitonskinks, vortices, and magnetic monopolesand their implications for the subject. The reader is led first through the simplest models in one spatial dimension, into more sophisticated cases that required more advanced topological methods. The author does quite a nice job of introducing the various concepts as required, and beginning students should be able to get a good grasp of the subject directly from the text without having to first go through the primary literature. The middle part of the book deals with the implications of these solitons for both cosmology and for duality. While the cosmological discussion is quite nice, the discussion on BPS solitons, supersymmetry and duality is rather condensed. It is

Theoretical investigation of bacteria polarizability under direct current electric fields.
PubMed
Dingari, Naga Neehar; Buie, Cullen R
20140422
We present a theoretical model to investigate the influence of soft polyelectrolyte layers on bacteria polarizability. We resolve softlayer electrokinetics by considering the pHdependent dissociation of ionogenic groups and specific interactions of ionogenic groups with the bulk electrolyte to go beyond approximating softlayer electrokinetics as surface conduction. We model the electrokinetics around a soft particle by modified PoissonNernstPlanck equations (PNP) to account for the effects of ion transport in the soft layer and electric double layer. Fluid flow is modeled by modified Stokes equations accounting for softlayer permeability. Two test cases are presented to demonstrate our model: fibrillated and unfibrillated Streptococcus salivarius bacteria. We show that electrolytic and pH conditions significantly influence the extent of softparticle polarizability in dc fields. Comparison with an approximate analytical model based on DukhinShilov theory for soft particles shows the importance of resolving softlayer electrokinetics. Insights from this study can be useful in understanding the parameters that influence softparticle dielectrophoresis in labonachip devices.

Effect of magnetic field on electron spectrum and probabilities of intraband quantum transitions in spherical quantumdotquantumwell
NASA Astrophysics Data System (ADS)
Holovatsky, V.; Bernik, I.; Yakhnevych, M.
20160901
The effect of magnetic field on electron energy spectrum, wave functions and probabilities of intraband quantum transitions in multilayered spherical quantumdotquantumwell (QDQW) CdSe/ZnS/CdSe/ZnS is studied. Computations are performed in the framework of the effective mass approximation and rectangular potential barriers model. The wave functions are expanded over the complete basis of functions obtained as exact solutions of the Schrodinger equation for the electron in QDQW without the magnetic field. It is shown that magnetic field takes off the spectrum degeneration with respect to the magnetic quantum number and changes the localization of electron in the nanostructure. The field stronger effects on the sphericallysymmetric states, especially in the case of electron location in the outer potential well. The magnetic field changes more the radial distribution of probability of electron location in QDQW than the angular one. The oscillator strengths of intraband quantum transitions are calculated as functions of the magnetic field induction and their selection rules are established.

Theoretical study of polarization insensitivity of carrierinduced refractive index change of multiple quantum well.
PubMed
Miao, Qingyuan; Zhou, Qunjie; Cui, Jun; He, PingAn; Huang, Dexiu
20141229
Characteristics of polarization insensitivity of carrierinduced refractive index change of 1.55 μm tensilestrained multiple quantum well (MQW) are theoretically investigated. A comprehensive MQW model is proposed to effectively extend the application range of previous models. The model considers the temperature variation as well as the nonuniform distribution of injected carrier in MQW. Tensilestrained MQW is expected to achieve polarization insensitivity of carrierinduced refractive index change over a wide wavelength range as temperature varies from 0°C to 40°C, while the magnitude of refractive index change keeps a large value (more than 3 × 10^{3}). And that the polarization insensitivity of refractive index change can maintain for a wide range of carrier concentration. Multiple quantum well with different material and structure parameters is anticipated to have the similar polarization insensitivity of refractive index change, which shows the design flexibility.

Theoretical study of polarization insensitivity of carrierinduced refractive index change of multiple quantum well.
PubMed
Miao, Qingyuan; Zhou, Qunjie; Cui, Jun; He, PingAn; Huang, Dexiu
20141229
Characteristics of polarization insensitivity of carrierinduced refractive index change of 1.55 μm tensilestrained multiple quantum well (MQW) are theoretically investigated. A comprehensive MQW model is proposed to effectively extend the application range of previous models. The model considers the temperature variation as well as the nonuniform distribution of injected carrier in MQW. Tensilestrained MQW is expected to achieve polarization insensitivity of carrierinduced refractive index change over a wide wavelength range as temperature varies from 0°C to 40°C, while the magnitude of refractive index change keeps a large value (more than 3 × 10^{3}). And that the polarization insensitivity of refractive index change can maintain for a wide range of carrier concentration. Multiple quantum well with different material and structure parameters is anticipated to have the similar polarization insensitivity of refractive index change, which shows the design flexibility. PMID:25607157

Entanglement of a quantum field with a dispersive medium.
PubMed
Klich, Israel
20120810
In this Letter we study the entanglement of a quantum radiation field interacting with a dielectric medium. In particular, we describe the quantum mixed state of a field interacting with a dielectric through plasma and Drude models and show that these generate very different entanglement behavior, as manifested in the entanglement entropy of the field. We also present a formula for a "Casimir" entanglement entropy, i.e., the distance dependence of the field entropy. Finally, we study a toy model of the interaction between two plates. In this model, the field entanglement entropy is divergent; however, as in the Casimir effect, its distancedependent part is finite, and the field matter entanglement is reduced when the objects are far.

Quantum mechanics. Mechanically detecting and avoiding the quantum fluctuations of a microwave field.
PubMed
Suh, J; Weinstein, A J; Lei, C U; Wollman, E E; Steinke, S K; Meystre, P; Clerk, A A; Schwab, K C
20140613
Quantum fluctuations of the light field used for continuous position detection produce stochastic backaction forces and ultimately limit the sensitivity. To overcome this limit, the backaction forces can be avoided by giving up complete knowledge of the motion, and these types of measurements are called "backaction evading" or "quantum nondemolition" detection. We present continuous twotone backaction evading measurements with a superconducting electromechanical device, realizing three longstanding goals: detection of backaction forces due to the quantum noise of a microwave field, reduction of this quantum backaction noise by 8.5 ± 0.4 decibels (dB), and measurement imprecision of a single quadrature of motion 2.4 ± 0.7 dB below the mechanical zeropoint fluctuations. Measurements of this type will find utility in ultrasensitive measurements of weak forces and nonclassical states of motion.

A quantum phase transition in a quantum external field: Superposing two magnetic phases
PubMed Central
Rams, Marek M.; Zwolak, Michael; Damski, Bogdan
20120101
We study an Ising chain undergoing a quantum phase transition in a quantum magnetic field. Such a field can be emulated by coupling the chain to a central spin initially in a superposition state. We show that – by adiabatically driving such a system – one can prepare a quantum superposition of any two ground states of the Ising chain. In particular, one can end up with the Ising chain in a superposition of ferromagnetic and paramagnetic phases – a scenario with no analogue in prior studies of quantum phase transitions. Remarkably, the resulting magnetization of the chain encodes the position of the critical point and universal critical exponents, as well as the ground state fidelity. PMID:22977730

Lorentz symmetry breaking as a quantum field theory regulator
SciTech Connect
Visser, Matt
20090715
Perturbative expansions of quantum field theories typically lead to ultraviolet (shortdistance) divergences requiring regularization and renormalization. Many different regularization techniques have been developed over the years, but most regularizations require severe mutilation of the logical foundations of the theory. In contrast, breaking Lorentz invariance, while it is certainly a radical step, at least does not damage the logical foundations of the theory. I shall explore the features of a Lorentz symmetry breaking regulator in a simple polynomial scalar field theory and discuss its implications. In particular, I shall quantify just 'how much' Lorentz symmetry breaking is required to fully regulate the quantum theory and render it finite. This scalar field theory provides a simple way of understanding many of the key features of Horava's recent article [Phys. Rev. D 79, 084008 (2009)] on 3+1 dimensional quantum gravity.

Reality, Causality, and Probability, from Quantum Mechanics to Quantum Field Theory
NASA Astrophysics Data System (ADS)
Plotnitsky, Arkady
20151001
These three lectures consider the questions of reality, causality, and probability in quantum theory, from quantum mechanics to quantum field theory. They do so in part by exploring the ideas of the key founding figures of the theory, such N. Bohr, W. Heisenberg, E. Schrödinger, or P. A. M. Dirac. However, while my discussion of these figures aims to be faithful to their thinking and writings, and while these lectures are motivated by my belief in the helpfulness of their thinking for understanding and advancing quantum theory, this project is not driven by loyalty to their ideas. In part for that reason, these lectures also present different and even conflicting ways of thinking in quantum theory, such as that of Bohr or Heisenberg vs. that of Schrödinger. The lectures, most especially the third one, also consider new physical, mathematical, and philosophical complexities brought in by quantum field theory visàvis quantum mechanics. I close by briefly addressing some of the implications of the argument presented here for the current state of fundamental physics.

Quantum field theory of the Casimir effect for real media
SciTech Connect
Mostepanenko, V.M.; Trunov, N.N.
19851101
The quantum field theory is developed for the corrections to the Casimir force arising when the field penetrates the material of the plates. A new type of divergence arising from the corresponding modification of the boundary conditions is analyzed. General expressions are obtained for the vacuum energy of the electromagnetic field in the space between nonideal plates, and the actual corrections to the Casimir force are calculated in firstorder perturbation theory in the penetration depth.

New method for calculating binding energies in quantum mechanics and quantum field theories
SciTech Connect
Gat, G.; Rosenstein, B. Institute of Physics, Academia Sinica, Taipei, 11529 )
19930104
We propose a systematic perturbative method for calculating the binding energy of threshold bound statesstates which exist for arbitrary small coupling. The starting point is a (regularized) free theory. Explicit calculations are performed for quantum mechanics with arbitrary shortrange potential in 1D and various (1+1)dimensional quantum field theories. We check the method by comparing the results with exact formulas available in solvable models.

Quantum reaction boundary to mediate reactions in laser fields.
PubMed
Kawai, Shinnosuke; Komatsuzaki, Tamiki
20110114
Dynamics of passage over a saddle is investigated for a quantum system under the effect of timedependent external field (laser pulse). We utilize the recently developed theories of nonlinear dynamics in the saddle region, and extend them to incorporate both timedependence of the external field and quantum mechanical effects of the system. Anharmonic couplings and laser fields with any functional form of time dependence are explicitly taken into account. As the theory is based on the Weyl expression of quantum mechanics, interpretation is facilitated by the classical phase space picture, while no "classical approximation" is involved. We introduce a quantum reactivity operator to extract the reactive part of the system. In a model system with an optimally controlled laser field for the reaction, it is found that the boundary of the reaction in the phase space, extracted by the reactivity operator, is modulated with time by the effect of the laser field, to "catch" the system excited in the reactant region, and then to "release" it into the product region. This method provides new insights in understanding the origin of optimal control of chemical reactions by laser fields.

Effects of a scalar scaling field on quantum mechanics
NASA Astrophysics Data System (ADS)
Benioff, Paul
20160701
This paper describes the effects of a complex scalar scaling field on quantum mechanics. The field origin is an extension of the gauge freedom for basis choice in gauge theories to the underlying scalar field. The extension is based on the idea that the value of a number at one space time point does not determine the value at another point. This, combined with the description of mathematical systems as structures of different types, results in the presence of separate number fields and vector spaces as structures, at different space time locations. Complex number structures and vector spaces at each location are scaled by a complex space time dependent scaling factor. The effect of this scaling factor on several physical and geometric quantities has been described in other work. Here the emphasis is on quantum mechanics of one and two particles, their states and properties. Multiparticle states are also briefly described. The effect shows as a complex, nonunitary, scalar field connection on a fiber bundle description of nonrelativistic quantum mechanics. The lack of physical evidence for the presence of this field so far means that the coupling constant of this field to fermions is very small. It also means that the gradient of the field must be very small in a local region of cosmological space and time. Outside this region, there are no restrictions on the field gradient.

Electric field engineering using quantumsizeeffecttuned heterojunctions
NASA Astrophysics Data System (ADS)
Adinolfi, V.; Ning, Z.; Xu, J.; Masala, S.; Zhitomirsky, D.; Thon, S. M.; Sargent, E. H.
20130701
A quantum junction solar cell architecture was recently reported that employs colloidal quantum dots (CQDs) on each side of the pn junction. This architecture extends the range of design opportunities for CQD photovoltaics, since the bandgap can be tuned across the lightabsorbing semiconductor layer via control over CQD size, employing solutionprocessed, roomtemperature fabricated materials. We exploit this feature by designing and demonstrating a fieldenhanced heterojunction architecture. We optimize the electric field profile within the solar cell through bandgap engineering, thereby improving carrier collection and achieving an increased open circuit voltage, resulting in a 12% improvement in power conversion efficiency.

Mirror moving in quantum vacuum of a massive scalar field
NASA Astrophysics Data System (ADS)
Wang, Qingdi; Unruh, William G.
20150901
We present a mirror model moving in the quantum vacuum of a massive scalar field and study its motion under infinitely fluctuating quantum vacuum stress. The model is similar to the one in [Q. Wang and W. G. Unruh, Motion of a mirror under infinitely fluctuating quantum vacuum stress Phys. Rev. D 89, 085009 (2014).], but this time there is no divergent effective mass to weaken the effect of divergent vacuum energy density. We show that this kind of weakening is not necessary. The vacuum friction and strong anticorrelation property of the quantum vacuum are enough to confine the mirror's position fluctuations. This is another example illustrating that while the actual value of the vacuum energy can be physically significant even for a nongravitational system, and that its infinite value makes sense, but that its physical effect can be small despite this infinity.

The polarization efficiency of the emitted light in quantum dots under the presence of external magnetic field.
NASA Astrophysics Data System (ADS)
Stavrou, V. N.
20161101
A theoretical description of the light polarization within asymmetric selfassembled coupled quantum dots (SACQDs) in the presence of an external magnetic field, is presented. The electron and hole wavefunctions and their energy eigenvalues have been evaluated by considering ellipsoidal shaped quantum dots (QDs). Predictions of circularly light polarization for specific polarization planes, a variety of different QD geometries and the presence of an external magnetic field are displayed and compared. The results show that for some specific polarization planes the circularly light polarization is very sensitive mainly to the size of the QDs asymmetry, the interdot distance and the external magnetic field.

Quantum field theory in spaces with closed timelike curves
NASA Astrophysics Data System (ADS)
Boulware, David G.
19921101
Gott spacetime has closed timelike curves, but no locally anomalous stress energy. A complete orthonormal set of eigenfunctions of the wave operator is found in the special case of a spacetime in which the total deficit angle is 2π. A scalar quantum field theory is constructed using these eigenfunctions. The resultant interacting quantum field theory is not unitary because the field operators can create real, onshell, particles in the noncausal region. These particles propagate for finite proper time accumulating an arbitrary phase before being annihilated at the same spacetime point as that at which they were created. As a result, the effective potential within the noncausal region is complex, and probability is not conserved. The stress tensor of the scalar field is evaluated in the neighborhood of the Cauchy horizon; in the case of a sufficiently small Compton wavelength of the field, the stress tensor is regular and cannot prevent the formation of the Cauchy horizon.

A molecularfield approximation for quantum crystals. Ph.D. Thesis; [considering ground state properties
NASA Technical Reports Server (NTRS)
Danilowicz, R.
19730101
Groundstate properties of quantum crystals have received considerable attention from both theorists and experimentalists. The theoretical results have varied widely with the Monte Carlo calculations being the most successful. The molecular field approximation yields groundstate properties which agree closely with the Monte Carlo results. This approach evaluates the dynamical behavior of each pair of molecules in the molecular field of the other N2 molecules. In addition to predicting groundstate properties that agree well with experiment, this approach yields data on the relative importance of interactions of different nearest neighbor pairs.

Toward a quantum theory of tachyon fields
NASA Astrophysics Data System (ADS)
Schwartz, Charles
20160301
We construct momentum space expansions for the wave functions that solve the KleinGordon and Dirac equations for tachyons, recognizing that the mass shell for such fields is very different from what we are used to for ordinary (slower than light) particles. We find that we can postulate commutation or anticommutation rules for the operators that lead to physically sensible results: causality, for tachyon fields, means that there is no connection between spacetime points separated by a timelike interval. Calculating the conserved charge and fourmomentum for these fields allows us to interpret the number operators for particles and antiparticles in a consistent manner; and we see that helicity plays a critical role for the spinor field. Some questions about Lorentz invariance are addressed and some remain unresolved; and we show how to handle the group representation for tachyon spinors.

Quantum synchrotron spectra from semirelativistic electrons in teragauss magnetic fields
NASA Technical Reports Server (NTRS)
Brainerd, J. J.
19870101
Synchrotron spectra are calculated from quantum electrodynamic transition rates for thermal and powerlaw electron distributions. It is shown that quantum effects appear in thermal spectra when the photon energy is greater than the electron temperature, and in powerlaw spectra when the electron energy in units of the electron rest mass times the magnetic field strength in units of the critical field strength is of order unity. These spectra are compared with spectra calculated from the ultrarelativistic approximation for synchrotron emission. It is found that the approximation for the powerlaw spectra is good, and the approximation for thermal spectra produces the shape of the spectrum accurately but fails to give the correct normalization. Single photon pair creation masks the quantum effects for powerlaw distributions, so only modifications to thermal spectra are important for gammaray bursts.

Decoherence and thermalization of a pure quantum state in quantum field theory.
PubMed
Giraud, Alexandre; Serreau, Julien
20100611
We study the realtime evolution of a selfinteracting O(N) scalar field initially prepared in a pure, coherent quantum state. We present a complete solution of the nonequilibrium quantum dynamics from a 1/N expansion of the twoparticleirreducible effective action at nexttoleading order, which includes scattering and memory effects. We demonstrate that, restricting one's attention (or ability to measure) to a subset of the infinite hierarchy of correlation functions, one observes an effective loss of purity or coherence and, on longer time scales, thermalization. We point out that the physics of decoherence is well described by classical statistical field theory.

Dynamical meanfield theory from a quantum chemical perspective.
PubMed
Zgid, Dominika; Chan, Garnet KinLic
20110301
We investigate the dynamical meanfield theory (DMFT) from a quantum chemical perspective. Dynamical meanfield theory offers a formalism to extend quantum chemical methods for finite systems to infinite periodic problems within a local correlation approximation. In addition, quantum chemical techniques can be used to construct new ab initio Hamiltonians and impurity solvers for DMFT. Here, we explore some ways in which these things may be achieved. First, we present an informal overview of dynamical meanfield theory to connect to quantum chemical language. Next, we describe an implementation of dynamical meanfield theory where we start from an ab initio HartreeFock Hamiltonian that avoids double counting issues present in many applications of DMFT. We then explore the use of the configuration interaction hierarchy in DMFT as an approximate solver for the impurity problem. We also investigate some numerical issues of convergence within DMFT. Our studies are carried out in the context of the cubic hydrogen model, a simple but challenging test for correlation methods. Finally, we finish with some conclusions for future directions.

Generating functionals for quantum field theories with random potentials
NASA Astrophysics Data System (ADS)
Jain, Mudit; Vanchurin, Vitaly
20160101
We consider generating functionals for computing correlators in quantum field theories with random potentials. Examples of such theories include cosmological systems in context of the string theory landscape (e.g. cosmic inflation) or condensed matter systems with quenched disorder (e.g. spin glass). We use the socalled replica trick to define two different generating functionals for calculating correlators of the quantum fields averaged over a given distribution of random potentials. The first generating functional is appropriate for calculating averaged (inout) amplitudes and involves a single replica of fields, but the replica limit is taken to an (unphysical) negative one number of fields outside of the path integral. When the number of replicas is doubled the generating functional can also be used for calculating averaged probabilities (squared amplitudes) using the inin construction. The second generating functional involves an infinite number of replicas, but can be used for calculating both inout and inin correlators and the replica limits are taken to only a zero number of fields. We discuss the formalism in details for a single real scalar field, but the generalization to more fields or to different types of fields is straightforward. We work out three examples: one where the mass of scalar field is treated as a random variable and two where the functional form of interactions is random, one described by a Gaussian random field and the other by a Euclidean action in the field configuration space.

Electric field for tuning quantum entanglement in supported clusters.
PubMed
Brovko, Oleg O; Farberovich, Oleg V; Stepanyuk, Valeri S
20140801
We show that quantum entanglement, nowadays so widely observed and used in a multitude of systems, can be traced in the atomic spins of metal clusters supported on metal surfaces. Most importantly, we show that it can be voluntarily altered with external electric fields. We use a combination of ab initio and model HeisenbergDiracVan Vleck quantum spin Hamiltonian calculations to show, with the example of a prototype system (Mn dimers on Ag(0 0 1) surface), that, in an inherently unentangled system an electric field can 'switch on' the entanglement and significantly change its critical temperature parameter. The physical mechanism allowing such rigorous control of entanglement by an electric field is the fieldinduced change in the internal magnetic coupling of the supported nanostructure.

Theoretical study of quantum capacitance and associated delay in armchairedge graphene nanoribbons
NASA Astrophysics Data System (ADS)
Hassan, Asif; Hossain, Md. Faruque; Rana, Md. Sohel; Kouzani, Abbas Z.
20150901
This work presents a comprehensive investigation of the quantum capacitance and the associated effects on the carrier transit delay in armchairedge graphene nanoribbons (AGNRs) based on semianalytical method. We emphasize on the realistic analysis of bandgap with taking edge effects into account by means of modified tight binding (TB) model. The results show that the edge effects have significant influence in defining the bandgap which is a necessary input in the accurate analyses of capacitance. The quantum capacitance is discussed in both nondegenerate (low gate voltage) and degenerate (high gate voltage) regimes. We observe that the classical capacitance limits the total gate (external) capacitance in the degenerate regime, whereas, quantum capacitance limits the external gate capacitance in the nondegenerate regime. The influence of gate capacitances on the gate delay is studied extensively to demonstrate the optimization of switching time. Moreover, the highfield behavior of a GNR is studied in the degenerate and nondegenerate regimes. We find that a smaller intrinsic capacitance appears in the channel due to high velocity carrier, which limits the quantum capacitance and thus limit the gate delay. Such detail analysis of GNRs considering a realistic model would be useful for the optimized design of GNRbased nanoelectronic devices.

How to take particle physics seriously: A further defence of axiomatic quantum field theory
NASA Astrophysics Data System (ADS)
Fraser, Doreen
Further arguments are offered in defence of the position that the variant of quantum field theory (QFT) that should be subject to interpretation and foundational analysis is axiomatic quantum field theory. I argue that the successful application of renormalization group (RG) methods within alternative formulations of QFT illuminates the empirical content of QFT, but not the theoretical content. RG methods corroborate the point of view that QFT is a case of the underdetermination of theory by empirical evidence. I also urge caution in extrapolating interpretive conclusions about QFT from the application of RG methods in other contexts (e.g., condensed matter physics). This paper replies to criticisms advanced by David Wallace, but aims to be selfcontained.

Binding energy of excitons in inhomogeneous quantum dots under uniform electric field
NASA Astrophysics Data System (ADS)
El Khamkhami, J.; Feddi, E.; Assaid, E.; Dujardin, F.; Stébé, B.; Diouri, J.
20021001
Excitons in inhomogenous quantum nanospheres have been theoretically studied within the effective mass approximation. An infinite deep potential has been used to describe the effects of quantum confinement. The binding energy with or without an applied electric field is determined by the Ritz variational method taking into account the correlation between the electron and the hole in the trial wave function. It appears that the binding energy strongly depends on the core and shell radii. The existence of a radius ratio critical value has been shown: it may be used to distinguish between tridimensional and spherical surface confinement. The influence of a uniform electric field is analyzed. It has been found that the Stark effect appears even for very small sizes and that the energy shift is more significant when the exciton is near the spherical surface.

Fractional Spin Fluctuations as a Precursor of Quantum Spin Liquids: Majorana Dynamical MeanField Study for the Kitaev Model
NASA Astrophysics Data System (ADS)
Yoshitake, Junki; Nasu, Joji; Motome, Yukitoshi
20161001
Experimental identification of quantum spin liquids remains a challenge, as the pristine nature is to be seen in asymptotically low temperatures. We here theoretically show that the precursor of quantum spin liquids appears in the spin dynamics in the paramagnetic state over a wide temperature range. Using the cluster dynamical meanfield theory and the continuoustime quantum Monte Carlo method, which are newly developed in the Majorana fermion representation, we calculate the dynamical spin structure factor, relaxation rate in nuclear magnetic resonance, and magnetic susceptibility for the honeycomb Kitaev model whose ground state is a canonical example of the quantum spin liquid. We find that dynamical spin correlations show peculiar temperature and frequency dependence even below the temperature where static correlations saturate. The results provide the experimentally accessible symptoms of the fluctuating fractionalized spins evincing the quantum spin liquids.

Perturbative quantum gravity in double field theory
NASA Astrophysics Data System (ADS)
Boels, Rutger H.; Horst, Christoph
20160401
We study perturbative general relativity with a twoform and a dilaton using the double field theory formulation which features explicit index factorisation at the Lagrangian level. Explicit checks to known tree level results are performed. In a natural covariant gauge a ghostlike scalar which contributes even at tree level is shown to decouple consistently as required by perturbative unitarity. In addition, a lightcone gauge is explored which bypasses the problem altogether. Using this gauge to study BCFW onshell recursion, we can show that most of the Ddimensional tree level Smatrix of the theory, including all pure graviton scattering amplitudes, is reproduced by the double field theory. More generally, we argue that the integrand may be reconstructed from its single cuts and provide limited evidence for offshell cancellations in the Feynman graphs. As a straightforward application of the developed technology double field theorylike expressions for four field string corrections are derived.

Role of electrical field in quantum Hall effect of graphene
NASA Astrophysics Data System (ADS)
Luo, Ji
20130101
The ballistic motion of carriers of graphene in an orthogonal electromagnetic field is investigated to explain quantum Hall effect of graphene under experimental conditions. With the electrical field, all electronic eigenstates have the same expectation value of the velocity operator, or classically, all carriers move in cycloidlike curves with the same average velocity. This velocity is the origin of the Hall conductance and its magnitude is just appropriate so that the quantized Hall conductance is exactly independent of the external field. Electrical field changes each Landau level into a bundle of energies. Hall conductance plateaus occur in small fields as bundle gaps exist and are destroyed in intermediate fields as bundles overlap. As the electrical field tends to the critical point, all bundles have the same width, and bundle gaps increase to infinity rapidly. As a result, saturation of the Hall conductance may be observed. Electrical field thus demonstrates nonlinear effects on the Hall conductance.

Relativistic and Field Theoretic Effects in the Nuclear ManyBody Problem.
NASA Astrophysics Data System (ADS)
Poorakkiat, Chaisingh
Field theoretic effects of a nucleon of an oxygen 17 have been studied. A computational scheme involving sigma and omega mesons has been set up. It employs the Furry picture of quantum field theory along with an introduction of vector and scalar WoodsSaxon potentials. Use of an adiabatic switching on an interaction leads to an energy shift in form of a symmetric GellMann and Low formula which contains the S matrix. The S matrix allows an expansion in terms of Feynman diagrams which in turn enables us to write a perturbative series analogous to that in manybody perturbation theory. Retardation effects and the firstorder energy correction E_{1} of two valence states, 1d_{5/2} and 2s_{1/2}, have been calculated from the diagrams. The selfenergy of the 1s _{1/2} state is investigated along with the use of a renormalization technique. The retardation effects are small in the order of 10 kev while the selfenergy and E_{1} corrections are big in the order of 700 and 10 Mev respectively.

Magnetic Field Control of the Quantum Chaotic Dynamics of Hydrogen Analogs in an Anisotropic Crystal Field
SciTech Connect
Zhou Weihang; Chen Zhanghai; Zhang Bo; Yu, C. H.; Lu Wei; Shen, S. C.
20100709
We report magnetic field control of the quantum chaotic dynamics of hydrogen analogues in an anisotropic solid state environment. The chaoticity of the system dynamics was quantified by means of energy level statistics. We analyzed the magnetic field dependence of the statistical distribution of the impurity energy levels and found a smooth transition between the Poisson limit and the Wigner limit, i.e., transition between regular Poisson and fully chaotic Wigner dynamics. The effect of the crystal field anisotropy on the quantum chaotic dynamics, which manifests itself in characteristic transitions between regularity and chaos for different field orientations, was demonstrated.

Dynamical meanfield theory for quantum chemistry.
PubMed
Lin, Nan; Marianetti, C A; Millis, Andrew J; Reichman, David R
20110301
The dynamical meanfield concept of approximating an unsolvable manybody problem in terms of the solution of an auxiliary quantum impurity problem, introduced to study bulk materials with a continuous energy spectrum, is here extended to molecules, i.e., finite systems with a discrete energy spectrum. The application to small clusters of hydrogen atoms yields ground state energies which are competitive with leading quantum chemical approaches at intermediate and large interatomic distances as well as good approximations to the excitation spectrum.

Nuclear magnetic resonance proton dipolar order relaxation in thermotropic liquid crystals: A quantum theoretical approach
NASA Astrophysics Data System (ADS)
Zamar, R. C.; Mensio, O.
20041201
By means of the JeenerBroekaert nuclear magnetic resonance pulse sequence, the proton spin system of a liquid crystal can be prepared in quasiequilibrium states of high dipolar order, which relax to thermal equilibrium with the molecular environment with a characteristic time (T1D). Previous studies of the Larmor frequency and temperature dependence of T1D in thermotropic liquid crystals, that included field cycling and conventional highfield experiments, showed that the slow hydrodynamic modes dominate the behavior of T1D, even at high Larmor frequencies. This noticeable predominance of the cooperative fluctuations (known as order fluctuations of the director, OFD) could not be explained by standard models based on the spinlattice relaxation theory in the limit of high temperature (weak order). This fact points out the necessity of investigating the role of the quantum terms neglected in the usual high temperature theory of dipolar order relaxation. In this work, we present a generalization of the proton dipolar order relaxation theory for highly correlated systems, which considers all the spins belonging to correlated domains as an open quantum system interacting with quantum bath. As starting point, we deduce a formulation of the Markovian master equation of relaxation for the statistical spin operator, valid for all temperatures, which is suitable for introducing a dipolar spin temperature in the quantum regime, without further assumptions about the form of the spinlattice Hamiltonian. In order to reflect the slow dynamics occurring in correlated systems, we lift the usual shortcorrelationtime assumption by including the average over the motion of the dipolar Hamiltonian together with the Zeeman Hamiltonian into the time evolution operator. In this way, we calculate the time dependence of the spin operators in the interaction picture in a closed form, valid for high magnetic fields, bringing into play the spinspin interactions within the microscopic time

Towards experimental quantumfield tomography with ultracold atoms
PubMed Central
Steffens, A.; Friesdorf, M.; Langen, T.; Rauer, B.; Schweigler, T.; Hübener, R.; Schmiedmayer, J.; Riofrío, C.A.; Eisert, J.
20150101
The experimental realization of largescale manybody systems in atomicoptical architectures has seen immense progress in recent years, rendering full tomography tools for state identification inefficient, especially for continuous systems. To work with these emerging physical platforms, new technologies for state identification are required. Here we present first steps towards efficient experimental quantumfield tomography. Our procedure is based on the continuous analogues of matrixproduct states, ubiquitous in condensedmatter theory. These states naturally incorporate the locality present in realistic physical settings and are thus prime candidates for describing the physics of locally interacting quantum fields. To experimentally demonstrate the power of our procedure, we quench a onedimensional Bose gas by a transversal split and use our method for a partial quantumfield reconstruction of the farfromequilibrium states of this system. We expect our technique to play an important role in future studies of continuous quantum manybody systems. PMID:26138511

Towards experimental quantumfield tomography with ultracold atoms.
PubMed
Steffens, A; Friesdorf, M; Langen, T; Rauer, B; Schweigler, T; Hübener, R; Schmiedmayer, J; Riofrío, C A; Eisert, J
20150703
The experimental realization of largescale manybody systems in atomicoptical architectures has seen immense progress in recent years, rendering full tomography tools for state identification inefficient, especially for continuous systems. To work with these emerging physical platforms, new technologies for state identification are required. Here we present first steps towards efficient experimental quantumfield tomography. Our procedure is based on the continuous analogues of matrixproduct states, ubiquitous in condensedmatter theory. These states naturally incorporate the locality present in realistic physical settings and are thus prime candidates for describing the physics of locally interacting quantum fields. To experimentally demonstrate the power of our procedure, we quench a onedimensional Bose gas by a transversal split and use our method for a partial quantumfield reconstruction of the farfromequilibrium states of this system. We expect our technique to play an important role in future studies of continuous quantum manybody systems.

Nonlinear Riccati equations as a unifying link between linear quantum mechanics and other fields of physics
NASA Astrophysics Data System (ADS)
Schuch, Dieter
20140401
Theoretical physics seems to be in a kind of schizophrenic state. Many phenomena in the observable macroscopic world obey nonlinear evolution equations, whereas the microscopic world is governed by quantum mechanics, a fundamental theory that is supposedly linear. In order to combine these two worlds in a common formalism, at least one of them must sacrifice one of its dogmas. I claim that linearity in quantum mechanics is not as essential as it apparently seems since quantum mechanics can be reformulated in terms of nonlinear Riccati equations. In a first step, it will be shown where complex Riccati equations appear in timedependent quantum mechanics and how they can be treated and compared with similar spacedependent Riccati equations in supersymmetric quantum mechanics. Furthermore, the timeindependent Schrödinger equation can also be rewritten as a complex Riccati equation. Finally, it will be shown that (real and complex) Riccati equations also appear in many other fields of physics, like statistical thermodynamics and cosmology.

Quantum fields and poisson processes: Interaction of a cutoff boson field with a quantum particle
NASA Astrophysics Data System (ADS)
Bertrand, Jacqueline; Gaveau, Bernard; Rideau, Guy
19850101
The solution of the Schrödinger equation for a boson field interacting with a quantum particle is written as an expectation on a Poisson process counting the variations of the bosonoccupation numbers for each momentum. An energy cutoff is needed for the expectation to be meaningful.

Wavefunction dynamics in a quantumdot electron pump under a high magnetic field
NASA Astrophysics Data System (ADS)
Ryu, Sungguen; Kataoka, Masaya; Sim, HeungSun
20150301
A quantumdot electron pump, formed and operated by applying timedependent potential barriers to a two dimensional electron gas system, provides a promising redefinition of ampere. The pump operation consists of capturing an electron from a reservoir into a quantum dot and ejecting it to another reservoir. The capturing process has been theoretically understood by a semiclassical treatment of the tunneling between the dot and reservoir. But the dynamics of the wavefunction of the captured electron in the ejection process has not been theoretically addressed, although it is useful for enhancing pump accuracy and for utilizing the pump as a singleelectron source for mesoscopic quantum electron devices. We study the dynamics under a strong magnetic field that leads to magnetic confinement of the captured electron, which dominates over the electrostatic confinement of the dot. We find that the wave packet of the captured electron has the Gaussian form with the width determined by the strength of the magnetic field, and that the time evolution of the packet follows the classical drift motion, with maintaining the Gaussian form. We discuss the possible signatures of the wave packet dynamics in experiments.

