I. Cirac (Max Planck Institute, Garching
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.
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.
Motivating quantum field theory: the boosted particle in a box
NASA Astrophysics Data System (ADS)
Vutha, Amar C.
20130701
It is a maxim often stated, yet rarely illustrated, that the combination of special relativity and quantum mechanics necessarily leads to quantum field theory. An elementary illustration is provided using the familiar particle in a box, boosted to relativistic speeds. It is shown that quantum fluctuations of momentum lead to energy fluctuations, which are inexplicable without a framework that endows the vacuum with dynamical degrees of freedom and allows particle creation/annihilation.
Euclidean quantum field theory: Curved spacetimes and gauge fields
NASA Astrophysics Data System (ADS)
Ritter, William Gordon
This thesis presents a new formulation of quantum field theory (QFT) on curved spacetimes, with definite advantages over previous formulations, and an introduction to the millennium prize problem on fourdimensional gauge theory. Our constructions are completely rigorous, making QFT on curved spacetimes into a subfield of mathematics, and we achieve the first analytic control over nonperturbative aspects of interacting theories on curved spacetimes. The success of Euclidean path integrals to capture nonperturbative aspects of QFT has been striking. The Euclidean path integral is the most accurate method of calculating strongcoupling effects in gauge theory (such as glueball masses). Euclidean methods are also useful in the study of black holes, as evidenced by the HartleHawking calculation of blackhole radiance. From a mathematical point of view, on flat spacetimes the Euclidean functional integral provides the most elegant method of constructing examples of interacting relativistic field theories. Yet until now, the incrediblyuseful Euclidean path integral had never been given a definitive mathematical treatment on curved backgrounds. It is our aim to rectify this situation. Along the way, we discover that the Dirac operator on an arbitrary Clifford bundle has a resolvent kernel which is the Laplace transform of a positive measure. In studying spacetime symmetries, we discover a new way of constructing unitary representations of noncompact Lie groups. We also define and explore an interesting notion of convergence for Laplacians. The same mathematical framework applies to scalar fields, fermions, and gauge fields. The later chapters are devoted to gauge theory. We present a rigorous, selfcontained introduction to the subject, aimed at mathematicians and using the language of modern mathematics, with a view towards nonperturbative renormalization in four dimensions. The latter ideas are unfinished. A completion of the final chapter would imply the construction
Coupled field induced conversion between destructive and constructive quantum interference
NASA Astrophysics Data System (ADS)
Jiang, Xiangqian; Sun, Xiudong
20161201
We study the control of quantum interference in a fourlevel atom driven by three coherent fields forming a closed loop. The spontaneous emission spectrum shows two sets of peaks which are dramatically influenced by the fields. Due to destructive quantum interference, a dark line can be observed in the emission spectrum, and the condition of the dark line is given. We found that the conversion between destructive and constructive quantum interference can be achieved through controlling the Rabi frequency of the external fields.
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.
Fieldtheoretic simulations of random copolymers with structural rigidity.
PubMed
Mao, Shifan; MacPherson, Quinn; Qin, Jian; Spakowitz, Andrew J
20170412
Copolymers play an important role in a range of softmaterials applications and biological phenomena. Prevalent works on block copolymer phase behavior use flexible chain models and incorporate interactions using a meanfield approximation. However, when phase separation takes place on length scales comparable to a few monomers, the structural rigidity of the monomers becomes important. In addition, concentration fluctuations become significant at short length scales, rendering the meanfield approximation invalid. In this work, we use simulation to address the role of finite monomer rigidity and concentration fluctuations in microphase segregation of random copolymers. Using a fieldtheoretic MonteCarlo simulation of semiflexible polymers with random chemical sequences, we generate phase diagrams for random copolymers. We find that the melt morphology of random copolymers strongly depends on chain flexibility and chemical sequence correlation. Chemically anticorrelated copolymers undergo firstorder phase transitions to local lamellar structures. With increasing degree of chemical correlation, this firstorder phase transition is softened, and melts form microphases with irregular shaped domains. Our simulations in the homogeneous phase exhibit agreement with the densitydensity correlation from meanfield theory. However, conditions near a phase transition result in deviations between simulation and meanfield theory for the densitydensity correlation and the critical wavemode. Chain rigidity and sequence randomness lead to frustration in the segregated phase, introducing heterogeneity in the resulting morphologies.
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.
The principle of stationary variance in quantum field theory
NASA Astrophysics Data System (ADS)
Siringo, Fabio
20140201
The principle of stationary variance is advocated as a viable variational approach to quantum field theory (QFT). The method is based on the principle that the variance of energy should be at its minimum when the state of a quantum system reaches its best approximation for an eigenstate. While not too much popular in quantum mechanics (QM), the method is shown to be valuable in QFT and three special examples are given in very different areas ranging from Heisenberg model of antiferromagnetism (AF) to quantum electrodynamics (QED) and gauge theories.
Electric field effect on the secondorder nonlinear optical properties in semiparabolic quantum wells
NASA Astrophysics Data System (ADS)
Yuan, JianHui; Chen, Ni; Zhang, Yan; Mo, Hua; Zhang, ZhiHai
20160301
Electric field effect on the secondorder nonlinear optical properties in semiparabolic quantum wells are studied theoretically. Both the secondharmonic generation susceptibility and nonlinear optical rectification depend dramatically on the direction and the strength of the electric field. Numerical results show that both the secondharmonic generation susceptibility and nonlinear optical rectification are always weakened as the electric field increases where the direction of the electric field is along the growth direction of the quantum wells, which is in contrast to the conventional case. However, the secondharmonic generation susceptibility is weakened, but the nonlinear optical rectification is strengthened as the electric field increases where the direction of the electric field is against the growth direction of the quantum wells. Also it is the blue (or red) shift of the resonance that is induced by increasing of the electric field when the direction of the electric field is along (or against) the growth direction of the quantum wells. Finally, the resonant peak and its corresponding to the resonant energy are also taken into account.
Avoiding Haag's Theorem with Parameterized Quantum Field Theory
NASA Astrophysics Data System (ADS)
Seidewitz, Ed
20170301
Under the normal assumptions of quantum field theory, Haag's theorem states that any field unitarily equivalent to a free field must itself be a free field. Unfortunately, the derivation of the Dyson series perturbation expansion relies on the use of the interaction picture, in which the interacting field is unitarily equivalent to the free field but must still account for interactions. Thus, the traditional perturbative derivation of the scattering matrix in quantum field theory is mathematically ill defined. Nevertheless, perturbative quantum field theory is currently the only practical approach for addressing scattering for realistic interactions, and it has been spectacularly successful in making empirical predictions. This paper explains this success by showing that Haag's Theorem can be avoided when quantum field theory is formulated using an invariant, fifth path parameter in addition to the usual four position parameters, such that the Dyson perturbation expansion for the scattering matrix can still be reproduced. As a result, the parameterized formalism provides a consistent foundation for the interpretation of quantum field theory as used in practice and, perhaps, for better dealing with other mathematical issues.

Enhanced upconversion of entangled photons and quantum interference under a localized field in nanostructures.
PubMed
Osaka, Yoshiki; Yokoshi, Nobuhiko; Nakatani, Masatoshi; Ishihara, Hajime
20140404
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.

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.

Quantum epistemology from subquantum ontology: Quantum mechanics from theory of classical random fields
NASA Astrophysics Data System (ADS)
Khrennikov, Andrei
20170201
The scientific methodology based on two descriptive levels, ontic (reality as it is) and epistemic (observational), is briefly presented. Following Schrödinger, we point to the possible gap between these two descriptions. Our main aim is to show that, although ontic entities may be unaccessible for observations, they can be useful for clarification of the physical nature of operational epistemic entities. We illustrate this thesis by the concrete example: starting with the concrete ontic model preceding quantum mechanics (the latter is treated as an epistemic model), namely, prequantum classical statistical field theory (PCSFT), we propose the natural physical interpretation for the basic quantum mechanical entitythe quantum state ("wave function"). The correspondence PCSFT ↦ QM is not straightforward, it couples the covariance operators of classical (prequantum) random fields with the quantum density operators. We use this correspondence to clarify the physical meaning of the pure quantum state and the superposition principleby using the formalism of classical field correlations.

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.

A field theoretical approach to the quasicontinuum method
NASA Astrophysics Data System (ADS)
Iyer, Mrinal; Gavini, Vikram
20110801
The quasicontinuum method has provided many insights into the behavior of lattice defects in the past decade. However, recent numerical analysis suggests that the approximations introduced in various formulations of the quasicontinuum method lead to inconsistencies—namely, appearance of ghost forces or residual forces, nonconservative nature of approximate forces, etc.—which affect the numerical accuracy and stability of the method. In this work, we identify the source of these errors to be the incompatibility of using quadrature rules, which is a local notion, on a nonlocal representation of energy. We eliminate these errors by first reformulating the extended interatomic interactions into a local variational problem that describes the energy of a system via potential fields. We subsequently introduce the quasicontinuum reduction of these potential fields using an adaptive finiteelement discretization of the formulation. We demonstrate that the present formulation resolves the inconsistencies present in previous formulations of the quasicontinuum method, and show using numerical examples the remarkable improvement in the accuracy of solutions. Further, this field theoretic formulation of quasicontinuum method makes mathematical analysis of the method more amenable using functional analysis and homogenization theories.

QuantumTheoretical Methods and Studies Relating to Properties of Materials
DTIC Science & Technology
19891219
V. B.; Halow, I.; Bailey, S. M.; Schumm, R. H. Selected Values of Chemical Thermodynamic Properties , NBS Technical Note 2703, Nat]. Bur. Stands... Thermodynamic Properties of Individual Substances (in Russian); Glyshko, W. P., Ed.; Science: Moscow, 1982. (14) Shimanouchi, T. J. Phys. Chem. Ref. Data...Theoretical Methods and Studies Relating to Properties of Materials. ’This research concernedthe development of new ab initio nonempirical quantum

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 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 fields with noncommutative target spaces
NASA Astrophysics Data System (ADS)
Balachandran, A. P.; Queiroz, A. R.; Marques, A. M.; TeotonioSobrinho, P.
20080501
Quantum field theories (QFT’s) on noncommutative spacetimes are currently under intensive study. Usually such theories have world sheet noncommutativity. In the present work, instead, we study QFT’s with commutative world sheet and noncommutative target space. Such noncommutativity can be interpreted in terms of twisted statistics and is related to earlier work of Oeckl [R. Oeckl, Commun. Math. Phys. 217, 451 (2001).CMPHAY0010361610.1007/s002200100375], and others [A. P. Balachandran, G. Mangano, A. Pinzul, and S. Vaidya, Int. J. Mod. Phys. A 21, 3111 (2006)IMPAEF0217751X10.1142/S0217751X06031764; A. P. Balachandran, A. Pinzul, and B. A. Qureshi, Phys. Lett. B 634, 434 (2006)PYLBAJ0370269310.1016/j.physletb.2006.02.006; A. P. Balachandran, A. Pinzul, B. A. Qureshi, and S. Vaidya, arXiv:hepth/0608138; A. P. Balachandran, T. R. Govindarajan, G. Mangano, A. Pinzul, B. A. Qureshi, and S. Vaidya, Phys. Rev. D 75, 045009 (2007)PRVDAQ0556282110.1103/PhysRevD.75.045009; A. Pinzul, Int. J. Mod. Phys. A 20, 6268 (2005)IMPAEF0217751X10.1142/S0217751X05029290; G. Fiore and J. Wess, Phys. Rev. D 75, 105022 (2007)PRVDAQ0556282110.1103/PhysRevD.75.105022; Y. Sasai and N. Sasakura, Prog. Theor. Phys. 118, 785 (2007)PTPKAV0033068X10.1143/PTP.118.785]. The twisted spectra of their free Hamiltonians has been found earlier by Carmona et al. [J. M. Carmona, J. L. Cortes, J. Gamboa, and F. Mendez, Phys. Lett. B 565, 222 (2003)PYLBAJ0370269310.1016/S03702693(03)007287; J. M. Carmona, J. L. Cortes, J. Gamboa, and F. Mendez, J. High Energy Phys.JHEPFG10298479 03 (2003) 05810.1088/11266708/2003/03/058]. We review their derivation and then compute the partition function of one such typical theory. It leads to a deformed blackbody spectrum, which is analyzed in detail. The difference between the usual and the deformed blackbody spectrum appears in the region of high frequencies. Therefore we expect that the deformed blackbody radiation may potentially be used to compute a

The Physical Renormalization of Quantum Field Theories
SciTech Connect
Binger, Michael William.; /Stanford U., Phys. Dept. /SLAC
20070220
The profound revolutions in particle physics likely to emerge from current and future experiments motivates an improved understanding of the precise predictions of the Standard Model and new physics models. Higher order predictions in quantum field theories inevitably requires the renormalization procedure, which makes sensible predictions out of the naively divergent results of perturbation theory. Thus, a robust understanding of renormalization is crucial for identifying and interpreting the possible discovery of new physics. The results of this thesis represent a broad set of investigations in to the nature of renormalization. The author begins by motivating a more physical approach to renormalization based on gaugeinvariant Green's functions. The resulting effective charges are first applied to gauge coupling unification. This approach provides an elegant formalism for understanding all threshold corrections, and the gauge couplings unify in a more physical manner compared to the usual methods. Next, the gaugeinvariant threegluon vertex is studied in detail, revealing an interesting and rich structure. The effective coupling for the threegluon vertex, {alpha}(k{sub 1}{sup 2}, k{sub 2}{sup 2}, k{sub 3}{sup 2}), depends on three momentum scales and gives rise to an effective scale Q{sub eff}{sup 2}(k{sub 1}{sup 2}, k{sub 2}{sup 2}, k{sub 3}{sup 2}) which governs the (sometimes surprising) behavior of the vertex. The effects of nonzero internal masses are important and have a complicated threshold and pseudothreshold structure. The pinchtechnique effective charge is also calculated to twoloops and several applications are discussed. The Higgs boson mass in Split Supersymmetry is calculated to twoloops, including all oneloop threshold effects, leading to a downward shift in the Higgs mass of a few GeV. Finally, the author discusses some ideas regarding the overall structure of perturbation theory. This thesis lays the foundation for a comprehensive multi

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.

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

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.

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.

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.

Theoretical examination of quantum coherence in a photosynthetic system at physiological temperature
PubMed Central
Ishizaki, Akihito; Fleming, Graham R.
20090101
The observation of longlived electronic coherence in a photosynthetic pigment–protein complex, the Fenna–Matthews–Olson (FMO) complex, is suggestive that quantum coherence might play a significant role in achieving the remarkable efficiency of photosynthetic electronic energy transfer (EET), although the data were acquired at cryogenic temperature [Engel GS, et al. (2007) Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems. Nature 446:782–786]. In this paper, the spatial and temporal dynamics of EET through the FMO complex at physiological temperature are investigated theoretically. The numerical results reveal that quantum wavelike motion persists for several hundred femtoseconds even at physiological temperature, and suggest that the FMO complex may work as a rectifier for unidirectional energy flow from the peripheral lightharvesting antenna to the reaction center complex by taking advantage of quantum coherence and the energy landscape of pigments tuned by the protein scaffold. A potential role of quantum coherence is to overcome local energetic traps and aid efficient trapping of electronic energy by the pigments facing the reaction center complex. PMID:19815512

Electric and magneticfield dependence of the electronic and optical properties of phosphorene quantum dots
NASA Astrophysics Data System (ADS)
Li, L. L.; Moldovan, D.; Xu, W.; Peeters, F. M.
20170201
Recently, black phosphorus quantum dots were fabricated experimentally. Motivated by these experiments, we theoretically investigate the electronic and optical properties of rectangular phosphorene quantum dots (RPQDs) in the presence of an inplane electric field and a perpendicular magnetic field. The energy spectra and wave functions of RPQDs are obtained numerically using the tightbinding approach. We find edge states within the band gap of the RPQD which are well separated from the bulk states. In an undoped RPQD and for inplane polarized light, due to the presence of welldefined edge states, we find three types of optical transitions which are between the bulk states, between the edge and bulk states, and between the edge states. The electric and magnetic fields influence the bulktobulk, edgetobulk, and edgetoedge transitions differently due to the different responses of bulk and edge states to these fields.