Quantum mechanical force field for water with explicit electronic polarization
PubMed Central
Han, Jaebeom; Mazack, Michael J. M.; Zhang, Peng; Truhlar, Donald G.; Gao, Jiali
20130101
A quantum mechanical force field (QMFF) for water is described. Unlike traditional approaches that use quantum mechanical results and experimental data to parameterize empirical potential energy functions, the present QMFF uses a quantum mechanical framework to represent intramolecular and intermolecular interactions in an entire condensedphase system. In particular, the internal energy terms used in molecular mechanics are replaced by a quantum mechanical formalism that naturally includes electronic polarization due to intermolecular interactions and its effects on the force constants of the intramolecular force field. As a quantum mechanical force field, both intermolecular interactions and the Hamiltonian describing the individual molecular fragments can be parameterized to strive for accuracy and computational efficiency. In this work, we introduce a polarizable molecular orbital model Hamiltonian for water and for oxygen and hydrogencontaining compounds, whereas the electrostatic potential responsible for intermolecular interactions in the liquid and in solution is modeled by a threepoint charge representation that realistically reproduces the total molecular dipole moment and the local hybridization contributions. The present QMFF for water, which is called the XP3P (explicit polarization with threepointcharge potential) model, is suitable for modeling both gasphase clusters and liquid water. The paper demonstrates the performance of the XP3P model for water and proton clusters and the properties of the pure liquid from about 900 × 106 selfconsistentfield calculations on a periodic system consisting of 267 water molecules. The unusual dipole derivative behavior of water, which is incorrectly modeled in molecular mechanics, is naturally reproduced as a result of an electronic structural treatment of chemical bonding by XP3P. We anticipate that the XP3P model will be useful for studying proton transport in solution and solid phases as well as across

Quantum mechanical force field for water with explicit electronic polarization.
PubMed
Han, Jaebeom; Mazack, Michael J M; Zhang, Peng; Truhlar, Donald G; Gao, Jiali
20130801
A quantum mechanical force field (QMFF) for water is described. Unlike traditional approaches that use quantum mechanical results and experimental data to parameterize empirical potential energy functions, the present QMFF uses a quantum mechanical framework to represent intramolecular and intermolecular interactions in an entire condensedphase system. In particular, the internal energy terms used in molecular mechanics are replaced by a quantum mechanical formalism that naturally includes electronic polarization due to intermolecular interactions and its effects on the force constants of the intramolecular force field. As a quantum mechanical force field, both intermolecular interactions and the Hamiltonian describing the individual molecular fragments can be parameterized to strive for accuracy and computational efficiency. In this work, we introduce a polarizable molecular orbital model Hamiltonian for water and for oxygen and hydrogencontaining compounds, whereas the electrostatic potential responsible for intermolecular interactions in the liquid and in solution is modeled by a threepoint charge representation that realistically reproduces the total molecular dipole moment and the local hybridization contributions. The present QMFF for water, which is called the XP3P (explicit polarization with threepointcharge potential) model, is suitable for modeling both gasphase clusters and liquid water. The paper demonstrates the performance of the XP3P model for water and proton clusters and the properties of the pure liquid from about 900 × 10(6) selfconsistentfield calculations on a periodic system consisting of 267 water molecules. The unusual dipole derivative behavior of water, which is incorrectly modeled in molecular mechanics, is naturally reproduced as a result of an electronic structural treatment of chemical bonding by XP3P. We anticipate that the XP3P model will be useful for studying proton transport in solution and solid phases as well as across

Quantum field theory for condensation of bosons and fermions
SciTech Connect
De Souza, Adriano N.; Filho, Victo S.
20130325
In this brief review, we describe the formalism of the quantum field theory for the analysis of the condensation phenomenon in bosonic systems, by considering the cases widely verified in laboratory of trapped gases as condensate states, either with attractive or with repulsive twobody interactions. We review the mathematical formulation of the quantum field theory for many particles in the meanfield approximation, by adopting contact interaction potential. We also describe the phenomenon of condensation in the case of fermions or the degenerate Fermi gas, also verified in laboratory in the crossover BECBCS limit. We explain that such a phenomenon, equivalent to the bosonic condensation, can only occur if we consider the coupling of particles in pairs behaving like bosons, as occurs in the case of Cooper's pairs in superconductivity.

Loop quantum gravity coupled to a scalar field
NASA Astrophysics Data System (ADS)
Lewandowski, Jerzy; Sahlmann, Hanno
20160101
We consider the model of gravity coupled to the KleinGordon time field. We do not deparametrize the theory using the scalar field before quantization, but quantize all degrees of freedom. Several new results for loop quantum gravity are obtained: (i) a Hilbert space for the gravitymatter system and a nonstandard representation of the scalar field thereon is constructed, (ii) a new operator for the scalar constraint of the coupled system is defined and investigated, (iii) methods for solving the constraint are developed. Commutators of the new quantum constraint operators correspond to the quantization of the Poisson bracket. This, however, poses problems for finding solutions. Hence the states we consider—and perhaps the whole setup—still needs some improvement. As a side result we describe a representation of the gravitational degrees of freedom in which the flux is diagonal. This representation is related to the BF theory vacuum of Dittrich and Geiller.

Quantum entanglement of local operators in conformal field theories.
PubMed
Nozaki, Masahiro; Numasawa, Tokiro; Takayanagi, Tadashi
20140321
We introduce a series of quantities which characterize a given local operator in any conformal field theory from the viewpoint of quantum entanglement. It is defined by the increased amount of (Rényi) entanglement entropy at late time for an excited state defined by acting the local operator on the vacuum. We consider a conformal field theory on an infinite space and take the subsystem in the definition of the entanglement entropy to be its half. We calculate these quantities for a free massless scalar field theory in two, four and six dimensions. We find that these results are interpreted in terms of quantum entanglement of a finite number of states, including EinsteinPodolskyRosen states. They agree with a heuristic picture of propagations of entangled particles.

Reconstruction in quantum field theory with a fundamental length
SciTech Connect
Soloviev, M. A.
20100915
In this paper, we establish an analog of Wightman's reconstruction theorem for nonlocal quantum field theory with a fundamental length. In our setting, the Wightman generalized functions are defined on test functions analytic in a complex lneighborhood of the real space and are localizable at scales large compared to l. The causality condition is formulated as continuity of the field commutator in an appropriate topology associated with the light cone. We prove that the relevant function spaces are nuclear and derive the kernel theorems for the corresponding classes of multilinear functionals, which provides the basis for the reconstruction procedure. Special attention is given to the accurate determination of the domain of the reconstructed quantum fields in the Hilbert space of states. We show that the primitive common invariant domain must be suitably extended to implement the (quasi)localizability and causality conditions.

Group field theories for all loop quantum gravity
NASA Astrophysics Data System (ADS)
Oriti, Daniele; Ryan, James P.; Thürigen, Johannes
20150201
Group field theories represent a second quantized reformulation of the loop quantum gravity state space and a completion of the spin foam formalism. States of the canonical theory, in the traditional continuum setting, have support on graphs of arbitrary valence. On the other hand, group field theories have usually been defined in a simplicial context, thus dealing with a restricted set of graphs. In this paper, we generalize the combinatorics of group field theories to cover all the loop quantum gravity state space. As an explicit example, we describe the group field theory formulation of the KKL spin foam model, as well as a particular modified version. We show that the use of tensor model tools allows for the most effective construction. In order to clarify the mathematical basis of our construction and of the formalisms with which we deal, we also give an exhaustive description of the combinatorial structures entering spin foam models and group field theories, both at the level of the boundary states and of the quantum amplitudes.

Electric field geometries dominate quantum transport coupling in silicon nanoring
SciTech Connect
Lee, TsungHan Email: sfhu.hu@gmail.com; Hu, ShuFen Email: sfhu.hu@gmail.com
20140328
Investigations on the relation between the geometries of silicon nanodevices and the quantum phenomenon they exhibit, such as the Aharonov–Bohm (AB) effect and the Coulomb blockade, were conducted. An arsenic doped silicon nanoring coupled with a nanowire by electron beam lithography was fabricated. At 1.47 K, Coulomb blockade oscillations were observed under modulation from the top gate voltage, and a periodic AB oscillation of ΔB = 0.178 T was estimated for a ring radius of 86 nm under a high sweeping magnetic field. Modulating the flat top gate and the pointed side gate was performed to cluster and separate the many electron quantum dots, which demonstrated that quantum confinement and interference effects coexisted in the doped silicon nanoring.

The successful merger of theoretical thermochemistry with fragmentbased methods in quantum chemistry.
PubMed
Ramabhadran, Raghunath O; Raghavachari, Krishnan
20141216
CONSPECTUS: Quantum chemistry and electronic structure theory have proven to be essential tools to the experimental chemist, in terms of both a priori predictions that pave the way for designing new experiments and rationalizing experimental observations a posteriori. Translating the wellestablished success of electronic structure theory in obtaining the structures and energies of small chemical systems to increasingly larger molecules is an exciting and ongoing central theme of research in quantum chemistry. However, the prohibitive computational scaling of highly accurate ab initio electronic structure methods poses a fundamental challenge to this research endeavor. This scenario necessitates an indirect fragmentbased approach wherein a large molecule is divided into small fragments and is subsequently reassembled to compute its energy accurately. In our quest to further reduce the computational expense associated with the fragmentbased methods and overall enhance the applicability of electronic structure methods to large molecules, we realized that the broad ideas involved in a different area, theoretical thermochemistry, are transferable to the area of fragmentbased methods. This Account focuses on the effective merger of these two disparate frontiers in quantum chemistry and how new concepts inspired by theoretical thermochemistry significantly reduce the total number of electronic structure calculations needed to be performed as part of a fragmentbased method without any appreciable loss of accuracy. Throughout, the generalized connectivity based hierarchy (CBH), which we developed to solve a longstanding problem in theoretical thermochemistry, serves as the linchpin in this merger. The accuracy of our method is based on two strong foundations: (a) the apt utilization of systematic and sophisticated errorcanceling schemes via CBH that result in an optimal cutting scheme at any given level of fragmentation and (b) the use of a less expensive second

Democracy of internal symmetries in supersymmetrical quantum field theory
SciTech Connect
Lopuszanski, J.T.
19811201
The freedom of choice of some discrete and internal symmetries in the supersymmetric, massive, interacting quantum field theory is discussed. It is shown that the discrete symmetry consisting of changing the sign of some (not all) scalar fields is incompatible with the supersymmetric structure of the theory. It is further demonstrated that an internal symmetry which transforms only some of the fields of fixed spin leaving the other fields invariant and which acts nontrivially on the supercharges can not be admitted as a symmetry; although it can be a good internal symmetry in absence of supersymmetric covariance. Moreover, in case of a model consisting of scalar, spinor and vector fields even a symmetry which transforms all of the scalar (vector) fields leaving spinor and vector (scalar) fields unaffected is ruled out provided it acts nontrivially on some of the supercharges.

Philosophy of scaling the quantum mechanical molecular force field versus philosophy of solving the inverse vibrational problem
NASA Astrophysics Data System (ADS)
Panchenko, Yurii N.; De Maré, George R.
20020601
The peculiarities characterising the traditional approach used in calculational vibrational spectroscopy and the approach based on using scaled quantum mechanical force fields are considered. Some results on the determination of the equilibrium geometry of benzene in both the harmonic approximation and in the approximation taking into account the kinematic and dynamic anharmonicity corrections by solving the inverse vibrational problem are discussed. Using the quantum mechanical force fields of the C 2F 6 molecule, calculated at three different theoretical levels as an example, the results of the determination of scale factors by different mathematical techniques are compared.

On observation of neutron quantum states in the Earth's gravitational field
NASA Astrophysics Data System (ADS)
Vankov, Anatoli Andrei
20100301
Observation of neutron gravitational quantum states En=mgzn in the peV energy range (z1 is about 10μm in the vertical direction) in the experiment conducted at LaueLangevin Institute, Grenoble, with ultracold neutrons was recently reported in a series of publications. The purpose of the present work is to analyze the experiment. The experimental apparatus is designed to measure a transmission function T(za), namely, a horizontal flux of relatively fast neutrons (k≫kz in wavelength terms) passing through a slit of variable height za of upper absorbing wall. The quantum states in question are defined by the socalled Airy functions, which are solutions to the stationary 1D equation for a neutron “bouncing” above the perfect mirror in a linear potential field. The Airy functions describe the quantum bouncer (QB), the concept of which is subject to theoretical study of toy 1D models of gravitationally bound particles in nonrelativistic quantum mechanics (QM). This is essentially different from the 3D nonstationary QM object, “the running QB,” investigated in the experiment. The authors assume that there is a connection between T(za) and the probability density distribution P(z,za) for QB states. They devised the “phenomenological model,” in which the quantum pattern should be visible in the transmission curve. We argue, however, that the measured curve T(za) is not sensitive to QB states. Instead, it is sensitive to dynamics of neutron horizontal transport inside the absorbing slit for neutrons of energy values about 105 times greater than eigenvalues En. The latter are related to the neutron transverse mode kz and cannot be termed “energies of neutron gravitational quantum states.” We conclude that the experiment setup and real conditions are not adequate to the claimed objective, and the methodology of measured data treatment is flawed. The authors’ claim that “neutron gravitational quantum states are observed” is neither theoretically nor

Generation of families of spectra in PTsymmetric quantum mechanics and scalar bosonic field theory.
PubMed
Schmidt, Steffen; Klevansky, S P
20130428
This paper explains the systematics of the generation of families of spectra for the symmetric quantummechanical Hamiltonians H=p(2)+x(2)(ix)(ε), H=p(2)+(x(2))(δ) and H=p(2)(x(2))(μ). In addition, it contrasts the results obtained with those found for a bosonic scalar field theory, in particular in one dimension, highlighting the similarities to and differences from the quantummechanical case. It is shown that the number of families of spectra can be deduced from the number of noncontiguous pairs of Stokes wedges that display PT symmetry. To do so, simple arguments that use the WentzelKramersBrillouin approximation are used, and these imply that the eigenvalues are real. However, definitive results are in most cases presently only obtainable numerically, and not all eigenvalues in each family may be real. Within the approximations used, it is illustrated that the difference between the quantummechanical and the fieldtheoretical cases lies in the number of accessible regions in which the eigenfunctions decay exponentially. This paper reviews and implements wellknown techniques in complex analysis and PTsymmetric quantum theory.

Is there a weak mixed polarity background field? Theoretical arguments
NASA Technical Reports Server (NTRS)
Spruit, H. C.; Title, A. M.; Van Ballegooijen, A. A.
19870101
A number of processes associated with the formation of active regions produce 'Uloops': fluxtubes having two ends at the photosphere but otherwise still embedded in the convection zone. The mass trapped on the field lines of such loops makes them behave in a qualitatively different way from the 'omegaloops' that form active regions. It is shown that Uloops will disperse though the convection zone and form a weak (down to a few gauss) field that covers a significant fraction of the solar surface. This field is tentatively identified with the innernetwork fields observed at Kitt Peak and Big Bear. The process by which these fields escape through the surface is described; a remarkable property is that it can make active region fields apparently disappear in situ. The mixed polarity moving magnetic features near sunspots are interpreted as a locally intense form of this disappearance by escape of Uloops.

Keldysh field theory for driven open quantum systems
NASA Astrophysics Data System (ADS)
Sieberer, L. M.; Buchhold, M.; Diehl, S.
20160901
Recent experimental developments in diverse areas—ranging from cold atomic gases to lightdriven semiconductors to microcavity arrays—move systems into the focus which are located on the interface of quantum optics, manybody physics and statistical mechanics. They share in common that coherent and driven–dissipative quantum dynamics occur on an equal footing, creating genuine nonequilibrium scenarios without immediate counterpart in equilibrium condensed matter physics. This concerns both their nonthermal stationary states and their manybody time evolution. It is a challenge to theory to identify novel instances of universal emergent macroscopic phenomena, which are tied unambiguously and in an observable way to the microscopic drive conditions. In this review, we discuss some recent results in this direction. Moreover, we provide a systematic introduction to the open system Keldysh functional integral approach, which is the proper technical tool to accomplish a merger of quantum optics and manybody physics, and leverages the power of modern quantum field theory to driven open quantum systems.

Keldysh field theory for driven open quantum systems.
PubMed
Sieberer, L M; Buchhold, M; Diehl, S
20160901
Recent experimental developments in diverse areasranging from cold atomic gases to lightdriven semiconductors to microcavity arraysmove systems into the focus which are located on the interface of quantum optics, manybody physics and statistical mechanics. They share in common that coherent and drivendissipative quantum dynamics occur on an equal footing, creating genuine nonequilibrium scenarios without immediate counterpart in equilibrium condensed matter physics. This concerns both their nonthermal stationary states and their manybody time evolution. It is a challenge to theory to identify novel instances of universal emergent macroscopic phenomena, which are tied unambiguously and in an observable way to the microscopic drive conditions. In this review, we discuss some recent results in this direction. Moreover, we provide a systematic introduction to the open system Keldysh functional integral approach, which is the proper technical tool to accomplish a merger of quantum optics and manybody physics, and leverages the power of modern quantum field theory to driven open quantum systems. PMID:27482736

Keldysh field theory for driven open quantum systems
NASA Astrophysics Data System (ADS)
Sieberer, L. M.; Buchhold, M.; Diehl, S.
20160901
Recent experimental developments in diverse areas—ranging from cold atomic gases to lightdriven semiconductors to microcavity arrays—move systems into the focus which are located on the interface of quantum optics, manybody physics and statistical mechanics. They share in common that coherent and drivendissipative quantum dynamics occur on an equal footing, creating genuine nonequilibrium scenarios without immediate counterpart in equilibrium condensed matter physics. This concerns both their nonthermal stationary states and their manybody time evolution. It is a challenge to theory to identify novel instances of universal emergent macroscopic phenomena, which are tied unambiguously and in an observable way to the microscopic drive conditions. In this review, we discuss some recent results in this direction. Moreover, we provide a systematic introduction to the open system Keldysh functional integral approach, which is the proper technical tool to accomplish a merger of quantum optics and manybody physics, and leverages the power of modern quantum field theory to driven open quantum systems.

Keldysh field theory for driven open quantum systems.
PubMed
Sieberer, L M; Buchhold, M; Diehl, S
20160901
Recent experimental developments in diverse areasranging from cold atomic gases to lightdriven semiconductors to microcavity arraysmove systems into the focus which are located on the interface of quantum optics, manybody physics and statistical mechanics. They share in common that coherent and drivendissipative quantum dynamics occur on an equal footing, creating genuine nonequilibrium scenarios without immediate counterpart in equilibrium condensed matter physics. This concerns both their nonthermal stationary states and their manybody time evolution. It is a challenge to theory to identify novel instances of universal emergent macroscopic phenomena, which are tied unambiguously and in an observable way to the microscopic drive conditions. In this review, we discuss some recent results in this direction. Moreover, we provide a systematic introduction to the open system Keldysh functional integral approach, which is the proper technical tool to accomplish a merger of quantum optics and manybody physics, and leverages the power of modern quantum field theory to driven open quantum systems.

The Evolution of Quantum Field Theory: From QED to Grand Unification
NASA Astrophysics Data System (ADS)
't Hooft, Gerard
20161001
In the early 1970s, after a slow start, and lots of hurdles, Quantum Field Theory emerged as the superior doctrine for understanding the interactions between relativistic subatomic particles. After the conditions for a relativistic field theoretical model to be renormalizable were established, there were two other developments that quickly accelerated acceptance of this approach: first the BroutEnglertHiggs mechanism, and then asymptotic freedom. Together, these gave us a complete understanding of the perturbative sector of the theory, enough to give us a detailed picture of what is now usually called the Standard Model. Crucial for this understanding were the strong indications and encouragements provided by numerous experimental findings. Subsequently, nonperturbative features of the quantum field theories were addressed, and the first proposals for completely unified quantum field theories were launched. Since the use of continuous symmetries of all sorts, together with other topics of advanced mathematics, were recognised to be of crucial importance, many new predictions were pointed out, such as the Higgs particle, supersymmetry, and baryon number violation. There are still many challenges ahead.

Gravity Dual for Reggeon Field Theory and Nonlinear Quantum Finance
NASA Astrophysics Data System (ADS)
Nakayama, Yu
We study scale invariant but not necessarily conformal invariant deformations of nonrelativistic conformal field theories from the dual gravity viewpoint. We present the corresponding metric that solves the Einstein equation coupled with a massive vector field. We find that, within the class of metric we study, when we assume the Galilean invariance, the scale invariant deformation always preserves the nonrelativistic conformal invariance. We discuss applications to scaling regime of Reggeon field theory and nonlinear quantum finance. These theories possess scale invariance but may or may not break the conformal invariance, depending on the underlying symmetry assumptions.

Magnetoquantumresistance oscillations in tunnelcoupled double quantum wells in tilted magnetic fields: Variable Landau biladders
SciTech Connect
Lyo, S.K.; Harff, N.E.; Simmons, J.A.
19980701
We present a linearresponse theory of magnetoquantumresistance oscillations of the inplane resistances R{sub xx} and R{sub yy} in two coupled quasitwodimensional electron layers in tilted magnetic fields {bold B}=(B{sub {parallel}},B{sub {perpendicular}}), and explain recent data from GaAs/Al{sub x}Ga{sub 1{minus}x}As double quantum wells. In this system, the electrons are in the two tunnelsplit ground sublevels. The cyclotron masses of the two orbits on the Fermi surface have opposite dependences on the inplane field B{sub {parallel}}: one increases monotonically, while the other decreases as a function of B{sub {parallel}} in the regime of interest. As a result, the rungs of one Landau ladder sweep up through the Fermi level, while those of the other Landau ladder sweep down when B{sub {parallel}} is increased at a fixed perpendicular field B{sub {perpendicular}}. Ridges are obtained in the threedimensional plots of both R{sub xx} and R{sub yy} and the density of states versus (B{sub {parallel}},B{sub {perpendicular}}) due to Fermilevel crossing by the rungs of the Landau ladders. Giant peaks are obtained when two ridges intersect each other. The (B{sub {parallel}},B{sub {perpendicular}}) dependence of R{sub xx} as well as theoretical evidence of magnetic breakdown yields good agreement with recent data from GaAs/Al{sub x}Ga{sub 1{minus}x}As double quantum wells. {copyright} {ital 1998} {ital The American Physical Society}

Quantum Humor: The Playful Side of Physics at Bohr's Institute for Theoretical Physics
NASA Astrophysics Data System (ADS)
Halpern, Paul
20120901
From the 1930s to the 1950s, a period of pivotal developments in quantum, nuclear, and particle physics, physicists at Niels Bohr's Institute for Theoretical Physics in Copenhagen took time off from their research to write humorous articles, letters, and other works. Best known is the Blegdamsvej Faust, performed in April 1932 at the close of one of the Institute's annual conferences. I also focus on the Journal of Jocular Physics, a humorous tribute to Bohr published on the occasions of his 50th, 60th, and 70th birthdays in 1935, 1945, and 1955. Contributors included Léon Rosenfeld, Victor Weisskopf, George Gamow, Oskar Klein, and Hendrik Casimir. I examine their contributions along with letters and other writings to show that they offer a window into some issues in physics at the time, such as the interpretation of complementarity and the nature of the neutrino, as well as the politics of the period.

Quantum dynamical simulations of local field enhancement in metal nanoparticles.
PubMed
Negre, Christian F A; Perassi, Eduardo M; Coronado, Eduardo A; Sánchez, Cristián G
20130327
Field enhancements (Γ) around small Ag nanoparticles (NPs) are calculated using a quantum dynamical simulation formalism and the results are compared with electrodynamic simulations using the discrete dipole approximation (DDA) in order to address the important issue of the intrinsic atomistic structure of NPs. Quite remarkably, in both quantum and classical approaches the highest values of Γ are located in the same regions around single NPs. However, by introducing a complete atomistic description of the metallic NPs in optical simulations, a different pattern of the Γ distribution is obtained. Knowing the correct pattern of the Γ distribution around NPs is crucial for understanding the spectroscopic features of molecules inside hot spots. The enhancement produced by surface plasmon coupling is studied by using both approaches in NP dimers for different interparticle distances. The results show that the trend of the variation of Γ versus interparticle distance is different for classical and quantum simulations. This difference is explained in terms of a charge transfer mechanism that cannot be obtained with classical electrodynamics. Finally, time dependent distribution of the enhancement factor is simulated by introducing a time dependent field perturbation into the Hamiltonian, allowing an assessment of the localized surface plasmon resonance quantum dynamics.

NMR profiling of quantum electron solids in high magnetic fields
NASA Astrophysics Data System (ADS)
Tiemann, L.; Rhone, T. D.; Shibata, N.; Muraki, K.
20140901
When the motion of electrons is restricted to a plane under a perpendicular magnetic field, a variety of quantum phases emerge at low temperatures, the properties of which are dictated by the Coulomb interaction and its interplay with disorder. At very strong magnetic field, the sequence of fractional quantum Hall liquid phases terminates in an insulating phase, which is widely believed to be due to the solidification of electrons into domains possessing Wigner crystal order. The existence of such Wigner crystal domains is signalled by the emergence of microwave pinningmode resonances, which reflect the mechanical properties characteristic of a solid. However, the most direct manifestation of the broken translational symmetry accompanying the solidificationthe spatial modulation of particles' probability amplitudeshas not been observed yet. Here, we demonstrate that nuclear magnetic resonance provides a direct probe of the density topography of electron solids in the integer and fractional quantum Hall regimes. The data uncover quantum and thermal fluctuations of lattice electrons resolved on the nanometre scale. Our results pave the way to studies of other exotic phases with nontrivial spatial spin/charge order.

Quantum confinement and magnetic field effects on the electron Landé g factor in GaAs(Ga,Al)As double quantum wells
NASA Astrophysics Data System (ADS)
Perea, J. Darío; MejíaSalazar, J. R.; PorrasMontenegro, N.
20111201
Nowadays the spinrelated phenomena have attracted great attention for the possible spintronic and optoelectronic applications. The manipulation of the Landé g factor by means of the control of the electron confinement, applied magnetic field and hydrostatic pressure offers the possibility of having a wide range of ways to control single qubit operation and to have pure spin states to guarantee that no losses occur when the electron spins transport information. In this work we have performed a theoretical study of the quantum confinement (geometrical and barrier potential confinements) and growth direction applied magnetic field effects on the conductionelectron effective Landé g factor in GaAs(Ga,Al)As double quantum wells. Our calculations of the Landé g factor are performed by using the OggMcCombe effective Hamiltonian, which includes nonparabolicity and anisotropy effects for the conductionband electrons. Our theoretical results are given as function of the central barrier widths for different values of the applied magnetic fields. We have found that in this type of heterostructure the geometrical confinement commands the behavior of the electron effective Landé g factor as compared to the effect of the applied magnetic field. Present theoretical reports are in very good agreement with previous experimental and theoretical results.

Multitime wave functions for quantum field theory
SciTech Connect
Petrat, Sören; Tumulka, Roderich
20140615
Multitime wave functions such as ϕ(t{sub 1},x{sub 1},…,t{sub N},x{sub N}) have one time variable t{sub j} for each particle. This type of wave function arises as a relativistic generalization of the wave function ψ(t,x{sub 1},…,x{sub N}) of nonrelativistic quantum mechanics. We show here how a quantum field theory can be formulated in terms of multitime wave functions. We mainly consider a particular quantum field theory that features particle creation and annihilation. Starting from the particle–position representation of state vectors in Fock space, we introduce multitime wave functions with a variable number of time variables, set up multitime evolution equations, and show that they are consistent. Moreover, we discuss the relation of the multitime wave function to two other representations, the Tomonaga–Schwinger representation and the Heisenberg picture in terms of operatorvalued fields on space–time. In a certain sense and under natural assumptions, we find that all three representations are equivalent; yet, we point out that the multitime formulation has several technical and conceptual advantages.  Highlights: •Multitime wave functions are manifestly Lorentzcovariant objects. •We develop consistent multitime equations with interaction for quantum field theory. •We discuss in detail a particular model with particle creation and annihilation. •We show how multitime wave functions are related to the Tomonaga–Schwinger approach. •We show that they have a simple representation in terms of operator valued fields.

Theoretical simulation of carrier capture and relaxation rates in quantumdot semiconductor optical amplifiers
SciTech Connect
Wu, Yunhu; Zhang, Guoping; Guo, Ling; Qi, Guoqun; Li, Xiaoming
20140614
Based on Auger scattering mechanism, carriercarrier scattering dynamics between the twodimensional carrier reservoir (also called wetting layer, i.e., WL) and the confined quantum dot ground and first excited state in quantumdot semiconductor optical amplifiers (QDSOAs) are investigated theoretically in this paper. The scattering rates for independent electron and hole densities are calculated. The results show an ultrafast carrier capture (relaxation) rate up to 1 ps{sup −1}, and there is a complex dependence of the Coulomb scattering rates on the WL electron and hole densities. In addition, due to the different effective mass and the level distribution, the scattering rates for electron and hole are very different. Finally, in order to provide a direction to control (increase or decrease) the input current in realistic QDSOA systems, a simple method is proposed to determine the trends of the carrier recovery rates with the WL carrier densities in the vicinity of the steadystate.

Perturbative quantum field theory in the framework of the fermionic projector
SciTech Connect
Finster, Felix
20140415
We give a microscopic derivation of perturbative quantum field theory, taking causal fermion systems and the framework of the fermionic projector as the starting point. The resulting quantum field theory agrees with standard quantum field theory on the tree level and reproduces all bosonic loop diagrams. The fermion loops are described in a different formalism in which no ultraviolet divergences occur.

Autonomy, explanation, and theoretical values: physicists and chemists on molecular quantum mechanics.
PubMed
Hendry, Robin Findlay
20030501
The emergence of quantum chemistry in the early twentieth century was an international as well as an interdisciplinary affair, involving dialogue between physicists and chemists in Germany, the United States, and Britain. Historians of science have recently documented both the causes and effects of this internationalism and interdisciplinarity. Chemists and physicists involved in the development of quantum chemistry in its first few decades tended to argue for opposing views on acceptable standards of explanation in their field, although the debate did not divide along disciplinary lines. The purpose of this paper is to investigate these different positions, through the methodological reflections of John Clarke Slater, Linus Pauling, and Charles Coulson. Slater tended to argue for quantummechanical rigor and the application of fundamental principles as the values guiding models of molecular bonding. Although they were on different sides of the debate between the valencebond and molecularorbital approaches, Pauling and Coulson both emphasized the recovery of traditional chemical explanations and systematic explanatory power within chemistry.

Enhanced current injection from a quantum well to a quantum dash in magnetic field
NASA Astrophysics Data System (ADS)
ParaviciniBagliani, Gian L.; Liverini, Valeria; Valmorra, Federico; Scalari, Giacomo; Gramm, Fabian; Faist, Jérôme
20140801
Resonant tunneling injection is a key ingredient in achieving population inversion in a putative quantum dot cascade laser. In a quantum dot based structure, such resonant current requires a matching of the wavefunction shape in kspace between the injector and the quantum dot. We show experimentally that the injection into an excited state of a dash structure can be enhanced tenfold by an inplane magnetic field that shifts the injector distribution in kspace. These experiments, performed on resonant tunneling diode structures, show unambiguously resonant tunneling into an ensemble of InAs dashes grown between two AlInAs barrier layers. They also show that interface roughness scattering can enhance the tunneling current.

A microscopic field theoretical approach for active systems
NASA Astrophysics Data System (ADS)
Alaimo, F.; Praetorius, S.; Voigt, A.
20160801
We consider a microscopic modeling approach for active systems. The approach extends the phase field crystal (PFC) model and allows us to describe generic properties of active systems within a continuum model. The approach is validated by reproducing results obtained with corresponding agentbased and microscopic phase field models. We consider binary collisions, collective motion and vortex formation. For larger numbers of particles we analyze the coarsening process in active crystals and identify giant number fluctuation in a cluster formation process.

Theoretical investigation of hyperfine field parameters through mossbauer gamma ray
SciTech Connect
Ali, Sikander; Hashim, Mohd
20120605
When a Mossbauer gammaray emitting or absorbing nucleus is placed in a crystalline environment, the quadrupole moment of the nucleus interacts with the electric field gradient set up by the ligands around it. In the transition 7/2>{yields}5/2> twelve lines are obtained. Applying the multipole radiation field theory and density matrix formalism, the determinant of coherency matrix, intensity and degree of polarization have been calculated for each line.

Clusterlike coordinates in supersymmetric quantum field theory
PubMed Central
Neitzke, Andrew
20140101
Recently it has become apparent that N=2 supersymmetric quantum field theory has something to do with cluster algebras. I review one aspect of the connection: supersymmetric quantum field theories have associated hyperkähler moduli spaces, and these moduli spaces carry a structure that looks like an extension of the notion of cluster variety. In particular, one encounters the usual variables and mutations of the cluster story, along with more exotic extra variables and generalized mutations. I focus on a class of examples where the underlying cluster varieties are moduli spaces of flat connections on surfaces, as considered by Fock and Goncharov [Fock V, Goncharov A (2006) Publ Math Inst Hautes Études Sci 103:1–211]. The work reviewed here is largely joint with Davide Gaiotto and Greg Moore. PMID:24982190

Geometric and Topological Methods for Quantum Field Theory
NASA Astrophysics Data System (ADS)
Cardona, Alexander; Contreras, Iván.; ReyesLega, Andrés. F.
20130501
Introduction; 1. A brief introduction to Dirac manifolds Henrique Bursztyn; 2. Differential geometry of holomorphic vector bundles on a curve Florent Schaffhauser; 3. Paths towards an extension of ChernWeil calculus to a class of infinite dimensional vector bundles Sylvie Paycha; 4. Introduction to Feynman integrals Stefan Weinzierl; 5. Iterated integrals in quantum field theory Francis Brown; 6. Geometric issues in quantum field theory and string theory Luis J. Boya; 7. Geometric aspects of the standard model and the mysteries of matter Florian Scheck; 8. Absence of singular continuous spectrum for some geometric Laplacians Leonardo A. Cano García; 9. Models for formal groupoids Iván Contreras; 10. Elliptic PDEs and smoothness of weakly Einstein metrics of Hölder regularity Andrés Vargas; 11. Regularized traces and the index formula for manifolds with boundary Alexander Cardona and César Del Corral; Index.

Does Quantum Cosmology Predict a Constant Dilatonic Field?
NASA Astrophysics Data System (ADS)
Alvarenga, F. G.; Batista, A. B.; Fabris, J. C.
Quantum cosmology may permit to determine the initial conditions of the Universe. In particular, it may select a specific model between many possible classical models. In this work, we study a quantum cosmological model based on the string effective action coupled to matter. The Schutz's formalism is employed in the description of the fluid. A radiation fluid is considered. In this way, a time coordinate may be identified and the WheelerDeWitt equation reduces in the minisuperspace to a Schrödingerlike equation. It is shown that, under some quite natural assumptions, the expectation values indicate a null axionic field and a constant dilatonic field. At the same time the scale factor exhibits a bounce revealing a singularityfree cosmological model. In some cases, the mininum value of the scale factor can be related to the value of gravitational coupling.

Clusterlike coordinates in supersymmetric quantum field theory.
PubMed
Neitzke, Andrew
20140701
Recently it has become apparent that N = 2 supersymmetric quantum field theory has something to do with cluster algebras. I review one aspect of the connection: supersymmetric quantum field theories have associated hyperkähler moduli spaces, and these moduli spaces carry a structure that looks like an extension of the notion of cluster variety. In particular, one encounters the usual variables and mutations of the cluster story, along with more exotic extra variables and generalized mutations. I focus on a class of examples where the underlying cluster varieties are moduli spaces of flat connections on surfaces, as considered by Fock and Goncharov [Fock V, Goncharov A (2006) Publ Math Inst Hautes Études Sci 103:1211]. The work reviewed here is largely joint with Davide Gaiotto and Greg Moore.

Quantum field as a quantum cellular automaton: The Dirac free evolution in one dimension
SciTech Connect
Bisio, Alessandro; D’Ariano, Giacomo Mauro; Tosini, Alessandro
20150315
We present a quantum cellular automaton model in one spacedimension which has the Dirac equation as emergent. This model, a discretetime and causal unitary evolution of a lattice of quantum systems, is derived from the assumptions of homogeneity, parity and timereversal invariance. The comparison between the automaton and the Dirac evolutions is rigorously set as a discrimination problem between unitary channels. We derive an exact lower bound for the probability of error in the discrimination as an explicit function of the mass, the number and the momentum of the particles, and the duration of the evolution. Computing this bound with experimentally achievable values, we see that in that regime the QCA model cannot be discriminated from the usual Dirac evolution. Finally, we show that the evolution of oneparticle states with narrowband in momentum can be efficiently simulated by a dispersive differential equation for any regime. This analysis allows for a comparison with the dynamics of wavepackets as it is described by the usual Dirac equation. This paper is a first step in exploring the idea that quantum field theory could be grounded on a more fundamental quantum cellular automaton model and that physical dynamics could emerge from quantum information processing. In this framework, the discretization is a central ingredient and not only a tool for performing nonperturbative calculation as in lattice gauge theory. The automaton model, endowed with a precise notion of local observables and a full probabilistic interpretation, could lead to a coherent unification of a hypothetical discrete Planck scale with the usual Fermi scale of highenergy physics.  Highlights: • The free Dirac field in one space dimension as a quantum cellular automaton. • Large scale limit of the automaton and the emergence of the Dirac equation. • Dispersive differential equation for the evolution of smooth states on the automaton. • Optimal discrimination between the

Nearfield turbulence effects on quantumkey distribution
SciTech Connect
Shapiro, Jeffrey H.
20030201
Bounds on average power transfer over a nearfield optical path through atmospheric turbulence are used to deduce bounds on the sift and error probabilities of a freespace quantumkey distribution system that uses the BennettBrassard 1984 (BB84) protocol. It is shown that atmospheric turbulence imposes at most a modest decrease in the sift probability and a modest increase in the conditional probability of error given that a sift event has occurred.