Electric and magneticfield dependence of the electronic and optical properties of phosphorene quantum dots.
PubMed
Li, L L; Moldovan, D; Xu, W; Peeters, F M
20170224
Recently, black phosphorus quantum dots were fabricated experimentally. Motivated by these experiments, we theoretically investigate the electronic and optical properties of rectangular phosphorene quantum dots (RPQDs) in the presence of an inplane electric field and a perpendicular magnetic field. The energy spectra and wave functions of RPQDs are obtained numerically using the tightbinding approach. We find edge states within the band gap of the RPQD which are well separated from the bulk states. In an undoped RPQD and for inplane polarized light, due to the presence of welldefined edge states, we find three types of optical transitions which are between the bulk states, between the edge and bulk states, and between the edge states. The electric and magnetic fields influence the bulktobulk, edgetobulk, and edgetoedge transitions differently due to the different responses of bulk and edge states to these fields.

Quantum and classical statistics of the electromagnetic zeropoint field
NASA Astrophysics Data System (ADS)
Ibison, Michael; Haisch, Bernhard
19961001
A classical electromagnetic zeropoint field (ZPF) analog of the vacuum of quantum field theory has formed the basis for theoretical investigations in the discipline known as random or stochastic electrodynamics (SED). In SED the statistical character of quantum measurements is imitated by the introduction of a stochastic classical background electromagnetic field. Random electromagnetic fluctuations are assumed to provide perturbations which can mimic certain quantum phenomena while retaining a purely classical basis, e.g., the Casimir force, the van der Waals force, the Lamb shift, spontaneous emission, the rms radius of a quantummechanical harmonic oscillator, and the radius of the Bohr atom. This classical ZPF is represented as a homogeneous, isotropic ensemble of plane electromagnetic waves whose amplitude is exactly equivalent to an excitation energy of hν/2 of the corresponding quantized harmonic oscillator, this being the state of zero excitation of such an oscillator. There is thus no randomness in the classical electricfield amplitudes: Randomness is introduced entirely in the phases of the waves, which are normally distributed. Averaging over the random phases is assumed to be equivalent to taking the groundstate expectation values of the corresponding quantum operator. We demonstrate that this is not precisely correct by examining the statistics of the classical ZPF in contrast to that of the electromagnetic quantum vacuum. Starting with a general technique for the calculation of classical probability distributions for quantum state operators, we derive the distribution for the individual modes of the electricfield amplitude in the ground state as predicted by quantum field theory. We carry out the same calculation for the classical ZPF analog, and show that the distributions are only in approximate agreement, diverging as the density of k states decreases. We then introduce an alternative classical ZPF with a different stochastic character, and

QubitProgrammable Operations on Quantum Light Fields
PubMed Central
Barbieri, Marco; Spagnolo, Nicolò; Ferreyrol, Franck; Blandino, Rémi; Smith, Brian J.; TualleBrouri, Rosa
20150101
Engineering quantum operations is a crucial capability needed for developing quantum technologies and designing new fundamental physics tests. Here we propose a scheme for realising a controlled operation acting on a travelling continuousvariable quantum field, whose functioning is determined by a discrete input qubit. This opens a new avenue for exploiting advantages of both information encoding approaches. Furthermore, this approach allows for the program itself to be in a superposition of operations, and as a result it can be used within a quantum processor, where coherences must be maintained. Our study can find interest not only in general quantum state engineering and information protocols, but also details an interface between different physical platforms. Potential applications can be found in linking optical qubits to optical systems for which coupling is best described in terms of their continuous variables, such as optomechanical devices. PMID:26468614

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.

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.

QubitProgrammable Operations on Quantum Light Fields.
PubMed
Barbieri, Marco; Spagnolo, Nicolò; Ferreyrol, Franck; Blandino, Rémi; Smith, Brian J; TualleBrouri, Rosa
20151015
Engineering quantum operations is a crucial capability needed for developing quantum technologies and designing new fundamental physics tests. Here we propose a scheme for realising a controlled operation acting on a travelling continuousvariable quantum field, whose functioning is determined by a discrete input qubit. This opens a new avenue for exploiting advantages of both information encoding approaches. Furthermore, this approach allows for the program itself to be in a superposition of operations, and as a result it can be used within a quantum processor, where coherences must be maintained. Our study can find interest not only in general quantum state engineering and information protocols, but also details an interface between different physical platforms. Potential applications can be found in linking optical qubits to optical systems for which coupling is best described in terms of their continuous variables, such as optomechanical devices.

Electromagnetically induced transparency in an asymmetric double quantum well under nonresonant, intense laser fields
NASA Astrophysics Data System (ADS)
Niculescu, E. C.
20170201
Electromagnetically induced transparency in an asymmetric double quantum well subjected to a nonresonant, intense laser field is theoretically investigated. We found that the energy levels configuration could be switched between a Λtype and a laddertype scheme by varying the nonresonant radiation intensity. This effect is due to the laserinduced electron tunneling between the wells and it allows a substantial flexibility in the manipulation of the optical properties. The dependence of the susceptibilities on the control field Rabi frequency, intensity of the nonresonant laser, and the control field detuning for both configurations are discussed and compared.

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.

Estimates on Functional Integrals of Quantum Mechanics and Nonrelativistic Quantum Field Theory
NASA Astrophysics Data System (ADS)
Bley, Gonzalo A.; Thomas, Lawrence E.
20170101
We provide a unified method for obtaining upper bounds for certain functional integrals appearing in quantum mechanics and nonrelativistic quantum field theory, functionals of the form {E[{exp}(A_T)]} , the (effective) action {A_T} being a function of particle trajectories up to time T. The estimates in turn yield rigorous lower bounds for ground state energies, via the FeynmanKac formula. The upper bounds are obtained by writing the action for these functional integrals in terms of stochastic integrals. The method is illustrated in familiar quantum mechanical settings: for the hydrogen atom, for a Schrödinger operator with {1/x^2} potential with small coupling, and, with a modest adaptation of the method, for the harmonic oscillator. We then present our principal applications of the method, in the settings of nonrelativistic quantum field theories for particles moving in a quantized Bose field, including the optical polaron and Nelson models.

Quantum de Finetti theorems and meanfield theory from quantum phase space representations
NASA Astrophysics Data System (ADS)
Trimborn, F.; Werner, R. F.; Witthaut, D.
20160401
We introduce the numberconserving quantum phase space description as a versatile tool to address fundamental aspects of quantum manybody systems. Using phase space methods we prove two alternative versions of the quantum de Finetti theorem for finitedimensional bosonic quantum systems, which states that a reduced density matrix of a manybody quantum state can be approximated by a convex combination of product states where the error is proportional to the inverse particle number. This theorem provides a formal justification for the meanfield description of manybody quantum systems, as it shows that quantum correlations can be neglected for the calculation of fewbody observables when the particle number is large. Furthermore we discuss methods to derive the exact evolution equations for quantum phase space distribution functions as well as upper and lower bounds for the ground state energy. As an important example, we consider the BoseHubbard model and show that the meanfield dynamics is given by a classical phase space flow equivalent to the discrete GrossPitaevskii equation.

Robust quantum memory using magneticfieldindependent atomic qubits
NASA Astrophysics Data System (ADS)
Langer, C.; Ozeri, R.; Jost, J. D.; Demarco, B.; BenKish, A.; Blakestad, B.; Britton, J.; Chiaverini, J.; Hume, D. B.; Itano, W. M.; Leibfried, D.; Reichle, R.; Rosenband, T.; Schmidt, P.; Wineland, D. J.
20060301
Scalable quantum information processing requires physical systems capable of reliably storing coherent superpositions for times over which quantum error correction can be implemented. We experimentally demonstrate a robust quantum memory using a magneticfieldindependent hyperfine transition in ^9Be^+ atomic ion qubits at a field B = 0.01194 T. Qubit superpositions are created and analyzed with twophoton stimulatedRaman transitions. We observe the single physical qubit memory coherence time to be greater than 10 seconds, an improvement of approximately five orders of magnitude from previous experiments. The probability of memory error for this qubit during the measurement period (the longest timescale in our system) is approximately 1.4 x 105 which is below faulttolerance threshold for common quantum error correcting codes.

TrappedIon Quantum Logic with Global Radiation Fields
NASA Astrophysics Data System (ADS)
Weidt, S.; Randall, J.; Webster, S. C.; Lake, K.; Webb, A. E.; Cohen, I.; Navickas, T.; Lekitsch, B.; Retzker, A.; Hensinger, W. K.
20161101
Trapped ions are a promising tool for building a largescale quantum computer. However, the number of required radiation fields for the realization of quantum gates in any proposed ionbased architecture scales with the number of ions within the quantum computer, posing a major obstacle when imagining a device with millions of ions. Here, we present a fundamentally different approach for trappedion quantum computing where this detrimental scaling vanishes. The method is based on individually controlled voltages applied to each logic gate location to facilitate the actual gate operation analogous to a traditional transistor architecture within a classical computer processor. To demonstrate the key principle of this approach we implement a versatile quantum gate method based on longwavelength radiation and use this method to generate a maximally entangled state of two quantum engineered clock qubits with fidelity 0.985(12). This quantum gate also constitutes a simpletoimplement tool for quantum metrology, sensing, and simulation.

TrappedIon Quantum Logic with Global Radiation Fields.
PubMed
Weidt, S; Randall, J; Webster, S C; Lake, K; Webb, A E; Cohen, I; Navickas, T; Lekitsch, B; Retzker, A; Hensinger, W K
20161125
Trapped ions are a promising tool for building a largescale quantum computer. However, the number of required radiation fields for the realization of quantum gates in any proposed ionbased architecture scales with the number of ions within the quantum computer, posing a major obstacle when imagining a device with millions of ions. Here, we present a fundamentally different approach for trappedion quantum computing where this detrimental scaling vanishes. The method is based on individually controlled voltages applied to each logic gate location to facilitate the actual gate operation analogous to a traditional transistor architecture within a classical computer processor. To demonstrate the key principle of this approach we implement a versatile quantum gate method based on longwavelength radiation and use this method to generate a maximally entangled state of two quantum engineered clock qubits with fidelity 0.985(12). This quantum gate also constitutes a simpletoimplement tool for quantum metrology, sensing, and simulation.

The Fifth Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories. Parts A, B. Proceedings.
NASA Astrophysics Data System (ADS)
Blair, D. G.; Buckingham, M. J.
Contents: Part A. 1. Rigorous and exact. Classical general relativity: highly nonlinear behaviour. Spin, geometry and topology. Approximation methods. Exact solutions. Black hole physics. Alternative theories and torsion. 2. Quantum gravity. Critical accelerations. Quantum gravity. String theories. Cosmic strings, superstrings and supergravity. Quantum cosmology: wavefunction of the universe. Quantum cosmology. 3. Cosmology. Early cosmology and quantum field theory. Supersymmetry, multidimensional cosmology and KaluzaKlein theory. Theoretical cosmology. Largescale structure of the universe. Dark matter. Part B. 4. Mathematical astrophysics. Algebraic computing. Numerical relativity. Astrophysics of collapsed objects. Self gravitating systems. History of general relativity. 5. Observational astrophysics. Sources of gravitational radiation. Relativistic astrophysics. Supernovae. Observation of collapsed objects. Cosmic background. 5. Precision experiments. The fifth force. Measuring the gravitational interaction in precision space experiments. Resonant bar antennas. Laser interferometer antennas. Detection of gravitational radiation. Quantum technology for gravitational radiation detection. Precision clocks in general relativity.

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.

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.

IR photodetector based on rectangular quantum wire in magnetic field
SciTech Connect
Jha, Nandan
20140424
In this paper we study rectangular quantum wire based IR detector with magnetic field applied along the wires. The energy spectrum of a particle in rectangular box shows level repulsions and crossings when external magnetic field is applied. Due to this complex level dynamics, we can tune the spacing between any two levels by varying the magnetic field. This method allows user to change the detector parameters according to his/her requirements. In this paper, we numerically calculate the energy subband levels of the square quantum wire in constant magnetic field along the wire and quantify the possible operating wavelength range that can be obtained by varying the magnetic field. We also calculate the photon absorption probability at different magnetic fields and give the efficiency for different wavelengths if the transition is assumed between two lowest levels.

Singleion microwave nearfield quantum sensor
NASA Astrophysics Data System (ADS)
Wahnschaffe, M.; Hahn, H.; Zarantonello, G.; Dubielzig, T.; Grondkowski, S.; BautistaSalvador, A.; Kohnen, M.; Ospelkaus, C.
20170101
We develop an intuitive model of 2D microwave nearfields in the unusual regime of centimeter waves localized to tens of microns. Close to an intensity minimum, a simple effective description emerges with five parameters that characterize the strength and spatial orientation of the zero and first order terms of the nearfield, as well as the field polarization. Such a field configuration is realized in a microfabricated planar structure with an integrated microwave conductor operating near 1 GHz. We use a single 9 Be+ ion as a highresolution quantum sensor to measure the field distribution through energy shifts in its hyperfine structure. We find agreement with simulations at the submicron and fewdegree level. Our findings give a clear and general picture of the basic properties of oscillatory 2D nearfields with applications in quantum information processing, neutral atom trapping and manipulation, chipscale atomic clocks, and integrated microwave circuits.

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.

Fieldemission from quantumdotinperovskite solids
NASA Astrophysics Data System (ADS)
García de Arquer, F. Pelayo; Gong, Xiwen; Sabatini, Randy P.; Liu, Min; Kim, GiHwan; Sutherland, Brandon R.; Voznyy, Oleksandr; Xu, Jixian; Pang, Yuangjie; Hoogland, Sjoerd; Sinton, David; Sargent, Edward
20170301
Quantum dot and well architectures are attractive for infrared optoelectronics, and have led to the realization of compelling light sensors. However, they require welldefined passivated interfaces and rapid charge transport, and this has restricted their efficient implementation to costly vacuumepitaxially grown semiconductors. Here we report solutionprocessed, sensitive infrared fieldemission photodetectors. Using quantumdotsinperovskite, we demonstrate the extraction of photocarriers via field emission, followed by the recirculation of photogenerated carriers. We use in operando ultrafast transient spectroscopy to sense biasdependent photoemission and recapture in fieldemission devices. The resultant photodiodes exploit the superior electronic transport properties of organometal halide perovskites, the quantumsizetuned absorption of the colloidal quantum dots and their matched interface. These fieldemission quantumdotinperovskite photodiodes extend the perovskite response into the shortwavelength infrared and achieve measured specific detectivities that exceed 1012 Jones. The results pave the way towards novel functional photonic devices with applications in photovoltaics and light emission.

Dynamics of plasmonic field polarization induced by quantum coherence in quantum dotmetallic nanoshell structures.
PubMed
Sadeghi, S M
20140901
When a hybrid system consisting of a semiconductor quantum dot and a metallic nanoparticle interacts with a laser field, the plasmonic field of the metallic nanoparticle can be normalized by the quantum coherence generated in the quantum dot. In this Letter, we study the states of polarization of such a coherentplasmonic field and demonstrate how these states can reveal unique aspects of the collective molecular properties of the hybrid system formed via coherent excitonplasmon coupling. We show that transition between the molecular states of this system can lead to ultrafast polarization dynamics, including sudden reversal of the sense of variations of the plasmonic field and formation of circular and elliptical polarization.

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.

Effects of a scalar scaling field on quantum mechanics
SciTech Connect
Benioff, Paul
20160418
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. Here, 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.