Horava—Lifshitz Type Quantum Field Theory and Hierarchy Problem
NASA Astrophysics Data System (ADS)
Wei, Chao
20160601
We study the Lifshitz type extension of the standard model (SM) at the UV, with dynamical critical exponent z = 3. One loop radiative corrections to the Higgs mass in such a model are calculated. Our result shows that, the Hierarchy problem, which has initiated many excellent extension of the minimal SM, may be weakened in the z = 3 Lifshitz type quantum field theory. Supported by the National Natural Science Foundation of China

Introduction to Nonequilibrium Statistical Mechanics with Quantum Field Theory
NASA Astrophysics Data System (ADS)
Kita, T.
20100401
In this article, we present a concise and selfcontained introduction to nonequilibrium statistical mechanics with quantum field theory by considering an ensemble of interacting identical bosons or fermions as an example. Readers are assumed to be familiar with the Matsubara formalism of equilibrium statistical mechanics such as Feynman diagrams, the proper selfenergy, and Dyson's equation. The aims are threefold: (i) to explain the fundamentals of nonequilibrium quantum field theory as simple as possible on the basis of the knowledge of the equilibrium counterpart; (ii) to elucidate the hierarchy in describing nonequilibrium systems from Dyson's equation on the Keldysh contour to the NavierStokes equation in fluid mechanics via quantum transport equations and the Boltzmann equation; (iii) to derive an expression of nonequilibrium entropy that evolves with time. In stage (i), we introduce nonequilibrium Green's function and the selfenergy uniquely on the roundtrip Keld ysh contour, thereby avoiding possible confusions that may arise from defining multiple Green's functions at the very beginning. We try to present the Feynman rules for the perturbation expansion as simple as possible. In particular, we focus on the selfconsistent perturbation expansion with the LuttingerWard thermodynamic functional, i.e., Baym's Phiderivable approximation, which has a crucial property for nonequilibrium systems of obeying various conservation laws automatically. We also show how the twoparticle correlations can be calculated within the Phiderivable approximation, i.e., an issue of how to handle the ``BogoliubovBornGreenKirkwoodYvons (BBGKY) hierarchy''. Aim (ii) is performed through successive reductions of relevant variables with the Wigner transformation, the gradient expansion based on the GroenewoldMoyal product, and Enskog's expansion from local equilibrium. This part may be helpful for convincing readers that nonequilibrium systems ca n be handled

Nonequilibrium forces between neutral atoms mediated by a quantum field
SciTech Connect
Behunin, Ryan O.; Hu, BeiLok
20100815
We study forces between two neutral atoms, modeled as threedimensional harmonic oscillators, arising from mutual influences mediated by an electromagnetic field but not from their direct interactions. We allow as dynamical variables the centerofmass motion of the atom, its internal degrees of freedom, and the quantum field treated relativistically. We adopt the method of nonequilibrium quantum field theory which can provide a firstprinciples, systematic, and unified description including the intrinsic and induced dipole fluctuations. The inclusion of selfconsistent backactions makes possible a fully dynamical description of these forces valid for general atom motion. In thermal equilibrium we recover the known forcesLondon, van der Waals, and CasimirPolderbetween neutral atoms in the longtime limit. We also reproduce a recently reported force between atoms when the system is out of thermal equilibrium at late times. More noteworthy is the discovery of the existence of a type of (or identification of the source of some known) interatomic force which we call the ''entanglement force,'' originating from the quantum correlations of the internal degrees of freedom of entangled atoms.

Analysis of the influence of external magnetic field on transition matrix elements in quantum well and quantum cascade laser structures
NASA Astrophysics Data System (ADS)
Demić, Aleksandar; Radovanović, Jelena; Milanović, Vitomir
20160801
We present a method for modeling nonparabolicity effects (NPE) in quantum nanostructures in presence of external electric and magnetic field by using second order perturbation theory. The method is applied to analysis of quantum well structure and active region of a quantum cascade laser (QCL). This model will allow us to examine the influence of magnetic field on dipole matrix element in QCL structures, which will provide a better insight to how NPE can affect the gain of QCL structures.

Axiomatics of Galileoinvariant quantum field theory
SciTech Connect
Dadashev, L.A.
19860301
The aim of this paper is to construct the axiomatics of Galileoinvariant quantum field theory. The importance of this problem is demonstrated from various points of view: general properties that the fields and observables must satisfy are considered; Smatrix nontriviality of one such model is proved; and the differences from the relativistic case are discussed. The proposed system of axioms is in many respects analogous to Wightman axiomatics, but is less general. The main result is contained in theorems which describe the admissible set of initial fields and total Hamiltonians, i.e., precisely the two entities that completely determine interacting fields. The author considers fields that prove the independence of some axioms.

Theoretical evaluation of the acoustic field in an ultrasonic bioreactor.
PubMed
Louw, Tobias M; Subramanian, Anuradha; Viljoen, Hendrik J
20150601
Ultrasoundassisted bioreactors that provide mechanical conditioning to cells have broad applicability in tissue engineering, but biological experiments with ultrasound are very sensitive to environmental conditions. A mathematical model was developed to complement experimental measurements, as well as to describe ultrasonic fields existing in regions where measurements are impossible, specifically, within microporous tissue engineering scaffolds. The model uniquely combines Biot theory to predict the ultrasonic field in the scaffold with an electromechanical transducer model to couple the mechanical stimulation experienced by cells to the external electrical input. In the specific example examined here, cells immobilized on scaffolds are subjected to different forms of ultrasonic stimulation due to the formation of standing wave fields and vertical highpressure bands. The model confirms the sensitivity of the supplied acoustic power to the liquid level in sonobioreactors and identifies the input electrical impedance as a method of detecting resonance effects.

Field theoretic treatment of gravitational interaction in electrodynamics
NASA Astrophysics Data System (ADS)
Serdyukov, A. N.
20110301
A theory of gravitational interaction in classical electrodynamics is developed on the basis of an earlierproposed minimal relativistic model of gravitation. From the variation principle, a system of gaugeinvariant equations of the interacting electromagnetic and gravitational fields is deduced and their common energymomentum tensor is constructed. A rigorous solution to the problem of regularizing the field mass of a point charge is given with consideration for the coupling energy of the gravitational interaction. The propagation of electromagnetic waves in the gravitational field is discussed. It is shown that, under the condition of the existing resonant ratio 2: 3 for the periods of Mercury's orbital revolution and daily rotation, tidal forces cause a regular shift in the planet's perihelion in an observable forward direction.

On some theoretical problems of laser wakefield accelerators
NASA Astrophysics Data System (ADS)
Bulanov, S. V.; Esirkepov, T. Zh.; Hayashi, Y.; Kiriyama, H.; Koga, J. K.; Kotaki, H.; Mori, M.; Kando, M.
20160601
> Enhancement of the quality of laser wakefield accelerated (LWFA) electron beams implies the improvement and controllability of the properties of the wake waves generated by ultrashort pulse lasers in underdense plasmas. In this work we present a compendium of useful formulas giving relations between the laser and plasma target parameters allowing one to obtain basic dependences, e.g. the energy scaling of the electrons accelerated by the wake field excited in inhomogeneous media including multistage LWFA accelerators. Consideration of the effects of using the chirped laser pulse driver allows us to find the regimes where the chirp enhances the wake field amplitude. We present an analysis of the threedimensional effects on the electron beam loading and on the unlimited LWFA acceleration in inhomogeneous plasmas. Using the conditions of electron trapping to the wakefield acceleration phase we analyse the multiequal stage and multiuneven stage LWFA configurations. In the first configuration the energy of fast electrons is a linear function of the number of stages, and in the second case, the accelerated electron energy grows exponentially with the number of stages. The results of the twodimensional particleincell simulations presented here show the high quality electron acceleration in the triple stage injectionacceleration configuration.

ELECTRON HOLOGRAPHY OF ELECTROMAGNETIC FIELDS  RECENT THEORETICAL ADVANCES.
SciTech Connect
BELEGGIA,M.; POZZI, G.; TONOMURA, A.
20070101
It has been shown in this work that the Fourier space approach can be fruitfully applied to the calculation of the fields and the associated electron optical phase shift of several magnetic and electrostatic structures, like superconducting vortices in conventional and highT{sub c} superconductors, reverse biased pn junctions, magnetic domains and nanoparticles. In all these cases, this novel approach has led to unexpected but extremely interesting results, very often expressed in analytical form, which allow the quantitative and reliable interpretation of the experimental data collected by means of electron holography or of more conventional Lorentz microscopy techniques. Moreover, it is worth recalling that whenever longrange electromagnetic fields are involved, a physical model of the object under investigation is necessary in order to take into account correctly the perturbation of the reference wave induced by the tail of the field protruding into the vacuum. For these reasons, we believe that the Fourier space approach for phase computations we have introduced and discussed in this chapter will represent an invaluable tool for the investigation of electromagnetic fields at the meso and nanoscale.

Is the quantum Hall effect influenced by the gravitational field?
PubMed
Hehl, Friedrich W; Obukhov, Yuri N; Rosenow, Bernd
20040827
Most of the experiments on the quantum Hall effect (QHE) were made at approximately the same height above sea level. A future international comparison will determine whether the gravitational field g(x) influences the QHE. In the realm of (1+2)dimensional phenomenological macroscopic electrodynamics, the OhmHall law is metric independent ("topological"). This suggests that it does not couple to g(x). We corroborate this result by a microscopic calculation of the Hall conductance in the presence of a postNewtonian gravitational field. PMID:15447125

Quantum κdeformed differential geometry and field theory
NASA Astrophysics Data System (ADS)
Mercati, Flavio
20160301
I introduce in κMinkowski noncommutative spacetime the basic tools of quantum differential geometry, namely bicovariant differential calculus, Lie and inner derivatives, the integral, the Hodge∗ and the metric. I show the relevance of these tools for field theory with an application to complex scalar field, for which I am able to identify a vectorvalued fourform which generalizes the energymomentum tensor. Its closedness is proved, expressing in a covariant form the conservation of energymomentum.

Quantum supersymmetric FRW cosmology with a scalar field
NASA Astrophysics Data System (ADS)
Ramírez, C.; VázquezBáez, V.
20160201
We analyze the quantum supersymmetric cosmological FriedmannRobertsonWalker model with a scalar field, with a conditional probability density and the scalar field identified as time. The Hilbert space has a spinorial structure and there is only one consistent solution, with a conserved probability density. The dynamics of the scale factor is obtained from its mean value. The uncertainty relations are fulfilled and the corresponding fluctuations are consistent with a semiclassical Universe. We give two examples which turn out to have negative potential.

Recent progress of quantum communication in China (Conference Presentation)
NASA Astrophysics Data System (ADS)
Zhang, Qiang
20160401
Quantum communication, based on the quantum physics, can provide information theoretical security. Building a global quantum network is one ultimate goal for the research of quantum information. Here, this talk will review the progress for quantum communication in China, including quantum key distribution over metropolitan area with untrustful relay, field test of quantum entanglement swapping over metropolitan network, the 2000 km quantum key distribution main trunk line, and satellite based quantum communication.

On refractive processes in strong laser field quantum electrodynamics
SciTech Connect
Di Piazza, A.
20131115
Refractive processes in strongfield QED are pure quantum processes, which involve only external photons and the background electromagnetic field. We show analytically that such processes occurring in a planewave field and involving external real photons are all characterized by a surprisingly modest net exchange of energy and momentum with the laser field, corresponding to a few laser photons, even in the limit of ultrarelativistic laser intensities. We obtain this result by a direct calculation of the transition matrix element of an arbitrary refractive QED process and accounting exactly for the background planewave field. A simple physical explanation of this modest net exchange of laser photons is provided, based on the fact that the laser field couples with the external photons only indirectly through virtual electron–positron pairs. For stronger and stronger laser fields, the pairs cover a shorter and shorter distance before they annihilate again, such that the laser can transfer to them an energy corresponding to only a few photons. These results can be relevant for the future experiments aiming to test strongfield QED at present and nextgeneration facilities.  Highlights: •Investigation of the oneloop amplitude of refractive QED processes in a laser field. •The amplitude is suppressed for a large number of netexchanged laser photons. •Suggestion for first observation of highnonlinear vacuum effects in a laser field.

Theoretical studies for experimental implementation of quantum computing with trapped ions
NASA Astrophysics Data System (ADS)
Yoshimura, Bryce T.
Certain quantum manybody physics problems, such as the transverse field Ising model are intractable on a classical computer, meaning that as the number of particles grows, or spins, the amount of memory and computational time required to solve the problem exactly increases faster than a polynomial behavior. However, quantum simulators are being developed to efficiently solve quantum problems that are intractable via conventional computing. Some of the most successful quantum simulators are based on ion traps. Their success depends on the ability to achieve long coherence time, precise spin control, and high fidelity in state preparation. In this work, I present calculations that characterizes the oblate Paul trap that creates twodimensional Coulomb crystals in a triangular lattice and phonon modes. We also calculate the spinspin Isinglike interaction that can be generated in the oblate Paul trap using the same techinques as the linear radiofrequency Paul trap. In addition, I discuss two possible challenges that arise in the Penning trap: the effects of defects ( namely when Be+ → BeH+) and the creation of a more uniform spinspin Isinglike interaction. We show that most properties are not significantly influenced by the appearance of defects, and that by adding two potentials to the Penning trap a more uniform spinspin Isinglike interaction can be achieved. Next, I discuss techniques tfor preparing the ground state of the Isinglike Hamiltonian. In particular, we explore the use of the bangbang protocol to prepare the ground state and compare optimized results to conventional adiabatic ramps ( the exponential and locally adiabatic ramp ). The bangbang optimization in general outperforms the exponential; however the locally adiabatic ramp consistently is somewhat better. However, compared to the locally adiabatic ramp, the bangbang optimization is simpler to implement, and it has the advantage of providingrovide a simple procedure for estimating the

Field Theoretic Formulation of Kinetic Theory: Basic Development
NASA Astrophysics Data System (ADS)
Das, Shankar P.; Mazenko, Gene F.
20121101
We show how kinetic theory, the statistics of classical particles obeying Newtonian dynamics, can be formulated as a field theory. The field theory can be organized to produce a selfconsistent perturbation theory expansion in an effective interaction potential. The need for a selfconsistent approach is suggested by our interest in investigating ergodicnonergodic transitions in dense fluids. The formal structure we develop has been implemented in detail for the simpler case of Smoluchowski dynamics. One aspect of the approach is the identification of a core problem spanned by the variables ρ the number density and B a response density. In this paper we set up the perturbation theory expansion with explicit development at zeroth and first order. We also determine all of the cumulants in the noninteracting limit among the core variables ρ and B.

Field effect in the quantum Hall regime of a high mobility graphene wire
NASA Astrophysics Data System (ADS)
Barraud, C.; Choi, T.; Butti, P.; Shorubalko, I.; Taniguchi, T.; Watanabe, K.; Ihn, T.; Ensslin, K.
20140801
In graphenebased electronic devices like in transistors, the field effect applied thanks to a gate electrode allows tuning the charge density in the graphene layer and passing continuously from the electron to the hole doped regime across the Dirac point. Homogeneous doping is crucial to understand electrical measurements and for the operation of future graphenebased electronic devices. However, recently theoretical and experimental studies highlighted the role of the electrostatic edge due to fringing electrostatic field lines at the graphene edges [P. Silvestrov and K. Efetov, Phys. Rev. B 77, 155436 (2008); F. T. Vasko and I. V. Zozoulenko, Appl. Phys. Lett. 97, 092115 (2010)]. This effect originates from the particular geometric design of the samples. A direct consequence is a charge accumulation at the graphene edges giving a value for the density, which deviates from the simple picture of a plate capacitor and also varies along the width of the graphene sample. Entering the quantum Hall regime would, in principle, allow probing this accumulation thanks to the extreme sensitivity of this quantum effect to charge density and the charge distribution. Moreover, the presence of an additional and counterpropagating edge channel has been predicted [P. Silvestrov and K. Efetov, Phys. Rev. B 77, 155436 (2008)] giving a fundamental aspect to this technological issue. In this article, we investigate this effect by tuning a high mobility graphene wire into the quantum Hall regime in which charge carriers probe the electrostatic potential at high magnetic field close to the edges. We observe a slight deviation to the linear shift of the quantum Hall plateaus with magnetic field and we study its evolution for different filling factors, which correspond to different probed regions in real space. We discuss the possible origins of this effect including an increase of the charge density towards the edges.

Field effect in the quantum Hall regime of a high mobility graphene wire
SciTech Connect
Barraud, C. Email: clement.barraud@univparisdiderot.fr; Choi, T.; Ihn, T.; Ensslin, K.; Butti, P.; Shorubalko, I.; Taniguchi, T.; Watanabe, K.
20140821
In graphenebased electronic devices like in transistors, the field effect applied thanks to a gate electrode allows tuning the charge density in the graphene layer and passing continuously from the electron to the hole doped regime across the Dirac point. Homogeneous doping is crucial to understand electrical measurements and for the operation of future graphenebased electronic devices. However, recently theoretical and experimental studies highlighted the role of the electrostatic edge due to fringing electrostatic field lines at the graphene edges [P. Silvestrov and K. Efetov, Phys. Rev. B 77, 155436 (2008); F. T. Vasko and I. V. Zozoulenko, Appl. Phys. Lett. 97, 092115 (2010)]. This effect originates from the particular geometric design of the samples. A direct consequence is a charge accumulation at the graphene edges giving a value for the density, which deviates from the simple picture of a plate capacitor and also varies along the width of the graphene sample. Entering the quantum Hall regime would, in principle, allow probing this accumulation thanks to the extreme sensitivity of this quantum effect to charge density and the charge distribution. Moreover, the presence of an additional and counterpropagating edge channel has been predicted [P. Silvestrov and K. Efetov, Phys. Rev. B 77, 155436 (2008)] giving a fundamental aspect to this technological issue. In this article, we investigate this effect by tuning a high mobility graphene wire into the quantum Hall regime in which charge carriers probe the electrostatic potential at high magnetic field close to the edges. We observe a slight deviation to the linear shift of the quantum Hall plateaus with magnetic field and we study its evolution for different filling factors, which correspond to different probed regions in real space. We discuss the possible origins of this effect including an increase of the charge density towards the edges.

A possible generalization of the fieldtheoretical Hamilton's equations
SciTech Connect
Savchin, V.M. )
19881101
The development of classical dynamics as well as many branches of physics shows that the solution or analysis of variety of problems can be greatly simplified if the basic equations admit an analytic representation in terms of Hamilton's equations. The author proposes a generalization of Hamilton's equations in field theory which is applicable to partial differential equations of physical relevance. It is shown that the equations constitute a conceivable basis for the generalization of the theory of contact transformations and of Poisson's method.

Effect of a magnetic field on intersubband polaritons in a quantum well: strong to weak coupling conversion
NASA Astrophysics Data System (ADS)
Pervishko, A. A.; Kibis, O. V.; Shelykh, I. A.
20160801
We investigate theoretically the effect of a magnetic field on intersubband polaritons in an asymmetric quantum well placed inside an optical resonator. It is demonstrated that the fieldinduced diamagnetic shift of electron subbands in the well increases the broadening of optical lines corresponding to intersubband electron transitions. As a consequence, the magnetic field can switch the polariton system from the regime of strong lightmatter coupling to the regime of weak one. This effect paves a way to the effective control of polaritonic devices with a magnetic field.

Geometric and Topological Methods for Quantum Field Theory
NASA Astrophysics Data System (ADS)
Ocampo, Hernan; Pariguan, Eddy; Paycha, Sylvie
20100401
Introduction; 1. The impact of QFT on lowdimensional topology Paul Kirk; 2. Differential equations aspects of quantum cohomology Martin A. Guest; 3. Index theory and groupoids Claire Debord and JeanMarie Lescure; 4. Renormalization Hopf algebras and combinatorial groups Alessandra Frabetti; 5. BRS invariance for massive boson fields José M. GraciaBondía; 6. Large N field theories and geometry David Berenstein; 7. Functional renormalization group equations, asymptotic safety, and quantum Einstein gravity Martin Reuter and Frank Saueressig; 8. When is a differentiable manifold the boundary of an orbifold? Andrés Angel; 9. Canonical group quantization, rotation generators and quantum indistinguishability Carlos Benavides and Andrés ReyesLega; 10. Conserved currents in Kähler manifolds Jaime R. Camacaro and Juan Carlos Moreno; 11. A symmetrized canonical determinant on oddclass pseudodifferential operators MarieFrançoise Ouedraogo; 12. Some remarks about cosymplectic metrics on maximal flag manifolds Marlio Paredes and Sofia Pinzón; 13. Heisenberg modules over real multiplication noncommutative tori and related algebraic structures Jorge Plazas; Index.

Identifying a cooperative control mechanism between an applied field and the environment of open quantum systems
NASA Astrophysics Data System (ADS)
Gao, Fang; ReydeCastro, Roberto; Wang, Yaoxiong; Rabitz, Herschel; Shuang, Feng
20160501
Many systems under control with an applied field also interact with the surrounding environment. Understanding the control mechanisms has remained a challenge, especially the role played by the interaction between the field and the environment. In order to address this need, here we expand the scope of the Hamiltonianencoding and observabledecoding (HEOD) technique. HEOD was originally introduced as a theoretical and experimental tool for revealing the mechanism induced by control fields in closed quantum systems. The results of opensystem HEOD analysis presented here provide quantitative mechanistic insights into the roles played by a Markovian environment. Two model open quantum systems are considered for illustration. In these systems, transitions are induced by either an applied field linked to a dipole operator or Lindblad operators coupled to the system. For modest control yields, the HEOD results clearly show distinct cooperation between the dynamics induced by the optimal field and the environment. Although the HEOD methodology introduced here is considered in simulations, it has an analogous direct experimental formulation, which we suggest may be applied to open systems in the laboratory to reveal mechanistic insights.

Nonlocal quantum field theory without acausality and nonunitarity at quantum level: Is SUSY the key?
NASA Astrophysics Data System (ADS)
Addazi, Andrea; Esposito, Giampiero
20150501
The realization of a nonlocal quantum field theory without losing unitarity, gauge invariance and causality is investigated. It is commonly retained that such a formulation is possible at tree level, but at quantum level acausality is expected to reappear at one loop. We suggest that the problem of acausality is, in a broad sense, similar to the one about anomalies in quantum field theory. By virtue of this analogy, we suggest that acausal diagrams resulting from the fermionic sector and the bosonic one might cancel each other, with a suitable content of fields and suitable symmetries. As a simple example, we show how supersymmetry can alleviate this problem in a simple and elegant way, i.e. by leading to exact cancellations of harmful diagrams, to all orders of perturbation theory. An infinite number of divergent diagrams cancel each other by virtue of the nonrenormalization theorem of supersymmetry. However, supersymmetry is not enough to protect a theory from all acausal divergences. For instance, acausal contributions to supersymmetric corrections to Dterms are not protected by supersymmetry. On the other hand, we show in detail how supersymmetry also helps in dealing with Dterms: divergences are not canceled but they become softer than in the nonsupersymmetric case. The supergraphs' formalism turns out to be a powerful tool to reduce the complexity of perturbative calculations.

Theoretical Aspects of Magnetic Fields for Gamma Ray Bursts
NASA Astrophysics Data System (ADS)
Hanami, Hitoshi
We propose magnetic cannon ball mechanism in which the collapse of a magnetosphere onto a black hole can generate strong outward Poynting flux which drives a baryonfree fireball called the magnetic cannon ball. In the early stage, the magnetic fields in the cannon ball can prepare the explanation for the cycrotoron absorptions observed by GINGA. The magnetic cannon ball can drive, in general, a relativistic outflow which interacts with the interstellar matter and forms a shock. The magnetic field in the shock approximately equal to 104 G can induce the synchrotron radiations with peaks at approximately equal to 10^2 keV observed. This magnetic field in the cannon ball can also confine the high energy protons (gamma_p > 30) which are required for delayed photons (>25 GeV) following a burst on 1994 February 17. Accretion induced collapse of a white dwarf of > 109 G, merger of a close binary and failed type Ib supernovae are possible scenarios even without the rotation of the central object. This mechanism works at the final phase of gravitational collapse even after a neutrino driven fireball proposed in most scenarios for gamma ray bursts. Twice bursts, which consist of primary neutrino driven fireball and secondary magnetic cannon ball can be induced sometime, can be explained in this model. It suggests that the magnetic cannon ball works some parts in multiple populations and delayed or multiple burst events. The final remnant in the model should be a black hole. It implies that any gamma ray bursts can have no optical counter part if they do not have a companion in a binary.

Quantum Matching Theory (with new complexitytheoretic, combinatorial and topical insights on the nature of the quantum entanglement)
SciTech Connect
Gurvits, L.
20020101
Classical matching theory can be defined in terms of matrices with nonnegative entries. The notion of Positive operator, central in Quantum Theory, is a natural generalization of matrices with nonnegative entries. Based on this point of view, we introduce a definition of perfect Quantum (operator) matching. We show that the new notion inherits many 'classical' properties, but not all of them. This new notion goes somewhere beyound matroids. For separable bipartite quantum states this new notion coinsides with the full rank property of the intersection of two corresponding geometric matroids. In the classical situation, permanents are naturally associated with perfects matchings. We introduce an analog of permanents for positive operators, called Quantum Permanent and show how this generalization of the permanent is related to the Quantum Entanglement. Besides many other things, Quantum Permanents provide new rational inequalities necessary for the separability of bipartite quantum states. Using Quantum Permanents, we give deterministic polytime algorithm to solve Hidden Matroids Intersection Problem and indicate some 'classical' complexity difficulties associated with the Quantum Entanglement. Finally, we prove that the weak membership problem for the convex set of separable bipartite density matrices is NPHARD.

A quantum mechanical polarizable force field for biomolecular interactions.
PubMed
Donchev, A G; Ozrin, V D; Subbotin, M V; Tarasov, O V; Tarasov, V I
20050531
We introduce a quantum mechanical polarizable force field (QMPFF) fitted solely to QM data at the MP2/aTZ(hp) level. Atomic charge density is modeled by pointcharge nuclei and floating exponentially shaped electron clouds. The functional form of interaction energy parallels quantum mechanics by including electrostatic, exchange, induction, and dispersion terms. Separate fitting of each term to the counterpart calculated from highquality QM data ensures high transferability of QMPFF parameters to different molecular environments, as well as accurate fit to a broad range of experimental data in both gas and liquid phases. QMPFF, which is much more efficient than ab initio QM, is optimized for the accurate simulation of biomolecular systems and the design of drugs.

The Quantum Field Theory of the Ensemble Operator
SciTech Connect
Porter, Richard N.
20090309
Quantum field theory (QFT) provides a systematic investigative tool for ensembles of molecules. The grandcanonical ensemble operator (GCEO) for an ideal gas is presented in terms of the Fock creation and annihilation operators. The ideal GCEO can be shown to obey a simple equation which facilitates calculation of quantumstatistical properties of bosonic and fermionic molecules. Examples are linkedcluster QFT derivations of the grandcanonical partition function and the Poisson distribution for noninteracting molecules. The Boltzmann limit is achieved by omitting exchange diagrams. Summations of Feynman diagrams for long and shortrange interactions to infinite order lead to a useful model of the paircorrelation function and a new avenue for the study of dynamics near the critical point for gasliquid phase transitions.

Quench echo and work statistics in integrable quantum field theories.
PubMed
Pálmai, T; Sotiriadis, S
20141101
We propose a boundary thermodynamic Bethe ansatz calculation technique to obtain the Loschmidt echo and the statistics of the work done when a global quantum quench is performed on an integrable quantum field theory. We derive an analytic expression for the lowest edge of the probability density function and find that it exhibits universal features, in the sense that its scaling form depends only on the statistics of excitations. We perform numerical calculations on the sinhGordon model, a deformation of the free boson theory, and we obtain that by turning on the interaction the density function develops fermionic properties. The calculations are facilitated by a previously unnoticed property of the thermodynamic Bethe ansatz construction.

BL Herculis stars  Theoretical models for field variables
NASA Technical Reports Server (NTRS)
Carson, R.; Stothers, R.
19820101
Type II Cepheids with periods between 1 and 3 days, commonly designated as Bl Herculis stars, have been modeled here with the aim of interpreting the wide variety of light curves observed among the field variables. Previously modeled globular cluster members are used as standard calibration objects. The major finding is that only a small range of luminosities is capable of generating a large variety of light curve types at a given period. For a mass of approximately 0.60 solar mass, the models are able to reproduce the observed mean luminosities, dispersion of mean luminosities, periods, light amplitudes, light asymmetries, and phases of secondary features in the light curves of known BL Her stars. It is possible that the metalrich variables (which are found only in the field) have luminosities lower than those of most metalpoor variables. The present revised mass for BL Her, a metalrich object, is not significantly different from the mean mass of the metalpoor variables.

Magnetic Field Assisted subTHz Quantum Cascade Lasers
NASA Astrophysics Data System (ADS)
Wade, A.; Kim, Y.; Smirnov, D.; Kumar, S.; Hu, Q.; Williams, B. S.; Reno, J.
20090301
In THz QCLs radiative transitions take place between closelyspaced 2D electronic subbands (1THz ˜ 4meV) of a multiQW semiconductor system. THz quantum cascade lasers now cover the frequency range from 1.2 THz to 5 THz, though cryogenic cooling is still required. Further progress towards the realization of devices emitting at longer wavelengths (subTHz QCLs) and higher temperatures may be realized in a system with additional lateral confinement. Here we use strong magnetic fields to achieve quasi0D confinement in THz QCL based on the resonance phonon design. We studied two designs: (a) 2well injector/2 well active region, emitting at 3 THz at B=0; and (b) 1well injector/3well active region, emitting at 2 THz at B=0 T. By applying the appropriate electrical bias and strong magnetic fields, we achieved laser emission at 0.80.9 THz at B>16 T [1], and 0.6 THz at B˜17 T, from devices a and b respectively. The ability to achieve subTHz lasing is due to magnetic field enhanced population inversion in a quasi0D QCL. [1] Wade, A et. al., Magnetic field assisted Terahertz quantum cascade laser operating up to 225K, Accepted for publication Nature Photonics (2009)

On the Mean Field and Classical Limits of Quantum Mechanics
NASA Astrophysics Data System (ADS)
Golse, François; Mouhot, Clément; Paul, Thierry
20160401
The main result in this paper is a new inequality bearing on solutions of the Nbody linear Schrödinger equation and of the mean field Hartree equation. This inequality implies that the mean field limit of the quantum mechanics of N identical particles is uniform in the classical limit and provides a quantitative estimate of the quality of the approximation. This result applies to the case of C 1,1 interaction potentials. The quantity measuring the approximation of the Nbody quantum dynamics by its mean field limit is analogous to the MongeKantorovich (or Wasserstein) distance with exponent 2. The inequality satisfied by this quantity is reminiscent of the work of Dobrushin on the mean field limit in classical mechanics [Func. Anal. Appl. 13, 115123, (1979)]. Our approach to this problem is based on a direct analysis of the Nparticle Liouville equation, and avoids using techniques based on the BBGKY hierarchy or on second quantization.

Electric field control of spin splitting in IIIV semiconductor quantum dots without magnetic field
NASA Astrophysics Data System (ADS)
Prabhakar, Sanjay; Melnik, Roderick
20151001
We provide an alternative means of electric field control for spin manipulation in the absence of magnetic fields by transporting quantum dots adiabatically in the plane of twodimensional electron gas. We show that the spin splitting energy of moving quantum dots is possible due to the presence of quasiHamiltonian that might be implemented to make the next generation spintronic devices of post CMOS technology. Such spin splitting energy is highly dependent on the material properties of semiconductor. It turns out that this energy is in the range of meV and can be further enhanced with increasing pulse frequency. In particular, we show that quantum oscillations in phonon mediated spinflip behaviors can be observed. We also confirm that no oscillations in spinflip behaviors can be observed for the pure Rashba or pure Dresselhaus cases.

Magnetooptical absorption in semiconducting spherical quantum dots: Influence of the dotsize, confining potential, and magnetic field
SciTech Connect
Kushwaha, Manvir S.
20141215
Semiconducting quantum dots – more fancifully dubbed artificial atoms – are quasizero dimensional, tiny, manmade systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement – or the lack of any degree of freedom for the electrons (and/or holes) – in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magnetooptical absorption in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of BohmPines’ randomphase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various singleparticle and manyparticle phenomena such as the FockDarwin spectrum; Fermi energy; magnetooptical transitions; probability distribution; and the magnetooptical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing) the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots: resulting into a blue (red) shift in the absorption spectrum. The Fermi energy diminishes with both increasing magneticfield and dotsize; and exhibits sawtoothlike oscillations at large values of field or dotsize. Unlike laterally confined quantum dots, both (upper and lower) magnetooptical transitions survive even in the extreme instances. However, the intraLandau level

Manipulating quantum fields with a single atom in a cavity
SciTech Connect
Haroche, Serge
19950401
Circular Rydberg atoms, detected by the very sensitive and state selective field ionization method, can be used to measure and manipulate quantum fields stored in a cavity. The method is based on an interferometric detection of the dispersive energy shifts experienced by these atoms when they interact with a slightly offresonant field mode sustained by a cavity which the atoms cross one at a time. These shifts give rise to a translation of the Ramsey fringe pattern observed in the field ionization signal of the atoms. The method consitutes a nondestructive way of photon counting. In this experiment, non local correlations between the atom and the cavity field are created, which could be used to perform new types of EinsteinPodolskyRosen experiments. Non classical fields could also be generated, which would display some of the properties discussed by Schroedinger in his famous 'cat paradox'. We present the theory of these experiments which until very recently would have been considered as mere 'gedanken' ones and we describe the operation of a Rydberg atom interferometer which has already enabled us to detect subphoton fields and to measure vacuum field effects in a cavity.

Quantum entanglement in three accelerating qubits coupled to scalar fields
NASA Astrophysics Data System (ADS)
Dai, Yue; Shen, Zhejun; Shi, Yu
20160701
We consider quantum entanglement of three accelerating qubits, each of which is locally coupled with a real scalar field, without causal influence among the qubits or among the fields. The initial states are assumed to be the GHZ and W states, which are the two representative threepartite entangled states. For each initial state, we study how various kinds of entanglement depend on the accelerations of the three qubits. All kinds of entanglement eventually suddenly die if at least two of three qubits have large enough accelerations. This result implies the eventual sudden death of all kinds of entanglement among three particles coupled with scalar fields when they are sufficiently close to the horizon of a black hole.

Quantum spin Hall effect induced by electric field in silicene
NASA Astrophysics Data System (ADS)
An, XingTao; Zhang, YanYang; Liu, JianJun; Li, ShuShen
20130101
We investigate the transport properties in a zigzag silicene nanoribbon in the presence of an external electric field. The staggered sublattice potential and two kinds of Rashba spinorbit couplings can be induced by the external electric field due to the buckled structure of the silicene. A bulk gap is opened by the staggered potential and gapless edge states appear in the gap by tuning the two kinds of Rashba spinorbit couplings properly. Furthermore, the gapless edge states are spinfiltered and are insensitive to the nonmagnetic disorder. These results prove that the quantum spin Hall effect can be induced by an external electric field in silicene, which may have certain practical significance in applications for future spintronics device.

Quantum Lifshitz Field Theory of a Frustrated Ferromagnet.
PubMed
Balents, Leon; Starykh, Oleg A
20160429
We propose a universal nonlinear sigma model field theory for onedimensional frustrated ferromagnets, which applies in the vicinity of a "quantum Lifshitz point," at which the ferromagnetic state develops a spin wave instability. We investigate the phase diagram resulting from perturbations of the exchange and of magnetic field away from the Lifshitz point, and uncover a rich structure with two distinct regimes of different properties, depending upon the value of a marginal, dimensionless, parameter of the theory. In the regime relevant for onedimensional systems with low spin, we find a metamagnetic transition line to a vector chiral phase. This line terminates in a critical end point, beyond which there is at least one multipolar or "spin nematic" phase. We show that the field theory is asymptotically exactly soluble near the Lifshitz point.

Limits of the measurability of the local quantum electromagneticfield amplitude
NASA Astrophysics Data System (ADS)
Compagno, G.; Persico, F.
19980301
The precision with which the amplitude of the free electromagnetic field can be measured locally in QED is evaluated by analyzing a wellknown gedanken experiment originally proposed by Bohr and Rosenfeld (BR). The analysis is performed by applying standard theoretical techniques familiar in quantum optics. The main result obtained for the precision is significantly different from the generally accepted BohrRosenfeld result. This leads to questioning the widely accepted notion of the compensating field, fostered by these authors. A misconception at the origin of this notion is pointed out by a careful investigation of the selfforce acting on the apparatus designed to measure the field. The correct expression for this selfforce is found to be at variance with that proposed by Bohr and Rosenfeld and generally accepted. It is argued that, as a consequence of this new expression and in contrast with the generally accepted view, no compensating force of nonelectromagnetic nature is required in order to perform measurements of the quantum field amplitude with any desired accuracy. It is shown that the only limitations to the precision of the measurement, in the BR gedanken experiment, arise from the timeenergy uncertainty principle, as well as from the finite dimensions of the measuring apparatus.

Photoluminescence of ndoped double quantum well—electron subbands under influence of inplane magnetic fields
NASA Astrophysics Data System (ADS)
Orlita, M.; Byszewski, M.; Döhler, G. H.; Grill, M.; Hlídek, P.; Malzer, S.; Zvára, M.
20060801
We report on photoluminescence (PL) measurements of a GaAs/AlGaAs double quantum well (DQW) in high magnetic fields. Measurements were carried out on a selectively contacted symmetric p δnDQW δnp structure, which allows a variation of the electron density in DQW by a pn bias and simultaneously a tilting of DQW, when a pp bias is applied. Attention was paid to phenomena in inplane magnetic fields, theoretically studied by Huang and Lyo (HL), [Phys. Rev. B 59, (1999) 7600]. In this paper, we compare our results for both symmetric and asymmetric DQWs with the theoretical model made by HL. Whereas the spectra from a symmetric DQW fully confirmed the theoretical predictions, the results gained from DQW with an electricfieldinduced asymmetry did not allow a proper study of anticipated effects. The reasons for that are discussed.

Tracing the interwell plasmon in a gridgated doublequantumwell fieldeffect transistor
NASA Astrophysics Data System (ADS)
Popov, Vyacheslav V.; Teperik, Tatiana V.; Zayko, Yuriy N.; Horing, Norman J. M.; Fateev, Denis V.
20050601
The terahertz (THz) absorption spectra of plasmon modes in a gridgated doublequantumwell (DQW) fieldeffect transistor (FET) structute is analyzed theoretically and numerically using the scattering matrix approach and is shown to faithfully reproduce strong resonant features of recent experimental observations of THz photoconductivity in such a structure. No traces ofthe interwell plasmon is found in THz absorption spectra.

Theoretical investigation of injectionlocked high modulation bandwidth quantum cascade lasers.
PubMed
Meng, Bo; Wang, Qi Jie
20120116
In this study, we report for the first time to our knowledge theoretical investigation of modulation responses of injectionlocked midinfrared quantum cascade lasers (QCLs) at wavelengths of 4.6 μm and 9 μm, respectively. It is shown through a threelevel rate equations model that the direct intensity modulation of QCLs gives the maximum modulation bandwidths of ~7 GHz at 4.6 μm and ~20 GHz at 9 μm. By applying the injection locking scheme, we find that the modulation bandwidths of up to ~30 GHz and ~70 GHz can be achieved for QCLs at 4.6 μm and 9 μm, respectively, with an injection ratio of 5 dB. The result also shows that an ultrawide modulation bandwidth of more than 200 GHz is possible with a 10 dB injection ratio for QCLs at 9 μm. An important characteristic of injectionlocked QCLs is the nonexistence of unstable locking region in the locking map, in contrast to their diode laser counterparts. We attribute this to the ultrashort upper laser state lifetimes of QCLs.

Quantum field as a quantum cellular automaton: The Dirac free evolution in one dimension
NASA Astrophysics Data System (ADS)
Bisio, Alessandro; D'Ariano, Giacomo Mauro; Tosini, Alessandro
20150301
We present a quantum cellular automaton model in one spacedimension which has the Dirac equation as emergent. This model, a discretetime and causal unitary evolution of a lattice of quantum systems, is derived from the assumptions of homogeneity, parity and timereversal invariance. The comparison between the automaton and the Dirac evolutions is rigorously set as a discrimination problem between unitary channels. We derive an exact lower bound for the probability of error in the discrimination as an explicit function of the mass, the number and the momentum of the particles, and the duration of the evolution. Computing this bound with experimentally achievable values, we see that in that regime the QCA model cannot be discriminated from the usual Dirac evolution. Finally, we show that the evolution of oneparticle states with narrowband in momentum can be efficiently simulated by a dispersive differential equation for any regime. This analysis allows for a comparison with the dynamics of wavepackets as it is described by the usual Dirac equation. This paper is a first step in exploring the idea that quantum field theory could be grounded on a more fundamental quantum cellular automaton model and that physical dynamics could emerge from quantum information processing. In this framework, the discretization is a central ingredient and not only a tool for performing nonperturbative calculation as in lattice gauge theory. The automaton model, endowed with a precise notion of local observables and a full probabilistic interpretation, could lead to a coherent unification of a hypothetical discrete Planck scale with the usual Fermi scale of highenergy physics.

Pseudopotentialbased electron quantum transport: Theoretical formulation and application to nanometerscale silicon nanowire transistors
NASA Astrophysics Data System (ADS)
Fang, Jingtian; Vandenberghe, William G.; Fu, Bo; Fischetti, Massimo V.
20160101
We present a formalism to treat quantum electronic transport at the nanometer scale based on empirical pseudopotentials. This formalism offers explicit atomistic wavefunctions and an accurate band structure, enabling a detailed study of the characteristics of devices with a nanometerscale channel and body. Assuming externally applied potentials that change slowly along the electrontransport direction, we invoke the envelopewavefunction approximation to apply the open boundary conditions and to develop the transport equations. We construct the fullband open boundary conditions (selfenergies of device contacts) from the complex band structure of the contacts. We solve the transport equations and present the expressions required to calculate the device characteristics, such as device current and charge density. We apply this formalism to study ballistic transport in a gateallaround (GAA) silicon nanowire fieldeffect transistor with a bodysize of 0.39 nm, a gate length of 6.52 nm, and an effective oxide thickness of 0.43 nm. Simulation results show that this device exhibits a subthreshold slope (SS) of ˜66 mV/decade and a draininduced barrierlowering of ˜2.5 mV/V. Our theoretical calculations predict that lowdimensionality channels in a 3D GAA architecture are able to meet the performance requirements of future devices in terms of SS swing and electrostatic control.

Quantum driven dissipative parametric oscillator in a blackbody radiation field
SciTech Connect
Pachón, Leonardo A.; Brumer, Paul
20140115
We consider the general open system problem of a charged quantum oscillator confined in a harmonic trap, whose frequency can be arbitrarily modulated in time, that interacts with both an incoherent quantized (blackbody) radiation field and with an arbitrary coherent laser field. We assume that the oscillator is initially in thermodynamic equilibrium with its environment, a nonfactorized initial density matrix of the system and the environment, and that at t = 0 the modulation of the frequency, the coupling to the incoherent and the coherent radiation are switched on. The subsequent dynamics, induced by the presence of the blackbody radiation, the laser field, and the frequency modulation, is studied in the framework of the influence functional approach. This approach allows incorporating, in analytic closed formulae, the nonMarkovian character of the oscillatorenvironment interaction at any temperature as well the nonMarkovian character of the blackbody radiation and its zeropoint fluctuations. Expressions for the time evolution of the covariance matrix elements of the quantum fluctuations and the reduced densityoperator are obtained.

The quantum field theory of electric and magnetic charge
NASA Astrophysics Data System (ADS)
Blagojević, M.; Senjanović, P.
19880101
The dynamics of monopoles as quantum objects is described by the quantum field theory of monopoles and charges. Owing to the presence of a preferred direction n, this is the first example of a theory which is not manifestly Lorentz invariant, though intrinsically it possesses this invariance. Another unusual property of this Abelian theory is that it has two coupling constants connected via the quatization condition. The investigation of the basic properties of the theory is facilitated by the existence of various formulations. Thus, Lorentz invariance, which is not easily seen in Schwinger's Hamiltonian framework, is transparent after the introduction of the particlepath representation of Zwanziger's local Langrarian formulation. Ultraviolet properties of the theory receive a superior, nindependent treatment in this representation, with the result that favors opposite renormalization of electric and magnetic charge. The physical content of infrared regularization is clearly described in the onepotential formulation. Several other topics are treated: Dirac's quantum mechanics of the monopole, connection with nonAbelian monopoles, a supersymmetric generalization of the theory, and its possible role in preon dynamics.

NMR probing of quantum electron solids in high magnetic fields
NASA Astrophysics Data System (ADS)
Rhone, Trevor David
20150301
In the presence of a high magnetic field, a two dimensional electron system (2DES) is expected to manifest Wigner crystal phases. Over thirty years ago, the search for the Wigner solid led to the discovery of the fractional quantum Hall effect (FQHE). Since then, with the advent of GaAs quantum wells with increasingly high mobility, 2DESs in the quantum Hall regime have proved to be a hunting ground for exceedingly rich manybody physics. Incompressible liquid FQHE states were found to occur in the first Landau level at several fractional filling factors v with odddenominator. The sequence of FQHE states is truncated by the formation of a Wigner crystal of electrons at very low filling factors, the transition being affected by disorder. In the second Landau level, composite fermions, the quasiparticles of the FQHE, can pair to yield a remarkable evendenominator FQHE state, whose properties are at the forefront of investigation. More recently, electron solid phases have been shown to emerge around integer quantum Hall states. In this talk, I will discuss a new tool, resistively detected NMR, which serves as a direct local probe of inplane charge density modulations in the 2DES. In our recent work [1] we probe the local charge density landscape of Wigner solids in the vicinity of v = 2 and v<1/3 revealing quantum correlations. This unprecedented access to the microscopic behavior of these exotic solid phases opens up new venues in FQH studies. Furthermore, our NMR technique can probe inplane charge density fluctuations due to disorder, allowing increased access to understanding roles of disorder in quantum Hall systems. In addition, our latest NMR measurements reveal evidence for charge inhomogeneity in the third Landau level which leads to the possibility of studying bubble and stripe phases in this regime. Future directions may find our NMR technique applied to other exotic phases such as quasiparticle solid phases, which have been proposed to emerge near the v

Quantum Mechanics with a MomentumSpace Artificial Magnetic Field
NASA Astrophysics Data System (ADS)
Price, Hannah M.; Ozawa, Tomoki; Carusotto, Iacopo
20141101
The Berry curvature is a geometrical property of an energy band which acts as a momentum space magnetic field in the effective Hamiltonian describing singleparticle quantum dynamics. We show how this perspective may be exploited to study systems directly relevant to ultracold gases and photonics. Given the exchanged roles of momentum and position, we demonstrate that the global topology of momentum space is crucially important. We propose an experiment to study the HarperHofstadter Hamiltonian with a harmonic trap that will illustrate the advantages of this approach and that will also constitute the first realization of magnetism on a torus.

Space–timebounded quantum fields for detection processes
PubMed Central
Aguayo, Fernando J.; Jaroszkiewicz, George
20140101
We discuss a quantum field detection model comprising two types of detection procedures: maximal detection, where the initial state of the system and detectors undergoes an irreversible evolution, and minimal detection, where the system–detector interaction consists of a small, reversible coupling and posterior maximal detection performed over the detector system. Combined, these detection procedures allow for a timedependent description of signalling experiments involving yes/no type of questions. A particular minimal detection model, stable in the presence of the vacuum, is presented and studied, successfully reproducing the localization of the state after a detection. PMID:24711717

Resource Letter QI1: Quantum Information
NASA Astrophysics Data System (ADS)
Strauch, Frederick W.
20160701
This Resource Letter surveys the history and modern developments in the field of quantum information. It is written to guide advanced undergraduates, beginning graduate students, and other new researchers to the theoretical and experimental aspects of this field. The topics covered include quantum states and processes, quantum coding and cryptography, quantum computation, the experimental implementation of quantum information processing, and the role of quantum information in the fundamental properties and foundations of physical theories.

Gauge fields and composite fermions in bilayer quantum Hall systems
NASA Astrophysics Data System (ADS)
Cipri, Robert
When placed in a strong magnetic field, a twodimensional electron gas can exhibit the quantum Hall effect in which a step like pattern forms in the Hall resistance, RH, which is defined to be the voltage drop perpendicular to the current driven through the plane of the sample divided by the magnitude of the current. The filling fraction nu = p/q defines the quantization condition where p and q are relatively prime integers and q is odd, with RH =h/(nu e2) where h is Planck's constant and e is the charge of the electron. At the same time the Hall resistance becomes quantized the longitudinal resistance vanishes indicating dissipationless current flow. The integer quantum Hall effect (nu = 1, 2, 3...) is simply modeled using singleparticle energy levels while the manybody fractional quantum Hall effect can be understood in terms of new particles known as composite fermions, electrons bound to an even number of statistical flux quanta. In this approach, the fractional quantum Hall effect for electrons is viewed as an effective integer quantum Hall effect for composite fermions. It was pointed out by Halperin, Lee and Read that for filling fraction nu = 1/2 the external magnetic field is exactly canceled by the average of the statistical flux quanta attached to the composite fermions. As a result, the composite fermions move in zero effective magnetic field with a welldefined Fermi surface at zero temperature. This "metallic" state is compressible and does not have a quantized Hall resistance. However, when two nu = 1/2 layers are brought close together, interactions between the layers lead to a new incompressible bilayer quantum Hall state in which electrons form a exciton condensate with total filling fraction nuT = 1/2 + 1/2 = 1. Recently it has been proposed that an interesting new transition may occur in this system in which interlayer Coulomb repulsion leads to excitonic condensation not of electrons but of composite fermions which are then free to tunnel

AbInitio Hamiltonian Approach to Light Nuclei And to Quantum Field Theory
SciTech Connect
Vary, J.P.; Honkanen, H.; Li, Jun; Maris, P.; Shirokov, A.M.; Brodsky, S.J.; Harindranath, A.; de Teramond, G.F.; Ng, E.G.; Yang, C.; Sosonkina, M.; /Ames Lab
20120622
Nuclear structure physics is on the threshold of confronting several longstanding problems such as the origin of shell structure from basic nucleonnucleon and threenucleon interactions. At the same time those interactions are being developed with increasing contact to QCD, the underlying theory of the strong interactions, using effective field theory. The motivation is clear  QCD offers the promise of great predictive power spanning phenomena on multiple scales from quarks and gluons to nuclear structure. However, new tools that involve nonperturbative methods are required to build bridges from one scale to the next. We present an overview of recent theoretical and computational progress with a Hamiltonian approach to build these bridges and provide illustrative results for the nuclear structure of light nuclei and quantum field theory.

Effect of the tilted magnetic field on the magnetosubbands and conductance in the bilayer quantum wire
NASA Astrophysics Data System (ADS)
Chwiej, T.
20161001
We theoretically study the single electron magnetotransport in GaAs and InGaAs vertically stacked bilayer nanowires. In considered geometry, the tilted magnetic field is always perpendicular to the main (transport) axis of the quantum wire and, therefore its transverse and vertical components allow separately for changing the magnitude of intralayer and interlayer subbands mixing. We study the changes introduced to energy dispersion relation E(k) by tilted magnetic field of strength up to several tesla and analyze their origins for symmetric as well as asymmetric confining potentials in the growth direction. Calculated energy dispersion relations are thereafter used to show that the value of a conductance of the bilayer nanowire may abruptly rise as well as fall by few conductance quanta when the Fermi energy in nanosystem is changed. It is also shown that such conductance oscillations, in conjunction with spin Zeeman effect, may give a moderately spin polarized current in the bilayer nanowire.

BOOK REVIEW: Mathematica for Theoretical Physics: Electrodynamics, Quantum Mechanics, General Relativity and Fractals
NASA Astrophysics Data System (ADS)
Heusler, Stefan
20061201
The main focus of the second, enlarged edition of the book Mathematica for Theoretical Physics is on computational examples using the computer program Mathematica in various areas in physics. It is a notebook rather than a textbook. Indeed, the book is just a printout of the Mathematica notebooks included on the CD. The second edition is divided into two volumes, the first covering classical mechanics and nonlinear dynamics, the second dealing with examples in electrodynamics, quantum mechanics, general relativity and fractal geometry. The second volume is not suited for newcomers because basic and simple physical ideas which lead to complex formulas are not explained in detail. Instead, the computer technology makes it possible to write down and manipulate formulas of practically any length. For researchers with experience in computing, the book contains a lot of interesting and nontrivial examples. Most of the examples discussed are standard textbook problems, but the power of Mathematica opens the path to more sophisticated solutions. For example, the exact solution for the perihelion shift of Mercury within general relativity is worked out in detail using elliptic functions. The virial equation of state for molecules' interaction with LennardJoneslike potentials is discussed, including both classical and quantum corrections to the second virial coefficient. Interestingly, closed solutions become available using sophisticated computing methods within Mathematica. In my opinion, the textbook should not show formulas in detail which cover three or more pages—these technical data should just be contained on the CD. Instead, the textbook should focus on more detailed explanation of the physical concepts behind the technicalities. The discussion of the virial equation would benefit much from replacing 15 pages of Mathematica output with 15 pages of further explanation and motivation. In this combination, the power of computing merged with physical intuition

Reconstruction of exciton wave functions of coupled quantum emitters including spin with ultrafast spectroscopy using localized nanooptical fields
NASA Astrophysics Data System (ADS)
Specht, Judith F.; Richter, Marten
20160401
Coulombinduced resonance energy transfer mechanisms between coupled nanostructures lead to the formation of new, delocalized exciton states. Their hybrid wave functions can be decomposed into the basis of local states of the uncoupled system by the use of coherent, spatially resolved spectroscopy. The suggested quantum state tomography protocol combines nanooptical fields with a fourwave mixing technique: At least one pulse of the pulse sequence is spatially localized at a specific quantum emitter. It was suggested to use nanoplasmonic structures together with pulseshaped fields for the localization. In this paper, the method is applied to a system of two coupled semiconductor quantum dots. The basic reconstruction concept first proposed in Richter et al. (Phys Rev B 86:085308, 2012) and Schlosser et al. (New J Phys 15:025004, 2013) is extended to the case of including different spin states of the excitons in the quantum dots. For this purpose, the theoretical scheme has to be modified and the localized fields need the ability to change their polarization. We show that the application of the developed reconstruction scheme to twodimensional spectra gives full access to the internal structure of the interacting quantum states.

Model for noncancellation of quantum electric field fluctuations
SciTech Connect
Parkinson, Victor; Ford, L. H.
20111215
A localized charged particle oscillating near a reflecting boundary is considered as a model for noncancellation of vacuum fluctuations. Although the mean velocity of the particle is sinusoidal, the velocity variance produced by vacuum fluctuations can either grow or decrease linearly in time, depending upon the product of the oscillation frequency and the distance to the boundary. This amounts to heating or cooling arising from noncancellation of electric field fluctuations, which are otherwise anticorrelated in time. Similar noncancellations arise in quantum field effects in timedependent curved spacetimes. We give some estimates of the magnitude of the effect, and discuss its potential observability. We also compare the effects of vacuum fluctuations with the shot noise due to emission of a finite number of photons. We find that the two effects can be comparable in magnitude, but have distinct characteristics, and hence could be distinguished in an experiment.

Classical and quantum particle dynamics in univariate background fields
NASA Astrophysics Data System (ADS)
Heinzl, T.; Ilderton, A.; King, B.
20160901
We investigate deviations from the plane wave model in the interaction of charged particles with strong electromagnetic fields. A general result is that integrability of the dynamics is lost when going from lightlike to timelike or spacelike field dependence. For a special scenario in the classical regime we show how the radiation spectrum in the spacelike (undulator) case becomes wellapproximated by the plane wave model in the highenergy limit, despite the two systems being Lorentz inequivalent. In the quantum problem, there is no analogue of the WKBexact Volkov solution. Nevertheless, WKB and uniformWKB approaches give good approximations in all cases considered. Other approaches that reduce the underlying differential equations from second to first order are found to miss the correct physics for situations corresponding to barrier transmission and wideangle scattering.

NonGaussian quantum states generation and robust quantum nonGaussianity via squeezing field
NASA Astrophysics Data System (ADS)
Tang, XuBing; Gao, Fang; Wang, YaoXiong; Kuang, Sen; Shuang, Feng
20150301
Recent studies show that quantum nonGaussian states or using nonGaussian operations can improve entanglement distillation, quantum swapping, teleportation, and cloning. In this work, employing a strategy of nonGaussian operations (namely subtracting and adding a single photon), we propose a scheme to generate nonGaussian quantum states named singlephotonadded and subtracted coherent (SPASC) superposition states by implementing Bell measurements, and then investigate the corresponding nonclassical features. By squeezed the input field, we demonstrate that robustness of nonGaussianity can be improved. Controllable phase space distribution offers the possibility to approximately generate a displaced coherent superposition states (DCSS). The fidelity can reach up to F ≥ 0.98 and F ≥ 0.90 for size of amplitude z = 1.53 and 2.36, respectively. Project supported by the National Natural Science Foundation of China (Grant Nos. 61203061 and 61074052), the Outstanding Young Talent Foundation of Anhui Province, China (Grant No. 2012SQRL040), and the Natural Science Foundation of Anhui Province, China (Grant No. KJ2012Z035).

Quantum mechanical solver for confined heterostructure tunnel fieldeffect transistors
SciTech Connect
Verreck, Devin Groeseneken, Guido; Van de Put, Maarten; Sorée, Bart; Magnus, Wim; Verhulst, Anne S.; Collaert, Nadine; Thean, Aaron; Vandenberghe, William G.
20140207
Heterostructure tunnel fieldeffect transistors (HTFET) are promising candidates for lowpower applications in future technology nodes, as they are predicted to offer high oncurrents, combined with a sub60 mV/dec subthreshold swing. However, the effects of important quantum mechanical phenomena like size confinement at the heterojunction are not well understood, due to the theoretical and computational difficulties in modeling realistic heterostructures. We therefore present a ballistic quantum transport formalism, combining a novel envelope function approach for semiconductor heterostructures with the multiband quantum transmitting boundary method, which we extend to 2D potentials. We demonstrate an implementation of a 2band version of the formalism and apply it to study confinement in realistic heterostructure diodes and pnin HTFETs. For the diodes, both transmission probabilities and current densities are found to decrease with stronger confinement. For the pnin HTFETs, the improved gate control is found to counteract the deterioration due to confinement.

Field electron and ion emission from charged surfaces: a strategic historical review of theoretical concepts.
PubMed
Forbes, Richard G
20030101
The fieldelectron (FE) and fieldion techniques directly observe and measure atomiclevel surface processes that occur in very high electric fields. In theoretical terms, the high fields put large additional terms into Hamiltonians and free energies, and significantly modify many aspects of the surface physics and chemistry, as compared with the fieldfree situation. This paper presents a strategic review of the fundamental science of some of these highfield surface effects and processes, as developed in the context of the field electron and ion emission techniques. It outlines the main theoretical concepts developed, notes some twists of scientific history, and suggests useful contributions made to mainstream science. Topics covered are basic aspects of FE emission, surface field ionisation, localised field adsorption, charged surfaces theory, fieldion image contrast theory and associated imaginggas kinetics, field evaporation, and aspects of the thermodynamics of charged surfaces. Despite many years of effort, important aspects of the theory remain incomplete. Some theoretical challenges are noted.

Quantum Optics
NASA Astrophysics Data System (ADS)
Orvil Scully, Marlan; Zubairy, Muhammad Suhail
19970901
Quantum optics has witnessed significant theoretical and experimental developments in recent years. This book provides an indepth and wideranging introduction to the subject, emphasizing throughout the basic principles and their applications. The book begins by developing the basic tools of quantum optics, and goes on to show the application of these tools in a variety of quantum optical systems, including lasing without inversion, squeezed states, and atom optics. The final four chapters discuss quantum optical tests of the foundations of quantum mechanics, and particular aspects of measurement theory. Assuming only a background of standard quantum mechanics and electromagnetic theory, and containing many problems and references, this book will be invaluable to graduate students of quantum optics, as well as to researchers in this field.

Gaugefields and integrated quantumclassical theory
SciTech Connect
Stapp, H.P.
19860101
Physical situations in which quantum systems communicate continuously to their classically described environment are not covered by contemporary quantum theory, which requires a temporary separation of quantum degrees of freedom from classical ones. A generalization would be needed to cover these situations. An incomplete proposal is advanced for combining the quantum and classical degrees of freedom into a unified objective description. It is based on the use of certain quantumclassical structures of light that arise from gauge invariance to coordinate the quantum and classical degrees of freedom. Also discussed is the question of where experimenters should look to find phenomena pertaining to the quantumclassical connection. 17 refs.

Quantum field theory and gravity in causal sets
NASA Astrophysics Data System (ADS)
Sverdlov, Roman M.
Causal set is a model of space time that allows to reconcile discreteness and manifest relativistic invariance. This is done by viewing space time as finite, partially ordered set. The elements of the set are viewed as points of space time, or events; the partial ordering between them is viewed as causal relations. It has been shown that, in discrete scenario, the information about causal relations between events can, indeed, approximate the metric. The goal of this thesis is to introduce matter fields and their Lagrangians into causal set context. This is a two step process. The first step is to redefine gauge fields, gravity, and distances in such a way that no reference to Lorentz index is made. This is done by defining gauge fields as twopoint real valued functions, and gravitational field as causal structure itself. Once the above is done, Lagrangians have to be defined in a way that they don't refer to Lorentzian indices either. This is done by introducing a notion of type 1 and type 2 Lagrangian generators, coupled with respective machinery that "translates" each generator into corresponding Lagrangian. The fields that are subject to these generators are, respectively, defined as type 1 and type 2. The main difference between two kinds of fields is the prediction of different behavior in different dimensions of type 2 fields. However, despite our inability to travel to different dimensions, gravity was shown to be type 2 based on the erroneous predictions of its 4dimensional behavior if it was viewed as type 1. However, no erroneous predictions are made if nongravitational fields are viewed as either type 1 or type 2, thus the nature of the latter is still an open question. Finally, an attempt was made to provide interpretation of quantum mechanics that would allow to limit fluctuations of causal structure to allow some topological background. However, due to its controversial nature, it is placed in the Appendix.

Consistency restrictions on maximal electricfield strength in quantum field theory.
PubMed
Gavrilov, S P; Gitman, D M
20080926
Quantum field theory with an external background can be considered as a consistent model only if backreaction is relatively small with respect to the background. To find the corresponding consistency restrictions on an external electric field and its duration in QED and QCD, we analyze the meanenergy density of quantized fields for an arbitrary constant electric field E, acting during a large but finite time T. Using the corresponding asymptotics with respect to the dimensionless parameter eET2, one can see that the leading contributions to the energy are due to the creation of particles by the electric field. Assuming that these contributions are small in comparison with the energy density of the electric background, we establish the abovementioned restrictions, which determine, in fact, the time scales from above of depletion of an electric field due to the backreaction.

Theoretical Study of AllElectrical Quantum Wire Valley Filters in Bilayer Graphene
NASA Astrophysics Data System (ADS)
Wu, YuShu; Lue, NingYuan; Chen, YenChun; Jiang, JiaHuei; Chou, MeiYin
Graphene electrons carry valley pseudospin, due to the double valley degeneracy in graphene band structure. In gapped graphene, the pseudospin is coupled to an inplane electric field, through the mechanism of valleyorbit interaction (VOI), Based on the VOI, a family of electricallycontrolled valleytronic devices have been proposed. Here, we report the theoretical study of a recently proposed valley filter consisting of a Q1D channel in bilayer graphene defined and controlled by electrical gates. We discuss two types of calculations  those of energy subband structure in the channel and electron transmission through a valley valve consisting of two proposed filters. For the former, we have developed a tight binding formulation in the continuum limit. For the latter, we employ the recursive Green's function method. Results from the calculations will be presented. Financial support by MoST, Taiwan, ROC is acknowledged.

A practical and theoretical definition of very small field size for radiotherapy output factor measurements
SciTech Connect
Charles, P. H. Crowe, S. B.; Langton, C. M.; Trapp, J. V.; CranmerSargison, G.; Thwaites, D. I.; Kairn, T.; Knight, R. T.; Kenny, J.
20140415
Purpose: This work introduces the concept of very small field size. Output factor (OPF) measurements at these field sizes require extremely careful experimental methodology including the measurement of dosimetric field size at the same time as each OPF measurement. Two quantifiable scientific definitions of the threshold of very small field size are presented. Methods: A practical definition was established by quantifying the effect that a 1 mm error in field size or detector position had on OPFs and setting acceptable uncertainties on OPF at 1%. Alternatively, for a theoretical definition of very small field size, the OPFs were separated into additional factors to investigate the specific effects of lateral electronic disequilibrium, photon scatter in the phantom, and source occlusion. The dominant effect was established and formed the basis of a theoretical definition of very small fields. Each factor was obtained using Monte Carlo simulations of a Varian iX linear accelerator for various square field sizes of side length from 4 to 100 mm, using a nominal photon energy of 6 MV. Results: According to the practical definition established in this project, field sizes ≤15 mm were considered to be very small for 6 MV beams for maximal field size uncertainties of 1 mm. If the acceptable uncertainty in the OPF was increased from 1.0% to 2.0%, or field size uncertainties are 0.5 mm, field sizes ≤12 mm were considered to be very small. Lateral electronic disequilibrium in the phantom was the dominant cause of change in OPF at very small field sizes. Thus the theoretical definition of very small field size coincided to the field size at which lateral electronic disequilibrium clearly caused a greater change in OPF than any other effects. This was found to occur at field sizes ≤12 mm. Source occlusion also caused a large change in OPF for field sizes ≤8 mm. Based on the results of this study, field sizes ≤12 mm were considered to be theoretically very small for 6

Mass Charge Interactions for Visualizing the Quantum Field
NASA Astrophysics Data System (ADS)
Baer, Wolfgang
Our goal is to integrate the objective and subjective aspects of our personal experience into a single complete theory of reality. To further this endeavor we replace elementary particles with elementary events as the building blocks of an event oriented description of that reality. The simplest event in such a conception is an adaptation of A. Wheeler's primitive explanatorymeasurement cycle between internal observations experienced by an observer and their assumed physical causes. We will show how internal forces between charge and mass are required to complete the cyclic sequence of activity. This new formulation of internal material is easier to visualize and map to cognitive experiences than current formulations of subatomic physics. In our formulation, called Cognitive Action Theory, such internal forces balance the external forces of gravityinertia and electricitymagnetism. They thereby accommodate outside influences by adjusting the internal structure of material from which all things are composed. Such accommodation is interpreted as the physical implementation of a model of the external physical world in the brain of a cognitive being or alternatively the response mechanism to external influences in the material of inanimate objects. We adopt the deBroglieBohm causal interpretation of QT to show that the nature of space in our model is mathematically equivalent to a field of clocks. Within this field small oscillations form deBroglie waves. This interpretation allows us to visualize the underlying structure of empty space with a chargemass separation field in equilibrium, and objects appearing in space with quantum wave disturbances to that equilibrium occurring inside material. Space is thereby associated with the internal structure of material and quantum mechanics is shown to be, paraphrasing Heisenberg, the physics of the material that knows the world.

Probing the effective nuclearspin magnetic field in a single quantum dot via full counting statistics
SciTech Connect
Xue, HaiBin; Nie, YiHang; Chen, Jingzhe; Ren, Wei
20150315
We study theoretically the full counting statistics of electron transport through a quantum dot weakly coupled to two ferromagnetic leads, in which an effective nuclearspin magnetic field originating from the configuration of nuclear spins is considered. We demonstrate that the quantum coherence between the two singlyoccupied eigenstates and the spin polarization of two ferromagnetic leads play an important role in the formation of superPoissonian noise. In particular, the orientation and magnitude of the effective field have a significant influence on the variations of the values of highorder cumulants, and the variations of the skewness and kurtosis values are more sensitive to the orientation and magnitude of the effective field than the shot noise. Thus, the highorder cumulants of transport current can be used to qualitatively extract information on the orientation and magnitude of the effective nuclearspin magnetic field in a single quantum dot.  Highlights: • The effective nuclearspin magnetic field gives rise to the offdiagonal elements of the reduced density matrix of single QD. • The offdiagonal elements of reduced density matrix of the QD have a significant impact on the highorder current cumulants. • The highorder current cumulants are sensitive to the orientation and magnitude of the effective nuclearspin magnetic field. • The FCS can be used to detect the orientation and magnitude of the effective nuclearspin magnetic field in a single QD.

Quantum cryptography: Theoretical protocols for quantum key distribution and tests of selected commercial QKD systems in commercial fiber networks
NASA Astrophysics Data System (ADS)
Jacak, Monika; Jacak, Janusz; Jóźwiak, Piotr; Jóźwiak, Ireneusz
20160601
The overview of the current status of quantum cryptography is given in regard to quantum key distribution (QKD) protocols, implemented both on nonentangled and entangled flying qubits. Two commercial R&D platforms of QKD systems are described (the Clavis II platform by idQuantique implemented on nonentangled photons and the EPR S405 Quelle platform by AIT based on entangled photons) and tested for feasibility of their usage in commercial TELECOM fiber metropolitan networks. The comparison of systems efficiency, stability and resistivity against noise and hacker attacks is given with some suggestion toward system improvement, along with assessment of two models of QKD.

Atomic electric fields revealed by a quantum mechanical approach to electron picodiffraction
PubMed Central
Müller, Knut; Krause, Florian F.; Béché, Armand; Schowalter, Marco; Galioit, Vincent; Löffler, Stefan; Verbeeck, Johan; Zweck, Josef; Schattschneider, Peter; Rosenauer, Andreas
20140101
By focusing electrons on probes with a diameter of 50 pm, aberrationcorrected scanning transmission electron microscopy (STEM) is currently crossing the border to probing subatomic details. A major challenge is the measurement of atomic electric fields using differential phase contrast (DPC) microscopy, traditionally exploiting the concept of a fieldinduced shift of diffraction patterns. Here we present a simplified quantum theoretical interpretation of DPC. This enables us to calculate the momentum transferred to the STEM probe from diffracted intensities recorded on a pixel array instead of conventional segmented brightfield detectors. The methodical development yielding atomic electric field, charge and electron density is performed using simulations for binary GaN as an ideal model system. We then present a detailed experimental study of SrTiO3 yielding atomic electric fields, validated by comprehensive simulations. With this interpretation and upgraded instrumentation, STEM is capable of quantifying atomic electric fields and highcontrast imaging of light atoms. PMID:25501385

Determining polarizable force fields with electrostatic potentials from quantum mechanical linear response theory
NASA Astrophysics Data System (ADS)
Wang, Hao; Yang, Weitao
20160601
We developed a new method to calculate the atomic polarizabilities by fitting to the electrostatic potentials (ESPs) obtained from quantum mechanical (QM) calculations within the linear response theory. This parallels the conventional approach of fitting atomic charges based on electrostatic potentials from the electron density. Our ESP fitting is combined with the induced dipole model under the perturbation of uniform external electric fields of all orientations. QM calculations for the linear response to the external electric fields are used as input, fully consistent with the induced dipole model, which itself is a linear response model. The orientation of the uniform external electric fields is integrated in all directions. The integration of orientation and QM linear response calculations together makes the fitting results independent of the orientations and magnitudes of the uniform external electric fields applied. Another advantage of our method is that QM calculation is only needed once, in contrast to the conventional approach, where many QM calculations are needed for many different applied electric fields. The molecular polarizabilities obtained from our method show comparable accuracy with those from fitting directly to the experimental or theoretical molecular polarizabilities. Since ESP is directly fitted, atomic polarizabilities obtained from our method are expected to reproduce the electrostatic interactions better. Our method was used to calculate both transferable atomic polarizabilities for polarizable molecular mechanics' force fields and nontransferable moleculespecific atomic polarizabilities.

Determining polarizable force fields with electrostatic potentials from quantum mechanical linear response theory.
PubMed
Wang, Hao; Yang, Weitao
20160614
We developed a new method to calculate the atomic polarizabilities by fitting to the electrostatic potentials (ESPs) obtained from quantum mechanical (QM) calculations within the linear response theory. This parallels the conventional approach of fitting atomic charges based on electrostatic potentials from the electron density. Our ESP fitting is combined with the induced dipole model under the perturbation of uniform external electric fields of all orientations. QM calculations for the linear response to the external electric fields are used as input, fully consistent with the induced dipole model, which itself is a linear response model. The orientation of the uniform external electric fields is integrated in all directions. The integration of orientation and QM linear response calculations together makes the fitting results independent of the orientations and magnitudes of the uniform external electric fields applied. Another advantage of our method is that QM calculation is only needed once, in contrast to the conventional approach, where many QM calculations are needed for many different applied electric fields. The molecular polarizabilities obtained from our method show comparable accuracy with those from fitting directly to the experimental or theoretical molecular polarizabilities. Since ESP is directly fitted, atomic polarizabilities obtained from our method are expected to reproduce the electrostatic interactions better. Our method was used to calculate both transferable atomic polarizabilities for polarizable molecular mechanics' force fields and nontransferable moleculespecific atomic polarizabilities.