Effects of a scalar scaling field on quantum mechanics
DOE PAGES
Benioff, Paul
20160418
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 eachmore » 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. Here, 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.« less

Field emission from quantum size GaN structures
NASA Astrophysics Data System (ADS)
Yilmazoglu, O.; Pavlidis, D.; Litvin, Yu. M.; Hubbard, S.; Tiginyanu, I. M.; Mutamba, K.; Hartnagel, H. L.; Litovchenko, V. G.; Evtukh, A.
20031201
Whisker structures and quantum dots fabricated by photoelectrochemical (PEC) etching of undoped and doped metalorganic chemical vapor deposition (MOCVD)grown GaN (2×10 17 or 3×10 18 cm 3) are investigated in relation with their fieldemission characteristics. Different surface morphologies, corresponding to different etching time and photocurrent, results in different fieldemission characteristics with low turnon voltage down to 4 V/μm and the appearance of quantumsize effect in the I V curves.

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.

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.

Magnetic Field Induced Circular Photogalvanic Effect in InAs Quantum Wells
DTIC Science & Technology
20010601
St Petersburg, Russia We report on the first observation of a magnetic field induced circular photogalvanic effect ( CPGE ) in quantum wells (QWs). The...the magnetic field. For the sake of brevity we refer to the effect under consideration as to the magneto CPGE . For bulk materials this effect was...theoretically treated in [2, 3] and observed in pGaAs [4]. Phenomenologically, the magneto CPGE is described by a thirdrank tensor as J, = itaiýyBj•i (E x

Quantum ring solitons and nonlocal effects in plasma wake field excitations
SciTech Connect
Fedele, R.; Tanjia, F.; De Nicola, S.; Jovanovic, D.; Shukla, P. K.
20121015
A theoretical investigation of the quantum transverse beam motion for a cold relativistic charged particle beam travelling in a cold, collisionless, strongly magnetized plasma is carried out. This is done by taking into account both the individual quantum nature of the beam particles (singleparticle uncertainty relations and spin) and the self consistent interaction generated by the plasma wake field excitation. By adopting a fluid model of a strongly magnetized plasma, the analysis is carried out in the overdense regime (dilute beams) and in the long beam limit. It is shown that the quantum description of the collective transverse beam dynamics is provided by a pair of coupled nonlinear governing equations. It comprises a Poissonlike equation for the plasma wake potential (driven by the beam density) and a 2D spinorial Schroedinger equation for the wave function, whose squared modulus is proportional to the beam density, that is obtained in the Hartree's mean field approximation, after disregarding the exchange interactions. The analysis of this pair of equations, which in general exhibits a strong nonlocal character, is carried out analytically as well as numerically in both the linear and the nonlinear regimes, showing the existence of the quantum beam vortices in the form of LaguerreGauss modes and ring envelope solitons, respectively. In particular, when the relation between the plasma wake field response and the beam probability density is strictly local, the pair of the governing equations is reduced to the 2D GrossPitaevskii equation that allows one to establish the conditions for the self focusing and collapse. These conditions include the quantum nature of the beam particles. Finally, when the relation between the plasma wake field response and the beam probability density is moderately nonlocal, the above pair of equations permits to follow the spatiotemporal evolution of a quantum ring envelope soliton. Such a structure exhibits small or violent

Radiation reaction in quantum field theory
NASA Astrophysics Data System (ADS)
Higuchi, Atsushi
20021101
We investigate radiationreaction effects for a charged scalar particle accelerated by an external potential realized as a spacedependent mass term in quantum electrodynamics. In particular, we calculate the position shift of the finalstate wave packet of the charged particle due to radiation at lowest order in the fine structure constant α and in the small ħ approximation. We show that it disagrees with the result obtained using the LorentzDirac formula for the radiationreaction force, and that it agrees with the classical theory if one assumes that the particle loses its energy to radiation at each moment of time according to the Larmor formula in the static frame of the potential. However, the discrepancy is much smaller than the Compton wavelength of the particle. We also point out that the electromagnetic correction to the potential has no classical limit.

Atomic electric fields revealed by a quantum mechanical approach to electron picodiffraction.
PubMed
Müller, Knut; Krause, Florian F; Béché, Armand; Schowalter, Marco; Galioit, Vincent; Löffler, Stefan; Verbeeck, Johan; Zweck, Josef; Schattschneider, Peter; Rosenauer, Andreas
20141215
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.

Acceleration of adiabatic quantum dynamics in electromagnetic fields
SciTech Connect
Masuda, Shumpei; Nakamura, Katsuhiro
20111015
We show a method to accelerate quantum adiabatic dynamics of wave functions under electromagnetic field (EMF) by developing the preceding theory [Masuda and Nakamura, Proc. R. Soc. London Ser. A 466, 1135 (2010)]. Treating the orbital dynamics of a charged particle in EMF, we derive the driving field which accelerates quantum adiabatic dynamics in order to obtain the final adiabatic states in any desired short time. The scheme is consolidated by describing a way to overcome possible singularities in both the additional phase and driving potential due to nodes proper to wave functions under EMF. As explicit examples, we exhibit the fast forward of adiabatic squeezing and transport of excited Landau states with nonzero angular momentum, obtaining the result consistent with the transitionless quantum driving applied to the orbital dynamics in EMF.

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.

Quantum phenomena and the zeropoint radiation field. II
NASA Astrophysics Data System (ADS)
de La Peña, L.; Cetto, A. M.
19950401
A previous paper was devoted to the discussion of a new version of stochastic electrodynamics (SED) and to the study of the conditions under which quantum mechanics can be derived from it, in the radiationless approximation. In this paper further effects on matter due to the zeropoint field are studied, such as atomic stability, radiative transitions, the Lamb shift, etc., and are shown to be correctly described by the proposed version of SED. Also, a detailed energybalance condition and a fluctuationdissipation relation are established; it is shown in particular that equilibrium is attained only with a field spectrum ˜Ω 3. The proposed approach is shown to suggest an understanding of quantum mechanics as a kind of limitcycle theory. Finally, a brief discussion is included about the nonchaotic behavior of the (bounded) SED system in the quantum regime, as measured by Lyapunov exponents.

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.

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
20110307
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.

Quantum Theory of a StronglyDissipative Scalar Field
NASA Astrophysics Data System (ADS)
Jafari, Marjan; Kheirandish, Fardin
20170401
The properties of a quantum dissipative scalar field is analyzed by CaldeiraLeggett model in strongcoupling regime. The Lagrangian of the total system is canonically quantized and the full Hamiltonian is diagonalized using Fano technique. A modedependent probability density is introduced. The steady state energy and correlation functions at finite temperature are calculated in terms of the probability density.

Fractional Spin Fluctuations as a Precursor of Quantum Spin Liquids: Majorana Dynamical MeanField Study for the Kitaev Model.
PubMed
Yoshitake, Junki; Nasu, Joji; Motome, Yukitoshi
20161007
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.

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.

SuperPlanckian spatial field variations and quantum gravity
NASA Astrophysics Data System (ADS)
Klaewer, Daniel; Palti, Eran
20170101
We study scenarios where a scalar field has a spatially varying vacuum expectation value such that the total field variation is superPlanckian. We focus on the case where the scalar field controls the coupling of a U(1) gauge field, which allows us to apply the Weak Gravity Conjecture to such configurations. We show that this leads to evidence for a conjectured property of quantum gravity that as a scalar field variation in field space asymptotes to infinity there must exist an infinite tower of states whose mass decreases as an exponential function of the scalar field variation. We determine the rate at which the mass of the states reaches this exponential behaviour showing that it occurs quickly after the field variation passes the Planck scale.

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.

Quantum group symmetry of N=1 superconformal field theories
NASA Astrophysics Data System (ADS)
Jiménez, F.
19901201
We use the GómezSierra contour deformation techniques to show that N=1 superconformal field theories with {2c}/{3<1}, in their Coulomb gas version, contain a quantum group structure as an underlying symmetry. In particular, we construct from the thermal subalgebras of these theories, the representation spaces of the quantized universal enveloping superalgebra U q osp(2, 1) and show how to compute its Rmatrix, the comultiplication rules and its quantum ClebschGordan coefficients by using a convenient definition of the screened vertex operators and an explicit realization of its generators.

Dynamical meanfield theory for quantum chemistry.
PubMed
Lin, Nan; Marianetti, C A; Millis, Andrew J; Reichman, David R
20110304
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.

Highresolution absorptive intermolecular multiplequantum coherence NMR spectroscopy under inhomogeneous fields
NASA Astrophysics Data System (ADS)
Lin, Meijin; Lin, Yanqin; Chen, Xi; Cai, Shuhui; Chen, Zhong
20120101
Intermolecular multiplequantum coherence (iMQC) is capable of improving NMR spectral resolution using a 2D shearing manipulation method. A pulse sequence termed CTiDH, which combines intermolecular doublequantum filter (iDQF) with a modified constanttime (CT) scheme, is designed to achieve fast acquisition of highresolution intermolecular zeroquantum coherences (iZQCs) and intermolecular doublequantum coherences (iDQCs) spectra without strong coupling artifacts. Furthermore, doubleabsorption lineshapes are first realized in 2D intermolecular multiquantum coherences (iMQCs) spectra under inhomogeneous fields through a combination of iZQC and iDQC signals to double the resolution without loss of sensitivity. Theoretically the spectral linewidth can be further reduced by half compared to original iMQC highresolution spectra. Several experiments were performed to test the feasibility of the new method and the improvements are evaluated quantitatively. The study suggests potential applications for in vivo spectroscopy.

Quantum Coherence and Random Fields at Mesoscopic Scales
SciTech Connect
Rosenbaum, Thomas F.
20160301
We seek to explore and exploit model, disordered and geometrically frustrated magnets where coherent spin clusters stably detach themselves from their surroundings, leading to extreme sensitivity to finite frequency excitations and the ability to encode information. Global changes in either the spin concentration or the quantum tunneling probability via the application of an external magnetic field can tune the relative weights of quantum entanglement and random field effects on the mesoscopic scale. These same parameters can be harnessed to manipulate domain wall dynamics in the ferromagnetic state, with technological possibilities for magnetic information storage. Finally, extensions from quantum ferromagnets to antiferromagnets promise new insights into the physics of quantum fluctuations and effective dimensional reduction. A combination of ac susceptometry, dc magnetometry, noise measurements, hole burning, nonlinear Fano experiments, and neutron diffraction as functions of temperature, magnetic field, frequency, excitation amplitude, dipole concentration, and disorder address issues of stability, overlap, coherence, and control. We have been especially interested in probing the evolution of the local order in the progression from spin liquid to spin glass to longrangeordered magnet.

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.

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
20130807
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 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.

Quantum Entanglement of Local Operators in Conformal Field Theories
NASA Astrophysics Data System (ADS)
Nozaki, Masahiro; Numasawa, Tokiro; Takayanagi, Tadashi
20140301
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.

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.

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.

SNS potential with exchange field in quantum dusty plasmas
NASA Astrophysics Data System (ADS)
Zeba, I.; Batool, Maryam; Khan, Arroj A.; Jamil, M.; Rozina, Ch
20170201
The shielding potential of a static test charge is studied in quantum dusty plasmas. The plasma system consisting upon electrons, ions and negatively static charged dust species, is embedded in an ambient magnetic field. The modified equation of dispersion is derived using quantum hydrodynamic model (QHD) for magnetized plasmas. The quantum effects are inculcated through Fermi degenerate pressure, tunneling effect and exchangecorrelation effects. The study of shielding is important to know the existence of the silence zones in space and astrophysical objects as well as crystal formation. The graphical description of the normalized potential depict the significance of the exchange and correlation effects arising through spin and other variables on the shielding potential.

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.

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.

Electric field dependence of hybridized gap in InAs/GaSb quantum well system
NASA Astrophysics Data System (ADS)
Ruan, Jiufu; Wei, Xiangfei; Wang, Weiyang
20170201
We demonstrate theoretically that exchange interaction induced by electronhole scattering via Coulomb interaction can cause a hybridized gap in InAs/GaSb based type II and brokengap quantum wells. The hybridized energy spectra are obtained analytically at the low temperature and long wave limits. An electric field depended hybridized gap about 4 meV opens at the anticrossing points of the hybridized energy spectra, in accordance with experimental measurements. The hybridized gap varies linearly with the gate electric voltage due to the fact that the electric field can change the exchange selfenergy by tuning the overlap of the wavefunctions and the Fermi energy. Our theoretical results can give a deep insight of the origin of the hybridized gap and provide a simple way to determine the value and the position of the hybridized gap in the presence of the gate electric voltage.

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.

New Shell Structures and Their Ground Electronic States in Spherical Quantum Dots (II) under Magnetic Field
NASA Astrophysics Data System (ADS)
Asari, Yusuke; Takeda, Kyozaburo; Tamura, Hiroyuki
20050401
We theoretically studied the electronic structure of the threedimensional spherical parabolic quantum dot (3DSPQD) under a magnetic field. We obtained the quantum dot orbitals (QDOs) and determined the ground state by using the extended UHF approach where the expectation values of the z component of the total orbital angular momentum <\\hat{L}z> are conserved during the scfprocedure. The singleelectron treatment predicts that the applied magnetic field (B) creates kth new shells at the magnetic field of Bk=k(k+2)/(k+1)ω0 with the shellenergy interval of \\hbarω0/(k+1), where ω0(=\\hbar/m*l02) is the characteristic frequency originating from the spherical parabolic confinement potential. These shells are formed by the level crossing among multiple QDOs. The interelectron interaction breaks the simple level crossing but causes complicated dependences among the total energy, the chemical potential and their differences (magic numbers) with the magnetic field or the number of confinement electrons. The ground state having a higher spin multiplicity is theoretically predicted on the basis of the \\textit{quasi}degeneracies of the QDOs around these shells.

Quantum entanglement in a twoelectron quantum dot in magnetic field
NASA Astrophysics Data System (ADS)
Nazmitdinov, R. G.; Chizhov, A. V.
20120301
The properties of quantum entanglement of the ground state in an exactly solvable model of a twoelectron QD have been investigated. It is shown that the degree of entanglement increases with enhancement of interaction between electrons, irrespective of the shape of electron confining potential in a QD. A magnetic field destroys electron entanglement. However, the entanglement in deformed QDs is more stable against magnetic field.

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

DC response of hot carriers under circularly polarized intense microwave fields and intense magnetic fields in quantum wells
SciTech Connect
Ishida, Norihisa
20131204
Hot carrier dynamics under intense microwave and crossed magnetic fields are investigated theoretically for the case that the dominant scattering process is inelastic collision, especially intersubband and intrasubband transition in Quantum wells. If the applied electric fields are circularly polarized, the equation of motion forms symmetric on the xy plane. But the carrier motions are complicated to accumulate because of acceleration and emission process. This situation makes possible to create a variation of the carrier motion, typically the carrier bunching is occurred. This state is a sort of population inversion. The DC response of this system attains strongly negative at appropriate field conditions. Through the simulation for the real case described below, it may include a type of induced emission.

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.

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.

Wave functions of elliptical quantum dots in a magnetic field
NASA Astrophysics Data System (ADS)
Zhou, Daming; Lorke, Axel
20150301
We use the variational principle to obtain the wave functions of elliptical quantum dots under the influence of an external magnetic field. For the first excited states, whose wave functions have recently been mapped experimentally, we find a simple expression, based on a linear combination of the wave functions in the absence of a magnetic field. The results illustrate how a magnetic field breaks the xy symmetry and mixes the corresponding eigenstates. The obtained eigenenergies agree well with those obtained by more involved analytical and numerical methods.