Oscillatorfield model of moving mirrors in quantum optomechanics
NASA Astrophysics Data System (ADS)
Galley, Chad R.; Behunin, Ryan O.; Hu, B. L.
20130401
We present a microphysics model for the kinematics and dynamics of optomechanics describing the coupling between an optical field, modeled here by a massless scalar field, and the internal and mechanical degrees of freedom of a movable mirror. Instead of implementing boundary conditions on the field, we introduce an internal degree of freedom and its dynamics to describe the mirror's reflectivity. Depending on parameter values, the internal degrees of freedom of the mirror in this model capture a range of its optical activities, from those exhibiting broadband reflective properties to those reflecting only in a narrow band. After establishing the model we show how appropriate parameter choices lead to other wellknown optomechanical models, including those of Barton and Calogeracos [Ann. Phys. (NY)0003491610.1006/aphy.1995.1021 238, 227 (1995)], Calogeracos and Barton, Ann. Phys. (NY)10.1006/aphy.1995.1022 238, 268 (1995), Law [Phys. Rev. APLRAAN1050294710.1103/PhysRevA.51.2537 51, 2537 (1995)], and Golestanian and Kardar [Phys. Rev. Lett.PRLTAO0031900710.1103/PhysRevLett.78.3421 78, 3421 (1997); Phys. Rev. APLRAAN1050294710.1103/PhysRevA.58.1713 58, 1713 (1998)]. As a simple illustrative application we derive classical radiation pressure cooling from this model. We then connect our microphysics model to the common descriptions of a moving mirror coupled to radiation pressure (e.g., with Nx coupling, where N is the photon number and x is the mirror displacement), making explicit the underlying assumptions made in these phenomenological models. Our model is also applicable to the lesser explored case of small N, which existing models based on sideband approximations [Kimble , Phys. Rev. DPRVDAQ1550799810.1103/PhysRevD.65.022002 65, 022002 (2001)] have not addressed. Interestingly, we also find that slowmoving mirrors in our model can be described by the ubiquitous Brownian motion model of quantum open systems. The scope of applications of this model ranges

Universal behavior after a quantum quench in interacting field theories
NASA Astrophysics Data System (ADS)
Mitra, Aditi
The dynamics of an isolated quantum system represented by a field theory with O(N) symmetry, and in d>2 spatial dimensions, is investigated after a quantum quench from a disordered initial state to the critical point. A perturbative renormalizationgroup approach involving an expansion around d=4 is employed to study the timeevolution, and is supplemented by an exact solution of the HartreeFock equations in the largeN limit. The results show that the dynamics is characterized by a prethermal regime controlled by elastic dephasing where excitations propagate ballistically, and a light cone emerges in correlation functions in real space. The memory of the initial state, together with the absence of timescales at the critical point, gives rise to universal powerlaw aging which is characterized by a new nonequilibrium shorttime exponent. The dynamics of the entanglement following a quench is also explored, and reveals that while the time evolution of the entanglement entropy itself is not much different between a free bosonic theory and an interacting bosonic theory, the lowenergy entanglement spectrum on the other hand shows clear signature of the nonequilibrium shorttime exponent related to aging. This work was done in collaboration with Y. Lemonik (NYU), M. Tavora (NYU), A. Chiocchetta (SISSA), A. Maraga (SISSA), and A. Gambassi (SISSA). Supported by NSFDMR 1303177.

Twodimensional quantum walk under artificial magnetic field
NASA Astrophysics Data System (ADS)
Yalcinkaya, Iskender; Gedik, Zafer
We introduce the Peierls substitution to a twodimensional discretetime quantum walk on a square lattice to examine the spreading dynamics and the coinposition entanglement in the presence of an artificial gauge field. We use the ratio of the magnetic flux through the unit cell to the flux quantum as a control parameter. For a given flux ratio, we obtain faster spreading for a small number of steps and the walker tends to be highly localized around the origin. Moreover, the spreading of the walk can be suppressed and decreased within a limited time interval for specific rational values of flux ratio. When the flux ratio is an irrational number, even for a large number of steps, the spreading exhibit diffusive behavior rather than the wellknown ballistic one as in the classical random walk and there is a significant probability of finding the walker at the origin. We also analyze the coinposition entanglement and show that the asymptotic behavior vanishes when the flux ratio is different from zero and the coinposition entanglement become nearly maximal in a periodic manner in a long time range.

Optimized quantum nondemolition measurement of a field quadrature
NASA Astrophysics Data System (ADS)
Paris, Matteo G.
20020101
We suggest an interferometric scheme assisted by squeezing and linear feedback to realize the whole class of fieldquadrature quantum nondemolition measurements, from Von Neumann projective measurement to a fully nondestructive noninformative one. In our setup, the signal under investigation is mixed with a squeezed probe in an interferometer and, at the output, one of the two modes is revealed through homodyne detection. The second beam is then amplitudemodulated according to the outcome of the measurement, and finally squeezed according to the transmittivity of the interferometer. Using strongly squeezed or antisqueezed probes respectively, one achieves either a projective measurement, i.e., homodyne statistics arbitrarily close to the intrinsic quadrature distribution of the signal, and conditional outputs approaching the corresponding eigenstates, or a fully nondestructive one, characterized by an almost uniform homodyne statistics, and by an output state arbitrarily close to the input signal. By varying the squeezing between these two extremes, or simply by tuning the internal phase shift of the interferometer, the whole set of intermediate cases may also be obtained. In particular, an optimal quantum nondemolition measurement of quadrature may be achieved, which minimizes the information gain versus state disturbance tradeoff.

Inequivalence of quantum field theories on noncommutative spacetimes: Moyal versus WickVoros planes
SciTech Connect
Balachandran, A. P.; Ibort, A.; Marmo, G.; Martone, M.
20100415
In this paper, we further develop the analysis started in an earlier paper on the inequivalence of certain quantum field theories on noncommutative spacetimes constructed using twisted fields. The issue is of physical importance. Thus it is well known that the commutation relations among spacetime coordinates, which define a noncommutative spacetime, do not constrain the deformation induced on the algebra of functions uniquely. Such deformations are all mathematically equivalent in a very precise sense. Here we show how this freedom at the level of deformations of the algebra of functions can fail on the quantum field theory side. In particular, quantum field theory on the WickVoros and Moyal planes are shown to be inequivalent in a few different ways. Thus quantum field theory calculations on these planes will lead to different physics even though the classical theories are equivalent. This result is reminiscent of chiral anomaly in gauge theories and has obvious physical consequences. The construction of quantum field theories on the WickVoros plane has new features not encountered for quantum field theories on the Moyal plane. In fact it seems impossible to construct a quantum field theory on the WickVoros plane which satisfies all the properties needed of field theories on noncommutative spaces. The Moyal twist seems to have unique features which make it a preferred choice for the construction of a quantum field theory on a noncommutative spacetime.

Realtime quantum trajectories for classically allowed dynamics in strong laser fields
NASA Astrophysics Data System (ADS)
Plimak, L. I.; Ivanov, Misha Yu.
20151001
Both the physical picture of the dynamics of atoms and molecules in intense infrared fields and its theoretical description use the concept of electron trajectories. Here, we address a key question which arises in this context: Are distinctly quantum features of these trajectories, such as the complexvalued coordinates, physically relevant in the classically allowed region of phase space, and what is their origin? First, we argue that solutions of classical equations of motion can account for quantum effects. To this end, we construct an exact solution to the classical HamiltonJacobi equation which accounts for dynamics of the wave packet, and show that this solution is physically correct in the limit ?. Second, we show that imaginary components of classical trajectories are directly linked to the finite size of the initial wave packet in momentum space. This way, if the electronic wave packet produced by optical tunnelling in strong infrared fields is localised both in coordinate and momentum, its motion after tunnelling ipso facto cannot be described with purely classical trajectories  in contrast to popular models in the literature.

C*algebraic scattering theory and explicitly solvable quantum field theories
NASA Astrophysics Data System (ADS)
Warchall, Henry A.
19850601
A general theoretical framework is developed for the treatment of a class of quantum field theories that are explicitly exactly solvable, but require the use of C*algebraic techniques because timedependent scattering theory cannot be constructed in any one natural representation of the observable algebra. The purpose is to exhibit mechanisms by which inequivalent representations of the observable algebra can arise in quantum field theory, in a setting free of other complications commonly associated with the specification of dynamics. One of two major results is the development of necessary and sufficient conditions for the concurrent unitary implementation of two automorphism groups in a class of quasifree representations of the algebra of the canonical commutation relations (CCR). The automorphism groups considered are induced by oneparameter groups of symplectic transformations on the classical phase space over which the Weyl algebra of the CCR is built; each symplectic group is conjugate by a fixed symplectic transformation to a oneparameter unitary group. The second result, an analog to the BirmanBelopol'skii theorem in twoHilbertspace scattering theory, gives sufficient conditions for the existence of Mo/ller wave morphisms in theories with timedevelopment automorphism groups of the above type. In a paper which follows, this framework is used to analyze a particular model system for which wave operators fail to exist in any natural representation of the observable algebra, but for which wave morphisms and an associated S matrix are easily constructed.

Quantum field theory of van der Waals friction
SciTech Connect
Volokitin, A. I.; Persson, B. N. J.
20061115
van der Waals friction between two semiinfinite solids, and between a small neutral particle and semiinfinite solid is studied using thermal quantum field theory in the Matsubara formulation. We show that the friction to linear order in the sliding velocity can be obtained from the equilibrium Green functions and that our treatment can be extended for bodies with complex geometry. The calculated friction agrees with the friction obtained using a dynamical modification of the Lifshitz theory, which is based on the fluctuationdissipation theorem. We show that it should be possible to measure the van der Waals friction in noncontact friction experiment using stateoftheart equipment.

Neutral current neutrino oscillation via quantum field theory approach
NASA Astrophysics Data System (ADS)
Ettefaghi, M. M.; Askaripour Ravari, Z.
20150701
Neutrino and antineutrino states coming from the neutral current or Z0 decay are blind with respect to the flavor. The neutrino oscillation is observed and formulated when its flavor is known. However, it has been shown that we can see neutrino oscillation pattern for Z0 decay neutrinos provided that both neutrino and antineutrino are detected. In this paper, we restudy this oscillation via quantum field theory approach. Through this approach, we find that the oscillation pattern ceases if the distance between the detectors is larger than the coherence length, while both neutrino and antineutrino states may be coherent. Also the uncertainty of source (region of Z0 decay) does not have any role in the coherency of neutrino and antineutrino.

Semianalytical quantum model for graphene fieldeffect transistors
SciTech Connect
Pugnaghi, Claudio; Grassi, Roberto Gnudi, Antonio; Di Lecce, Valerio; Gnani, Elena; Reggiani, Susanna; Baccarani, Giorgio
20140921
We develop a semianalytical model for monolayer graphene fieldeffect transistors in the ballistic limit. Two types of devices are considered: in the first device, the source and drain regions are doped by charge transfer with Schottky contacts, while, in the second device, the source and drain regions are doped electrostatically by a back gate. The model captures two important effects that influence the operation of both devices: (i) the finite density of states in the source and drain regions, which limits the number of states available for transport and can be responsible for negative output differential resistance effects, and (ii) quantum tunneling across the potential steps at the sourcechannel and drainchannel interfaces. By comparison with a selfconsistent nonequilibrium Green's function solver, we show that our model provides very accurate results for both types of devices, in the bias region of quasisaturation as well as in that of negative differential resistance.

Cyclotron resonance in InAs/AlSb quantum wells in magnetic fields up to 45 T
SciTech Connect
Spirin, K. E. Krishtopenko, S. S.; Sadofyev, Yu. G.; Drachenko, O.; Helm, M.; Teppe, F.; Knap, W.; Gavrilenko, V. I.
20151215
Electron cyclotron resonance in InAs/AlSb heterostructures with quantum wells of various widths in pulsed magnetic fields up to 45 T are investigated. Our experimental cyclotron energies are in satisfactory agreement with the results of theoretical calculations performed using the eightband kp Hamiltonian. The shift of the cyclotron resonance (CR) line, which corresponds to the transition from the lowest Landau level to the low magneticfield region, is found upon varying the electron concentration due to the negative persistent photoconductivity effect. It is shown that the observed shift of the CR lines is associated with the finite width of the density of states at the Landau levels.

AAstacked bilayer graphene quantum dots in magnetic field
NASA Astrophysics Data System (ADS)
Belouad, Abdelhadi; Zahidi, Youness; Jellal, Ahmed
20160501
By applying the infinitemass boundary condition, we analytically calculate the confined states and the corresponding wave functions of AAstacked bilayer graphene (BLG) quantum dots (QDs) in the presence of an uniform magnetic field B. It is found that the energy spectrum shows two set of levels, which are the double copies of the energy spectrum for single layer graphene, shifted up–down by +γ and γ , respectively. However, the obtained spectrum exhibits different symmetries between the electron and hole states as well as the intervalley symmetries. It is noticed that, the applied magnetic field breaks all symmetries, except one related to the intervalley electron–hole symmetry, i.e. {E}{{e}}(τ ,m)={E}{{h}}(τ ,m). Two different regimes of confinement are found: the first one is due to the infinitemass barrier at weak B and the second is dominated by the magnetic field as long as B is large. We numerically investigated the basics features of the energy spectrum to show the main similarities and differences with respect to monolayer graphene, ABstacked BLG and semiconductor QDs. Dedicated to Professor Dr Hachim A Yamani on the occasion of his 70th birthday.

Quantum corrections to the cosmological evolution of conformally coupled fields
SciTech Connect
Cembranos, Jose A.R.; Olive, Keith A.; Peloso, Marco; Uzan, JeanPhilippe Email: olive@physics.umn.edu Email: uzan@iap.fr
20090701
Because the source term for the equations of motion of a conformally coupled scalar field, such as the dilaton, is given by the trace of the matter energy momentum tensor, it is commonly assumed to vanish during the radiation dominated epoch in the early universe. As a consequence, such fields are generally frozen in the early universe. Here we compute the finite temperature radiative correction to the source term and discuss its consequences on the evolution of such fields in the early universe. We discuss in particular, the case of scalar tensor theories of gravity which have general relativity as an attractor solution. We show that, in some cases, the universe can experience an early phase of contraction, followed by a nonsingular bounce, and standard expansion. This can have interesting consequences for the abundance of thermal relics; for instance, it can provide a solution to the gravitino problem. We conclude by discussing the possible consequences of the quantum corrections to the evolution of the dilaton.

Notes on Translational and Rotational Properties of Tensor Fields in Relativistic Quantum Mechanics
NASA Astrophysics Data System (ADS)
Dvoeglazov, V. V.
Recently, several discussions on the possible observability of 4vector fields have been published in literature. Furthermore, several authors recently claimed existence of the helicity=0 fundamental field. We reexamine the theory of antisymmetric tensor fields and 4vector potentials. We study the massless limits. In fact, a theoretical motivation for this venture is the old papers of Ogievetskiĭ and Polubarinov, Hayashi, and Kalb and Ramond. Ogievetskiĭ and Polubarinov proposed the concept of the notoph, whose helicity properties are complementary to those of the photon. We analyze the quantum field theory with taking into account mass dimensions of the notoph and the photon. It appears to be possible to describe both photon and notoph degrees of freedom on the basis of the modified BargmannWigner formalism for the symmetric secondrank spinor. Next, we proceed to derive equations for the symmetric tensor of the second rank on the basis of the BargmannWigner formalism in a straightforward way. The symmetric multispinor of the fourth rank is used. Due to serious problems with the interpretation of the results obtained on using the standard procedure we generalize it and obtain the spin2 relativistic equations, which are consistent with the general relativity. Thus, in fact we deduced the gravitational field equations from relativistic quantum mechanics. The relations of this theory with the scalartensor theories of gravitation and f(R) are discussed. Particular attention has been paid to the correct definitions of the energymomentum tensor and other Nöther currents in the electromagnetic theory, the relativistic theory of gravitation, the general relativity, and their generalizations. We estimate possible interactions, fermionnotoph, gravitonnotoph, photonnotoph, and we conclude that they can probably be seen in experiments in the next few years.

Auxiliaryfield quantum Monte Carlo calculations of the molybdenum dimer.
PubMed
Purwanto, Wirawan; Zhang, Shiwei; Krakauer, Henry
20160628
Chemical accuracy is difficult to achieve for systems with transition metal atoms. Third row transition metal atoms are particularly challenging due to strong electronelectron correlation in localized dorbitals. The Cr2 molecule is an outstanding example, which we previously treated with highly accurate auxiliaryfield quantum Monte Carlo (AFQMC) calculations [W. Purwanto et al., J. Chem. Phys. 142, 064302 (2015)]. Somewhat surprisingly, computational description of the isoelectronic Mo2 dimer has also, to date, been scattered and less than satisfactory. We present highlevel theoretical benchmarks of the Mo2 singlet ground state (X(1)Σg (+)) and first triplet excited state (a(3)Σu (+)), using the phaseless AFQMC calculations. Extrapolation to the complete basis set limit is performed. Excellent agreement with experimental spectroscopic constants is obtained. We also present a comparison of the correlation effects in Cr2 and Mo2. PMID:27369514

Auxiliaryfield quantum Monte Carlo calculations of the molybdenum dimer
NASA Astrophysics Data System (ADS)
Purwanto, Wirawan; Zhang, Shiwei; Krakauer, Henry
20160601
Chemical accuracy is difficult to achieve for systems with transition metal atoms. Third row transition metal atoms are particularly challenging due to strong electronelectron correlation in localized dorbitals. The Cr2 molecule is an outstanding example, which we previously treated with highly accurate auxiliaryfield quantum Monte Carlo (AFQMC) calculations [W. Purwanto et al., J. Chem. Phys. 142, 064302 (2015)]. Somewhat surprisingly, computational description of the isoelectronic Mo2 dimer has also, to date, been scattered and less than satisfactory. We present highlevel theoretical benchmarks of the Mo2 singlet ground state (X1Σg+) and first triplet excited state (a3Σu+), using the phaseless AFQMC calculations. Extrapolation to the complete basis set limit is performed. Excellent agreement with experimental spectroscopic constants is obtained. We also present a comparison of the correlation effects in Cr2 and Mo2.

Calculation of Zeeman splitting and Zeeman transition energies of spherical quantum dot in uniform magnetic field
NASA Astrophysics Data System (ADS)
Çakır, Bekir; Atav, Ülfet; Yakar, Yusuf; Özmen, Ayhan
20160801
In this study we report a detailed theoretical investigation of the effect of an external magnetic field on the 1s, 2p, 3d and 4fenergy states of a spherical quantum dot. We treat the contribution of the diamagnetic term as a perturbation and discuss the effect of the diamagnetic term on the 1s, 2p, 3d and 4fenergy states. We also have calculated the Zeeman transition energies between 2p → 1s and 3d → 2p states with m = 0, ±1 and 0, ±1, ±2 as a function of dot radius and the magnetic field strength. The results show that the magnetic field, impurity charge and dot radius have a strong influence on the energy states and the Zeeman transitions. It is found that the energies of the electronic states with m < 0 addition of the diamagnetic term firstly decrease toward a minimum, and then increase with the increasing magnetic field strength. We have seen that as magnetic field intensity is adjusted, frequency of the emitted light can be changed for Zeeman transitions.

Demonstration of the spatial separation of the entangled quantum sidebands of an optical field
SciTech Connect
Huntington, E.H.; Milford, G.N.; Robilliard, C.; Ralph, T.C.; Gloeckl, O.; Andersen, U.L.; Lorenz, S.; Leuchs, G.
20050401
Quantum optics experiments on 'bright' beams are based on the spectral analysis of field fluctuations and typically probe correlations between radiofrequency sideband modes. However, the extra degree of freedom represented by this dualmode picture is generally ignored. We demonstrate the experimental operation of a device which can be used to separate the quantum sidebands of an optical field. We use this device to explicitly demonstrate the quantum entanglement between the sidebands of a squeezed beam.

The molecular recognition of βcyclodextrin modified CdSe quantum dots with tyrosine enantiomers: Theoretical calculation and experimental study
NASA Astrophysics Data System (ADS)
Cao, Yujuan; Wu, Shuangshuang; Liang, Yaozhen; Yu, Ying
20130101
In the present work, the molecular recognition of mono(6mercapto)βcyclodextrin modified CdSe quantum dots (βCD/CdSe QDs) with tyrosine enantiomers were investigated with theoretical calculation and fluorescence spectroscopy. The inclusion processes and the most probable structures of the inclusion complexes were simulated using PM3 energy scanning and optimization method. The trends of stability of the two inclusion complexes deduced from their calculated stabilization energies were studied. Moreover, the fluorescence spectra of βCD/CdSe QDs in the presence of tyrosine enantiomers as well as the effect of ionic strength on the complexation of βCD/CdSe QDstyrosine were discussed. The experimental results indicated that the βCD/CdSe QDs have better enantioselectivity to Ltyrosine than that to Dtyrosine, and good linearity between the fluorescence intensity of βCD/CdSe QDs and Ltyrosine over the concentration range from 0.10 × 104 mol/L to 4.00 × 104 mol/L with relative coefficient of 0.9909 was obtained. The experimental data agrees well with that obtained from theoretical calculation, indicating that βcyclodextrin modified CdSe quantum dots contained good inclusion capability and fluorescence property, it has good potential application in the field of biological diagnosis, analysis, etc.

States of maximum polarization for a quantum light field and states of a maximum sensitivity in quantum interferometry
NASA Astrophysics Data System (ADS)
Peřinová, Vlasta; Lukš, Antonín
20150601
The SU(2) group is used in two different fields of quantum optics, the quantum polarization and quantum interferometry. Quantum degrees of polarization may be based on distances of a polarization state from the set of unpolarized states. The maximum polarization is achieved in the case where the state is pure and then the distribution of the photonnumber sums is optimized. In quantum interferometry, the SU(2) intelligent states have also the property that the Fisher measure of information is equal to the inverse minimum detectable phase shift on the usual simplifying condition. Previously, the optimization of the Fisher information under a constraint was studied. Now, in the framework of constraint optimization, states similar to the SU(2) intelligent states are treated.

Theoretical research of the distortion of quantum circuit in Grover's algorithm
NASA Astrophysics Data System (ADS)
Gubaidullina, K. V.; Chivilikhin, S. A.
20160801
Grover's algorithm is a quantum search algorithm among unsorted elements that can do several operations at the same time due to their wave like properties. In addition, it could solve problems of global optimization and graph coloring. This work presents the results of the simulation of Grover's algorithm and research of its resistance to the effects of perturbations of quantum logic circuit elements. These dependencies can be useful for creating optical circuit.

A multiplexed quantum memory.
PubMed
Lan, SY; Radnaev, A G; Collins, O A; Matsukevich, D N; Kennedy, T A; Kuzmich, A
20090801
A quantum repeater is a system for longdistance quantum communication that employs quantum memory elements to mitigate optical fiber transmission losses. The multiplexed quantum memory (O. A. Collins, S. D. Jenkins, A. Kuzmich, and T. A. B. Kennedy, Phys. Rev. Lett. 98, 060502 (2007)) has been shown theoretically to reduce quantum memory time requirements. We present an initial implementation of a multiplexed quantum memory element in a cold rubidium gas. We show that it is possible to create atomic excitations in arbitrary memory element pairs and demonstrate the violation of Bell's inequality for light fields generated during the write and read processes.

Luminescence of double quantum wells subject to inplane magnetic fields
NASA Astrophysics Data System (ADS)
Orlita, M.; Grill, R.; Hlídek, P.; Zvára, M.; Döhler, G. H.; Malzer, S.; Byszewski, M.
20051001
We report on photoluminescence (PL) measurements of a symmetric GaAs/AlGaAs double quantum well (DQW) in high magnetic fields. For this study, a selectively contacted pδnDQWδnp structure was chosen, allowing an independent tuning of the electron density in the DQW and thus a creation of a twodimensional electron gas. Our attention was focused on phenomena in inplane magnetic fields, where the fieldinduced depopulation of the antibonding subband observable in the PL spectra as a socalled N type kink was predicted by Huang and Lyo (HL) [Phys. Rev. B 59, 7600 (1999)]. Whereas the equivalent behavior has been observed several times in the electric transport measurements and a proper theoretical description has been found, to the best of our knowledge, no PL experiment in a direct comparison with the theoretical model developed by HL has ever been published. We carried out a selfconsistent calculation based on their model and achieved a good agreement with our experimental results. Additionally, the influence of the excitonic interaction on the PL spectra, not taken into account by HL, is also discussed. This enables us to explain small deviations from the HL theory. The interpretation of the inplane magnetic field measurements is supported by the experiment with the magnetic field in the perpendicular orientation that allows a sufficiently accurate estimation of the electron density in the DQW. Distinctive renormalization effects of DQW subbands at various electron densities are also observed and discussed.

Effect of inplane magnetic field and applied strain in quantum spin Hall systems: Application to InAs/GaSb quantum wells
NASA Astrophysics Data System (ADS)
Hu, LunHui; Xu, DongHui; Zhang, FuChun; Zhou, Yi
20160801
Motivated by the recent discovery of quantized spin Hall effect in InAs/GaSb quantum wells [Du, Knez, Sullivan, and Du, Phys. Rev. Lett. 114, 096802 (2015), 10.1103/PhysRevLett.114.096802], we theoretically study the effects of inplane magnetic field and strain effect to the quantization of charge conductance by using LandauerB ütikker formalism. Our theory predicts a robustness of the conductance quantization against the inplane magnetic field up to a very high field of 20 T. We use a disordered hopping term to model the strain and show that the strain may help the quantization of the conductance. Relevance to the experiments will be discussed.

Quantum Fields Obtained from Convoluted Generalized White Noise Never Have Positive Metric
NASA Astrophysics Data System (ADS)
Albeverio, Sergio; Gottschalk, Hanno
20160501
It is proven that the relativistic quantum fields obtained from analytic continuation of convoluted generalized (Lévy type) noise fields have positive metric, if and only if the noise is Gaussian. This follows as an easy observation from a criterion by Baumann, based on the Dell'AntonioRobinsonGreenberg theorem, for a relativistic quantum field in positive metric to be a free field.

Quantum Mechanics Action of ELF Electromagnetic Fields on Living Organisms
NASA Astrophysics Data System (ADS)
GodinaNava, J. J.
20101001
There is presently an intense discussion if extremely low frequency electromagnetic field (ELFEMF) exposure has consequences for human health. This include exposure to structures and appliances from this range of frequency in the electromagnetic (EM) spectrum. Biological effects of such exposures have been noted frequently, although the implications for specific health effects is not that clear. The basic interactions mechanisms between such fields and living matter is unknown. Numerous hypotheses have been suggested, although none is convincingly supported by experimental data. Various cellular components, processes, and systems can be affected by EMF exposure. Since it is unlikely that EMF can induce DNA damage directly, most studies have examined EMF effects on the cell membrane level, general and specific gene expression, and signal transduction pathways. Even more, a large number of studies have been performed regarding cell proliferation, cell cycle regulation, cell differentiation, metabolism, and various physiological characteristics of cells. The aim of this letter is present the hypothesis of a possible quantum mechanic effect generated by the exposure of ELF EMF, an event which is compatible with the multitude of effects observed after exposure. Based on an extensive literature review, we suggest that ELF EMF exposure is able to perform such activation restructuring the electronic level of occupancy of free radicals in molecules interacting with DNA structures.

Universal scaling in fast quantum quenches in conformal field theories.
PubMed
Das, Sumit R; Galante, Damián A; Myers, Robert C
20140501
We study the time evolution of a conformal field theory deformed by a relevant operator under a smooth but fast quantum quench which brings it to the conformal point. We argue that when the quench time scale δt is small compared to the scale set by the relevant coupling, the expectation value of the quenched operator scales universally as δλ/δt(2Δd), where δλ is the quench amplitude. This growth is further enhanced by a logarithmic factor in even dimensions. We present explicit results for free scalar and fermionic field theories, supported by an analytic understanding of the leading contribution for fast quenches. Our results suggest that this scaling result, first found in holography, is in fact quite general. Our considerations also show that this limit of fast smooth quenches is quite different from an instantaneous quench from one timeindependent Hamiltonian to another, where the state at the time of the quench serves as an initial condition for subsequent evolution with the final Hamiltonian.

Quantum revivals in conformal field theories in higher dimensions
NASA Astrophysics Data System (ADS)
Cardy, John
20161001
We investigate the behavior of the return amplitude { F }(t)= < {{\\Psi }}(0) {{\\Psi }}(t)>  following a quantum quench in a conformal field theory (CFT) on a compact spatial manifold of dimension d1 and linear size O(L), from a state  {{\\Psi }}(0)> of extensive energy with shortrange correlations. After an initial gaussian decay { F }(t) reaches a plateau value related to the density of available states at the initial energy. However for d=3,4 this value is attained from below after a single oscillation. For a holographic CFT the plateau persists up to times at least O({σ }1/(d1)L), where σ \\gg 1 is the dimensionless StefanBoltzmann constant. On the other hand for a free field theory on manifolds with high symmetry there are typically revivals at times t˜ {{integer}}× L. In particular, on a sphere {S}d1 of circumference 2π L, there is an action of the modular group on { F }(t) implying structure near all rational values of t/L, similar to what happens for rational CFTs in d=2.

P/NP, and the quantum field computer.
PubMed
Freedman, M H
19980101
The central problem in computer science is the conjecture that two complexity classes, P (polynomial time) and NP (nondeterministic polynomial timeroughly those decision problems for which a proposed solution can be checked in polynomial time), are distinct in the standard Turing model of computation: P not equal NP. As a generality, we propose that each physical theory supports computational models whose power is limited by the physical theory. It is well known that classical physics supports a multitude of implementation of the Turing machine. NonAbelian topological quantum field theories exhibit the mathematical features necessary to support a model capable of solving all #P problems, a computationally intractable class, in polynomial time. Specifically, Witten [Witten, E. (1989) Commun. Math. Phys. 121, 351391] has identified expectation values in a certain SU(2)field theory with values of the Jones polynomial [Jones, V. (1985) Bull. Am. Math. Soc. 12, 103111] that are #Phard [Jaeger, F., Vertigen, D. & Welsh, D. (1990) Math. Proc. Comb. Philos. Soc. 108, 3553]. This suggests that some physical system whose effective Lagrangian contains a nonAbelian topological term might be manipulated to serve as an analog computer capable of solving NP or even #Phard problems in polynomial time. Defining such a system and addressing the accuracy issues inherent in preparation and measurement is a major unsolved problem.

Field evaporation of insulators and semiconductors: Theoretical insights for ZnO.
PubMed
Karahka, Markus; Kreuzer, H J
20151201
We look at the new challenges associated with Atom Probe Tomography of insulators and semiconductors with regard to local fields inside and on the surface of such materials. The theoretical discovery that in high fields the band gap in these materials is drastically reduced to the point where at the evaporation field strength it vanishes will be crucial in our discussion. To understand Atom Probe results on the field evaporation of insulators and semiconductors we use density functional theory on ZnO clusters to follow the structural and electronic changes during field evaporation and to obtain potential energy curves, HOMOLUMO gaps, field distributions, desorption pathways and fragments, dielectric constants, and polarizabilities. We also examine the effects of electric field reversal on the evaporation of ZnO and compare the results with Si. PMID:25825027

Field evaporation of insulators and semiconductors: Theoretical insights for ZnO.
PubMed
Karahka, Markus; Kreuzer, H J
20151201
We look at the new challenges associated with Atom Probe Tomography of insulators and semiconductors with regard to local fields inside and on the surface of such materials. The theoretical discovery that in high fields the band gap in these materials is drastically reduced to the point where at the evaporation field strength it vanishes will be crucial in our discussion. To understand Atom Probe results on the field evaporation of insulators and semiconductors we use density functional theory on ZnO clusters to follow the structural and electronic changes during field evaporation and to obtain potential energy curves, HOMOLUMO gaps, field distributions, desorption pathways and fragments, dielectric constants, and polarizabilities. We also examine the effects of electric field reversal on the evaporation of ZnO and compare the results with Si.

Effects of Shannon entropy and electric field on polaron in RbCl triangular quantum dot
NASA Astrophysics Data System (ADS)
M, Tiotsop; A, J. Fotue; S, C. Kenfack; N, Issofa; H, Fotsin; L, C. Fai
20160401
In this paper, the time evolution of the quantum mechanical state of a polaron is examined using the Pekar type variational method on the condition of the electricLOphonon strongcoupling and polar angle in RbCl triangular quantum dot. We obtain the eigenenergies, and the eigenfunctions of the ground state, and the first excited state respectively. This system in a quantum dot can be treated as a twolevel quantum system qubit and the numerical calculations are performed. The effects of Shannon entropy and electric field on the polaron in the RbCl triangular quantum dot are also studied.

Fermionfermion scattering in quantum field theory with superconducting circuits.
PubMed
GarcíaÁlvarez, L; Casanova, J; Mezzacapo, A; Egusquiza, I L; Lamata, L; Romero, G; Solano, E
20150220
We propose an analogdigital quantum simulation of fermionfermion scattering mediated by a continuum of bosonic modes within a circuit quantum electrodynamics scenario. This quantum technology naturally provides strong coupling of superconducting qubits with a continuum of electromagnetic modes in an open transmission line. In this way, we propose qubits to efficiently simulate fermionic modes via digital techniques, while we consider the continuum complexity of an open transmission line to simulate the continuum complexity of bosonic modes in quantum field theories. Therefore, we believe that the complexitysimulatingcomplexity concept should become a leading paradigm in any effort towards scalable quantum simulations. PMID:25763944

Fermionfermion scattering in quantum field theory with superconducting circuits.
PubMed
GarcíaÁlvarez, L; Casanova, J; Mezzacapo, A; Egusquiza, I L; Lamata, L; Romero, G; Solano, E
20150220
We propose an analogdigital quantum simulation of fermionfermion scattering mediated by a continuum of bosonic modes within a circuit quantum electrodynamics scenario. This quantum technology naturally provides strong coupling of superconducting qubits with a continuum of electromagnetic modes in an open transmission line. In this way, we propose qubits to efficiently simulate fermionic modes via digital techniques, while we consider the continuum complexity of an open transmission line to simulate the continuum complexity of bosonic modes in quantum field theories. Therefore, we believe that the complexitysimulatingcomplexity concept should become a leading paradigm in any effort towards scalable quantum simulations.

Historical Perspectives: Pioneering Definitions and Theoretical Positions in the Field of Gifted Education
ERIC Educational Resources Information Center
Jolly, Jennifer L.
20050101
The previous Historical Perspectives column focused on the foundations of gifted education and the influence that Francis Galton, Alfred Binet, and Cesare Lombroso had in shaping the field. This work seeks to extend the examination of the historical roots of gifted education by focusing on definitions and theoretical underpinnings of giftedness…

Theoretical and Experimental Research of Error of Method of Thermocouple with Controlled Profile of Temperature Field
NASA Astrophysics Data System (ADS)
Jun, Su; Kochan, O.; Chunzhi, Wang; Kochan, R.
20151201
The method of study and experimental researches of the error of method of the thermocouple with controlled profile of temperature field along the main thermocouple are considered in this paper. Experimentally determined values of error of method are compared to the theoretical estimations done using Newton's law of cooling. They converge well.

Theoretical investigation of impurity scattering limited mobility in quantum wells: The influence of wavefunction modeling
NASA Astrophysics Data System (ADS)
Thobel, J. L.; Baudry, L.; Dessenne, F.; Charef, M.; Fauquembergue, R.
19930101
A theoretical investigation of the impurity scattering limited mobility in quantum wells is presented. Emphasis is put on the influence of wavefunction modeling, since the literature about this topic is contradictory. For an infinite square well, Dirac and sine wave functions yield the same evolutions of the mobility with temperature, carrier density, and well width. These results contradict those published by Lee [J. Appl. Phys. 54, 6995 (1983)], which are shown to be wrong. Selfconsistent wave functions have also been used to compute the mobility in finite barrier height quantum wells. A strong influence of the presence of electrons inside the doped barrier has been demonstrated. It is suggested that, although simple models are useful for qualitative discussions, accurate evaluation of mobility requires a reasonably realistic description of wave functions.

Ballistic graphene nanoribbon metaloxidesemiconductor fieldeffect transistors: A full realspace quantum transport simulation
NASA Astrophysics Data System (ADS)
Liang, Gengchiau; Neophytou, Neophytos; Lundstrom, Mark S.; Nikonov, Dmitri E.
20070901
A realspace quantum transport simulator for graphene nanoribbon (GNR) metaloxidesemiconductor fieldeffect transistors (MOSFETs) has been developed and used to examine the ballistic performance of GNR MOSFETs. This study focuses on the impact of quantum effects on these devices and on the effect of different type of contacts. We found that twodimensional (2D) semiinfinite graphene contacts produce metalinducedgap states (MIGS) in the GNR channel. These states enhance quantum tunneling, particularly in short channel devices, they cause Fermi level pinning and degrade the device performance in both the ONstate and OFFstate. Devices with infinitely long contacts having the same width as the channel do not indicate MIGS. Even without MIGS quantum tunneling effects such as bandtoband tunneling still play an important role in the device characteristics and dominate the OFFstate current. This is accurately captured in our nonequilibrium Greens' function quantum simulations. We show that both narrow (1.4 nm width) and wider (1.8 nm width) GNRs with 12.5 nm channel length have the potential to outperform ultrascaled Si devices in terms of drive current capabilities and electrostatic control. Although their subthreshold swings under forward bias are better than in Si transistors, tunneling currents are important and prevent the achievement of the theoretical limit of 60 mV/dec.