Exact Classical and Quantum Dynamics in Background Electromagnetic Fields
NASA Astrophysics Data System (ADS)
Heinzl, Tom; Ilderton, Anton
20170301
Analytic results for (Q)ED processes in external fields are limited to a few special cases, such as plane waves. However, the strong focusing of intense laser fields implies a need to go beyond the plane wave model. By exploiting Poincaré symmetry and superintegrability we show how to construct, and solve without approximation, new models of lasermatter interactions. We illustrate the method with a model of a radially polarized (TM) laser beam, for which we exactly determine the classical orbits and quantum wave functions. Including in this way the effects of transverse field structure should improve predictions and analyses for experiments at intense laser facilities.

Cold atom simulation of interacting relativistic quantum field theories.
PubMed
Cirac, J Ignacio; Maraner, Paolo; Pachos, Jiannis K
20101105
We demonstrate that Dirac fermions selfinteracting or coupled to dynamic scalar fields can emerge in the low energy sector of designed bosonic and fermionic cold atom systems. We illustrate this with two examples defined in two spacetime dimensions. The first one is the selfinteracting Thirring model. The second one is a model of Dirac fermions coupled to a dynamic scalar field that gives rise to the GrossNeveu model. The proposed cold atom experiments can be used to probe spectral or correlation properties of interacting quantum field theories thereby presenting an alternative to lattice gauge theory simulations.

Electric Fields in the 5/2 fractional quantum Hall effect
NASA Astrophysics Data System (ADS)
TylanTyler, Anthony; LyandaGeller, Yuli
The potential for nonAbelian quasiholes in the 5/2 fractional quantum Hall effect makes the state of interest theoretically and experimentally. The presence of such features in the ground state of the system would allow for the implementation of a topological quantum computation scheme. In order to probe the system for these features, a small measuring voltage, i.e. an electric field, is applied. In Corbino geometries, these electric fields are applied radially. This breaks the Galilean invariance, which in an infinite planar geometry allows us to transform to a moving frame of reference, eliminating the electric field. To study the effects of these fields, we carry out exact diagonalization calculations in a disk geometry. We find that application of small fields can lead to an improvement in the overlap with the MooreRead Pfaffian long before the state is destroyed by the field. Additionally, we find that the coherence length of quasiholes travelling along the edge of the sample increases significantly when compared to the case with no applied field. This research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DESC0010544.

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.

Nonexponential decay in Quantum Mechanics and Quantum Field Theory
NASA Astrophysics Data System (ADS)
Giacosa, Francesco
20141001
We describe some salient features as well as some recent developments concerning shorttime deviations from the exponential decay law in the context of Quantum Mechanics by using the Lee Hamiltonian approach and Quantum Field Theory by using relativistic Lagrangians. In particular, the case in which two decay channels are present is analyzed: the ratio of decay probability densities, which is a constant equal to the ratio of decay widths in the exponential limit, shows in general sizable fluctuations which persist also at long times.

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.

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.

Tachyon field in loop quantum cosmology: Inflation and evolution picture
SciTech Connect
Xiong Huaui; Zhu Jianyang
20070415
Loop quantum cosmology (LQC) predicts a nonsingular evolution of the universne through a bounce in the high energy region. We show that this is always true in tachyon matter LQC. Differing from the classical FriedmanRobertsonWalker (FRW) cosmology, the super inflation can appear in the tachyon matter LQC; furthermore, the inflation can be extended to the region where classical inflation stops. Using the numerical method, we give an evolution picture of the tachyon field with an exponential potential in the context of LQC. It indicates that the quantum dynamical solutions have the same attractive behavior as the classical solutions do. The whole evolution of the tachyon field is that in the distant past, the tachyon fieldbeing in the contracting cosmologyaccelerates to climb up the potential hill with a negative velocity; then at the boundary the tachyon field is bounced into an expanding universe with positive velocity rolling down to the bottom of the potential. In the slow roll limit, we compare the quantum inflation with the classical case in both an analytic and a numerical way.

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 and computational analysis of the quantum radar cross section for simple geometrical targets
NASA Astrophysics Data System (ADS)
Brandsema, Matthew J.; Narayanan, Ram M.; Lanzagorta, Marco
20170101
The concept of the quantum radar cross section (QRCS) has generated interest due to its promising feature of enhanced side lobe target visibility in comparison to the classical radar cross section. Researchers have simulated the QRCS for very limited geometries and even developed approximations to reduce the computational complexity of the simulations. This paper develops an alternate theoretical framework for calculating the QRCS. This new framework yields an alternative form of the QRCS expression in terms of Fourier transforms. This formulation is much easier to work with mathematically and allows one to derive analytical solutions for various geometries, which provides an explanation for the aforementioned sidelobe advantage. We also verify the resulting equations by comparing with numerical simulations, as well as provide an error analysis of these simulations to ensure the accuracy of the results. Comparison of our simulation results with the analytical solutions reveal that they agree with one another extremely well.

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.

Determining Student Competency in Field Placements: An Emerging Theoretical Model
ERIC Educational Resources Information Center
Salm, Twyla L.; Johner, Randy; Luhanga, Florence
20160101
This paper describes a qualitative case study that explores how twentythree field advisors, representing three human service professions including education, nursing, and social work, experience the process of assessment with students who are struggling to meet minimum competencies in field placements. Five themes emerged from the analysis of…

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.

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.

Informationtheoretic security proof for quantumkeydistribution protocols
NASA Astrophysics Data System (ADS)
Renner, Renato; Gisin, Nicolas; Kraus, Barbara
20050701
We present a technique for proving the security of quantumkeydistribution (QKD) protocols. It is based on direct informationtheoretic arguments and thus also applies if no equivalent entanglement purification scheme can be found. Using this technique, we investigate a general class of QKD protocols with oneway classical postprocessing. We show that, in order to analyze the full security of these protocols, it suffices to consider collective attacks. Indeed, we give new lower and upper bounds on the secretkey rate which only involve entropies of twoqubit density operators and which are thus easy to compute. As an illustration of our results, we analyze the BennettBrassard 1984, the sixstate, and the Bennett 1992 protocols with oneway error correction and privacy amplification. Surprisingly, the performance of these protocols is increased if one of the parties adds noise to the measurement data before the error correction. In particular, this additional noise makes the protocols more robust against noise in the quantum channel.

Informationtheoretic security proof for quantumkeydistribution protocols
SciTech Connect
Renner, Renato; Gisin, Nicolas; Kraus, Barbara
20050715
We present a technique for proving the security of quantumkeydistribution (QKD) protocols. It is based on direct informationtheoretic arguments and thus also applies if no equivalent entanglement purification scheme can be found. Using this technique, we investigate a general class of QKD protocols with oneway classical postprocessing. We show that, in order to analyze the full security of these protocols, it suffices to consider collective attacks. Indeed, we give new lower and upper bounds on the secretkey rate which only involve entropies of twoqubit density operators and which are thus easy to compute. As an illustration of our results, we analyze the BennettBrassard 1984, the sixstate, and the Bennett 1992 protocols with oneway error correction and privacy amplification. Surprisingly, the performance of these protocols is increased if one of the parties adds noise to the measurement data before the error correction. In particular, this additional noise makes the protocols more robust against noise in the quantum channel.

Nonperturbative studies in quantum field theory
SciTech Connect
Abada, A.
19920101
This dissertation is composed of three different research topics. The first part deals with the Study of the socalled local lattice Yukawa theory. The motivation for this study is to investigate the interior of the phase diagram of this theory. A strong y expansion (y being the bare Yukawa coupling) is performed of the partition function and show that within the (finite) range of convergence of the series expansion, the lattice Yukawa theory is equivalent to a purely bosonic theory, with a shifted action. The author explicitly calculated the shifted action to the fourth order in 1/y and find that it is composed of competing interactions. This suggests that away from y = [infinity] towards the interior of the phase diagram, there is a more complicated ordering than simple ferromagnetic or antiferromagnetic. In the second part, the question is addressed of formation of bound states out of constituent fields in an exactly soluble theory, i.e. multifermion electrodynamics in two spacetime dimensions. The author exactly calculates the correlation function corresponding to a neutral composite fermion operator and discuss the pole structure of its Fourier transform. It does not exhibit a simple pole in p[sup 2], hence the corresponding neutral composite operator does not create an asymptotic state in the spectrum of the theory. In part three, the author puts multifermion QED[sub 2] in a heat bath and address the same question as in part two. The author first exactly calculates a bosonic correlation function at finite temperature and density, and discuss its behavior. The author then exactly calculates the correlation function corresponding to the neutral composite fermion operator at finite temperature and density and discusses its behavior. It is concluded that the temperature does not help the composite fermion operator create a particle in the spectrum of the theory.

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.

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

Clusterlike coordinates in supersymmetric quantum field theory.
PubMed
Neitzke, Andrew
20140708
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

Quantum field theory on curved spacetimes: Axiomatic framework and examples
NASA Astrophysics Data System (ADS)
Fredenhagen, Klaus; Rejzner, Kasia
20160301
In this review article, we want to expose a systematic development of quantum field theory on curved spacetimes. The leading principle is the emphasis on local properties. It turns out that this requires a reformulation of the QFT framework which also yields a new perspective for the theories on Minkowski space. The aim of the present work is to provide an almost selfcontained introduction into the framework, which should be accessible for both mathematical physicists and mathematicians.

HighField Fractional Quantum Hall Effect in Optical Lattices
SciTech Connect
Palmer, R.N.; Jaksch, D.
20060512
We consider interacting bosonic atoms in an optical lattice subject to a large simulated magnetic field. We develop a model similar to a bilayer fractional quantum Hall system valid near simple rational numbers of magnetic flux quanta per lattice cell. Then we calculate its ground state, magnetic lengths, fractional fillings, and find unexpected sign changes in the Hall current. Finally we study methods for detecting these novel features via shot noise and Hall current measurements.

Quantum systems with positions and momenta on a Galois field
NASA Astrophysics Data System (ADS)
Vourdas, A.
20080301
Quantum systems with positions and momenta in the Galois field GF(pe), are considered. The HeisenbergWeyl group of displacements and the Sp(2,GF(pe)) group of symplectic transformations, are studied. Frobenius symmetries, are a unique feature of these systems and lead to constants of motion. The engineering of such systems from l spins with j = (p  1)/2, which are coupled in a particular way, is discussed.

Magnetic field effects in fewlevel quantum dots: Theory and application to experiment
NASA Astrophysics Data System (ADS)
Wright, Christopher J.; Galpin, Martin R.; Logan, David E.
20110901
We examine several effects of an applied magnetic field on Andersontype models for both single and twolevel quantum dots, and we make direct comparison between numerical renormalization group (NRG) calculations and recent conductance measurements. On the theoretical side, the focus is on magnetization, singleparticle dynamics, and zerobias conductance, with emphasis on the universality arising in strongly correlated regimes, including a method to obtain the scaling behavior of fieldinduced Kondo resonance shifts over a very wide field range. NRG is also used to interpret recent experiments on spin(1)/(2) and spin1 quantum dots in a magnetic field, which we argue do not wholly probe universal regimes of behavior, and the calculations are shown to yield good qualitative agreement with essentially all features seen in experiment. The results capture in particular the observed field dependence of the Kondo conductance peak in a spin(1)/(2) dot, with quantitative deviations from experiment occurring at fields in excess of ˜5T, indicating the eventual inadequacy of using the equilibrium singleparticle spectrum to calculate the conductance at finite bias.

Electricfield controlled ferromagnetism in MnGe magnetic quantum dots.
PubMed
Xiu, Faxian; Wang, Yong; Zou, Jin; Wang, Kang L
20110101
Electricfield control of ferromagnetism in magnetic semiconductors at room temperature has been actively pursued as one of the important approaches to realize practical spintronics and nonvolatile logic devices. While Mndoped IIIV semiconductors were considered as potential candidates for achieving this controllability, the search for an ideal material with high Curie temperature (T(c)>300 K) and controllable ferromagnetism at room temperature has continued for nearly a decade. Among various dilute magnetic semiconductors (DMSs), materials derived from group IV elements such as Si and Ge are the ideal candidates for such materials due to their excellent compatibility with the conventional complementary metaloxidesemiconductor (CMOS) technology. Here, we review recent reports on the development of highCurie temperature Mn(0.05)Ge(0.95) quantum dots (QDs) and successfully demonstrate electricfield control of ferromagnetism in the Mn(0.05)Ge(0.95) quantum dots up to 300 K. Upon the application of gatebias to a metaloxidesemiconductor (MOS) capacitor, the ferromagnetism of the channel layer (i.e. the Mn(0.05)Ge(0.95) quantum dots) was modulated as a function of the hole concentration. Finally, a theoretical model based upon the formation of magnetic polarons has been proposed to explain the observed field controlled ferromagnetism.

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.

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.

Global Symmetries, Volume Independence, and Continuity in Quantum Field Theories.
PubMed
Sulejmanpasic, Tin
20170106
We discuss quantum field theories with global SU(N) and O(N) symmetries for which temporal direction is compactified on a circle of size L with periodicity of fields up to a global symmetry transformation, i.e., twisted boundary conditions. Such boundary conditions correspond to an insertion of the global symmetry operator in the partition function. We argue in general and prove in particular for CP(N1) and O(N) nonlinear sigma models that largeN volume independence holds. Further we show that the CP(N1) theory is free from the Affleck phase transition confirming the ÜnsalDunne continuity conjecture.

Neutron stars. [quantum mechanical processes associated with magnetic fields
NASA Technical Reports Server (NTRS)
Canuto, V.
19780101
Quantummechanical processes associated with the presence of high magnetic fields and the effect of such fields on the evolution of neutron stars are reviewed. A technical description of the interior of a neutron star is presented. The neutron starpulsar relation is reviewed and consideration is given to supernovae explosions, flux conservation in neutron stars, gaugeinvariant derivation of the equation of state for a strongly magnetized gas, neutron betadecay, and the stability condition for a neutron star.

Gaugefieldassisted Kekulé quantum criticality
NASA Astrophysics Data System (ADS)
Scherer, Michael M.; Herbut, Igor F.
20161101
We study the quantum phase transition of U (1 ) charged Dirac fermions Yukawa coupled to the Kekulé valencebondsolid order parameter with Z3 symmetry of the honeycomb lattice. The symmetry allows for the presence of the term in the action which is cubic in the Kekulé order parameter and which is expected to prevent the quantum phase transition in question from being continuous. The GrossNeveuYukawa theory for the transition is investigated using a perturbative renormalization group and within the ɛ expansion close to four spacetime dimensions. For a vanishing U (1 ) charge we show that quantum fluctuations may render the phase transition continuous only sufficiently far away from 3+1 dimensions, where the validity of the conclusions based on the leadingorder ɛ expansion appears questionable. In the presence of a fluctuating gauge field, on the other hand, we find quantum critical behavior even at weak coupling to appear close to 3+1 dimensions, that is, within the domain of validity of the perturbation theory. We also determine the renormalizationgroup scaling of the cubic coupling at higherloop orders and for a large number of Dirac fermions for vanishing charge.

Theoretical Studies of High Field Transport in IIIV Semiconductors.
DTIC Science & Technology
19800901
ADA123 947 THEORETICAL STUDIES OF HIGH FIELD TRANSPORT IN IllV 1/2 SENXCONDUCTORS(U) ILLINOIS UNIV AT URBANA COORDINATED SCIENCE LAB H SHICHIJO...CATALOG NUMBER 4. TITLE (and Subtitleo S. TYPE Of REPORT & PERIOD COVERED THEORETICAL STUDIES OF HIGH FIELD TRANSPORT Technical Report IN IllIV...Continue on reverse aide It necessary and identitfy by block number) High field transport , 35 semicopductors, Monte Carlo simulation 20. ABSTRACT

A Theoretical Mechanism of Szilard Engine Function in Nucleic Acids and the Implications for Quantum Coherence in Biological Systems
SciTech Connect
Matthew Mihelic, F.
20101222
Nucleic acids theoretically possess a Szilard engine function that can convert the energy associated with the Shannon entropy of molecules for which they have coded recognition, into the useful work of geometric reconfiguration of the nucleic acid molecule. This function is logically reversible because its mechanism is literally and physically constructed out of the information necessary to reduce the Shannon entropy of such molecules, which means that this information exists on both sides of the theoretical engine, and because information is retained in the geometric degrees of freedom of the nucleic acid molecule, a quantum gate is formed through which multistate nucleic acid qubits can interact. Entangled biophotons emitted as a consequence of symmetry breaking nucleic acid Szilard engine (NASE) function can be used to coordinate relative positioning of different nucleic acid locations, both within and between cells, thus providing the potential for quantum coherence of an entire biological system. Theoretical implications of understanding biological systems as such 'quantum adaptive systems' include the potential for multiagent based quantum computing, and a better understanding of systemic pathologies such as cancer, as being related to a loss of systemic quantum coherence.