A straight quantum wave guide with mixed Dirichlet and Neumann boundary conditions in uniform magnetic fields
NASA Astrophysics Data System (ADS)
Olendski, O.; Mikhailovska, L.
20070401
A straight quasionedimensional Dirichlet wave guide with a Neumann window of length L on one or two confining surfaces is considered theoretically with and without perpendicular homogeneous magnetic field \\bf B . It is shown that for the fieldfree case, a bound state in the continuum (BIC) for one Neumann window exists for some critical lengths only, while for the two Neumann segments symmetrically located on the opposite walls, due to the restored transverse symmetry of the system, BICs exist for the arbitrary L. Bound states lying below the fundamental propagation threshold of the Dirichlet strip survive any strength of the uniform magnetic field and do not depend on its direction. Moreover, an increasing field induces new bound states regularly arranged with the levels present at B = 0. For two Neumann windows, strong magnetic fields lead to the degeneracy of the adjacent odd and even bound states with their energies almost equal to each other and to their corresponding counterpart for one Neumann segment, which is explained by mapping the problem onto the fieldfree one or two purely attractive onedimensional quantum wells with fielddependent depth. Miscellaneous magnetotransport characteristics of the structures are also considered; in particular, it is demonstrated that small fields applied to the channel with two Neumann windows destroy BICs by coupling them to the continuum states. This is manifested in the conductanceFermi energy dependence by Fano resonances. Currents flowing in the wave guide are investigated too, and it is shown that current density patterns near the resonances form vortices which change their chirality as energy sweeps through the resonant region. Generalizations to any other arbitrary combination of the boundary conditions are provided. Comparison with other structures such as windowcoupled Dirichlet wave guides, a bent strip or straight Dirichlet channel with electrostatic impurity inside, is performed.

Proposed Robust EntanglementBased Magnetic Field Sensor Beyond the Standard Quantum Limit
NASA Astrophysics Data System (ADS)
Tanaka, Tohru; Knott, Paul; Matsuzaki, Yuichiro; Dooley, Shane; Yamaguchi, Hiroshi; Munro, William J.; Saito, Shiro
20151001
Recently, there have been significant developments in entanglementbased quantum metrology. However, entanglement is fragile against experimental imperfections, and quantum sensing to beat the standard quantum limit in scaling has not yet been achieved in realistic systems. Here, we show that it is possible to overcome such restrictions so that one can sense a magnetic field with an accuracy beyond the standard quantum limit even under the effect of decoherence, by using a realistic entangled state that can be easily created even with current technology. Our scheme could pave the way for the realizations of practical entanglementbased magnetic field sensors.

Proposed Robust EntanglementBased Magnetic Field Sensor Beyond the Standard Quantum Limit.
PubMed
Tanaka, Tohru; Knott, Paul; Matsuzaki, Yuichiro; Dooley, Shane; Yamaguchi, Hiroshi; Munro, William J; Saito, Shiro
20151023
Recently, there have been significant developments in entanglementbased quantum metrology. However, entanglement is fragile against experimental imperfections, and quantum sensing to beat the standard quantum limit in scaling has not yet been achieved in realistic systems. Here, we show that it is possible to overcome such restrictions so that one can sense a magnetic field with an accuracy beyond the standard quantum limit even under the effect of decoherence, by using a realistic entangled state that can be easily created even with current technology. Our scheme could pave the way for the realizations of practical entanglementbased magnetic field sensors.

Classical and quantum Big Brake cosmology for scalar field and tachyonic models
SciTech Connect
Kamenshchik, A. Yu.; Manti, S.
20130221
We study a relation between the cosmological singularities in classical and quantum theory, comparing the classical and quantum dynamics in some models possessing the Big Brake singularity  the model based on a scalar field and two models based on a tachyonpseudotachyon field . It is shown that the effect of quantum avoidance is absent for the soft singularities of the Big Brake type while it is present for the Big Bang and Big Crunch singularities. Thus, there is some kind of a classical  quantum correspondence, because soft singularities are traversable in classical cosmology, while the strong Big Bang and Big Crunch singularities are not traversable.

Multiband electron resonant Raman scattering in quantum wells in a magnetic field
NASA Astrophysics Data System (ADS)
LópezRichard, V.; Hai, G.Q.; TralleroGiner, C.; Marques, G. E.
20030401
A theoretical model has been developed for the electronic resonant Raman scattering processes in direct band zinc blende type semiconductor quantum wells in a magnetic field. In order to take into account the spinflip transitions, anomalous behavior of the Landau levels and the Landè g factor, an 8×8 KaneWeiler Hamiltonian model has been considered for the evaluation of the Raman scattering amplitude. Elements concerning the selection rules of resonant inelastic light scattering in quantum well systems are reported. The multiband model predicts conditions for resonant spinflip Raman processes in several light scattering configurations for crossed and parallel polarization. Special emphasis is given to the effects of the interlevel coupling and mixing within the conduction subband and their relation to spinflip and interLandau level transitions. Symmetry and electronic properties of the level structure in the first conduction subband as well as anomalous Landè factors are discussed in terms of complementary Raman scattering configurations, Fermi energy, and multiband parameters.

Femtosecond quantum fluid dynamics of helium atom under an intense laser field
SciTech Connect
Dey, B.K.; Deb, B.M. 
19981005
A comprehensive, nonperturbative, timedependent quantum mechanical (TDQM) approach is proposed for studying the dynamics of a helium atom under an intense, ultrashort (femtoseconds) laser pulse. The method combines quantum fluid dynamics (QFD) and density functional theory. It solves a single generalized nonlinear Schroedinger equation of motion (EOM), involving time and three space variables, which is obtained from two QFD equations, namely, a continuity equation and an Eulertype equation. A highly accurate finite difference scheme along with a stability analysis is presented for numerically solving the EOM. Starting from the groundstate HartreeFock density for He at t = 0, the EOM yields the timedependent (TD) electron density, effective potential surface, difference density, difference effective potential, groundstate probability, {l_angle}r{r_angle}, magnetic susceptibility, polarizability, flux, etc. By a Fourier transformation of the TD dipole moment along the linearly polarizedfield direction, the power and rate spectra for photoemission are calculated. eleven mechanistic routes for photoemission are identified, which include high harmonic generation as well as many other spectral transitions involving ionized, singly excited, doubly excited (autoionizing), and continuum He states, based on the evolution of the system up to a particular time. Intimate connections between photoionization and photoemission are clearly observed through computer visualizations. Apart from being consistent with current experimental and theoretical results, the present results offer certain predictions on spectral transitions which are open to experimental verification.

Static and dynamical quantum correlations in phases of an alternatingfield X Y model
NASA Astrophysics Data System (ADS)
Chanda, Titas; Das, Tamoghna; Sadhukhan, Debasis; Pal, Amit Kumar; SenDe, Aditi; Sen, Ujjwal
20161001
We investigate the static and dynamical patterns of entanglement in an anisotropic X Y model with an alternating transverse magnetic field, which is equivalent to a twocomponent onedimensional Fermi gas on a lattice, a system realizable with current technology. Apart from the antiferromagnetic and paramagnetic phases, the model possesses a dimer phase which is not present in the transverse X Y model. At zero temperature, we find that the first derivative of bipartite entanglement can detect all the three phases. We analytically show that the model has a "factorization line" on the plane of system parameters, in which the zerotemperature state is separable. Along with investigating the effect of temperature on entanglement in a phase plane, we also report a nonmonotonic behavior of entanglement with respect to temperature in the antiferromagnetic and paramagnetic phases, which is surprisingly absent in the dimer phase. Since the time dynamics of entanglement in a realizable physical system plays an important role in quantum information processing tasks, the evolutions of entanglement at small as well as large time are examined. Consideration of largetime behavior of entanglement helps us to prove that in this model, entanglement is always ergodic. We observe that other quantum correlation measures can qualitatively show similar features in zero and finite temperatures. However, unlike nearestneighbor entanglement, the nearestneighbor informationtheoretic measures can be both ergodic as well as nonergodic, depending on the system parameters.

Quantum Field Theories on the Lattice : Concepts behind their Numerical Simulations
NASA Astrophysics Data System (ADS)
Bietenholz, Wolfgang
20110901
We review the basic ideas behind numerical simulations of quantum field theory, which lead to nonperturbative results in particle physics. We first sketch the functional integral formulation of quantum mechanics, its transition to Euclidean time and the link to statistical mechanics. Then we proceed to quantum field theory in the lattice regularization, and its applications to scalar fields, gauge fields and fermions. In particular we address the treatment of chiral symmetry. At last we describe the formulation of lattice QCD and comment on simulations and results.

A theoretical investigation of the sound radiation fields associated with a Bellmouth inlet
NASA Technical Reports Server (NTRS)
Meyer, W. L.; Zinn, B. T.
19830101
Analytical results are obtained by numerical integration of a cylindrically symmetric integral representation of the external solutions of the Helmholtz equation. The accuracy of this method is checked by comparisons of computed results with 'exact' solutions generated by the point source method. In all cases, the average error for the amplitude and phase of the points calculated in the field is found to be less than ten percent. Theoretical studies which model experiments run for the NASA Langely Bellmouth inlet configuration are presented and comparisons are made with the experimental results. In all cases very good agreement is obtained between the experimental and theoretically calculated values.

A theoretical investigation of the sound radiation fields associated with a Bellmouth inlet
NASA Astrophysics Data System (ADS)
Meyer, W. L.; Zinn, B. T.
19830401
Analytical results are obtained by numerical integration of a cylindrically symmetric integral representation of the external solutions of the Helmholtz equation. The accuracy of this method is checked by comparisons of computed results with 'exact' solutions generated by the point source method. In all cases, the average error for the amplitude and phase of the points calculated in the field is found to be less than ten percent. Theoretical studies which model experiments run for the NASA Langely Bellmouth inlet configuration are presented and comparisons are made with the experimental results. In all cases very good agreement is obtained between the experimental and theoretically calculated values.

Quantum Darwinism Requires an ExtraTheoretical Assumption of Encoding Redundancy
NASA Astrophysics Data System (ADS)
Fields, Chris
20101001
Observers restricted to the observation of pointer states of apparatus cannot conclusively demonstrate that the pointer of an apparatus mathcal{A} registers the state of a system of interest S without perturbing S. Observers cannot, therefore, conclusively demonstrate that the states of a system S are redundantly encoded by pointer states of multiple independent apparatus without destroying the redundancy of encoding. The redundancy of encoding required by quantum Darwinism must, therefore, be assumed from outside the quantummechanical formalism and without the possibility of experimental demonstration.

Elementary Theoretical Forms for the Spatial Power Spectrum of Earth's Crustal Magnetic Field
NASA Technical Reports Server (NTRS)
Voorhies, C.
19980101
The magnetic field produced by magnetization in Earth's crust and lithosphere can be distinguished from the field produced by electric currents in Earth's core because the spatial magnetic power spectrum of the crustal field differs from that of the core field. Theoretical forms for the spectrum of the crustal field are derived by treating each magnetic domain in the crust as the point source of a dipole field. The geologic nullhypothesis that such moments are uncorrelated is used to obtain the magnetic spectrum expected from a randomly magnetized, or unstructured, spherical crust of negligible thickness. This simplest spectral form is modified to allow for uniform crustal thickness, ellipsoidality, and the polarization of domains by an periodically reversing, geocentric axial dipole field from Earth's core. Such spectra are intended to describe the background crustal field. Magnetic anomalies due to correlated magnetization within coherent geologic structures may well be superimposed upon this background; yet representing each such anomaly with a single point dipole may lead to similar spectral forms. Results from attempts to fit these forms to observational spectra, determined via spherical harmonic analysis of MAGSAT data, are summarized in terms of amplitude, source depth, and misfit. Each theoretical spectrum reduces to a source factor multiplied by the usual exponential function of spherical harmonic degree n due to geometric attenuation with attitude above the source layer. The source factors always vary with n and are approximately proportional to n(exp 3) for degrees 12 through 120. The theoretical spectra are therefore not directly proportional to an exponential function of spherical harmonic degree n. There is no radius at which these spectra are flat, level, or otherwise independent of n.

An ontological study of quantum fields and their symmetries
NASA Astrophysics Data System (ADS)
Baker, David John
This dissertation interprets the formalism of quantum field theory (QFT) to help determine which physical properties are fundamental in worlds with natural laws like ours. I begin by arguing briefly that good metaphysical evidence can be drawn from mathematically rigorous forms of QFT. Although these rigorous QFTs are presently limited in their domain of applicability, insofar as our world resembles that domain we should expect these theories to be approximately true. Chapter Two addresses the most central question about the fundamental ontology of QFT: is it a theory of fields or of particles? Any theory describes reality in terms of some basic constituents. Historically, philosophers have assumed these to be either point particles (following Locke and the atomists) or continuous fields (following Descartes). Recent philosophical arguments suggest that the most basic ontology of QFT cannot consist of particles; it is commonly supposed that it must therefore consist of fields (Halvorson and Clifton, 2001; Malament, 1996). To the contrary, I show that two of the most persuasive arguments against particles are also arguments against the most widely advocated form of field interpretation. First, the configuration of fields, like the number of particles, cannot generally be carried over between different inequivalent representations of QFT. Since the differences between some representations encode only perspectival information about the observer, it follows that QFT states possess no objective field content. Second, arguments which rule out the possibility of particle states in interacting QFT also rule out the standard way of representing states as field configurations. So what is the most basic ontology of QFT? Chapter Three examines a possible answer, according to which fundamental reality is made up of properties, called quasilocal observables, which can be measured in regions of space and do not depend on our choice of representation. This third way has the

An Algebraic Construction of Boundary Quantum Field Theory
NASA Astrophysics Data System (ADS)
Longo, Roberto; Witten, Edward
20110401
We build up local, time translation covariant Boundary Quantum Field Theory nets of von Neumann algebras {mathcal A_V} on the Minkowski halfplane M + starting with a local conformal net {mathcal A} of von Neumann algebras on {mathbb R} and an element V of a unitary semigroup {mathcal E(mathcal A)} associated with {mathcal A}. The case V = 1 reduces to the net {mathcal A_+} considered by Rehren and one of the authors; if the vacuum character of {mathcal A} is summable, {mathcal A_V} is locally isomorphic to {mathcal A_+}. We discuss the structure of the semigroup {mathcal E(mathcal A)}. By using a oneparticle version of Borchers theorem and standard subspace analysis, we provide an abstract analog of the BeurlingLax theorem that allows us to describe, in particular, all unitaries on the oneparticle Hilbert space whose second quantization promotion belongs to {mathcal E(mathcal A^{(0)})} with {mathcal A^{(0)}} the U(1)current net. Each such unitary is attached to a scattering function or, more generally, to a symmetric inner function. We then obtain families of models via any BuchholzMackTodorov extension of {mathcal A^{(0)}}. A further family of models comes from the Ising model.

Quantum Chromodynamics  The Perfect YangMills Gauge Field Theory
NASA Astrophysics Data System (ADS)
Gross, David
David Gross: My talk today is about the most beautiful of all YangMills Theories (nonAbelian gauge theories), the theory of the strong nuclear interactions, Quantum Chromodynamics, QCD. We are celebrating 60 years of the publication of a remarkable paper which introduced the concept of nonAbelian local gauge symmetries, now called the YangMills theory, to physics. In the introduction to this paper it is noted that the usual principle of isotopic spin symmetry is not consistent with the concept of localized fields. This sentence has drawn attention over the years because the usual principle of isotopic spin symmetry is consistent, it is just not satisfactory. The authors, Yang and Mills, introduced a more satisfactory notion of local symmetry which did not require one to rotate (in isotopic spin space) the whole universe at once to achieve the symmetry transformation. Global symmetries are thus are similar to `action at a distance', whereas YangMills theory is manifestly local...

Transient quantum coherent response to a partially coherent radiation field.
PubMed
Sadeq, Zaheen S; Brumer, Paul
20140221
The response of an arbitrary closed quantum system to a partially coherent electric field is investigated, with a focus on the transient coherences in the system. As a model we examine, both perturbatively and numerically, the coherences induced in a three level V system. Both rapid turnon and pulsed turnon effects are investigated. The effect of a long and incoherent pulse is also considered, demonstrating that during the pulse the system shows a coherent response which reduces after the pulse is over. Both the pulsed scenario and the thermally broadened CW case approach a mixed state in the long time limit, with rates dictated by the adjacent level spacings and the coherence time of the light, and via a mechanism that is distinctly different from traditional decoherence. These two excitation scenarios are also explored for a minimal "toy" model of the electronic levels in pigment protein complex PC645 by both a collisionally broadened CW laser and by a noisy pulse, where unexpectedly long transient coherence times are observed and explained. The significance of environmentally induced decoherence is noted.

Electromagnetic Form Factors of Hadrons in Quantum Field Theories
SciTech Connect
Dominguez, C. A.
20081013
In this talk, recent results are presented of calculations of electromagnetic form factors of hadrons in the framework of two quantum field theories (QFT), (a) DualLarge N{sub c} QCD (DualQCD{sub {infinity}}) for the pion, proton, and {delta}(1236), and (b) the KrollLeeZumino (KLZ) fully renormalizable Abelian QFT for the pion form factor. Both theories provide a QFT platform to improve on naive (treelevel) Vector Meson Dominance (VMD). DualQCD{sub {infinity}} provides a treelevel improvement by incorporating an infinite number of zerowidth resonances, which can be subsequently shifted from the real axis to account for the timelike behaviour of the form factors. The renormalizable KLZ model provides a QFT improvement of VMD in the framework of perturbation theory. Due to the relative mildness of the {rho}{pi}{pi} coupling, and the size of loop suppression factors, the perturbative expansion is well defined in spite of this being a strong coupling theory. Both approaches lead to considerable improvements of VMD predictions for electromagnetic form factors, in excellent agreement with data.

Spin operator and entanglement in quantum field theory
NASA Astrophysics Data System (ADS)
Fujikawa, Kazuo; Oh, C. H.; Zhang, Chengjie
20140701
Entanglement is studied in the framework of Dyson's Smatrix theory in relativistic quantum field theory, which leads to a natural definition of entangled states of a particleantiparticle pair and the spin operator from a Noether current. As an explicit example, the decay of a massive pseudoscalar particle into a pair of electron and positron is analyzed. Two spin operators are extracted from the Noether current. The Wigner spin operator characterizes spin states at the rest frame of each fermion and, although not measurable in the laboratory, gives rise to a straightforward generalization of lowenergy analysis of entanglement to the ultrarelativistic domain. In contrast, if one adopts a (modified) Dirac spin operator, the entanglement measured by spin correlation becomes maximal near the threshold of the decay, while the entanglement is replaced by the classical correlation for the ultrarelativistic electronpositron pair by analogy to the case of neutrinos, for which a hiddenvariables type of description is possible. Chiral symmetry differentiates the spin angular momentum and the magnetic moment. The use of weak interaction that can measure helicity is suggested in the analysis of entanglement at high energies instead of a SternGerlach apparatus, which is useless for the electron. A difference between the electron spin at high energies and the photon linear polarization is also noted. The Standard Model can describe all of the observable properties of leptons.

Lattice simulations of realtime quantum fields
NASA Astrophysics Data System (ADS)
Berges, J.; Borsányi, Sz.; Sexty, D.; Stamatescu, I.O.
20070201
We investigate lattice simulations of scalar and nonAbelian gauge fields in Minkowski spacetime. For SU(2) gaugetheory expectation values of link variables in 3+1 dimensions are constructed by a stochastic process in an additional (5th) “Langevintime.” A sufficiently small Langevin step size and the use of a tilted realtime contour leads to converging results in general. All fixed point solutions are shown to fulfil the infinite hierarchy of DysonSchwinger identities, however, they are not unique without further constraints. For the nonAbelian gauge theory the thermal equilibrium fixed point is only approached at intermediate Langevintimes. It becomes more stable if the complex time path is deformed towards Euclidean spacetime. We analyze this behavior further using the realtime evolution of a quantum anharmonic oscillator, which is alternatively solved by diagonalizing its Hamiltonian. Without further optimization stochastic quantization can give accurate descriptions if the realtime extent of the lattice is small on the scale of the inverse temperature.

Transient quantum coherent response to a partially coherent radiation field
SciTech Connect
Sadeq, Zaheen S.; Brumer, Paul
20140221
The response of an arbitrary closed quantum system to a partially coherent electric field is investigated, with a focus on the transient coherences in the system. As a model we examine, both perturbatively and numerically, the coherences induced in a three level V system. Both rapid turnon and pulsed turnon effects are investigated. The effect of a long and incoherent pulse is also considered, demonstrating that during the pulse the system shows a coherent response which reduces after the pulse is over. Both the pulsed scenario and the thermally broadened CW case approach a mixed state in the long time limit, with rates dictated by the adjacent level spacings and the coherence time of the light, and via a mechanism that is distinctly different from traditional decoherence. These two excitation scenarios are also explored for a minimal “toy” model of the electronic levels in pigment protein complex PC645 by both a collisionally broadened CW laser and by a noisy pulse, where unexpectedly long transient coherence times are observed and explained. The significance of environmentally induced decoherence is noted.

Derivation of the Rules of Quantum Mechanics from InformationTheoretic Axioms
NASA Astrophysics Data System (ADS)
Fivel, Daniel I.
20120201
Conventional quantum mechanics with a complex Hilbert space and the Born Rule is derived from five axioms describing experimentally observable properties of probability distributions for the outcome of measurements. Axioms I, II, III are common to quantum mechanics and hidden variable theories. Axiom IV recognizes a phenomenon, first noted by von Neumann (in Mathematical Foundations of Quantum Mechanics, Princeton University Press, Princeton, 1955) and independently by Turing (Teuscher and Hofstadter, Alan Turing: Life and Legacy of a Great Thinker, Springer, Berlin, 2004), in which the increase in entropy resulting from a measurement is reduced by a suitable intermediate measurement. This is shown to be impossible for local hidden variable theories. Axiom IV, together with the first three, almost suffice to deduce the conventional rules but allow some exotic, alternatives such as real or quaternionic quantum mechanics. Axiom V recognizes a property of the distribution of outcomes of random measurements on qubits which holds only in the complex Hilbert space model. It is then shown that the five axioms also imply the conventional rules for any finite dimension.

A new class of ensemble conserving algorithms for approximate quantum dynamics: Theoretical formulation and model problems
SciTech Connect
Smith, Kyle K. G.; Poulsen, Jens Aage Nyman, Gunnar; Rossky, Peter J.
20150628
We develop two classes of quasiclassical dynamics that are shown to conserve the initial quantum ensemble when used in combination with the FeynmanKleinert approximation of the density operator. These dynamics are used to improve the FeynmanKleinert implementation of the classical Wigner approximation for the evaluation of quantum time correlation functions known as FeynmanKleinert linearized pathintegral. As shown, both classes of dynamics are able to recover the exact classical and high temperature limits of the quantum time correlation function, while a subset is able to recover the exact harmonic limit. A comparison of the approximate quantum time correlation functions obtained from both classes of dynamics is made with the exact results for the challenging model problems of the quartic and doublewell potentials. It is found that these dynamics provide a great improvement over the classical Wigner approximation, in which purely classical dynamics are used. In a special case, our first method becomes identical to centroid molecular dynamics.

Concepts and their dynamics: a quantumtheoretic modeling of human thought.
PubMed
Aerts, Diederik; Gabora, Liane; Sozzo, Sandro
20131001
We analyze different aspects of our quantum modeling approach of human concepts and, more specifically, focus on the quantum effects of contextuality, interference, entanglement, and emergence, illustrating how each of them makes its appearance in specific situations of the dynamics of human concepts and their combinations. We point out the relation of our approach, which is based on an ontology of a concept as an entity in a state changing under influence of a context, with the main traditional concept theories, that is, prototype theory, exemplar theory, and theory theory. We ponder about the question why quantum theory performs so well in its modeling of human concepts, and we shed light on this question by analyzing the role of complex amplitudes, showing how they allow to describe interference in the statistics of measurement outcomes, while in the traditional theories statistics of outcomes originates in classical probability weights, without the possibility of interference. The relevance of complex numbers, the appearance of entanglement, and the role of Fock space in explaining contextual emergence, all as unique features of the quantum modeling, are explicitly revealed in this article by analyzing human concepts and their dynamics.

A new class of ensemble conserving algorithms for approximate quantum dynamics: Theoretical formulation and model problems.
PubMed
Smith, Kyle K G; Poulsen, Jens Aage; Nyman, Gunnar; Rossky, Peter J
20150628
We develop two classes of quasiclassical dynamics that are shown to conserve the initial quantum ensemble when used in combination with the FeynmanKleinert approximation of the density operator. These dynamics are used to improve the FeynmanKleinert implementation of the classical Wigner approximation for the evaluation of quantum time correlation functions known as FeynmanKleinert linearized pathintegral. As shown, both classes of dynamics are able to recover the exact classical and high temperature limits of the quantum time correlation function, while a subset is able to recover the exact harmonic limit. A comparison of the approximate quantum time correlation functions obtained from both classes of dynamics is made with the exact results for the challenging model problems of the quartic and doublewell potentials. It is found that these dynamics provide a great improvement over the classical Wigner approximation, in which purely classical dynamics are used. In a special case, our first method becomes identical to centroid molecular dynamics.

The Impact of Quantum Theoretical Models of Consciousness on the Study of Education.
ERIC Educational Resources Information Center
Andris, James F.
This paper abstracts and discusses the approaches of five educational theorists who have used quantum theory as a model for educational phenomena, sets forth and uses metatheoretical criteria to evaluate the work of these theorists, and states guidelines for further work in this domain. The paper abstracts and discusses the works of the following…

A new class of ensemble conserving algorithms for approximate quantum dynamics: Theoretical formulation and model problems.
PubMed
Smith, Kyle K G; Poulsen, Jens Aage; Nyman, Gunnar; Rossky, Peter J
20150628
We develop two classes of quasiclassical dynamics that are shown to conserve the initial quantum ensemble when used in combination with the FeynmanKleinert approximation of the density operator. These dynamics are used to improve the FeynmanKleinert implementation of the classical Wigner approximation for the evaluation of quantum time correlation functions known as FeynmanKleinert linearized pathintegral. As shown, both classes of dynamics are able to recover the exact classical and high temperature limits of the quantum time correlation function, while a subset is able to recover the exact harmonic limit. A comparison of the approximate quantum time correlation functions obtained from both classes of dynamics is made with the exact results for the challenging model problems of the quartic and doublewell potentials. It is found that these dynamics provide a great improvement over the classical Wigner approximation, in which purely classical dynamics are used. In a special case, our first method becomes identical to centroid molecular dynamics. PMID:26133415

Proposal of a Communications Theory of Quantum Mechanics. Theoretical Examination of the 'Gyromagnetic Ratio'
SciTech Connect
Coogan, Anthony
20090309
Is the 'TwoSlit' experiment best explained by aliasing, first solved by Harry Nyquist (1926)? Does light reflected by an electron rotate through double the angle through which the electron itself rotates? Can a barchart represent the uncertainty principle?A very simple model of quantum mechanics is presented.

Spinglass behavior of Sn0.9Fe3.1N: An experimental and quantumtheoretical study
NASA Astrophysics Data System (ADS)
Scholz, Tanja; Dronskowski, Richard
20160501
Based on comprehensive experimental and quantumtheoretical investigations, we identify Sn0.9Fe3.1N as a canonical spin glass and the first ternary iron nitride with a frustrated spin ground state. Sn0.9Fe3.1N is the end member of the solid solution SnxFe4xN (0 < x ≤ 0.9) derived from ferromagnetic γ'Fe4N. Within the solid solution, the gradual incorporation of tin is accompanied by a drastic weakening of the ferromagnetic interactions. To explore the dilution of the ferromagnetic coupling, the highly tinsubstituted Sn0.9Fe3.1N has been magnetically reinvestigated. DC magnetometry reveals diverging susceptibilities for FC and ZFC measurements at low temperatures and an unsaturated hysteretic loop even at high magnetic fields. The temperature dependence of the real component of the AC susceptibility at different frequencies proves the spinglass transition with the characteristic parameters Tg = 12.83(6) K, τ* = 1011.8(2) s, zv = 5.6(1) and ΔTm/(Tm ṡ Δlgω) = 0.015. The timedependent response of the magnetic spins to the external field has been studied by extracting the distribution function of relaxation times g(τ, T) up to Tg from the complex plane of AC susceptibilities. The weakening of the ferromagnetic coupling by substituting tin into γ'Fe4N is explained by the Stoner criterion on the basis of electronic structure calculations and a quantumtheoretical bonding analysis.

Ultrafast Modulation and Switching of QuantumWell Lasers using Terahertz Fields
NASA Technical Reports Server (NTRS)
Ning, CunZheng; Hughes, S.; Citrin, D.; Saini, Subhash (Technical Monitor)
19980101
Modulation and switching of semiconductor lasers are important for laserbased information technology. Typically the speed of modulation and switching is limited by interband processes such as stimulated and spontaneous recombinations which occur on a nanosecond time scale. This is why the diode laser modulation has been restricted to tens of GHz. Modulation at higher speed is highly desirable as the information technology enters into the socalled teraera. In this paper, we study the possibility of utilizing THzfieldinduced plasma heating to modulate quantumwell lasers. This is a timely study since, with the advancement of THz solidstate sources and freeelectron lasers, THz physics and related technology is currently coming out of its infancy. The investigation of interplaying THz and optical fields is also of intruiging fundamental interest. First, we introduce theoretical plasma heating results for the quantumwell optical amplifier in the presense of an intense halfcycle THz pulse. The heated carrier distributions are then utilized to calculate the THzpulseinduced change in refractive index and gain profile. Since the electronholeplasma is heated using intraband transitions, we circumvent the usual complications due to an overall change in density, and the nonlinear recovery is governed solely by the carrierLOphonon interactions, typically 5 ps for a complete recovery. This procedure implies THz and subTHz switching and recovery rates, respectively; using either gain modulation or index modulation. Plasma heating via steadystate THz fields is also studied. Finally, numerical simulation of a coupled set of equations to investigate the THz modulation based on a simplified model for quantumwell lasers is presented. Our results show that a semiconductor laser can be modulated at up to 1 THz with little distortion with a THz field amplitude at the order of a few kV/cm. Laser responses to a change in THz frequency will be shown. Constraints

Polaron effect on the optical rectification in spherical quantum dots with electric field
NASA Astrophysics Data System (ADS)
Feng, ZhenYu; Yan, ZuWei
20161001
The polaron effect on the optical rectification in spherical quantum dots with a shallow hydrogenic impurity in the presence of electric field is theoretically investigated by taking into account the interactions of the electrons with both confined and surface optical phonons. Besides, the interaction between impurity and phonons is also considered. Numerical calculations are presented for typical Zn1x Cd x Se/ZnSe material. It is found that the polaronic effect or electric field leads to the redshifted resonant peaks of the optical rectification coefficients. It is also found that the peak values of the optical rectification coefficients with the polaronic effect are larger than without the polaronic effect, especially for smaller Cd concentrations or stronger electric field. Project supported by the National Natural Science Foundation of China (Grant No. 11364028), the Major Projects of the Natural Science Foundation of Inner Mongolia Autonomous Region, China (Grant No. 2013ZD02), and the Project of “Prairie Excellent” Engineering in Inner Mongolia Autonomous Region, China.

Quantum field theory of gravity with spin and scaling gauge invariance and spacetime dynamics with quantum inflation
NASA Astrophysics Data System (ADS)
Wu, YueLiang
20160101
Treating the gravitational force on the same footing as the electroweak and strong forces, we present a quantum field theory of gravity based on spin and scaling gauge symmetries. A biframe spacetime is initiated to describe such a quantum gravity theory. The gravifield sided on both locally flat noncoordinate spacetime and globally flat Minkowski spacetime is an essential ingredient for gauging global spin and scaling symmetries. The locally flat gravifield spacetime spanned by the gravifield is associated with a noncommutative geometry characterized by a gaugetype field strength of the gravifield. A coordinateindependent and gaugeinvariant action for the quantum gravity is built in the gravifield basis. In the coordinate basis, we derive equations of motion for all quantum fields including the gravitational effect and obtain basic conservation laws for all symmetries. The equation of motion for the gravifield tensor is deduced in connection directly with the total energymomentum tensor. When the spin and scaling gauge symmetries are broken down to a background structure that possesses the global Lorentz and scaling symmetries, we obtain exact solutions by solving equations of motion for the background fields in a unitary basis. The massless graviton and massive spinon result as physical quantum degrees of freedom. The resulting Lorentzinvariant and conformally flat background gravifield spacetime is characterized by a cosmic vector with a nonzero cosmological mass scale. The evolving Universe is, in general, not isotropic in terms of conformal proper time. The conformal size of the Universe becomes singular at the cosmological horizon and turns out to be inflationary in light of cosmic proper time. A mechanism for quantum scalinon inflation is demonstrated such that it is the quantum effect that causes the breaking of global scaling symmetry and generates the inflation of the early Universe, which is ended when the evolving vacuum expectation value of the

Cardiovascular alterations in Macaca monkeys exposed to stationary magnetic fields: experimental observations and theoretical analysis
SciTech Connect
Tenforde, T.S.; Gaffey, C.T.; Moyer, B.R.; Budinger, T.F.
19830101
Simultaneous measurements were made of the electrocardiogram (ECG) and the intraarterial blood pressure of adult male Macaca monkeys during acute exposure to homogeneous stationary magnetic fields ranging in strength up to 1.5 tesla. An instantaneous, field strengthdependent increase in the ECG signal amplitude at the locus of the T wave was observed in fields greater than 0.1 tesla. The temporal sequence of this signal in the ECG record and its reversibility following termination of the magnetic field exposure are consistent with an earlier suggestion that it arises from a magnetically induced aortic blood flow potential superimposed on the native Twave signal. No measurable alterations in blood pressure resulted from exposure to fields up to 1.5 tesla. This experimental finding is in agreement with theoretical calculations of the magnetohydrodynamic effect on blood flow in the major arteries of the cardiovascular system. 27 references, 1 figure, 1 table.

Combined action of static and alternating magnetic fields on ion motion in a macromolecule: theoretical aspects.
PubMed
Zhadin, M N
19980101
This is an attempt to solve the energetic problem of the primary detection of weak parallel static (DC) and alternating (AC) extremely low frequency (ELF) magnetic fields. We studied the equations of motion for an ion situated inside a macromolecule under the influence of these fields. The main concern is with the magnetic field influence on thermal motion of the ion in the macromolecule. The resonance effects are revealed at discrete frequencies of the ion thermal oscillations determined by the DC field magnitude and the AC field frequency. These phenomena result from the Larmor precession of the ion thermal motion. When the DC field or, to a greater extent, the combined DC and AC fields with the specific frequencies are turned on or cut off, changes occur in the energy of the ion thermal motion. If, inside the macromolecule, the ion is sufficiently protected against immediate impacts of particles of the medium surrounding the macromolecule, these changes may be enough to trigger alteration in the quantum state of the macromolecule.

Entropy of massive quantum fields in de Sitter spacetime
NASA Astrophysics Data System (ADS)
Takook, M. V.
20160401
Using the quantum states or Hilbert spaces for the quantum field theory in de Sitter ambient space formalism the entropy of the massive quantum field theory is calculated. In this formalism, the homogeneous spaces which are used for construction of the unitary irreducible representation of de Sitter group are compact. The unique feature of this homogeneous space is that by imposing certain physical conditions its total number of quantum oneparticle states, N1p, becomes finite although the Hilbert space has infinite dimensions. N1p is de Sitter invariant and a continuous function of the Hubble constant H and the eigenvalue of the Casimir operators of de Sitter group. The entropy of the quantum fields is finite and invariant for all inertial observers on de Sitter hyperboloid.

Entanglement of a coarse grained quantum field in the expanding universe
SciTech Connect
Nambu, Yasusada; Ohsumi, Yuji
20091215
We investigate the entanglement of a quantum field in the expanding universe. By introducing a bipartite system using a coarsegrained scalar field, we apply the separability criterion based on the partial transpose operation and numerically calculate the bipartite entanglement between separate spatial regions. We find that the initial entangled state becomes separable or disentangled after the spatial separation of two points exceed the Hubble horizon. This provides the necessary conditions for the appearance of classicality of the quantum fluctuation. We also investigate the condition of classicality that the quantum field can be treated as the classical stochastic variables.

BetheSalpeter equation for exciton states in quantum well in a nonhomogeneous magnetic field
NASA Astrophysics Data System (ADS)
Koinov, Z.; Nash, P.; Witzel, J.
20030301
The trapping of excitons in a single quantum well due to the presence of an external strong constant magnetic field and a small nonhomogeneous cylindrical symmetric magnetic field, created by a magnetized disk on top of the quantum well, is studied by applying the BetheSalpeter formalism. The numerical calculations are performed for GaAs/AlGaAs quantum wells. We find that the nonhomogeneous magnetic field leads to the formation of bound exciton states with nonzero values for the centerofmass exciton wave function only in a sufficiently small area.