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.

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.

Classical and quantum mechanics of diatomic molecules in tilted fields.
PubMed
Arango, Carlos A; Kennerly, William W; Ezra, Gregory S
20050508
We investigate the classical and quantum mechanics of diatomic molecules in noncollinear (tilted) static electric and nonresonant linearly polarized laser fields. The classical diatomic in tilted fields is a nonintegrable system, and we study the phase space structure for physically relevant parameter regimes for the molecule KCl. While exhibiting lowenergy (pendular) and highenergy (freerotor) integrable limits, the rotor in tilted fields shows chaotic dynamics at intermediate energies, and the degree of classical chaos can be tuned by changing the tilt angle. We examine the quantum mechanics of rotors in tilted fields. Energylevel correlation diagrams are computed, and the presence of avoided crossings quantified by the study of nearestneighbor spacing distributions as a function of energy and tilting angle. Finally, we examine the influence of classical periodic orbits on rotor wave functions. Many wave functions in the tilted field case are found to be highly nonseparable in spherical polar coordinates. Localization of wave functions in the vicinity of classical periodic orbits, both stable and unstable, is observed for many states.

Influence of incoherent pumping field on spatial evolution of gain without inversion in a fourlevel quantum dot nanostructure
NASA Astrophysics Data System (ADS)
Karimi, R.; Asadpour, S. H.; Batebi, S.; Rahimpour Soleimani, H.
20150901
We investigated the propagation effect on gain without inversion (GWI) phenomena in an open four level quantum dot nanostructure in the presence and absence of incoherent pumping field. The simulation results show that, the ratio of the injection rates and strength of incoherent pumping field has remarkable effect on spatial evolution of GWI and output. We can obtain the optimal GWI and output by choosing appropriate values of parameters. The theoretical results show that, in the open system the value of gain (output) in the absence of incoherent pumping field is much larger than that in the presence of incoherent pumping field.

Effect of a magnetic field on intersubband polaritons in a quantum well: strong to weak coupling conversion.
PubMed
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 a weak one. This effect paves a way for the effective control of polaritonic devices with a magnetic field.

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.

Capture and emission of electrons in quantum wells under applied electric field
NASA Astrophysics Data System (ADS)
Vinter, B.; Luc, F.; Bois, P.; Thibaudeau, L.; Rosencher, E.
19940601
Important characteristics of Quantum Well Infrared Photodetectors are determined almost entirely by the photoionization rate of electrons out of the Quantum Well (QW) and the recapture into the QWs. To elucidate these processes microscopically we have made structures in which the QWs are isolated from one contact by a completely blocking barrier, so that the steady state current vanishes. The transient current induced by photoionization out of the QWs gives a direct measurement of the photoionization cross section and the escape probability of a photoexcited electron. We have found that the variation of the latter with the electric field may be described by a simple barrier lowering model combined with statistical fluctuation of the QW width. The capture process has been studied by impedance spectroscopy in samples containing only one well. The capture velocity thus measured is found to decrease with increasing applied electric field but within experimental uncertainties it does not depend on the width of the well for well widths between 3 and 7.5 nm. Theoretical results on optical phonon mediated transitions in the applied field from barrier to well states show a generally good agreement with experiment at low fields but less dependence on the 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

The secondharmonic generation susceptibility in semiparabolic quantum wells with applied electric field
NASA Astrophysics Data System (ADS)
Yuan, JianHui; Zhang, Yan; Mo, Hua; Chen, Ni; Zhang, Zhihai
20151201
The secondharmonic generation susceptibility in semiparabolic quantum wells with applied electric field is investigated theoretically. For the same topic studied by Zhang and Xie [Phys. Rev. B 68 (2003) 235315] [1], some new and reliable results are obtained by us. It is easily observed that the second harmonic generation susceptibility decreases and the blue shift of the resonance is induced with increasing of the frequencies of the confined potential. Moreover, a transition from a twophoton resonance to two singlephoton resonances will appear adjusted by the frequencies of the confined potential. Similar results can also be obtained by controlling the applied electric field. Surprisingly, the second harmonic generation susceptibility is weakened in the presence of the electric field, which is in contrast to the conventional case. Finally, the resonant peak and its corresponding resonant energy are also taken into account.

Topics in topological and holomorphic quantum field theory
NASA Astrophysics Data System (ADS)
Vyas, Ketan
We investigate topological quantum field theories (TQFTs) in two, three, and four dimensions, as well as holomorphic quantum field theories (HQFTs) in four dimensions. After a brief overview of the twodimensional (gauged) A and B models and the corresponding the category of branes, we construct analogous threedimensional (gauged) A and B models and discuss the twocategory of boundary conditions. Compactification allows us to identify the category of line operators in the threedimensional A and B models with the category of branes in the corresponding twodimensional A and B models. Furthermore, we use compactification to identify the twocategory of surface operators in the fourdimensional GL theory at t = 1 and t = i with the twocategory of boundary conditions in the corresponding threedimensional A and B model, respectively. We construct a fourdimensional HQFT related to N = 1 supersymmetric quantum chromodynamics (SQCD) with gauge group SU(2) and two flavors, as well as a fourdimensional HQFT related to the Seiberg dual chiral model. On closed K ̈ahler surfaces with h^(2,0) > 0, we show that the correlation functions of holomorphic SQCD formally compute certain Donaldson invariants. For simplyconnected elliptic surfaces (and their blowups), we show that the corresponding correlation functions in the holomorphic chiral model explicitly compute these Donaldson invariants.

Quantum field theory on toroidal topology: Algebraic structure and applications
NASA Astrophysics Data System (ADS)
Khanna, F. C.; Malbouisson, A. P. C.; Malbouisson, J. M. C.; Santana, A. E.
20140501
The development of quantum theory on a torus has a long history, and can be traced back to the 1920s, with the attempts by Nordström, Kaluza and Klein to define a fourth spatial dimension with a finite size, being curved in the form of a torus, such that Einstein and Maxwell equations would be unified. Many developments were carried out considering cosmological problems in association with particle physics, leading to methods that are useful for areas of physics, in which size effects play an important role. This interest in finite size effect systems has been increasing rapidly over the last decades, due principally to experimental improvements. In this review, the foundations of compactified quantum field theory on a torus are presented in a unified way, in order to consider applications in particle and condensed matter physics. The theory on a torus ΓDd=(S1)d×RDd is developed from a Liegroup representation and c*c*algebra formalisms. As a first application, the quantum field theory at finite temperature, in its real and imaginarytime versions, is addressed by focusing on its topological structure, the torus Γ41. The toroidal quantumfield theory provides the basis for a consistent approach of spontaneous symmetry breaking driven by both temperature and spatial boundaries. Then the superconductivity in films, wires and grains are analyzed, leading to some results that are comparable with experiments. The Casimir effect is studied taking the electromagnetic and Dirac fields on a torus. In this case, the method of analysis is based on a generalized Bogoliubov transformation, that separates the Green function into two parts: one is associated with the empty spacetime, while the other describes the impact of compactification. This provides a natural procedure for calculating the renormalized energymomentum tensor. Self interacting fourfermion systems, described by the GrossNeveu and NambuJonaLasinio models, are considered. Then finite size effects on

Noninvasive detection of charge rearrangement in a quantum dot in high magnetic fields
NASA Astrophysics Data System (ADS)
Fricke, C.; Rogge, M. C.; Harke, B.; Reinwald, M.; Wegscheider, W.; Hohls, F.; Haug, R. J.
20051101
We demonstrate electron redistribution caused by magnetic field on a single quantum dot measured by means of a quantum point contact as noninvasive detector. Our device, which is fabricated by local anodic oxidation, allows us to control independently the quantum point contact and all tunneling barriers of the quantum dot. Thus we are able to measure both the change of the quantum dot charge and also changes of the electron configuration at constant number of electrons on the quantum dot. We use these features to exploit the quantum dot in a high magnetic field where transport through the quantum dot displays the effects of Landau shells and spin blockade. We confirm the internal rearrangement of electrons as function of the magnetic field for a fixed number of electrons on the quantum dot.

Topological Duality Between Real Scalar and Spinor Fields in Quantum Field Theory, Cosmology, Quantum Theories of Fundamental Extended Objects
NASA Astrophysics Data System (ADS)
Goncharov, Yu. P.
This survey is devoted to possible manifestations of remarkable topological duality between real scalar and spinor fields (TDSS) existing on a great number of manifolds important in physical applications. The given manifestations are demonstrated to occur within the framework of miscellaneous branches in ordinary and supersymmetric quantum field theories, supergravity, KaluzaKlein type theories, cosmology, strings, membranes and pbranes. All this allows one to draw the condusion that the above duality will seem to be an essential ingredient in many questions of present and future investigations.

A quantum mechanical polarizable force field for biomolecular interactions
PubMed Central
Donchev, A. G.; Ozrin, V. D.; Subbotin, M. V.; Tarasov, O. V.; Tarasov, V. I.
20050101
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. PMID:15911753

Nearfield hyperspectral quantum probing of multimodal plasmonic resonators
NASA Astrophysics Data System (ADS)
Cuche, A.; Berthel, M.; Kumar, U.; Colas des Francs, G.; Huant, S.; Dujardin, E.; Girard, C.; Drezet, A.
20170301
Quantum systems, excited by an external source of photons, display a photodynamics that is ruled by a subtle balance between radiative or nonradiative energy channels when interacting with metallic nanostructures. We apply and generalize this concept to achieve a quantum probing of multimodal plasmonic resonators by collecting and filtering the broad emission spectra generated by a nanodiamond (ND) hosting a small set of nitrogenvacancy (NV) color centers attached at the apex of an optical tip. Spatially and spectrally resolved information on the photonic local density of states (phLDOS) can be recorded with this technique in the immediate vicinity of plasmonic resonators, paving the way for a complete nearfield optical characterization of any kind of nanoresonators in the single photon regime.

Causal, Selfconsistent Field Quantum MassSpacetimes
NASA Astrophysics Data System (ADS)
Scofield, Dillon
20170101
An ab initio selfconsistent field (SCF) description of the causal, current conserving, evolution of quantum massspacetime (QMST) manifolds is presented. The properties of QMSTs are shown to follow from the properties of their homogeneous, isotropic, affine tangent spaces as characterized by the Poincaré group. QMSTs with C l (4,C) Clifford algebra structure and tangent spaces are shown to be compatible with the Standard Model of elementary particle interactions. These QMSTs include the protonelectronneutrinoneutron excitation system. Expressions for conserved Noether currents, stressenergies, and angularmomenta are shown to be corollaries of the theory. Methods to compute the quantum geometry of fewbody QMSTs are discussed.

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.

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.

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.

Topological fieldeffect quantum transistors in HgTe nanoribbons.
PubMed
Fu, HuaHua; Gao, JinHua; Yao, KaiLun
20140606
We propose practical designs to realize topological fieldeffect quantum transistors in an HgTe nanoribbon with an inverted band structure. Our theoretical calculations show that, as a stripshape top gate is placed on the HgTe nanoribbon and with an increasing gate voltage, two new conductance channels develop in the HgTe nanoribbon and are localized to the lattice sites neighboring the boundaries of the gate, leading to an additional quantization of the conductance of 2e(2)/h. The quantum states in the new channels are not only robust against a shortrange Anderson disorder, but can also couple with the intrinsic helical edge states in the boundaries of the HgTe nanoribbon to open a gap in the energy spectrum, indicating their topological characteristics. More importantly, the newly developed conductance channels can be turned on or off easily by adjusting the gate voltage. The proposal of controllable topological edge states produced by the gate voltage opens a new route for future topological fieldeffect quantum transistors in nanoelectronics and spintronics.

Quantum Corrections and Effective Action in Field Theory
NASA Astrophysics Data System (ADS)
Dalvit, Diego A. R.
19980701
In this Thesis we study quantum corrections to the classical dynamics for mean values in field theory. To that end we make use of the formalism of the closed time path effective action to get real and causal equations of motion. We introduce a coarse grained effective action, which is useful in the study of phase transitions in field theory. We derive an exact renormalization group equation that describes how this action varies with the coarse graining scale. We develop different approximation methods to solve that equation, and we obtain non perturbative improvements to the effective potential for a self interacting scalar field theory. We also discuss the stochastic aspects contained in this action. On the other hand, using the effective action, we find low energy and large distance quantum corrections for the gravitational potential, treating relativity as an effective low energy theory. We include the effect of scalar fields, fermions and gravitons. The inclusion of metric fluctuations causes Einstein semiclassical equations to depend on the gauge fixing parameters, and they are therefore non physical. We solve this problem identifying as a physical observable the trayectory of a test particle. We explicitly show that the geodesic equation for such particle is independent of the arbitrary parameters of the gauge fixing.

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

Magnetooptical absorption in semiconducting spherical quantum dots: Influence of the dotsize, confining potential, and magnetic field
NASA Astrophysics Data System (ADS)
Kushwaha, Manvir S.
20141201
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 transitions are seen

Unified Field Theoretical Models from Generalized Affine Geometries II
NASA Astrophysics Data System (ADS)
CiriloLombardo, Diego Julio
20110601
The spacetime structure of the new Unified Field Theory presented in previous reference (Int. J. Theor. Phys. 49:12881301, 2010) is analyzed from its SL(2C) underlying structure in order to make precise the notion of minimal coupling. To this end, the framework is the language of tensors and particularly differential forms and the condition a priory of the existence of a potential for the torsion is relaxed. We shown trough exact cosmological solutions from this model, where the geometry is Euclidean R⊗ O 3˜ R⊗ SU(2), the relation between the spacetime geometry and the structure of the gauge group. Precisely this relation is directly connected with the relation of the spin and torsion fields. The solution of this model is explicitly compared with our previous ones and we find that: (i) the torsion is not identified directly with the Yang Mills type strength field, (ii) there exists a compatibility condition connected with the identification of the gauge group with the geometric structure of the spacetime: this fact lead the identification between derivatives of the scale factor a( τ) with the components of the torsion in order to allows the HosoyaOgura ansatz (namely, the alignment of the isospin with the frame geometry of the spacetime), (iii) this compatibility condition precisely mark the fact that local gauge covariance, coordinate independence and arbitrary space time geometries are harmonious concepts and (iv) of two possible structures of the torsion the "tratorial" form (the only one studied here) forbids wormhole configurations, leading only, cosmological instanton spacetime in eternal expansion.

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.

Effects of applied electric and magnetic fields on the nonlinear optical rectification and secondharmonic generation in a graded quantum well under intense laser field
NASA Astrophysics Data System (ADS)
Ungan, Fatih
20170101
In this present study, the effects of electric and magnetic fields on the nonlinear optical rectification and secondharmonic generation in a graded quantum well under intense laser field have been investigated theoretically. The energy eigenvalues and their corresponding eigenfunctions are obtained by solving Schrödinger equation within the framework of effective mass approximation. The analytic expressions for the optical properties are calculated by the compactdensitymatrix approach and iterative method. The numerical results are presented for a typical GaAs/Ga1 x Al x As quantum well. The results show that the nonlinear optical rectification and secondharmonic generation coefficients are considerably affected by the electromagnetic fields and intense laser field.

Nonlinear optical rectification and secondharmonic generation in a semiparabolic quantum well under intense laser field: Effects of electric and magnetic fields
NASA Astrophysics Data System (ADS)
Ungan, F.; MartínezOrozco, J. C.; Restrepo, R. L.; MoraRamos, M. E.; Kasapoglu, E.; Duque, C. A.
20150501
The effects of electric and magnetic fields on the nonlinear optical rectification and second harmonic generation coefficients related with intersubband transitions in a semiparabolic quantum well under intense laser field are theoretically studied. The energy levels and corresponding wave functions are obtained by solving the conduction band Schrödingerlike equation in the parabolic approximation and the envelope function approach. Numerical calculations are presented for a typical GaAs/Ga1xAlxAs quantum well. The results show that both the nonresonant intense laser field and the static external fields have significant influences on the magnitude and resonant peak energy positions of the coefficients under study.

Nonlinear optical rectification in laterallycoupled quantum well wires with applied electric field
NASA Astrophysics Data System (ADS)
Liu, Guanghui; Guo, Kangxian; Zhang, Zhongmin; Hassanbadi, Hassan; Lu, Liangliang
20170301
Nonlinear optical rectification coefficient χ0(2) in laterallycoupled AlxGa1xAs/GaAs quantum well wires with an applied electric field is theoretically investigated using the effective mass approximation as well as the numerical energy levels and wavefunctions of electrons. We find that χ0(2) is greatly influenced by the electric field as well as both the distance and the radius of the coupled system. A blue shift of χ0(2) with increasing electric field is exhibited while a red shift followed by a blue shift with increasing distance or radius is exhibited. A nonmonotonic behavior can be found in the resonant peak values of χ0(2) along with the increase of the electric field, the distance or the radius. One or two of the following physical mechanisms: the increased localization of the ground and firstexcited states, the reduced coupling and the reduced quantum confinement effect are applied to elucidate the results above. Our results play a potential role in infrared photodetectors based on the coupled system.

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.

Exciton effects on the nonlinear optical properties of semiparabolic quantum dot under electric field
NASA Astrophysics Data System (ADS)
Bejan, D.
20170201
The effects of exciton and electric field on the nonlinear optical properties, such as refraction index change, optical absorption coefficient and optical rectification of semiparabolic onedimensional quantum dot, were theoretically investigated. The energy eigenvalues and eigenfunctions are calculated numerically within the effective mass approximation for a typical GaAs/ Al0.3Ga0.7 As quantum dot, for the cases where there is an exciton or a single electron/hole in the structure. Optical properties are obtained using the compact density matrix approach and steady state solutions. Our results show that: i) if the increasing electric field is oriented along the growth direction, the refractive index change structure and the resonance peaks of the absorption coefficient and optical rectification present a blue shift and are weakened for exciton and electron systems but have a red shift and are strengthened for the hole system; ii) when the field, oriented against the growth direction, augments, the above optical parameters present a red shift and are increased for exciton and electron systems but have a blue shift and are lowered for the hole system; iii) the exciton presence in the structure enhances the amplitude of the resonant peaks of all optical parameters even at zero electric field.

Quantum paradoxes, entanglement and their explanation on the basis of quantization of fields
NASA Astrophysics Data System (ADS)
Melkikh, A. V.
20170101
Quantum entanglement is discussed as a consequence of the quantization of fields. The inclusion of quantum fields selfconsistently explains some quantum paradoxes (EPR and Hardy’s paradox). The definition of entanglement was introduced, which depends on the maximum energy of the interaction of particles. The destruction of entanglement is caused by the creation and annihilation of particles. On this basis, an algorithm for quantum particle evolution was formulated.

Quantum fields near phantomenergy ''sudden'' singularities
SciTech Connect
Calderon, Hector H.
20080815
This paper is committed to calculations near a type of future singularity driven by phantom energy. At the singularities considered, the scale factor remains finite but its derivative diverges. The general behavior of barotropic phantom energy producing this singularity is calculated under the assumption that near the singularity such fluid is the dominant contributor. We use the semiclassical formula for renormalized stress tensors of conformally invariant fields in conformally flat spacetimes and analyze the softening/enhancing of the singularity due to quantum vacuum contributions. This dynamical analysis is then compared to results from thermodynamical considerations. In both cases, the vacuum states of quantized scalar and spinor fields strengthen the accelerating expansion near the singularity whereas the vacuum states of vector fields weaken it.

Quantum processes in short and intensive electromagnetic fields
NASA Astrophysics Data System (ADS)
Titov, A. I.; Kämpfer, Burkhard; Hosaka, Atsushi; Takabe, Hideaki
20160501
This work provides an overview of our recent results in studying two most important and widely discussed quantum processes: electronpositron pairs production off a probe photon propagating through a polarized shortpulsed electromagnetic (e.g. laser) wave field or generalized BreitWheeler process, and a single a photon emission off an electron interacting with the laser pules, socalled nonlinear Compton scattering. We show that the probabilities of particle production in both processes are determined by interplay of two dynamical effects, where the first one is related to the shape and duration of the pulse and the second one is nonlinear dynamics of the interaction of charged fermions with a strong electromagnetic field. We elaborate suitable expressions for the production probabilities and cross sections, convenient for studying evolution of the plasma in presence of strong electromagnetic fields.

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.

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.

Dynamiclocalfield approximation for the quantum solids
NASA Technical Reports Server (NTRS)
Etters, R. D.; Danilowicz, R. L.
19740101
A localmolecularfield description for the groundstate properties of the quantum solids is presented. The dynamical behavior of atoms contributing to the local field, which acts on an arbitrary pair of test particles, is incorporated by decoupling the pair correlations between these field atoms. The energy, pressure, compressibility, singleparticledistribution function, and the rms atomic deviations about the equilibrium lattice sites are calculated for H2, He3, and He4 over the volume range from 5 to 24.5 cu cm/mole. The results are in close agreement with existing Monte Carlo calculations wherever comparisons are possible. At very high pressure, the results agree with simplified descriptions which depend on negligible overlap of the system wave function between neighboring lattice sites.

Theoretical framework for thin film superfluid optomechanics: towards the quantum regime
NASA Astrophysics Data System (ADS)
Baker, Christopher G.; Harris, Glen I.; McAuslan, David L.; Sachkou, Yauhen; He, Xin; Bowen, Warwick P.
20161201
Excitations in superfluid helium represent attractive mechanical degrees of freedom for cavity optomechanics schemes. Here we numerically and analytically investigate the properties of optomechanical resonators formed by thin films of superfluid 4He covering micrometerscale whispering gallery mode cavities. We predict that through proper optimization of the interaction between film and optical field, large optomechanical coupling rates {g}0> 2π × 100 {kHz} and single photon cooperativities {C}0> 10 are achievable. Our analytical model reveals the unconventional behaviour of these thin films, such as thicker and heavier films exhibiting smaller effective mass and larger zero point motion. The optomechanical system outlined here provides access to unusual regimes such as {g}0> {{{Ω }}}M and opens the prospect of laser cooling a liquid into its quantum ground state.

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.

Pseudopotentialbased electron quantum transport: Theoretical formulation and application to nanometerscale silicon nanowire transistors
SciTech Connect
Fang, Jingtian Vandenberghe, William G.; Fu, Bo; Fischetti, Massimo V.
20160121
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.

LETTER TO THE EDITOR: Quantum field theory and phylogenetic branching
NASA Astrophysics Data System (ADS)
Jarvis, P. D.; Bashford, J. D.
20011201
A calculational framework is proposed for phylogenetics, using nonlocal quantum field theories in hypercubic geometry. Quadratic terms in the Hamiltonian give the underlying Markov dynamics, while higher degree terms represent branching events. The spatial dimension L is the number of leaves of the evolutionary tree under consideration. Momentum conservation modulo ←1 scattering corresponds to tree edge labelling using binary Lvectors. The bilocal quadratic term allows for momentumdependent rate constants  only the tree or trees compatible with selected nonzero edge rates contribute to the branching probability distribution. Applications to models of evolutionary branching processes are discussed.

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.

Quarkgluon plasma and topological quantum field theory
NASA Astrophysics Data System (ADS)
Luo, M. J.
20170301
Based on an analogy with topologically ordered new state of matter in condensed matter systems, we propose a low energy effective field theory for a parity conserving liquidlike quarkgluon plasma (QGP) around critical temperature in quantum chromodynamics (QCD) system. It shows that below a QCD gap which is expected several times of the critical temperature, the QGP behaves like topological fluid. Many exotic phenomena of QGP near the critical temperature discovered at Relativistic Heavy Ion Collision (RHIC) are more readily understood by the suggestion that QGP is a topologically ordered state.

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

Quantum field theory results for neutrino oscillations and new physics
SciTech Connect
Delepine, D.; Gonzalez Macias, Vannia; Khalil, Shaaban; Lopez Castro, G.
20090501
The CP asymmetry in neutrino oscillations, assuming new physics at production and/or detection processes, is analyzed. We compute this CP asymmetry using the standard quantum field theory within a general new physics scenario that may generate new sources of CP and flavor violation. Wellknown results for the CP asymmetry are reproduced in the case of VA operators, and additional contributions from new physics operators are derived. We apply this formalism to SUSY extensions of the standard model where the contributions from new operators could produce a CP asymmetry observable in the next generation of neutrino experiments.

Delocalization and quantum chaos in atomfield systems.
PubMed
BastarracheaMagnani, M A; LópezdelCarpio, B; ChávezCarlos, J; LermaHernández, S; Hirsch, J G
20160201
Employing efficient diagonalization techniques, we perform a detailed quantitative study of the regular and chaotic regions in phase space in the simplest nonintegrable atomfield system, the Dicke model. A close correlation between the classical Lyapunov exponents and the quantum Participation Ratio of coherent states on the eigenenergy basis is exhibited for different points in the phase space. It is also shown that the Participation Ratio scales linearly with the number of atoms in chaotic regions and with its square root in the regular ones.

tRNA structure from a graph and quantum theoretical perspective.
PubMed
Galindo, Johan F; Bermúdez, Clara I; Daza, Edgar E
20060621
One of the objectives of theoretical biochemistry is to find a suitable representation of molecules allowing us to encode what we know about their structures, interactions and reactivity. Particularly, tRNA structure is involved in some processes like aminoacylation and genetic code translation, and for this reason these molecules represent a biochemical object of the utmost importance requiring characterization. We propose here two fundamental aspects for characterizing and modeling them. The first takes into consideration the connectivity patterns, i.e. the set of linkages between atoms or molecular fragments (a key tool for this purpose is the use of graph theory), and the second one requires the knowledge of some properties related to the interactions taking place within the molecule, at least in an approximate way, and perhaps of its reactivity in certain means. We used quantum mechanics to achieve this goal; specifically, we have used partial charges as a manifestation of the reply to structural changes. These charges were appropriately modified to be used as weighted factors for elements constituting the molecular graph. This new graphtRNA context allow us to detect some structurefunction relationships.

Quantum Interference, Geometricphase Effects, and Semiclassical Transport in Quantum Hall Systems at Low Magnetic Fields
NASA Astrophysics Data System (ADS)
Huang, ChunFeng; Tsai, I.H.
It is wellestablished how the quantum interference induces strong localization leading to quantum Hall effect at high enough magnetic fields. Decreasing the magnetic fields, however, the localization strength can be reduced and the semiclassical magnetooscillations following Shubnikovde Haas formula appear in most quantum Hall systems. To understand the transport properties as the localization strength becomes weak, our team has investigated the magnetoresistance in some quantum Hall systems at low magnetic fields. Under the semiclassical transport, the crossing points in Hall plateaus showed Landauband quantization and microwaveinduced heating demonstrated the bandedge equivalence important to Landaulevel addition transformation. We note that such equivalence is consistent with the edge universality based on the random matrices of Wigner type, and the Landauband quantization can be explained by considering geometric phase effects. From our study, some quantum Hall features can survive as the semiclassical transport reveals the insufficient localization.

Field Effect Optoelectronic Modulation of QuantumConfined Carriers in Black Phosphorus.
PubMed
Whitney, William S; Sherrott, Michelle C; Jariwala, Deep; Lin, WeiHsiang; Bechtel, Hans A; Rossman, George R; Atwater, Harry A
20170111
We report measurements of the infrared optical response of thin black phosphorus under fieldeffect modulation. We interpret the observed spectral changes as a combination of an ambipolar BursteinMoss (BM) shift of the absorption edge due to bandfilling under gate control, and a quantum confined FranzKeldysh (QCFK) effect, phenomena that have been proposed theoretically to occur for black phosphorus under an applied electric field. Distinct optical responses are observed depending on the flake thickness and starting carrier concentration. Transmission extinction modulation amplitudes of more than two percent are observed, suggesting the potential for use of black phosphorus as an active material in midinfrared optoelectronic modulator applications.

Field Effect Optoelectronic Modulation of QuantumConfined Carriers in Black Phosphorus
NASA Astrophysics Data System (ADS)
Whitney, William S.; Sherrott, Michelle C.; Jariwala, Deep; Lin, WeiHsiang; Bechtel, Hans A.; Rossman, George R.; Atwater, Harry A.
20170101
We report measurements of the infrared optical response of thin black phosphorus under fieldeffect modulation. We interpret the observed spectral changes as a combination of an ambipolar BursteinMoss (BM) shift of the absorption edge due to bandfilling under gate control, and a quantum confined FranzKeldysh (QCFK) effect, phenomena which have been proposed theoretically to occur for black phosphorus under an applied electric field. Distinct optical responses are observed depending on the flake thickness and starting carrier concentration. Transmission extinction modulation amplitudes of more than two percent are observed, suggesting the potential for use of black phosphorus as an active material in midinfrared optoelectronic modulator applications.

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.

Symmetries in ThreeDimensional Superconformal Quantum Field Theories
NASA Astrophysics Data System (ADS)
Bashkirov, Denis
Many examples of gaugegravity duality and quantum equivalences of differentlooking threedimensional Quantum Field Theories indicate the existence of continuous symmetries whose currents are not built from elementary, or perturbative, fields used to write down the Lagrangian. These symmetries are called hidden or nonperturbative. We describe a method for studying continuous symmetries in a large class of threedimensional supersymmetric gauge theories which, in particular, enables one to explore nonperturbative global symmetries and supersymmetries. As an application of the method, we prove conjectured supersymmetry enhancement in strongly coupled ABJM theory from N = 6 to N = 8 and find additional nonperturbative evidence for its duality to the N = 8 U(N) SYM theory for the minimal value of the ChernSimons coupling. Hidden supersymmetry is also shown to occur in N = 4 d = 3 SQCD with one fundamental and one adjoint hypermultiplets. An infinite family of N = 6 d = 3 ABJ theories is proved to have hidden N = 8 superconformal symmetry and hidden parity on the quantum level. We test several conjectural dualities between ABJ theories and theories proposed by Bagger and Lambert, and Gustavsson by comparing superconformal indices of these theories. Comparison of superconformal indices is also used to test dualities between N = 2 d = 3 theories proposed by Aharony, the analysis of whose chiral rings teaches some general lessons about nonperturbative chiral operators of strongly coupled 3d supersymmetric gauge theories. As another application of our method we consider examples of hidden global symmetries in a class of quiver threedimensional N = 4 superconformal gauge theories. Finally, we point out to the relations between some basic propeties of superconformal N ≥ 6 theories and their symmetries. The results presented in this thesis were obtained in a series of papers [1, 2, 3, 4, 5].

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.

Holographic Duals for FiveDimensional Superconformal Quantum Field Theories.
PubMed
D'Hoker, Eric; Gutperle, Michael; Uhlemann, Christoph F
20170310
We construct global solutions to type IIB supergravity with 16 residual supersymmetries whose spacetime is AdS_{6}×S^{2} warped over a Riemann surface. Families of solutions are labeled by an arbitrary number L≥3 of asymptotic regions, in each of which the supergravity fields match those of a (p,q) fivebrane, and may therefore be viewed as nearhorizon limits of fully localized intersections of fivebranes in type IIB string theory. These solutions provide compelling candidates for holographic duals to a large class of fivedimensional superconformal quantum field theories which arise as nontrivial UV fixed points of perturbatively nonrenormalizable YangMills theories, thereby making them more directly accessible to quantitative analysis.