Theoretical modeling of the plasmaassisted catalytic growth and field emission properties of graphene sheet
SciTech Connect
Sharma, Suresh C.; Gupta, Neha
20151215
A theoretical modeling for the catalystassisted growth of graphene sheet in the presence of plasma has been investigated. It is observed that the plasma parameters can strongly affect the growth and field emission properties of graphene sheet. The model developed accounts for the charging rate of the graphene sheet; number density of electrons, ions, and neutral atoms; various elementary processes on the surface of the catalyst nanoparticle; surface diffusion and accretion of ions; and formation of carbonclusters and large graphene islands. In our investigation, it is found that the thickness of the graphene sheet decreases with the plasma parameters, number density of hydrogen ions and RF power, and consequently, the field emission of electrons from the graphene sheet surface increases. The time evolution of the height of graphene sheet with ion density and sticking coefficient of carbon species has also been examined. Some of our theoretical results are in compliance with the experimental observations.

Finitetemperature scaling at the quantum critical point of the Ising chain in a transverse field
NASA Astrophysics Data System (ADS)
Haelg, Manuel; Huvonen, Dan; Guidi, Tatiana; QuinteroCastro, Diana Lucia; Boehm, Martin; Regnault, LouisPierre; Zheludev, Andrey
20150301
Inelastic neutron scattering is used to study the finitetemperature scaling behavior of spin correlations at the quantum critical point in an experimental realization of the onedimensional Ising model in a transverse field. The target compound is the wellcharacterized, anisotropic and bondalternating Heisenberg spin1 chain material NTENP. The validity and the limitations of the dynamic structure factor scaling are tested, discussed and compared to theoretical predictions. For this purpose neutron data have been collected on the threeaxes spectrometers IN14 at ILL and FLEXX at HZB as well as on the time of flight multichopper spectrometer LET at ISIS. In addition to the general statement about quantum criticality and universality, present study also reveals new insight into the properties of the spin chain compound NTENP in particular.

Dynamical gap generation in graphene nanoribbons: An effective relativistic field theoretical model
SciTech Connect
Chaves, A. J.; Paula, W. de; Frederico, T.; Lima, G. D.; Cordeiro, C. E.; Delfino, A.
20110415
We show that the assumption of a nontrivial zero band gap for a graphene sheet within an effective relativistic field theoretical model description of interacting Dirac electrons on the surface of graphene describes the experimental band gap of graphene nanoribbons for a wide range of widths. The graphene band gap is dynamically generated, corresponding to a nontrivial gapless solution, found in the limit of an infinitely wide graphene ribbon. The nanoribbon band gap is determined by the experimental graphene work function.

A theoretical study of soft mode behavior and ferroelectric phase transition in 18Oisotope exchanged SrTiO3: evidence of phase coexistence at the quantum critical point
NASA Astrophysics Data System (ADS)
Mkam Tchouobiap, S. E.
20140201
Motivated by recent experiments, the dynamics of the ferroelectric soft mode and the ferroelectric phase transition mechanism in 18O isotope exchanged systems SrTi(16O1x18Ox)3 (abbreviated as STO18x) are reinvestigated as a function of the 18O isotope exchange rate x, within a quasiharmonic model (QHM) for quantum ferroelectric modes in doubleMorse local potential with meanfield approximation interactions between modes. The approach was realized within the framework of the variational principle method at finite temperature through the quantum meanfield approximation and by taking into account the effect of isotope replacement through the predominant mass effect, the cell volume effect, homogeneity of the composition throughout the material and the concentrationdependent ferroelectric mode distortion effect. The dynamics of the lowestfrequency soft phonon mode clearly presents an increased softening phenomenon with increasing x and a complete one at the corresponding phase transition temperature Tc, demonstrating the perfect softmodetype quantum ferroelectric phase transition for x ⩾ xc. Also, a ferroelectricparaelectric phase coexistence state has been found near the quantum critical point xc and its origin is discussed. The ferroelectric phase transition mechanism is analyzed and its nature discussed, where a secondorder phase transition close to the tricritical point is predicted. In addition, the effect of quantum fluctuations on the soft mode dynamics is discussed which reveals its reduction with increasing x and the crossover of the soft mode dynamics from the quantum to the classic one at the full 18O exchange limit x = 1, for which the origin seems to lie in the new homogeneity associated with the direct reduction of quantum fluctuations effects on the soft mode behavior. Within the QHM, consistent agreement with some of the previous experimental results and theoretical predictions of quantum ferroelectricity throughout the full range of x are

Comparison of experimental and theoretical reaction rail currents, rail voltages, and airgap fields for the linear induction motor research vehicle
NASA Technical Reports Server (NTRS)
Elliott, D. G.
19770101
Measurements of reaction rail currents, reaction rail voltages, and airgap magnetic fields in tests of the Linear Induction Motor Research Vehicle (LIMRV) were compared with theoretical calculations from the mesh/matrix theory. It was found that the rail currents and magnetic fields predicted by the theory are within 20 percent of the measured currents and fields at most motor locations in most of the runs, but differ by as much as a factor of two in some cases. The most consistent difference is a higher experimental than theoretical magnetic field near the entrance of the motor and a lower experimental than theoretical magnetic field near the exit. The observed differences between the theoretical and experimental magnetic fields and currents do not account for the differences of as much as 26 percent between the theoretical and experimental thrusts.

Investigation of the interfacial tension of complex coacervates using fieldtheoretic simulations
NASA Astrophysics Data System (ADS)
Riggleman, Robert A.; Kumar, Rajeev; Fredrickson, Glenn H.
20120101
Complex coacervation, a liquidliquid phase separation that occurs when two oppositely charged polyelectrolytes are mixed in a solution, has the potential to be exploited for many emerging applications including wet adhesives and drug delivery vehicles. The ultralow interfacial tension of coacervate systems against water is critical for such applications, and it would be advantageous if molecular models could be used to characterize how various system properties (e.g., salt concentration) affect the interfacial tension. In this article we use fieldtheoretic simulations to characterize the interfacial tension between a complex coacervate and its supernatant. After demonstrating that our model is free of ultraviolet divergences (calculated properties converge as the collocation grid is refined), we develop two methods for calculating the interfacial tension from fieldtheoretic simulations. One method relies on the mechanical interpretation of the interfacial tension as the interfacial pressure, and the second method estimates the change in free energy as the area between the two phases is changed. These are the first calculations of the interfacial tension from full fieldtheoretic simulation of which we are aware, and both the magnitude and scaling behaviors of our calculated interfacial tension agree with recent experiments.

Investigation of the interfacial tension of complex coacervates using fieldtheoretic simulations
SciTech Connect
Kumar, Rajeev
20120101
Complex coacervation, a liquidliquid phase separation that occurs when two oppositely charged polyelectrolytes are mixed in a solution, has the potential to be exploited for many emerging applications including wet adhesives and drug delivery vehicles. The ultralow interfacial tension of coacervate systems against water is critical for such applications, and it would be advantageous if molecular models could be used to characterize how various system properties (e.g., salt concentration) affect the interfacial tension. In this article we use fieldtheoretic simulations to characterize the interfacial tension between a complex coacervate and its supernatant. After demonstrating that our model is free of ultraviolet divergences (calculated properties converge as the collocation grid is refined), we develop two methods for calculating the interfacial tension from fieldtheoretic simulations. One method relies on the mechanical interpretation of the interfacial tension as the interfacial pressure, and the second method estimates the change in free energy as the area between the two phases is changed. These are the first calculations of the interfacial tension from full field theoretic simulation of which we are aware, and both the magnitude and scaling behaviors of our calculated interfacial tension agree with recent experiments.

Electric field driven fractal growth in polymer electrolyte composites: Experimental evidence of theoretical simulations
NASA Astrophysics Data System (ADS)
Dawar, Anit; Chandra, Amita
20121101
The influence of electric field on the diffusion limited aggregation has been observed experimentally. The observation provides experimental confirmation of the theoretical model proposed by ZhiJie Tan et al. [Phys. Lett. A 268 (2000) 112]. Most strikingly, a transition from a disordered ramified pattern to an ordered pattern (chainlike growth) has been observed. The growth is governed by diffusion, convection and migration in an electric field which give rise to the different patterns. This Letter can also be considered as an experimental evidence of computer simulated fractal growth given by Huang and Hibbert [Physica A 233 (1996) 888].

Two phase discharge of liquefied gases through pipes. Field experiments with ammonia and theoretical model
NASA Astrophysics Data System (ADS)
Nyren, K.; Winter, S.
19840101
Field experiments with full scale releases of pressurized through siphon pipes from a storage tank were performed. It is found that the flow is a damped critical flow causing a violent turbulent spray jet. The pronounced atomization of the liquid and the quick air entrainment prevent rainout and no traces of land spills are observed. A theoretical model is also presented. Comparisons with the field experiments and laboratory experiments show that the model gives very good predictions of the mass flow rate and the jet determining parameters. The model is useful also for long pipe systems as it takes into account friction and other resistances.

Fieldtheoretic model of inhomogeneous supramolecular polymer networks and gels
NASA Astrophysics Data System (ADS)
Mohan, Aruna; Elliot, Richard; Fredrickson, Glenn H.
20101101
We present a fieldtheoretic model of the gelation transition in inhomogeneous reversibly bonding systems and demonstrate that our model reproduces the classical FloryStockmayer theory of gelation in the homogeneous limit. As an illustration of our model in the context of inhomogeneous gelation, we analyze the meanfield behavior of an equilibrium system of reacting trifunctional units in a good solvent confined within a slit bounded by parallel, repulsive walls. Our results indicate higher conversions and, consequently, higher concentrations of gel following the gelation transition near the center of the slit relative to the edges.

Fieldtheoretic model of inhomogeneous supramolecular polymer networks and gels.
PubMed
Mohan, Aruna; Elliot, Richard; Fredrickson, Glenn H
20101101
We present a fieldtheoretic model of the gelation transition in inhomogeneous reversibly bonding systems and demonstrate that our model reproduces the classical FloryStockmayer theory of gelation in the homogeneous limit. As an illustration of our model in the context of inhomogeneous gelation, we analyze the meanfield behavior of an equilibrium system of reacting trifunctional units in a good solvent confined within a slit bounded by parallel, repulsive walls. Our results indicate higher conversions and, consequently, higher concentrations of gel following the gelation transition near the center of the slit relative to the edges. PMID:21054065

On a derivation of the Boltzmann equation in Quantum Field Theory
NASA Astrophysics Data System (ADS)
Leiler, Gregor
The Boltzmann equation (BE) is a commonly used tool for the study of nonequilibrium many particle systems. It has been introduced in 1872 by Ludwig Boltzmann and has been widely generalized throughout the years. Today it is commonly used in physical applications, from the study of ordinary fluids to problems in particle Cosmology where Quantum Field Theoretical techniques are essential. Despite its numerous experimental successes, the conceptual basis of the BE is not entirely clear. For instance, it is well known that it is not a fundamental equation of physics like, say, the Heisenberg equation (HE). A natural question then arises whether it is possible to derive the BE from physical first principles, i.e. the Heisenberg equation in Quantum Field Theory. In this work we attempted to answer this question and succeeded in deriving the BE from the HE, thus further clarifying its conceptual status. In particular, the results we have obtained are as follows. Firstly, we establish the nonperturbative validity of what we call the "preBoltzmann equation". The crucial point here is that this latter equation is equivalent to the Heisenberg equation. Secondly, we proceed to consider various limits of the preBoltzmann equation, namly the "low density" and the "weak coupling" limits, to obtain two equations that can be considered as generalizations of the BE. These limits are always taken together with the "long time" limit, which allows us to interpret the BE as an appropriate long time limit of the HE. The generalization we obtain consists in additional "correction" terms to the usual Boltzmann collision factor, and can be associated to multiple particle scattering. Unlike the preBoltzmann equation, these latter results are only valid pertubatively. Finally, we briefly consider the possibility to extend these results beyond said limits and outline some important aspects in this case.

A theoretical study for parallel electric field in nonlinear magnetosonic waves in threecomponent plasmas
NASA Astrophysics Data System (ADS)
Toida, Mieko
20160701
The electric field parallel to the magnetic field in nonlinear magnetosonic waves in three component plasmas (twoionspecies plasma and electronpositronion plasma) is theoretically studied based on a threefluid model. In a twoionspecies plasma, a magnetosonic mode has two branches, highfrequency mode and lowfrequency mode. The parallel electric field E ∥ and its integral along the magnetic field, F =  ∫ E ∥ d s , in the two modes propagating quasiperpendicular to the magnetic field are derived as functions of the wave amplitude ɛ and the density ratio and cyclotron frequency ratio of the two ion species. The theory shows that the magnitude of F in the highfrequencymode pulse is much greater than that in the lowfrequencymode pulse. Theoretical expressions for E ∥ and F in nonlinear magnetosonic pulses in an electronpositronion plasma are also obtained under the assumption that the wave amplitudes are in the range of ( m e / m i ) 1 / 2 < ɛ < 1 , where m e / m i is the electron to ion mass ratio.

An Interacting Gauge Field Theoretic Model for Hodge Theory: Basic Canonical Brackets
NASA Astrophysics Data System (ADS)
R., Kumar; Gupta, S.; R. P., Malik
20140601
We derive the basic canonical brackets amongst the creation and annihilation operators for a two (1 + 1)dimensional (2D) gauge held theoretic model of an interacting Hodge theory where a U(1) gauge field (Aμ) is coupled with the fermionic Dirac fields (ψ and bar psi). In this derivation, we exploit the spinstatistics theorem, normal ordering and the strength of the underlying six infinitesimal continuous symmetries (and the concept of their generators) that are present in the theory. We do not use the definition of the canonical conjugate momenta (corresponding to the basic fields of the theory) anywhere in our whole discussion. Thus, we conjecture that our present approach provides an alternative to the canonical method of quantization for a class of gauge field theories that are physical examples of Hodge theory where the continuous symmetries (and corresponding generators) provide the physical realizations of the de Rham cohomological operators of differential geometry at the algebraic level.

Theoretical analysis of AC electric field transmission into biological tissue through frozen saline for electroporation.
PubMed
Xiao, Chunyan; Rubinsky, Boris
20141201
An analytical model was used to explore the feasibility of sinusoidal electric field transmission across a frozen saline layer into biological tissue. The study is relevant to electroporation and permeabilization of the cell membrane by electric fields. The concept was analyzed for frequencies in the range of conventional electroporation frequencies and electric field intensity. Theoretical analysis for a variety of tissues show that the transmission of electroporation type electric fields through a layer of frozen saline into tissue is feasible and the behavior of this composite system depends on tissue type, frozen domain temperature, and frequency. Freezing could become a valuable method for adherence of electroporation electrodes to moving tissue surfaces, such as the heart in the treatment of atrial fibrillation or blood vessels for the treatment of restenosis.

Scalar field equations from quantum gravity during inflation
SciTech Connect
Kahya, E. O.; Woodard, R. P.
20080415
We exploit a previous computation of the selfmasssquared from quantum gravity to include quantum corrections to the scalar evolution equation. The plane wave mode functions are shown to receive no significant one loop corrections at late times. This result probably applies as well to the inflaton of scalardriven inflation. If so, there is no significant correction to the {phi}{phi} correlator that plays a crucial role in computations of the power spectrum.

Gaussian effective potential: Quantum mechanics
NASA Astrophysics Data System (ADS)
Stevenson, P. M.
19841001
We advertise the virtues of the Gaussian effective potential (GEP) as a guide to the behavior of quantum field theories. Much superior to the usual oneloop effective potential, the GEP is a natural extension of intuitive notions familiar from quantum mechanics. A variety of quantummechanical examples are studied here, with an eye to fieldtheoretic analogies. Quantum restoration of symmetry, dynamical mass generation, and "quantummechanical resuscitation" are among the phenomena discussed. We suggest how the GEP could become the basis of a systematic approximation procedure. A companion paper will deal with scalar field theory.

ATOMIC AND MOLECULAR PHYSICS: Apparent diffusion behaviour of intermolecular doublequantum coherence modulated by a distant dipolar field in solution NMR
NASA Astrophysics Data System (ADS)
Shen, GuiPing; Cai, CongBo; Cai, ShuHui; Chen, Zhong
20091101
A modified correlated spectroscopy (COSY) revamped with asymmetric Zgradient echo detection sequence was designed to investigate the influence of diffusion behaviour on intermolecular doublequantum coherence signal attenuation during the preacquisition period. Theoretical formulas were deduced and experimental measurements and simulations were performed. It is found that the diffusion behaviour of intermolecular doublequantum coherence in the preacquisition period may be different from that of conventional singlequantum coherence, depending on the relative orientation of diffusion weighting gradients to coherence selection gradients. When the orientation of the diffusion weighting gradients is parallel or antiparallel to the orientation of the coherence selection gradients, the diffusion is modulated by the distant dipolar field. This study is helpful for understanding the signal properties in intermolecular doublequantum coherence magnetic resonance imaging.

On estimating perturbative coefficients in quantum field theory and statistical physics
SciTech Connect
Samuel, M.A. 
19940501
The authors present a method for estimating perturbative coefficients in quantum field theory and Statistical Physics. They are able to obtain reliable errorbars for each estimate. The results, in all cases, are excellent.

Theoretical study on electromagnetically induced transparency in molecular aggregate models using quantum Liouville equation method
SciTech Connect
Minami, Takuya; Nakano, Masayoshi
20150122
Electromagnetically induced transparency (EIT), which is known as an efficient control method of optical absorption property, is investigated using the polarizability spectra and population dynamics obtained by solving the quantum Liouville equation. In order to clarify the intermolecular interaction effect on EIT, we examine several molecular aggregate models composed of threestate monomers with the dipoledipole coupling. On the basis of the present results, we discuss the applicability of EIT in molecular aggregate systems to a new type of optical switch.

Fieldwidened Michelson interferometer for spectral discrimination in highspectralresolution lidar: theoretical framework.
PubMed
Cheng, Zhongtao; Liu, Dong; Luo, Jing; Yang, Yongying; Zhou, Yudi; Zhang, Yupeng; Duan, Lulin; Su, Lin; Yang, Liming; Shen, Yibing; Wang, Kaiwei; Bai, Jian
20150501
A fieldwidened Michelson interferometer (FWMI) is developed to act as the spectral discriminator in highspectralresolution lidar (HSRL). This realization is motivated by the wideangle Michelson interferometer (WAMI) which has been used broadly in the atmospheric wind and temperature detection. This paper describes an independent theoretical framework about the application of the FWMI in HSRL for the first time. In the framework, the operation principles and application requirements of the FWMI are discussed in comparison with that of the WAMI. Theoretical foundations for designing this type of interferometer are introduced based on these comparisons. Moreover, a general performance estimation model for the FWMI is established, which can provide common guidelines for the performance budget and evaluation of the FWMI in the both design and operation stages. Examples incorporating many practical imperfections or conditions that may degrade the performance of the FWMI are given to illustrate the implementation of the modeling. This theoretical framework presents a complete and powerful tool for solving most of theoretical or engineering problems encountered in the FWMI application, including the designing, parameter calibration, prior performance budget, posterior performance estimation, and so on. It will be a valuable contribution to the lidar community to develop a new generation of HSRLs based on the FWMI spectroscopic filter.

Simulations of magnetic field gradients due to micromagnets on a triple quantum dot circuit
SciTech Connect
PoulinLamarre, G.; BureauOxton, C.; Kam, A.; Zawadzki, P.; Aers, G.; Studenikin, S.; PioroLadrière, M.; Sachrajda, A. S.
20131204
To quantify the effects of local magnetic fields on triple quantum dots, the Heisenberg Hamiltonian has been diagonalized for three electrons coupled via the exchange interaction. In particular, we have investigated different geometries of micromagnets located on top of the triple dot in order to optimize the field gradient characteristics. In this paper, we focus on two geometries which are candidates for an addressable EDSR triple quantum dot device.

Quantum cluster algorithm for frustrated Ising models in a transverse field
NASA Astrophysics Data System (ADS)
Biswas, Sounak; Rakala, Geet; Damle, Kedar
20160601
Working within the stochastic series expansion framework, we introduce and characterize a plaquettebased quantum cluster algorithm for quantum Monte Carlo simulations of transverse field Ising models with frustrated Ising exchange interactions. As a demonstration of the capabilities of this algorithm, we show that a relatively small ferromagnetic nextnearestneighbor coupling drives the transverse field Ising antiferromagnet on the triangular lattice from an antiferromagnetic threesublattice ordered state at low temperature to a ferrimagnetic threesublattice ordered state.

Quantum beats in hydrogen and antihydrogen atoms in an external electric field.
PubMed
Labzowsky, L; Sharipov, V
20040401
An effect of quantum beats that arises due to the coherent excitation of 2s and 2p states of hydrogen and antihydrogen atoms in an external electric field is described. It is shown that the quantum beat signal contains terms linear in electric field, i.e., is of opposite sign for the hydrogen and antihydrogen atoms. The conditions for the observation of this effect are discussed.

Ramsey's method of separated oscillating fields and its application to gravitationally induced quantum phase shifts
SciTech Connect
Abele, H.; Jenke, T.; Leeb, H.; Schmiedmayer, J.
20100315
We propose to apply Ramsey's method of separated oscillating fields to the spectroscopy of the quantum states in the gravity potential above a horizontal mirror. This method allows a precise measurement of quantum mechanical phaseshifts of a Schroedinger wave packet bouncing off a hard surface in the gravitational field of the Earth. Measurements with ultracold neutrons will offer a sensitivity to Newton's law or hypothetical shortranged interactions, which is about 21 orders of magnitude below the energy scale of electromagnetism.

Experimental and theoretical study on field emission properties of zinc oxide nanoparticles decorated carbon nanotubes
NASA Astrophysics Data System (ADS)
Li, Xin; Zhou, WeiMan; Liu, WeiHua; Wang, XiaoLi
20150501
Field emission properties of zinc oxide (ZnO) nanoparticles (NPs) decorated carbon nanotubes (CNTs) are investigated experimentally and theoretically. CNTs are in situ decorated with ZnO NPs during the growth process by chemical vapor deposition using a carbon source from the iron phthalocyanine pyrolysis. The experimental field emission test shows that the ZnO NP decoration significantly improves the emission current from 50 μA to 275 μA at 550 V and the reduced threshold voltage from 450 V to 350 V. The field emission mechanism of ZnO NPs on CNTs is theoretically studied by the density functional theory (DFT) combined with the PennPlummer method. The ZnO NPs reconstruct the ZnOCNT structure and pull down the surface barrier of the entire emitter system to 0.49 eV so as to reduce the threshold electric field. The simulation results suggest that the presence of ZnO NPs would increase the LDOS near the Fermi level and increase the emission current. The calculation results are consistent with the experiment results. Project supported by the National Natural Science Foundation of China (Grant Nos. 91123018, 61172040, and 61172041) and the Natural Science Foundation of Shaanxi Province, China (Grant No. 2014JM7277).

Singleparticle and collective excitations in quantum wires made up of vertically stacked quantum dots: zero magnetic field.
PubMed
Kushwaha, Manvir S
20110928
We report on the theoretical investigation of the elementary electronic excitations in a quantum wire made up of vertically stacked selfassembled InAs/GaAs quantum dots. The length scales (of a few nanometers) involved in the experimental setups prompt us to consider an infinitely periodic system of twodimensionally confined (InAs) quantum dot layers separated by GaAs spacers. The resultant quantum wire is characterized by a twodimensional harmonic confining potential in the xy plane and a periodic (KronigPenney) potential along the z (or the growth) direction within the tightbinding approximation. Since the wells and barriers are formed from two different materials, we employ the Bastard's boundary conditions in order to determine the eigenfunctions along the z direction. These wave functions are then used to generate the Wannier functions, which, in turn, constitute the legitimate Bloch functions that govern the electron dynamics along the direction of periodicity. Thus, the Bloch functions and the Hermite functions together characterize the whole system. We then make use of the BohmPines' (full) randomphase approximation in order to derive a general nonlocal, dynamic dielectric function. Thus, developed theoretical framework is then specified to work within a (lowest miniband and) twosubband model that enables us to scrutinize the singleparticle as well as collective responses of the system. We compute and discuss the behavior of the eigenfunctions, bandwidths, density of states, Fermi energy, singleparticle and collective excitations, and finally size up the importance of studying the inverse dielectric function in relation with the quantum transport phenomena. It is remarkable to notice how the variation in the barrier and wellwidths can allow us to tailor the excitation spectrum in the desired energy range. Given the advantage of the vertically stacked quantum dots over the planar ones and the foreseen applications in the singleelectron devices

Analytical method for determining quantum well exciton properties in a magnetic field
NASA Astrophysics Data System (ADS)
Stépnicki, Piotr; Piétka, Barbara; MorierGenoud, François; Deveaud, Benoît; Matuszewski, Michał
20150501
We develop an analytical approximate method for determining the Bohr radii of WannierMott excitons in thin quantum wells under the influence of magnetic field perpendicular to the quantum well plane. Our hybrid variationalperturbative method allows us to obtain simple closed formulas for exciton binding energies and optical transition rates. We confirm the reliability of our method through excitonpolariton experiments realized in a GaAs/AlAs microcavity with an 8 nm InxGa1 xAs quantum well and magnetic field strengths as high as 14 T.

Quantum aspects of a moving magnetic quadrupole moment interacting with an electric field
SciTech Connect
Fonseca, I. C.; Bakke, K.
20150615
The quantum dynamics of a moving particle with a magnetic quadrupole moment that interacts with electric and magnetic fields is introduced. By dealing with the interaction between an electric field and the magnetic quadrupole moment, it is shown that an analogue of the Coulomb potential can be generated and bound state solutions can be obtained. Besides, the influence of the Coulombtype potential on the harmonic oscillator is investigated, where bound state solutions to both repulsive and attractive Coulombtype potentials are achieved and the arising of a quantum effect characterized by the dependence of the harmonic oscillator frequency on the quantum numbers of the system is discussed.

EnvironmentAssisted Speedup of the Field Evolution in Cavity Quantum Electrodynamics.
PubMed
Cimmarusti, A D; Yan, Z; Patterson, B D; Corcos, L P; Orozco, L A; Deffner, S
20150612
We measure the quantum speed of the state evolution of the field in a weakly driven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environmentassisted speedup is realized: the quantum speed of the state repopulation in the optical cavity increases with the coupling strength between the optical cavity mode and this nonMarkovian environment (the number of atoms). PMID:26196802

Optical fieldstrength generalized polarization of nonstationary quantum states in waveguiding photonic devices
NASA Astrophysics Data System (ADS)
Barral, David; Liñares, Jesús; Nistal, María C.
20130701
A quantum analysis of the generalized polarization properties of multimode nonstationary states based on their optical fieldstrength probability distributions is presented. The quantum generalized polarization is understood as a significant confinement of the probability distribution along certain regions of a multidimensional optical fieldstrength space. The analysis is addressed to quantum states generated in multimode linear and nonlinear waveguiding (integrated) photonic devices, such as multimode waveguiding directional couplers and waveguiding parametric amplifiers, whose modes fulfill a spatial modal orthogonality. In particular, the generalized polarization degree of coherent, squeezed and Schrödinger's cat states is analyzed.

Dynamics of Crowd Behaviors: From Complex Plane to Quantum Random Fields
NASA Astrophysics Data System (ADS)
Ivancevic, Vladimir G.; Reid, Darryn J.
20151101
The following sections are included: * Complex Plane Dynamics of Crowds and Groups * Introduction * ComplexValued Dynamics of Crowd and Group Behaviors * Kähler Geometry of Crowd and Group Dynamics * Computer Simulations of Crowds and Croups Dynamics * Braids of Agents' Behaviors in the Complex Plane * HilbertSpace Control of Crowds and Groups Dynamics * Quantum Random Fields: A Unique Framework for Simulation, Optimization, Control and Learning * Introduction * Adaptive Quantum Oscillator * Optimization and Learning on Banach and Hilbert Spaces * Appendix * ComplexValued Image Processing * Linear Integral Equations * RiemannLiouville Fractional Calculus * Rigorous Geometric Quantization * Supervised MachineLearning Methods * FirstOrder Logic and Quantum Random Fields

EnvironmentAssisted Speedup of the Field Evolution in Cavity Quantum Electrodynamics.
PubMed
Cimmarusti, A D; Yan, Z; Patterson, B D; Corcos, L P; Orozco, L A; Deffner, S
20150612
We measure the quantum speed of the state evolution of the field in a weakly driven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environmentassisted speedup is realized: the quantum speed of the state repopulation in the optical cavity increases with the coupling strength between the optical cavity mode and this nonMarkovian environment (the number of atoms).

EnvironmentAssisted Speedup of the Field Evolution in Cavity Quantum Electrodynamics
SciTech Connect
Cimmarusti, A. D.; Yan, Z.; Patterson, B. D.; Corcos, L. P.; Orozco, L. A.; Deffner, S.
20150611
We measure the quantum speed of the state evolution of the field in a weaklydriven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environment assisted speedup is realized: the quantum speed of the state repopulation in the optical cavity increases with the coupling strength between the optical cavity mode and this nonMarkovian environment (the number of atoms).

Fieldinduced periodic distortions in a nematic liquid crystal: deuterium NMR study and theoretical analysis.
PubMed
Sugimura, A; Zakharov, A V
20110801
The peculiarities in the dynamic of the director reorientation in a liquid crystal (LC) film under the influence of the electric E field directed at an angle α to the magnetic B field have been investigated both experimentally and theoretically. Timeresolved deuterium NMR spectroscopy is employed to investigate the fieldinduced director dynamics. Analysis of the experimental results, based on the predictions of hydrodynamic theory including both the director motion and fluid flow, provides an evidence for the appearance of the spatially periodic patterns in 4npentyl4'cyanobiphenyl LC film, at the angles α>60∘, in response to the suddenly applied E. These periodic distortions produce a lower effective rotational viscosity. This gives a faster response of the director rotation than for a uniform mode, as observed in our NMR experiment. PMID:21929001

Inferring electric fields and currents from ground magnetometer data  A test with theoretically derived inputs
NASA Astrophysics Data System (ADS)
Wolf, R. A.; Kamide, Y.
19831001
Advanced techniques considered by Kamide et al. (1981) seem to have the potential for providing observationbased high time resolution pictures of the global ionospheric current and electric field patterns for interesting events. However, a reliance on the proposed magnetograminversion schemes for the deduction of global ionospheric current and electric field patterns requires proof that reliable results are obtained. 'Theoretical' tests of the accuracy of the magnetogram inversion schemes have, therefore, been considered. The present investigation is concerned with a test, involving the developed KRM algorithm and the Rice Convection Model (RCM). The test was successful in the sense that there was overall agreement between electric fields and currents calculated by the RCM and KRM schemes.

Inferring electric fields and currents from ground magnetometer data  A test with theoretically derived inputs
NASA Technical Reports Server (NTRS)
Wolf, R. A.; Kamide, Y.
19830101
Advanced techniques considered by Kamide et al. (1981) seem to have the potential for providing observationbased high time resolution pictures of the global ionospheric current and electric field patterns for interesting events. However, a reliance on the proposed magnetograminversion schemes for the deduction of global ionospheric current and electric field patterns requires proof that reliable results are obtained. 'Theoretical' tests of the accuracy of the magnetogram inversion schemes have, therefore, been considered. The present investigation is concerned with a test, involving the developed KRM algorithm and the Rice Convection Model (RCM). The test was successful in the sense that there was overall agreement between electric fields and currents calculated by the RCM and KRM schemes.

Predicting excitonic gaps of semiconducting singlewalled carbon nanotubes from a field theoretic analysis
NASA Astrophysics Data System (ADS)
Konik, Robert M.; Sfeir, Matthew Y.; Misewich, James A.
20150201
We demonstrate that a nonperturbative framework for the treatment of the excitations of singlewalled carbon nanotubes based upon a field theoretic reduction is able to accurately describe experiment observations of the absolute values of excitonic energies. This theoretical framework yields a simple scaling function from which the excitonic energies can be read off. This scaling function is primarily determined by a single parameter, the charge Luttinger parameter of the tube, which is in turn a function of the tube chirality, dielectric environment, and the tube's dimensions, thus expressing disparate influences on the excitonic energies in a unified fashion. We test this theory explicitly on the data reported by Dukovic et al. [Nano Lett. 5, 2314 (2005), 10.1021/nl0518122] and Sfeir et al. [Phys. Rev. B 82, 195424 (2010), 10.1103/PhysRevB.82.195424] and so demonstrate the method works over a wide range of reported excitonic spectra.

Predicting excitonic gaps of semiconducting singlewalled carbon nanotubes from a field theoretic analysis
SciTech Connect
Konik, Robert M.; Sfeir, Matthew Y.; Misewich, James A.
20150217
We demonstrate that a nonperturbative framework for the treatment of the excitations of single walled carbon nanotubes based upon a field theoretic reduction is able to accurately describe experiment observations of the absolute values of excitonic energies. This theoretical framework yields a simple scaling function from which the excitonic energies can be read off. This scaling function is primarily determined by a single parameter, the charge Luttinger parameter of the tube, which is in turn a function of the tube chirality, dielectric environment, and the tube's dimensions, thus expressing disparate influences on the excitonic energies in a unified fashion. As a result, we test this theory explicitly on the data reported in [NanoLetters 5, 2314 (2005)] and [Phys. Rev. B 82, 195424 (2010)] and so demonstrate the method works over a wide range of reported excitonic spectra.

Predicting excitonic gaps of semiconducting singlewalled carbon nanotubes from a field theoretic analysis
DOE PAGES
Konik, Robert M.; Sfeir, Matthew Y.; Misewich, James A.
20150217
We demonstrate that a nonperturbative framework for the treatment of the excitations of single walled carbon nanotubes based upon a field theoretic reduction is able to accurately describe experiment observations of the absolute values of excitonic energies. This theoretical framework yields a simple scaling function from which the excitonic energies can be read off. This scaling function is primarily determined by a single parameter, the charge Luttinger parameter of the tube, which is in turn a function of the tube chirality, dielectric environment, and the tube's dimensions, thus expressing disparate influences on the excitonic energies in a unified fashion. Asmore » a result, we test this theory explicitly on the data reported in [NanoLetters 5, 2314 (2005)] and [Phys. Rev. B 82, 195424 (2010)] and so demonstrate the method works over a wide range of reported excitonic spectra.« less

Effect of transverse electric field and temperature on light absorption in GaAs/AlGaAs tunnelcoupled quantum wells
SciTech Connect
Firsov, D. A.; Vorobjev, L. E.; Vinnichenko, M. Ya. Balagula, R. M.; Kulagina, M. M.; Vasil’iev, A. P.
20151115
The photoluminescence and intersubband absorption spectra are studied in GaAs/AlGaAs tunnel coupled quantum well structures. The peak positions in the photoluminescence and absorption spectra are consistent with the theoretically calculated energies of optical carrier transitions. The effect of a transverse electric field and temperature on intersubband light absorption is studied. It is caused by electron redistribution between the sizequantization levels and a variation in the energy spectrum of quantum wells. The variation in the refractive index in the energy region of observed intersubband transitions is estimated using Kramers–Kronig relations.