Entertainment Computing, Social Transformation and the Quantum Field
NASA Astrophysics Data System (ADS)
Rauterberg, Matthias
The abstract should summaritinment computing is on its way getting an established academic discipline. The scope of entertainment computing is quite broad (see the scope of the international journal Entertainment Computing). One unifying idea in this diverse community of entertainment researchers and developers might be a normative position to enhance human living through social transformation. One possible option in this direction is a shared ‘conscious’ field. Several ideas about a new kind of field based on quantum effects are presented and discussed. Assuming that social transformation is based on a shared collective unconscious I propose designing entertainment technology for a new kind of user experience that can transform in a positive manner the individual unconscious and therefore the collective unconscious as well. Our ALICE project can be seen as a first attempt in this direction.

Holographic Duals for FiveDimensional Superconformal Quantum Field Theories
NASA Astrophysics Data System (ADS)
D'Hoker, Eric; Gutperle, Michael; Uhlemann, Christoph F.
20170301
We construct global solutions to type IIB supergravity with 16 residual supersymmetries whose spacetime is AdS6×S2 warped over a Riemann surface. Families of solutions are labeled by an arbitrary number L ≥3 of asymptotic regions, in each of which the supergravity fields match those of a (p ,q ) fivebrane, and may therefore be viewed as nearhorizon limits of fully localized intersections of fivebranes in type IIB string theory. These solutions provide compelling candidates for holographic duals to a large class of fivedimensional superconformal quantum field theories which arise as nontrivial UV fixed points of perturbatively nonrenormalizable YangMills theories, thereby making them more directly accessible to quantitative analysis.

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.

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

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.

Preheating in an asymptotically safe quantum field theory
NASA Astrophysics Data System (ADS)
Svendsen, Ole; Moghaddam, Hossein Bazrafshan; Brandenberger, Robert
20161001
We consider reheating in a class of asymptotically safe quantum field theories recently studied in [D. F. Litim and F. Sannino, Asymptotic safety guaranteed, J. High Energy Phys. 12 (2014) 178; D. F. Litim, M. Mojaza, and F. Sannino, Vacuum stability of asymptotically safe gaugeYukawa theories, J. High Energy Phys. 01 (2016) 081]. These theories allow for an inflationary phase in the very early universe. Inflation ends with a period of reheating. Since the models contain many scalar fields which are intrinsically coupled to the inflaton there is the possibility of parametric resonance instability in the production of these fields, and the danger that the induced curvature fluctuations will become too large. Here we show that the parametric instability indeed arises, and that hence the energy transfer from the inflaton condensate to fluctuating fields is rapid. Demanding that the curvature fluctuations induced by the parametrically amplified entropy modes do not exceed the upper observational bounds puts a lower bound on the number of fields which the model followed in [D. F. Litim and F. Sannino, Asymptotic safety guaranteed, J. High Energy Phys. 12 (2014) 178; D. F. Litim, M. Mojaza, and F. Sannino, Vacuum stability of asymptotically safe gaugeYukawa theories, J. High Energy Phys. 01 (2016) 081] must contain. This bound also depends on the total number of e foldings of the inflationary phase.

PREFACE: Quantum Field Theory Under the Influence of External Conditions (QFEXT07)
NASA Astrophysics Data System (ADS)
Bordag, M.; Mostepanenko, V. M.
20080401
This special issue contains papers reflecting talks presented at the 8th Workshop on Quantum Field Theory Under the Influence of External Conditions (QFEXT07), held on 17 21 September 2007, at Leipzig University. This workshop gathered 108 physicists and mathematicians working on problems which are focused on the following topics: •Casimir and van der Waals forces—progress in theory and new experiments, applications at micro and nanoscale •Casimir effect—exact results, approximate methods and mathematical problems •Vacuum quantum effects in classical background fields—renormalization issues, singular backgrounds, applications to particle and high energy physics •Vacuum energy and gravity, vacuum energy in supersymmetric and noncommutative theories. This workshop is part of a series started in 1989 and 1992 in Leipzig by Dieter Robaschik, and continued in 1995, 1998 and 2001 in Leipzig by Michael Bordag. In 2003 this Workshop was organized by Kimball A Milton in Oklahoma, in 2005 by Emilio Elizalde in Barcelona and in 2007 it returned to Leipzig. The field of physics after which this series of workshops is named is remarkably broad. It stretches from experimental work on the measurement of dispersion forces between macroscopic bodies to quantum corrections in the presence of classical background fields. The underlying physical idea is that even in its ground state (vacuum) a quantum system responds to changes in its environment. The universality of this idea makes the field of its application so very broad. The most prominent manifestation of vacuum energy is the Casimir effect. This is, in its original formulation, the attraction between conducting planes due to the vacuum fluctuations of the electromagnetic field. In a sense, this is the longrange tail of the more general dispersion forces acting between macroscopic bodies. With the progress in nanotechnology, dispersion forces become of direct practical significance. On a more theoretical side

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.

Exact integrability in quantum field theory and statistical systems
NASA Astrophysics Data System (ADS)
Thacker, H. B.
19810401
The properties of exactly integrable twodimensional quantum systems are reviewed and discussed. The nature of exact integrability as a physical phenomenon and various aspects of the mathematical formalism are explored by discussing several examples, including detailed treatments of the nonlinear Schrödinger (deltafunction gas) model, the massive Thirring model, and the sixvertex (ice) model. The diagonalization of a Hamiltonian by Bethe's Ansatz is illustrated for the nonlinear Schrödínger model, and the integral equation method of Lieb for obtaining the spectrum of the manybody system from periodic boundary conditions is reviewed. Similar methods are applied to the massive Thirring model, where the fermionantifermion and boundstate spectrum are obtained explicitly by the integral equation method. After a brief review of the classical inverse scattering method, the quantum inverse method for the nonlinear Schrödinger model is introduced and shown to be an algebraization of the Bethe Ansatz technique. In the quantum inverse method, an auxiliary linear problem is used to define nonlocal operators which are functionals of the original local field on a fixedtime string of arbitrary length. The particular operators for which the string is infinitely long (free boundary conditions) or forms a closed loop around a cylinder (periodic boundary conditions) correspond to the quantized scattering data and have a special significance. One of them creates the Bethe eigenstates, while the other is the generating function for an infinite number of conservation laws. The analogous operators on a lattice are constructed for the symmetric sixvertex model, where the object which corresponds to a solution of the auxiliary linear problem is a string of vertices contracted over horizontal links (arrows). The relationship between the quantum inverse method and the transfer matrix formalism is exhibited. The inverse Gel'fandLevitan transform which expresses the local field

Prediction of lowfield nuclear singlet lifetimes with molecular dynamics and quantumchemical property surface.
PubMed
Håkansson, Pär
20170125
Molecular dynamics and quantum chemistry methods are implemented to quantify nuclear spin1/2 pair singletstate relaxation rates for three molecular systems at low magnetic field and room temperature. Computational methodology is developed for weak interactions, particularly important for singlet states at low field. These include spinrotation and spininternalmotion effects, which describe the coupling of the spincarrying nuclei to fluctuating local magnetic fields induced by the overall and internal molecular fluctuations, respectively. A highdimensional tensor property surface using Kriging interpolation is developed to circumvent costly quantumchemical calculations. Together with the intramolecular dipolar relaxation, all the simulated relaxation mechanisms are accounted for with a common theoretical framework. Comparison with experiment indicates that quantitative accuracy is obtained, sufficient to enable guidance in the molecular design of molecules with longlived singlet order.

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.

A Comparison of Two ToposTheoretic Approaches to Quantum Theory
NASA Astrophysics Data System (ADS)
Wolters, Sander A. M.
20130101
The aim of this paper is to compare the two topostheoretic approaches to quantum mechanics that may be found in the literature to date. The first approach, which we will call the contravariant approach, was originally proposed by Isham and Butterfield, and was later extended by Döring and Isham. The second approach, which we will call the covariant approach, was developed by Heunen, Landsman and Spitters. Motivated by coarsegraining and the KochenSpecker theorem, the contravariant approach uses the topos of presheaves on a specific context category, defined as the poset of commutative von Neumann subalgebras of some given von Neumann algebra. In particular, the approach uses the spectral presheaf. The intuitionistic logic of this approach is given by the (complete) Heyting algebra of closed open subobjects of the spectral presheaf. We show that this Heyting algebra is, in a natural way, a locale in the ambient topos, and compare this locale with the internal Gelfand spectrum of the covariant approach. In the covariant approach, a noncommutative C*algebra (in the topos Set) defines a commutative C*algebra internal to the topos of covariant functors from the context category to the category of sets. We give an explicit description of the internal Gelfand spectrum of this commutative C*algebra, from which it follows that the external spectrum is spatial. Using the daseinisation of selfadjoint operators from the contravariant approach, we give a new definition of the daseinisation arrow in the covariant approach and compare it with the original version. States and stateproposition pairing in both approaches are compared. We also investigate the physical interpretation of the covariant approach.

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.

ElectricFieldInduced Energy Tuning of OnDemand EntangledPhoton Emission from SelfAssembled Quantum Dots.
PubMed
Zhang, Jiaxiang; Zallo, Eugenio; Höfer, Bianca; Chen, Yan; Keil, Robert; Zopf, Michael; Böttner, Stefan; Ding, Fei; Schmidt, Oliver G
20170111
We explore a method to achieve electrical control over the energy of ondemand entangledphoton emission from selfassembled quantum dots (QDs). The device used in our work consists of an electrically tunable diodelike membrane integrated onto a piezoactuator, which is capable of exerting a uniaxial stress on QDs. We theoretically reveal that, through application of the quantumconfined Stark effect to QDs by a vertical electric field, the critical uniaxial stress used to eliminate the fine structure splitting of QDs can be linearly tuned. This feature allows experimental realization of a triggered source of energytunable entangledphoton emission. Our demonstration represents an important step toward realization of a solidstate quantum repeater using indistinguishable entangled photons in Bell state measurements.

Intrinsic Gap of the 5/2 Fractional Quantum Hall State and Tilted Field Experiments
NASA Astrophysics Data System (ADS)
Gervais, Guillaume
20090301
Nearly twenty years since the first discovery of a an even denominator fractional quantum Hall state (FQHE), a complete understanding of the the 5/2state continues to be among the most important questions in semiconductor physics. It is widely believed that this unique state of matter is theoretically best described by the MooreRead Pfaffian wavefunction,resulting from a BCSlike pairing of composite fermions [1]. In recent years this wavefunction has received special interest owing to its nonabelian quantum statistics which underlies a new paradigm for topological (fault tolerant) quantum computation. However, in spite of several important theoretical advancements, an unequivocal experimental verification of the MooreRead description is still missing. We present results from a study of the 5/2 state in a sample with the lowest electron density reported to date (by nearly a factor of two) [2]. This allows for the observation of the 5/2 in a regime where the cyclotron energy is smaller than the Coulomb interaction energy. We discuss our results in the context of previous work, and we examine the role of disorder on the activation energy gap. Measurements of the energy gap for the 5/2 and the 7/3 FQH states in a tilted field geometry also reveals an unexpected and contrasting dichotomy between the two. Whereas the 7/3 FQH gap is observed to be enhanced by an applied parallel magnetic field, the 5/2 gap is strongly suppressed, in spite of the two gaps being energetically comparable at zero parallel fields in our sample. This calls into question the prevailing theoretical belief that they should behave similarly if both are spinpolarized, and raises doubt as to whether or not the 5/2 state is indeed described by a spinpolarized Pfaffian MooreRead wavefunction. [4pt] [1] G. Moore and N. Read, Nucl. Phys. B 360, 362 (1991).[0pt] [2] C.R. Dean, B.A. Piot, P. Hayden, S. Das Sarma, G. Gervais, L.N. Pfeiffer, K.W. West, Phys. Rev. Lett. 100, 146803 (2008).[0pt] [3] C

Renormalization and nonlinear symmetries in quantum field theory
NASA Astrophysics Data System (ADS)
Velenich, Andrea
Most of the phenomena we experience, from the microscopic world to the universe at its largest scales, are out of equilibrium and their comprehensive formalization is one of the open problems in theoretical physics. Fluids of interacting particles cooled down or compressed quickly enough to become amorphous solids are an example of rich outofequilibrium systems with very slow relaxation dynamics. Even though the equilibrium phases are ordered, these systems remain trapped in glassy metastable states, with disordered microscopic structures. As a realistic model of this phenomenology, in the first part of this work I focused on a field theory of particles obeying a Brownian dynamics. The fieldtheoretic action displays a timereversal symmetry leading to FluctuationDissipation relations. For noninteracting particles I solved the field theory exactly, providing the explicit form of all the correlation functions, with their space and time dependence. As a nonperturbative result, the distribution of the density field has been proven to be Poissonian and not Gaussian. For interacting particles the field theory presents two major challenges: its apparent nonrenormalizability and a nonlinear implementation of the timereversal symmetry. Nonlinear field redefinitions can be used to make the symmetry linear and might even lead to the solution of the interacting equations of motion. However they also alter the renormalizability properties of a field theory. These challenges inspired the second part of the work, where a more abstract approach was taken. Using algebraic methods I investigated the effect of nonlinear field redefinitions both on symmetry and on renormalization by focusing on simple scalar field theories as toy models. In the formal setting of the Hopf algebra of Feynman diagrams, symmetries take the form of Hopf ideals and enforce relations among scattering amplitudes; such relations can drastically reduce the number of independent couplings in a field

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.

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.

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.

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.
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.

Nonlinear susceptibility of a quantum spin glass under uniform transverse and random longitudinal magnetic fields
NASA Astrophysics Data System (ADS)
Magalhaes, S. G.; Morais, C. V.; Zimmer, F. M.; Lazo, M. J.; Nobre, F. D.
20170201
The interplay between quantum fluctuations and disorder is investigated in a quantum spinglass model, in the presence of a uniform transverse field Γ , as well as of a longitudinal random field hi, which follows a Gaussian distribution characterized by a width proportional to Δ . The interactions are infiniteranged, and the model is studied through the replica formalism, within a onestep replicasymmetrybreaking procedure; in addition, the dependence of the AlmeidaThouless eigenvalue λAT (replicon) on the applied fields is analyzed. This study is motivated by experimental investigations on the LiHoxY1 xF4 compound, where the application of a transverse magnetic field yields rather intriguing effects, particularly related to the behavior of the nonlinear magnetic susceptibility χ3, which have led to a considerable experimental and theoretical debate. We have analyzed two physically distinct situations, namely, Δ and Γ considered as independent, as well as these two quantities related, as proposed recently by some authors. In both cases, a spinglass phase transition is found at a temperature Tf, with such phase being characterized by a nontrivial ergodicity breaking; moreover, Tf decreases by increasing Γ towards a quantum critical point at zero temperature. The situation where Δ and Γ are related [Δ ≡Δ (Γ )] appears to reproduce better the experimental observations on the LiHoxY1 xF4 compound, with the theoretical results coinciding qualitatively with measurements of the nonlinear susceptibility χ3. In this later case, by increasing Γ gradually, χ3 becomes progressively rounded, presenting a maximum at a temperature T* (T*>Tf ), with both the amplitude of the maximum and the value of T* decreasing gradually. Moreover, we also show that the random field is the main responsible for the smearing of the nonlinear susceptibility, acting significantly inside the paramagnetic phase, leading to two regimes delimited by the temperature T*, one for Tf

Multifunctional quantum node based on double quantum dot in laser and cavity fields
NASA Astrophysics Data System (ADS)
Tsukanov, Alexander V.
20161201
The concept of multifunctional device (a quantum node) composed of a semiconductor singleelectron fourlevel doublequantum dot coupled to an optical microcavity resonator is developed. The terahertz laser field and voltage biases provide an external control. The structure enables flexible driving via appropriate variations of field amplitudes and switching between resonant and offresonant modes. As shown this hybrid electronphoton system can be used as the charge qubit with flyingtostationary qubit conversion or the singlephoton transistor and several others. Each of listed devices works in the specific regime of system evolution. For example, the qubit is robust when the optical resonator and laser Rabi frequencies dominate the dissipation rates  the socalled strong coupling or coherent regime. From another hand, in order to attain the steadystate one has to work in the socalled weak coupling or incoherent regime when the dissipation rates are comparable to or greater than the Rabi frequencies. Further, the singlephoton driving is required for spectroscopic applications of this system. We numerically investigate the population dynamics to reveal the parameter choice corresponding to each device. The model is based on Lindblad formalism where all incoherent processes are considered as the markovian ones. The time dependencies of populations and spectrograms for different pairs of parameters are obtained. The specific features concerned with working characteristics of the quantum node in different modes are discussed.