Topics in brane world and quantum field theory
NASA Astrophysics Data System (ADS)
Corradini, Olindo
In the first part of the thesis we study various issues in the Brane World scenario with particular emphasis on gravity and the cosmological constant problem. First, we study localization of gravity on smooth domainwall solutions of gravity coupled to a scalar field. In this context we discuss how the aforementioned localization is affected by including higher curvature terms in the theory, pointing out among other things that, general combinations of such terms lead to delocalization of gravity with the only exception of the GaussBonnet combination (and its higher dimensional counterparts). We then find a solitonic 3brane solution in 6D bulk in the EinsteinHilbertGaussBonnet theory of gravity. Near to the brane the metric is that for a product of the 4D flat Minkowski space with a 2D wedge whose deficit angle is proportional to the brane tension. Consistency tests imposed on such backgrounds appear to require the localized matter on the brane to be conformal. We then move onto infinite volume extra dimension Brane World scenarios where we study gravity in a codimension2 model, generalizing the work of Dvali, Gabadadze and Porrati to tensionful branes. We point out that, in the presence of the bulk GaussBonnet combination, the EinsteinHilbert term is induced on the brane already at the classical level. Consistency tests are presented here as well. To conclude we discuss, using String Theory, an interesting class of largeN gauge theories which have vanishing energy density even though these theories are noncovariant and nonsupersymmetric. In the second part of the thesis we study a formulation of Quantum Mechanical Path Integrals in curved space. Such Path Integrals present superficial divergences which need to be regulated. We perform a threeloop calculation in mode regularization as a nontrivial check of the noncovariant counterterms required by such scheme. We discover that dimensional regularization can be successfully adopted to evaluate the

Quantum entanglement formation by repeated spin blockade measurements in a spin fieldeffect transistor structure embedded with quantum dots
NASA Astrophysics Data System (ADS)
Yoh, Kanji; Yuasa, Kazuya; Nakazato, Hiromichi
20051101
We propose a method of operating a quantum state machine made of stacked quantum dots buried in adjacent to the channel of a spin fieldeffect transistor (FET) [S. Datta, B. Das, Appl. Phys. Lett. 56 (1990) 665; K. Yoh, et al., Proceedings of the 23rd International Conference on Physics of Semiconductors (ICPS) 2004; H. Ohno, K. Yoh et al., Jpn. J. Appl. Phys. 42 (2003) L87; K. Yoh, J. Konda, S. Shiina, N. Nishiguchi, Jpn. J. Appl. Phys. 36 (1997) 4134]. In this method, a spin blockade measurement extracts the quantum state of a nearest quantum dot through Coulomb blockade [K. Yoh, J. Konda, S. Shiina, N. Nishiguchi, Jpn. J. Appl. Phys. 36 (1997) 4134; K. Yoh, H. Kazama, Physica E 7 (2000) 440] of the adjacent channel conductance. Repeated quantum Zenolike (QZ) measurements [H. Nakazato, et al., Phys. Rev. Lett. 90 (2003) 060401] of the spin blockade is shown to purify the quantum dot states within several repetitions. The growth constraints of the stacked InAs quantum dots are shown to provide an exchange interaction energy in the range of 0.011 meV [S. Itoh, et al., Jpn. J. Appl. Phys. 38 (1999) L917; A. Tackeuchi, et al., Jpn. J. Appl. Phys. 42 (2003) 4278]. We have verified that one can reach the fidelity of 90% by repeating the measurement twice, and that of 99.9% by repeating only eleven QZ measurements. Entangled states with two and three vertically stacked dots are achieved with the sampling frequency of the order of 100 MHz.

Towards Noncommutative Topological Quantum Field Theory: New invariants for 3manifolds
NASA Astrophysics Data System (ADS)
Zois, I. P.
20160801
We present some ideas for a possible Noncommutative Topological Quantum Field Theory (NCTQFT for short) and Noncommutative Floer Homology (NCFH for short). Our motivation is twofold and it comes both from physics and mathematics: On the one hand we argue that NCTQFT is the correct mathematical framework for a quantum field theory of all known interactions in nature (including gravity). On the other hand we hope that a possible NCFH will apply to practically every 3manifold (and not only to homology 3spheres as ordinary Floer Homology currently does). The two motivations are closely related since, at least in the commutative case, Floer Homology Groups constitute the space of quantum observables of (3+1)dim Topological Quantum Field Theory. Towards this goal we define some new invariants for 3manifolds using the space of taut codim1 foliations modulo coarse isotopy along with various techniques from noncommutative geometry.

Exact scattering matrix of graphs in magnetic field and quantum noise
SciTech Connect
Caudrelier, Vincent; Mintchev, Mihail; Ragoucy, Eric
20140815
We consider arbitrary quantum wire networks modelled by finite, noncompact, connected quantum graphs in the presence of an external magnetic field. We find a general formula for the total scattering matrix of the network in terms of its local scattering properties and its metric structure. This is applied to a quantum ring with N external edges. Connecting the external edges of the ring to heat reservoirs, we study the quantum transport on the graph in ambient magnetic field. We consider two types of dynamics on the ring: the free Schrödinger and the free massless Dirac equations. For each case, a detailed study of the thermal noise is performed analytically. Interestingly enough, in presence of a magnetic field, the standard linear JohnsonNyquist law for the low temperature behaviour of the thermal noise becomes nonlinear. The precise regime of validity of this effect is discussed and a typical signature of the underlying dynamics is observed.

Quantum rings of nonuniform thickness in magnetic field
SciTech Connect
RodríguezPrada, F. A.; García, L. F.; Mikhailov, I. D.
20140515
We consider a model of cratershaped quantum dot in form of a thin layer whose thickness linearly increases with the distance from the axis. We show that oneparticle wave equation for the electron confined in such structure can be completely separated in the adiabatic limit when the quantum dot thickness is much smaller than its lateral dimension. Analytical solutions found for this model has been used as base functions for analysing the effect of nonhomogeneity on the electronic spectrum in the framework of the exact diagonalization method.

Trappedion quantum logic gates based on oscillating magnetic fields.
PubMed
Ospelkaus, C; Langer, C E; Amini, J M; Brown, K R; Leibfried, D; Wineland, D J
20080829
Oscillating magnetic fields and field gradients can be used to implement singlequbit rotations and entangling multiqubit quantum gates for trappedion quantum information processing (QIP). With fields generated by currents in microfabricated surfaceelectrode traps, it should be possible to achieve gate speeds that are comparable to those of optically induced gates for realistic distances between the ion crystal and the electrode surface. Magneticfieldmediated gates have the potential to significantly reduce the overhead in laserbeam control and motionalstate initialization compared to current QIP experiments with trapped ions and will eliminate spontaneous scattering, a fundamental source of decoherence in lasermediated gates.

Monotonically convergent optimal control theory of quantum systems under a nonlinear interaction with the control field
NASA Astrophysics Data System (ADS)
Lapert, M.; Tehini, R.; Turinici, G.; Sugny, D.
20080801
We consider the optimal control of quantum systems interacting nonlinearly with an electromagnetic field. We propose monotonically convergent algorithms to solve the optimal equations. The monotonic behavior of the algorithm is ensured by a nonstandard choice of the cost, which is not quadratic in the field. These algorithms can be constructed for pure and mixedstate quantum systems. The efficiency of the method is shown numerically for molecular orientation with a nonlinearity of order 3 in the field. Discretizing the amplitude and the phase of the Fourier transform of the optimal field, we show that the optimal solution can be well approximated by pulses that could be implemented experimentally.

Theoretical investigation of the behavior of CuSe2O5 compound in high magnetic fields
NASA Astrophysics Data System (ADS)
Saghafi, Z.; Jahangiri, J.; Mahdavifar, S.; Hadipour, H.; Farjami Shayesteh, S.
20160101
Based on the analytical and numerical approaches, we investigate thermodynamic properties of CuSe2O5 compound at high magnetic fields which is a candidate for the strong intrachain interaction in quasi onedimensional (1D) quantum magnets. Magnetic behavior of the system can be described by the 1D spin1/2 XXZ model in the presence of the DzyaloshinskiiMoriya (DM) interaction. Under these circumstances, there is one quantum critical field in this compound. Below the quantum critical field the spin chain system is in the gapless Luttinger liquid (LL) regime, whereas above it one observes a crossover to the gapped saturation magnetic phase. Indications on the thermodynamic curves confirm the occurrence of such a phase transition. The main characteristics of the LL phase are gapless and spinspin correlation functions decay algebraic. The effects of zerotemperature quantum phase transition are observed even at rather high temperatures in comparison with the counterpart compounds. In addition, we calculate the Wilson ratio in the model. The Wilson ratio at a fixed temperature remains almost independent of the field in the LL region. In the vicinity of the quantum critical field, the Wilson ratio increases and exhibits anomalous enhancement.

Origin of the ZeroField Splitting in Mononuclear Octahedral Mn(IV) Complexes: A Combined Experimental and Theoretical Investigation.
PubMed
Zlatar, Matija; Gruden, Maja; Vassilyeva, Olga Yu; Buvaylo, Elena A; Ponomarev, A N; Zvyagin, S A; Wosnitza, J; Krzystek, J; GarciaFernandez, Pablo; Duboc, Carole
20160201
The aim of this work was to determine and understand the origin of the electronic properties of Mn(IV) complexes, especially the zerofield splitting (ZFS), through a combined experimental and theoretical investigation on five wellcharacterized mononuclear octahedral Mn(IV) compounds, with various coordination spheres (N6, N3O3, N2O4 in both trans (transN2O4) and cis configurations (cisN2O4) and O4S2). Highfrequency and field EPR (HFEPR) spectroscopy has been applied to determine the ZFS parameters of two of these compounds, MnL(transN2O4) and MnL(O4S2). While at Xband EPR, the axialcomponent of the ZFS tensor, D, was estimated to be +0.47 cm(1) for MnL(O4S2), and a Dvalue of +2.289(5) cm(1) was determined by HFEPR, which is the largest Dmagnitude ever measured for a Mn(IV) complex. A moderate D value of 0.997(6) cm(1) has been found for MnL(transN2O4). Quantum chemical calculations based on two theoretical frameworks (the Density Functional Theory based on a coupled perturbed approach (CPDFT) and the hybrid LigandField DFT (LFDFT)) have been performed to define appropriate methodologies to calculate the ZFS tensor for Mn(IV) centers, to predict the orientation of the magnetic axes with respect to the molecular ones, and to define and quantify the physical origin of the different contributions to the ZFS. Except in the case of MnL(transN2O4), the experimental and calculated D values are in good agreement, and the sign of D is well predicted, LFDFT being more satisfactory than CPDFT. The calculations performed on MnL(cisN2O4) are consistent with the orientation of the principal anisotropic axis determined by singlecrystal EPR, validating the calculated ZFS tensor orientation. The different contributions to D were analyzed demonstrating that the dd transitions mainly govern D in Mn(IV) ion. However, a deep analysis evidences that many factors enter into the game, explaining why no obvious magnetostructural correlations can be drawn in this

Wick rotation for quantum field theories on degenerate Moyal space(time)
SciTech Connect
Grosse, Harald; Lechner, Gandalf; Ludwig, Thomas; Verch, Rainer
20130215
In this paper the connection between quantum field theories on flat noncommutative space(times) in Euclidean and Lorentzian signature is studied for the case that time is still commutative. By making use of the algebraic framework of quantum field theory and an analytic continuation of the symmetry groups which are compatible with the structure of Moyal space, a general correspondence between field theories on Euclidean space satisfying a time zero condition and quantum field theories on Moyal Minkowski space is presented ('Wick rotation'). It is then shown that field theories transferred to Moyal space(time) by Rieffel deformation and warped convolution fit into this framework, and that the processes of Wick rotation and deformation commute.

Pulsed Quantum Optomechanics
NASA Astrophysics Data System (ADS)
Vanner, Michael R.; Pikovski, Igor; Cole, Garrett D.; Kim, Myungshik; Brukner, Caslav; Hammerer, Klemens; Milburn, Gerard J.; Aspelmeyer, Markus
20110301
By combining quantum optics with mechanical resonators an avenue is opened to extend investigations of quantum behavior into unprecendented mass regimes. The field resulting from this combination  ``cavity quantum optomechanics''  is receiving a surge of interest for its potential to contribute to quantum measurement and control, studies of decoherence and nonclassical state preparation of macroscopic objects. However, quantum state preparation and especially quantum state reconstruction of mechanical oscillators is currently a significant challenge. We are pursuing a scheme that employs short optical pulses to realize quantum state tomography, squeezing via measurement and state purifcation of a mechanical resonator. The pulsed scheme has considerable resilience to initial thermal occupation, provides a promising means to explore the quantum nature of massive oscillators and can be applied to other systems such as trapped ions. Our theoretical proposal and experimental results will be discussed.

Towards hybrid circuit quantum electrodynamics with quantum dots
NASA Astrophysics Data System (ADS)
Viennot, Jérémie J.; Delbecq, Matthieu R.; Bruhat, Laure E.; Dartiailh, Matthieu C.; Desjardins, Matthieu M.; Baillergeau, Matthieu; Cottet, Audrey; Kontos, Takis
20160801
Cavity quantum electrodynamics allows one to study the interaction between light and matter at the most elementary level. The methods developed in this field have taught us how to probe and manipulate individual quantum systems like atoms and superconducting quantum bits with an exquisite accuracy. There is now a strong effort to extend further these methods to other quantum systems, and in particular hybrid quantum dot circuits. This could turn out to be instrumental for a noninvasive study of quantum dot circuits and a realization of scalable spin quantum bit architectures. It could also provide an interesting platform for quantum simulation of simple fermionboson condensed matter systems. In this short review, we discuss the experimental state of the art for hybrid circuit quantum electrodynamics with quantum dots, and we present a simple theoretical modeling of experiments.

Theoretical investigation of single dopant in core/shell nanocrystal in magnetic field
NASA Astrophysics Data System (ADS)
Talbi, A.; Feddi, E.; Oukerroum, A.; Assaid, E.; Dujardin, F.; Addou, M.
20150901
The control of single dopant or "solitary dopant" in semiconductors constitute a challenge to achieve new range of tunable optoelectronic devices. Knowing that the properties of doped monocrystals are very sensitive to different external perturbations, the aim of this study is to understand the effect of a magnetic field on the ground state energy of an offcenter ionized donor in a core/shell quantum dot (CSQD). The binding energies with and without an applied magnetic field are determined by the Ritz variational method taking into account the electronimpurity correlation in the trial wave function deduced from the secondorder perturbation. It has been found that the external magnetic field affects strongly the binding energy, and its effect varies as a function of the core radius and the shell thickness. We have shown the existence of a threshold ratio (a / b) crit which represents the limit between the tridimensional and the spherical surface confinement. In addition our analysis demonstrates the important influence of the position of ionized donor in the shell material.

Perturbative Quantum Analysis and Classical Limit of the Electron Scattering by a Solenoidal Magnetic Field
SciTech Connect
Murguia, Gabriela; Moreno, Matias; Torres, Manuel
20090420
A well known example in quantum electrodynamics (QED) shows that Coulomb scattering of unpolarized electrons, calculated to lowest order in perturbation theory, yields a results that exactly coincides (in the nonrelativistic limit) with the Rutherford formula. We examine an analogous example, the classical and perturbative quantum scattering of an electron by a magnetic field confined in an infinite solenoid of finite radius. The results obtained for the classical and the quantum differential cross sections display marked differences. While this may not be a complete surprise, one should expect to recover the classical expression by applying the classical limit to the quantum result. This turn not to be the case. Surprisingly enough, it is shown that the classical result can not be recuperated even if higher order corrections are included. To recover the classic correspondence of the quantum scattering problem a suitable nonperturbative methodology should be applied.

Control of the binding energy by tuning the single dopant position, magnetic field strength and shell thickness in ZnS/CdSe core/shell quantum dot
NASA Astrophysics Data System (ADS)
Talbi, A.; Feddi, E.; Zouitine, A.; Haouari, M. El; Zazoui, M.; Oukerroum, A.; Dujardin, F.; Assaid, E.; Addou, M.
20161001
Recently, the new tunable optoelectronic devices associated to the inclusion of the single dopant are in continuous emergence. Combined to other effects such as magnetic field, geometrical confinement and dielectric discontinuity, it can constitute an approach to adjusting new transitions. In this paper, we present a theoretical investigation of magnetic field, donor position and quantum confinement effects on the ground state binding energy of single dopant confined in ZnS/CdSe core/shell quantum dot. Within the framework of the effective mass approximation, the Schrödinger equation was numerically been solved by using the Ritz variational method under the finite potential barrier. The results show that the binding energy is very affected by the core/shell sizes and by the external magnetic field. It has been shown that the single dopant energy transitions can be controlled by tuning the dopant position and/or the field strength.

Ordinary versus PTsymmetric Φ³ quantum field theory
SciTech Connect
Bender, Carl M.; Branchina, Vincenzo; Messina, Emanuele
20120402
A quantummechanical theory is PTsymmetric if it is described by a Hamiltonian that commutes with PT, where the operator P performs space reflection and the operator T performs time reversal. A PTsymmetric Hamiltonian often has a parametric region of unbroken PT symmetry in which the energy eigenvalues are all real. There may also be a region of broken PT symmetry in which some of the eigenvalues are complex. These regions are separated by a phase transition that has been repeatedly observed in laboratory experiments. This paper focuses on the properties of a PTsymmetric igΦ³ quantum field theory. This quantum field theory is the analog of the PTsymmetric quantummechanical theory described by the Hamiltonian H=p²+ix³, whose eigenvalues have been rigorously shown to be all real. This paper compares the renormalization group properties of a conventional Hermitian gΦ³ quantum field theory with those of the PTsymmetric igΦ³ quantum field theory. It is shown that while the conventional gΦ³ theory in d=6 dimensions is asymptotically free, the igΦ³ theory is like a gΦ⁴ theory in d=4 dimensions; it is energetically stable, perturbatively renormalizable, and trivial.

Real applications of quantum imaging
NASA Astrophysics Data System (ADS)
Genovese, Marco
20160701
In previous years the possibility of creating and manipulating quantum states of light has paved the way for the development of new technologies exploiting peculiar properties of quantum states, such as quantum information, quantum metrology and sensing, quantum imaging, etc. In particular quantum imaging addresses the possibility of overcoming limits of classical optics by using quantum resources such as entanglement or subPoissonian statistics. Albeit, quantum imaging is a more recent field than other quantum technologies, e.g. quantum information, it is now mature enough for application. Several different protocols have been proposed, some of them only theoretically, others with an experimental implementation and a few of them pointing to a clear application. Here we present a few of the most mature protocols ranging from ghost imaging to sub shot noise imaging and subRayleigh imaging.

A theoretical investigation of the influence of gold nanosphere size on the decay and energy transfer rates and efficiencies of quantum emitters
NASA Astrophysics Data System (ADS)
Marocico, Cristian A.; Zhang, Xia; Bradley, A. Louise
20160101
We present in this contribution a comprehensive investigation of the effect of the size of gold nanospheres on the decay and energy transfer rates of quantum systems placed close to these nanospheres. These phenomena have been investigated before, theoretically and experimentally, but no comprehensive study of the influence of the nanoparticle size on important dependences of the decay and energy transfer rates, such as the dependence on the donoracceptor spectral overlap and the relative positions of the donor, acceptor, and nanoparticle, exists. As such, different accounts of the energy transfer mechanism have been presented in the literature. We perform an investigation of the energy transfer mechanisms between emitters and gold nanospheres and between donoracceptor pairs in the presence of the gold nanospheres using a Green's tensor formalism, experimentally verified in our lab. We find that the energy transfer rate to small nanospheres is greatly enhanced, leading to a strong quenching of the emission of the emitter. When the nanosphere size is increased, it acts as an antenna, increasing the emission of the emitter. We also investigate the emission wavelength and intrinsic quantum yield dependence of the energy transfer to the nanosphere. As evidenced from the literature, the energy transfer process between the quantum system and the nanosphere can have a complicated distance dependence, with a r6 regime, characteristic of the Förster energy transfer mechanism, but also exhibiting other distance dependences. In the case of a donoracceptor pair of quantum systems in the presence of a gold nanosphere, when the donor couples strongly to the nanosphere, acting as an enhanced dipole; the donoracceptor energy transfer rate then follows a Förster trend, with an increased Förster radius. The coupling of the acceptor to the nanosphere has a different distance dependence. The angular dependence of the energy transfer efficiency between donor and acceptor

A theoretical investigation of the influence of gold nanosphere size on the decay and energy transfer rates and efficiencies of quantum emitters.
PubMed
Marocico, Cristian A; Zhang, Xia; Bradley, A Louise
20160114
We present in this contribution a comprehensive investigation of the effect of the size of gold nanospheres on the decay and energy transfer rates of quantum systems placed close to these nanospheres. These phenomena have been investigated before, theoretically and experimentally, but no comprehensive study of the influence of the nanoparticle size on important dependences of the decay and energy transfer rates, such as the dependence on the donoracceptor spectral overlap and the relative positions of the donor, acceptor, and nanoparticle, exists. As such, different accounts of the energy transfer mechanism have been presented in the literature. We perform an investigation of the energy transfer mechanisms between emitters and gold nanospheres and between donoracceptor pairs in the presence of the gold nanospheres using a Green's tensor formalism, experimentally verified in our lab. We find that the energy transfer rate to small nanospheres is greatly enhanced, leading to a strong quenching of the emission of the emitter. When the nanosphere size is increased, it acts as an antenna, increasing the emission of the emitter. We also investigate the emission wavelength and intrinsic quantum yield dependence of the energy transfer to the nanosphere. As evidenced from the literature, the energy transfer process between the quantum system and the nanosphere can have a complicated distance dependence, with a r(6) regime, characteristic of the Förster energy transfer mechanism, but also exhibiting other distance dependences. In the case of a donoracceptor pair of quantum systems in the presence of a gold nanosphere, when the donor couples strongly to the nanosphere, acting as an enhanced dipole; the donoracceptor energy transfer rate then follows a Förster trend, with an increased Förster radius. The coupling of the acceptor to the nanosphere has a different distance dependence. The angular dependence of the energy transfer efficiency between donor and acceptor

Theoretical Study of the Inverting Mechanism in a Processive Cellobiohydrolase with Quantum Mechanical Calculations
SciTech Connect
Kim, S.; Payne, C. M.; Himmel, M. E.; Crowley, M. F.; Paton, R. S.; Beckham, G. T.
20120101
The Hypocrea jecorina Family 6 cellobiohydrolase (Cel6A) is one of most efficient enzymes for cellulose deconstruction to soluble sugars and is thus of significant current interest for the growing biofuels industry. Cel6A is known to hydrolyze b(1,4)glycosidic linkages in cellulose via an inverting mechanism, but there are still questions that remain regarding the role of water and the catalytic base. Here we study the inverting, single displacement, hydrolytic reaction mechanism in Cel6A using density functional theory (DFT) calculations. The computational model used to follow the reaction is a truncated active site model with several explicit waters based on structural studies of H. jecorina Cel6A. Proposed mechanisms are evaluated with several density functionals. From our calculations, the role of the water in nucleophilic attack on the anomeric carbon, and the roles of several residues in the active site loops are elucidated explicitly for the first time. We also apply quantum mechanical calculations to understand the proton transfer reaction which completes the catalytic cycle.

Experimental and Theoretical Electron Density Analysis of Copper Pyrazine Nitrate QuasiLowDimensional Quantum Magnets.
PubMed
Dos Santos, Leonardo H R; Lanza, Arianna; Barton, Alyssa M; Brambleby, Jamie; Blackmore, William J A; Goddard, Paul A; Xiao, Fan; Williams, Robert C; Lancaster, Tom; Pratt, Francis L; Blundell, Stephen J; Singleton, John; Manson, Jamie L; Macchi, Piero
20160224
The accurate electron density distribution and magnetic properties of two metalorganic polymeric magnets, the quasionedimensional (1D) Cu(pyz)(NO3)2 and the quasitwodimensional (2D) [Cu(pyz)2(NO3)]NO3·H2O, have been investigated by highresolution singlecrystal Xray diffraction and density functional theory calculations on the whole periodic systems and on selected fragments. Topological analyses, based on quantum theory of atoms in molecules, enabled the characterization of possible magnetic exchange pathways and the establishment of relationships between the electron (charge and spin) densities and the exchangecoupling constants. In both compounds, the experimentally observed antiferromagnetic coupling can be quantitatively explained by the CuCu superexchange pathway mediated by the pyrazine bridging ligands, via a σtype interaction. From topological analyses of experimental chargedensity data, we show for the first time that the pyrazine tilt angle does not play a role in determining the strength of the magnetic interaction. Taken in combination with molecular orbital analysis and spin density calculations, we find a synergistic relationship between spin delocalization and spin polarization mechanisms and that both determine the bulk magnetic behavior of these Cu(II)pyz coordination polymers.

Experimental and Theoretical Electron Density Analysis of Copper Pyrazine Nitrate QuasiLowDimensional Quantum Magnets.
PubMed
Dos Santos, Leonardo H R; Lanza, Arianna; Barton, Alyssa M; Brambleby, Jamie; Blackmore, William J A; Goddard, Paul A; Xiao, Fan; Williams, Robert C; Lancaster, Tom; Pratt, Francis L; Blundell, Stephen J; Singleton, John; Manson, Jamie L; Macchi, Piero
20160224
The accurate electron density distribution and magnetic properties of two metalorganic polymeric magnets, the quasionedimensional (1D) Cu(pyz)(NO3)2 and the quasitwodimensional (2D) [Cu(pyz)2(NO3)]NO3·H2O, have been investigated by highresolution singlecrystal Xray diffraction and density functional theory calculations on the whole periodic systems and on selected fragments. Topological analyses, based on quantum theory of atoms in molecules, enabled the characterization of possible magnetic exchange pathways and the establishment of relationships between the electron (charge and spin) densities and the exchangecoupling constants. In both compounds, the experimentally observed antiferromagnetic coupling can be quantitatively explained by the CuCu superexchange pathway mediated by the pyrazine bridging ligands, via a σtype interaction. From topological analyses of experimental chargedensity data, we show for the first time that the pyrazine tilt angle does not play a role in determining the strength of the magnetic interaction. Taken in combination with molecular orbital analysis and spin density calculations, we find a synergistic relationship between spin delocalization and spin polarization mechanisms and that both determine the bulk magnetic behavior of these Cu(II)pyz coordination polymers. PMID:26811927

Temperature and magneticfield dependence of radiative decay in colloidal germanium quantum dots.
PubMed
Robel, István; Shabaev, Andrew; Lee, Doh C; Schaller, Richard D; Pietryga, Jeffrey M; Crooker, Scott A; L Efros, Alexander; Klimov, Victor I
20150401
We conduct spectroscopic and theoretical studies of photoluminescence (PL) from Ge quantum dots (QDs) fabricated via colloidal synthesis. The dynamics of latetime PL exhibit a pronounced dependence on temperature and applied magnetic field, which can be explained by radiative decay involving two closely spaced, slowly emitting exciton states. In 3.5 nm QDs, these states are separated by ∼1 meV and are characterized by ∼82 μs and ∼18 μs lifetimes. By using a fourband formalism, we calculate the fine structure of the indirect bandedge exciton arising from the electronhole exchange interaction and the Coulomb interaction of the Γpoint hole with the anisotropic charge density of the Lpoint electron. The calculations suggest that the observed PL dynamics can be explained by phononassisted recombination of excitons thermally distributed between the lowerenergy "dark" state with the momentum projection J = ± 2 and a higher energy "bright" state with J = ± 1. A fairly small difference between lifetimes of these states is due to their mixing induced by the exchange term unique to crystals with a highly symmetric cubic lattice such as Ge.

Recent Developments in Fully Fluctuating FieldTheoretic Simulations of Polymer Melts and Solutions.
PubMed
Delaney, Kris T; Fredrickson, Glenn H
20160811
We review the latest developments in computational methods for direct simulation of fully fluctuating field theories of polymeric assemblies. In this context, we describe a newly developed theoretical and computational framework for accurately computing fluctuationcorrected phase diagrams of mesostructured polymer systems and report the first such complete phase diagram for a diblock copolymer melt. The method is based on complex Langevin sampling of a UV regularized fieldtheoretic model, with Helmholtz free energies computed using thermodynamic integration. UV regularization ensures that the free energies do not have an arbitrary reference; they can be compared between incommensurate phases, permitting for the first time the computation of orderorder transitions with fluctuation corrections. We further demonstrate that computed free energies are accurate in the disordered phase by comparison to perturbation theory on the oneloop level. Importantly, we note that our method uses no uncontrolled approximations beyond the initial definition of a coarsegrained molecular model for the polymer melt or solution. The method can be applied straightforwardly to melts and solutions containing multiple species with diverse polymer architectures. PMID:27414265

Linear and nonlinear optical properties in an asymmetric double quantum well under intense laser field: Effects of applied electric and magnetic fields
NASA Astrophysics Data System (ADS)
Yesilgul, U.; Al, E. B.; MartínezOrozco, J. C.; Restrepo, R. L.; MoraRamos, M. E.; Duque, C. A.; Ungan, F.; Kasapoglu, E.
20160801
In the present study, the effects of electric and magnetic fields on the linear and thirdorder nonlinear optical absorption coefficients and relative change of the refractive index in asymmetric GaAs/GaAlAs double quantum wells under intense laser fields are theoretically investigated. The electric field is oriented along the growth direction of the heterostructure while the magnetic field is taken inplane. The intense laser field is linear polarization along the growth direction. Our calculations are made using the effectivemass approximation and the compact densitymatrix approach. Intense laser effects on the system are investigated with the use of the Floquet method with the consequent change in the confinement potential of heterostructures. Our results show that the increase of the electric and magnetic fields blueshifts the peak positions of the total absorption coefficient and of the total refractive index while the increase of the intense laser field firstly blueshifts the peak positions and later results in their redshifting.

Quantum wavefunction controllability
NASA Astrophysics Data System (ADS)
Turinici, Gabriel; Rabitz, Herschel
20010601
Theoretical results are presented on the ability to arbitrarily steer about a wavefunction for a quantum system under timedependent external field control. Criteria on the field free Hamiltonian and the field coupling term in the Hamiltonian are presented that assure full wavefunction controllability. Numerical simulations are given to illustrate the criteria. A discussion on the theoretical and practical relationship between dynamical conservation laws and controllability is also included.

Quantum Correlation of Two Entangled Atoms Interacting with the Binomial Optical Field
NASA Astrophysics Data System (ADS)
Liu, TangKun; Tao, Yu; Shan, ChuanJia; Liu, Jibing
20161001
Quantum correlations of two atoms in a system of two entangled atoms interacting with the binomial optical field are investigated. In eight different initial states of the two atoms, the influence of the strength of the dipoledipole interaction, probabilities of a the Bernoulli trial and particle number of the binomial optical field on the temporal evolution of the geometrical quantum discord between two atoms are discussed. The result shows that two atoms always exist the correlation for different parameters. In addition, when and only when the two atoms are initially in the maximally entangled state, the temporal evolution of geometrical quantum discord is not affected by the parameters, and always keep in the degree of geometrical quantum discord that is a fixed value.

Quantum dynamical field theory for nonequilibrium phase transitions in driven open systems
NASA Astrophysics Data System (ADS)
Marino, Jamir; Diehl, Sebastian
20160801
We develop a quantum dynamical field theory for studying phase transitions in driven open systems coupled to Markovian noise, where nonlinear noise effects and fluctuations beyond semiclassical approximations influence the critical behavior. We systematically compare the diagrammatics, the properties of the renormalization group flow, and the structure of the fixed points of the quantum dynamical field theory and of its semiclassical counterpart, which is employed to characterize dynamical criticality in threedimensional drivendissipative condensates. As an application, we perform the Keldysh functional renormalization of a onedimensional driven open Bose gas, where a tailored diffusion Markov noise realizes an analog of quantum criticality for drivendissipative condensation. We find that the associated nonequilibrium quantum phase transition does not map into the critical behavior of its threedimensional classical driven counterpart.

On classical and quantum dynamics of tachyonlike fields and their cosmological implications
SciTech Connect
Dimitrijević, Dragoljub D. Djordjević, Goran S. Milošević, Milan; Vulcanov, Dumitru
20141124
We consider a class of tachyonlike potentials, motivated by string theory, Dbrane dynamics and inflation theory in the context of classical and quantum mechanics. A formalism for describing dynamics of tachyon fields in spatially homogenous and onedimensional  classical and quantum mechanical limit is proposed. A few models with concrete potentials are considered. Additionally, possibilities for padic and adelic generalization of these models are discussed. Classical actions and corresponding quantum propagators, in the Feynman path integral approach, are calculated in a form invariant on a change of the background number fields, i.e. on both archimedean and nonarchimedean spaces. Looking for a quantum origin of inflation, relevance of padic and adelic generalizations are briefly discussed.

Low field magnetoresistance in a 2D topological insulator based on wide HgTe quantum well
NASA Astrophysics Data System (ADS)
Olshanetsky, E. B.; Kvon, Z. D.; Gusev, G. M.; Mikhailov, N. N.; Dvoretsky, S. A.
20160901
Low field magnetoresistance is experimentally studied in a twodimensional topological insulator (TI) in both diffusive and quasiballistic samples fabricated on top of a wide (14 nm) HgTe quantum well. In all cases a pronounced quasilinear positive magnetoresistance is observed similar to that found previously in diffusive samples based on a narrow (8 nm) HgTe well. The experimental results are compared with the main existing theoretical models based on different types of disorder: sample edge roughness, nonmagnetic disorder in an otherwise coherent TI and metallic puddles due to locally trapped charges that act like local gate on the sample. The quasiballistic samples with resistance close to the expected quantized values also show a positive lowfield magnetoresistance but with a pronounced admixture of mesoscopic effects.

Quantum computing
PubMed Central
Li, ShuShen; Long, GuiLu; Bai, FengShan; Feng, SongLin; Zheng, HouZhi
20010101
Quantum computing is a quickly growing research field. This article introduces the basic concepts of quantum computing, recent developments in quantum searching, and decoherence in a possible quantum dot realization. PMID:11562459

Nonequilibrium GREEN’S Functions for HighField Quantum Transport Theory
NASA Astrophysics Data System (ADS)
Bertoncini, Rita
A formulation of the KadanoffBaymKeldysh theory of nonequilibrium quantum statistical mechanics is developed in order to describe nonperturbatively the effects of the electric field on electronphonon scattering in nondegenerate semiconductors. We derive an analytic, gaugeinvariant model for the spectral density of energy states that accounts for both intracollisional field effect and collisional broadening simultaneously. A kinetic equation for the quantum distribution function is derived and solved numerically. The nonlinear drift velocity versus applied field characteristics is also evaluated numerically. Many features of our nonlinear theory bear formal resemblance to linearresponse theory.

Tightly bound 3D quantum dot energy states in a magnetic field
NASA Astrophysics Data System (ADS)
Morgenstern Horing, Norman J.; Liu, S. Y.; Sawamura, M.
20100101
We have analyzed the detailed quantum dynamics of a 3D quantum dot in a magnetic field. The dot is taken to be lodged in a bulk medium in a high magnetic field and it is represented by a threedimensional Dirac delta function potential which would support just one subband state if there were no magnetic field. The integral equation for the Schrödinger Green's function of this system is solved in closed form analytically and the single particle subband energy spectrum and the density of states are examined taking account of splintering of the subband spectrum by landau quantization.

Dipolar polaritons in microcavityembedded coupled quantum wells in electric and magnetic fields
NASA Astrophysics Data System (ADS)
Wilkes, J.; Muljarov, E. A.
20160901
We present a microscopic calculation of spatially indirect exciton states in semiconductor coupled quantum wells and polaritons formed from their coupling to the optical mode of a microcavity. We include the presence of electric and magnetic fields applied perpendicular to the quantum well plane. Our model predicts the existence of polaritons that are in the strongcoupling regime and at the same time possess a large static dipole moment. We demonstrate, in particular, that a magnetic field can compensate for the reduction in lightmatter coupling that occurs when an electric field impresses a dipole moment on the polariton.

Optical response of a quantum dotmetal nanoparticle hybrid interacting with a weak probe field.
PubMed
Kosionis, Spyridon G; Terzis, Andreas F; Sadeghi, Seyed M; Paspalakis, Emmanuel
20130130
We study optical effects in a hybrid system composed of a semiconductor quantum dot and a spherical metal nanoparticle that interacts with a weak probe electromagnetic field. We use modified nonlinear density matrix equations for the description of the optical properties of the system and obtain a closedform expression for the linear susceptibilities of the quantum dot, the metal nanoparticle, and the total system. We then investigate the dependence of the susceptibility on the interparticle distance as well as on the material parameters of the hybrid system. We find that the susceptibility of the quantum dot exhibits optical transparency for specific frequencies. In addition, we show that there is a range of frequencies of the applied field for which the susceptibility of the semiconductor quantum dot leads to gain. This suggests that in such a hybrid system quantum coherence can reverse the course of energy transfer, allowing flow of energy from the metallic nanoparticle to the quantum dot. We also explore the susceptibility of the metal nanoparticle and show that it is strongly influenced by the presence of the quantum dot.

Quantum tunneling from scalar fields in rotating black strings
NASA Astrophysics Data System (ADS)
Gohar, H.; Saifullah, K.
20130801
Using the HamiltonJacobi method of quantum tunneling and complex path integration, we study Hawking radiation of scalar particles from rotating black strings. We discuss tunneling of both charged and uncharged scalar particles from the event horizons. For this purpose, we use the KleinGordon equation and find the tunneling probability of outgoing scalar particles. The procedure gives Hawking temperature for rotating charged black strings as well.

Group field theory as the second quantization of loop quantum gravity
NASA Astrophysics Data System (ADS)
Oriti, Daniele
20160401
We construct a second quantized reformulation of canonical loop quantum gravity (LQG) at both kinematical and dynamical level, in terms of a Fock space of spin networks, and show in full generality that it leads directly to the group field theory (GFT) formalism. In particular, we show the correspondence between canonical LQG dynamics and GFT dynamics leading to a specific GFT model from any definition of quantum canonical dynamics of spin networks. We exemplify the correspondence of dynamics in the specific example of 3d quantum gravity. The correspondence between canonical LQG and covariant spin foam models is obtained via the GFT definition of the latter.
 