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.

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.

NearField Heat Flow Between Two Quantum Oscillators
NASA Astrophysics Data System (ADS)
Barton, Gabriel
20161201
We calculate the exact steadystate heat flow P between two Ohmically damped quantum oscillators 1 and 2, with natural frequency ω 0, interacting through their nearfield dipoledipole potential V. To keep them at nominally constant temperatures T1, T2 respectively, they have to be coupled to thermostats functioning in a way one must specify explicitly unless one assumes local thermal equilibrium, which would, inadequately as a rule, restrict the calculation to leading order in V. Here the thermostats are modelled as stretched strings, one end attached to the oscillator, and the other to an infinitely distant device ensuring that the string carries thermal noise appropriate to T1 or T2 in addition to whatever motion is enforced by the oscillator. Aiming at insight rather than numerics, we focus mainly on simple approximations by powers of T1 and T2 for weak damping in the essentially quantum lowtemperature regime where kBT_{1,2}≪ ω 0. From P it is easy to find the heat flux between two insulating Drudemodelled halfspaces.

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.

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.

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.

Reality, measurement and locality in Quantum Field Theory
NASA Astrophysics Data System (ADS)
Tommasini, Daniele
20020701
It is currently believed that the local causality of Quantum Field Theory (QFT) is destroyed by the measurement process. This belief is also based on the EinsteinPodolskyRosen (EPR) paradox and on the socalled Bell's theorem, that are thought to prove the existence of a mysterious, instantaneous action between distant measurements. However, I have shown recently that the EPR argument is removed, in an interpretationindependent way, by taking into account the fact that the Standard Model of Particle Physics prevents the production of entangled states with a definite number of particles. This result is used here to argue in favor of a statistical interpretation of QFT and to show that it allows for a full reconciliation with locality and causality. Within such an interpretation, as Ballentine and Jarret pointed out long ago, Bell's theorem does not demonstrate any nonlocality.

Matterenhanced transition probabilities in quantum field theory
SciTech Connect
Ishikawa, Kenzo Tobita, Yutaka
20140515
The relativistic quantum field theory is the unique theory that combines the relativity and quantum theory and is invariant under the Poincaré transformation. The ground state, vacuum, is singlet and one particle states are transformed as elements of irreducible representation of the group. The covariant one particles are momentum eigenstates expressed by plane waves and extended in space. Although the Smatrix defined with initial and final states of these states hold the symmetries and are applied to isolated states, outgoing states for the amplitude of the event that they are detected at a finitetime interval T in experiments are expressed by microscopic states that they interact with, and are surrounded by matters in detectors and are not plane waves. These matterinduced effects modify the probabilities observed in realistic situations. The transition amplitudes and probabilities of the events are studied with the Smatrix, S[T], that satisfies the boundary condition at T. Using S[T], the finitesize corrections of the form of 1/T are found. The corrections to Fermi’s golden rule become larger than the original values in some situations for light particles. They break Lorentz invariance even in high energy region of short de Broglie wave lengths.  Highlights: •Smatrix S[T] for the finitetime interval in relativistic field theory. •S[T] satisfies the boundary condition and gives correction of 1/T . •The large corrections for light particles breaks Lorentz invariance. •The corrections have implications to neutrino experiments.

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.

Scaling of conductance through quantum dots with magnetic field
NASA Astrophysics Data System (ADS)
Hamad, I. J.; Gazza, C.; Andrade, J. A.; Aligia, A. A.; Cornaglia, P. S.; RouraBas, P.
20151101
Using different techniques, and Fermiliquid relationships, we calculate the variation with the applied magnetic field (up to second order) of the zerotemperature equilibrium conductance through a quantum dot described by the impurity Anderson model. We focus on the strongcoupling limit U ≫Δ , where U is the Coulomb repulsion and Δ is half the resonantlevel width, and consider several values of the dot level energy Ed, ranging from the Kondo regime ɛFEd≫Δ to the intermediatevalence regime ɛFEd˜Δ , where ɛF is the Fermi energy. We have mainly used the densitymatrix renormalization group (DMRG) and the numerical renormalization group (NRG) combined with renormalized perturbation theory (RPT). Results for the dot occupancy and magnetic susceptibility from the DMRG and NRG +RPT are compared with the corresponding Bethe ansatz results for U →∞ , showing an excellent agreement once Ed is renormalized by a constant Haldane shift. For U <3 Δ a simple perturbative approach in U agrees very well with the other methods. The conductance decreases with the applied magnetic field for dot occupancies nd˜1 and increases for nd˜0.5 or nd˜1.5 regardless of the value of U . We also relate the energy scale for the magneticfield dependence of the conductance with the width of the lowenergy peak in the spectral density of the dot.

a Unified Formalism of Thermal Quantum Field Theory
NASA Astrophysics Data System (ADS)
Chu, H.; Umezawa, H.
We present a comprehensive review of the most fundamental and practical aspects of thermofield dynamics (TFD), including some of the most recent developments in the field. To make TFD fully consistent, some suitable changes in the structure of the thermal doublets and the Bogoliubov transformation matrices have been made. A close comparison between TFD and the SchwingerKeldysh closed time path formalism (SKF) is presented. We find that TFD and SKF are in many ways the same in form; in particular, the two approaches are identical in stationary situations. However, TFD and SKF are quite different in timedependent nonequilibrium situations. The main source of this difference is that the time evolution of the density matrix itself is ignored in SKF while in TFD it is replaced by a timedependent Bogoliubov transformation. In this sense TFD is a better candidate for timedependent quantum field theory. Even in equilibrium situations, TFD has some remarkable advantages over the Matsubara approach and SKF, the most notable being the Feynman diagram recipes, which we will present. We will show that the calculations of twopoint functions are simplified, instead of being complicated, by the matrix nature of the formalism. We will present some explicit calculations using TFD, including spacetime inhomogeneous situations and the vacuum polarization in equilibrium relativistic QED.

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.

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 updown 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 electronhole 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.

Derivation of anomalous hydrodynamics from quantum field theory
NASA Astrophysics Data System (ADS)
Hongo, Masaru; Hayata, Tomoya; Hidaka, Yoshimasa; Minami, Yuki; Noumi, Toshifumi
20140901
Hydrodynamics is a lowenergy effective theory which describes a longdistance and longtime behavior of manybody systems. It has been recently pointed out that triangle anomalies affect macroscopic transport properties and generate anomalyinduced transports. These transport phenomena have a common feature that they are dissipationless, or in other words, they don't cause the entropy production. One example is the chiral magnetic effect, which represents the existence of a dissipationless vector current along the magnetic field and is expected to occur in ultrarelativistic heavy ion collisions. In this study, we derive anomalous hydrodynamic equations from the point of view of quantum field theory. Assuming the local Gibbs distribution at initial time, we derive a thermodynamic potential for relativistic hydrodynamics. This action has a form in the curved spacetime whose metric is determined by the thermodynamic variables such as the temperature. We show that anomalyinduced transports manifest from this thermodynamic potential if systems do not have the parity symmetry, and, therefore, are dissipationless. We also discuss a relation between our work and other recent approaches that aim at deriving hydrodynamic equations for the parityviolating systems. Hydrodynamics is a lowenergy effective theory which describes a longdistance and longtime behavior of manybody systems. It has been recently pointed out that triangle anomalies affect macroscopic transport properties and generate anomalyinduced transports. These transport phenomena have a common feature that they are dissipationless, or in other words, they don't cause the entropy production. One example is the chiral magnetic effect, which represents the existence of a dissipationless vector current along the magnetic field and is expected to occur in ultrarelativistic heavy ion collisions. In this study, we derive anomalous hydrodynamic equations from the point of view of quantum field theory. Assuming

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.

Zerofield quantum critical point in CeCoIn5.
PubMed
Tokiwa, Y; Bauer, E D; Gegenwart, P
20130906
Quantum criticality in the normal and superconducting states of the heavyfermion metal CeCoIn5 is studied by measurements of the magnetic Grüneisen ratio ΓH and specific heat in different field orientations and temperatures down to 50 mK. A universal temperature over magnetic field scaling of ΓH in the normal state indicates a hidden quantum critical point at zero field. Within the superconducting state, the quasiparticle entropy at constant temperature increases upon reducing the field towards zero, providing additional evidence for zerofield quantum criticality.

A geometrical crossover in excited states of twoelectron quantum dots in a magnetic field
NASA Astrophysics Data System (ADS)
Nazmitdinov, R. G.; Simonović, N. S.; Plastino, A. R.; Chizhov, A. V.
20121101
We use the entanglement measure to study the evolution of quantum correlations in twoelectron axiallysymmetric parabolic quantum dots under a perpendicular magnetic field. We found that the entanglement indicates on the shape transition in the density distribution of two electrons in the lowest state with zero angular momentum projection at the specific value of the applied magnetic field.

Quantum Field Theory Tools:. a Mechanism of Mass Generation of Gauge Fields
NASA Astrophysics Data System (ADS)
FloresBaez, F. V.; GodinaNava, J. J.; OrdazHernandez, G.
We present a simple mechanism for mass generation of gauge fields for the YangMills theory, where two gauge SU(N)connections are introduced to incorporate the mass term. Variations of these two sets of gauge fields compensate each other under local gauge transformations with the local gauge transformations of the matter fields, preserving gauge invariance. In this way the mass term of gauge fields is introduced without violating the local gauge symmetry of the Lagrangian. Because the Lagrangian has strict local gauge symmetry, the model is a renormalizable quantum model. This model, in the appropriate limit, comes from a class of universal Lagrangians which define a new massive YangMills theories without Higgs bosons.

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 field theory in noninteger dimensions
SciTech Connect
Eyink, G.L.
19870101
In a 1973 paper entitled Quantum FieldTheory Models in Less Than 4 Dimensions, Kenneth G. Wilson studied fieldtheories for spacetime dimension d between 2 and 4. With unconventional renormalizations, these models were found to have nonGaussian ultraviolet renormalization group fixed points. Wilson's method was perturbative dimensional regularization: the Feynmangraph integrals were analytically continued to noninteger d. His work left open the question of the nonperturbative existence of the models. Since that landmark paper, Yuval Gefen, Amnon Aharony and Benoit B. Mandelbrot have shown that Ising spin models on fractal lattices have critical properties like those predicted for noninteger dimensions by the analytic continuation, or {epsilon}expansion method. This work shows that fractal lattices and continua provide also a nonperturbative definition of fieldtheories in noninteger dimensions. The fractal pointsets employed are the Sierpinski carpets and their higherdimensional generalizations. This class of pointsets has a tunable dimension which allows the approach to four from below. Furthermore, the carpets have discrete groups of scale or dilation invariances and infinite order of ramification. A class of scalar field models are defined on these sets which should reduce to the standard models when d {nearrow}4. The propagator for these models is given by a propertime or heatkernel representation. For this propagator, reflectionpositivity is established, a general scaling law is conjectured (and established in a special case), and the perturbative renormalizability shown to be governed by the spectral dimensionality. Scalar models with another choice of propagator, the hierarchical propagator, are studied by rigorous renormalizationgroup methods.

Controlling Quantumdot Light Absorption and Emission by a Surfaceplasmon Field
DTIC Science & Technology
20141103
Controlling quantumdot light absorption and emission by a surface plasmon field Danhong Huang,1∗ Michelle Easter,2 Godfrey Gumbs,3 A. A. Maradudin,4...as well as photon conversion by a surface plasmon  polariton near field is explored for a quantum dot located above a metal surface. In contrast to the...resulting from the interference between the surface plasmon field and the probe or selfemitted light field in such a stronglycoupled nonlinear system. Our

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.

Electrostatic Field Influence on Luminescence Features of Cadmium Sulphide Quantum Dots in Silica Matrix
NASA Astrophysics Data System (ADS)
Voznesenskiy, S. S.; Sergeev, A. A.; Postnova, I. V.; Shchipunov, Y. A.
The effect of electrostatic field on optical properties of silicate nanocomposite with cadmium sulfide quantum dots was investigated. It was found that the electrostatic field causes quantum dot orientation along the field force lines leading to changes in the polarized components of the luminescence spectrum. The influence of field force line direction on photoinduced absorption characteristics arised from λ = 405.9 nm laser radiation exposure to nanocomposite was shown.

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.

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.

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.

Theoretical analysis of the particle gradient distribution in centrifugal field during solidification
SciTech Connect
Liu, Q.; Jiao, Y.; Yang, Y.; Hu, Z.
19961201
A theoretical analysis is presented to obtain gradient distribution of particles in centrifugal field, by which the particle distribution in gradient composite can be predicted. Particle movement in liquid is described and gradient distribution of particles in composite is calculated in a centrifugal field during the solidification. The factors which affect the particle distribution and its gradient are discussed in detail. The theoretical analysis indicated that a composite zone and a blank zone exist in gradient composite, which can be controlled to the outside or inside of the tubular composite by the density difference of particle and liquid metal. The comparison of the SiC particle distribution in Al matrix composite produced by centrifugal casting between the theory model and the experiment denotes that the theoretical analysis is reasonable.

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.

Elementary framework for cold field emission: Incorporation of quantumconfinement effects
SciTech Connect
Patterson, A. A. Akinwande, A. I.
20131221
Although the FowlerNordheim (FN) equation serves as the foundation of cold field emission theory, it may not be suitable for predicting the emitted current density (ECD) from emitters with a quantumconfined electron supply. This work presents an analytical framework for treating cold field emission from metals that includes the effects of a quantumconfined electron supply. Within the framework, quantum confinement in emitters is classified into transverse and normal quantum confinement based on the orientation of the confinement relative to the emission direction. The framework is used to generate equations predicting the ECD from rectangular and cylindrical emitter geometries comprised of electron supplies of reduced dimensionality. Transverse quantum confinement of the electron supply leads to a reduction in the total ECD as transverse emitter dimensions decrease and normal quantum confinement results in an oscillatory ECD as a function of the normal quantum well width. Incorporating a geometrydependent field enhancement factor into the model reveals an optimal transverse well width for which quantum confinement of the electron supply and field enhancement equally affect the ECD and a maximum total ECD for the emitter geometry at a given applied field is obtained. As a result, the FN equation overpredicts the ECD from emitters with transverse dimensions under approximately 5 nm, and in those cases, geometryspecific ECD equations incorporating quantumconfinement effects should be employed instead.

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…

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.

Classical and quantum Big Brake cosmology for scalar field and tachyonic models
NASA Astrophysics Data System (ADS)
Kamenshchik, A. Yu.; Manti, S.
20130201
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.

Classical and quantum big brake cosmology for scalar field and tachyonic models
NASA Astrophysics Data System (ADS)
Kamenshchik, Alexander Y.; Manti, Serena
20120601
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 classicalquantum correspondence, because soft singularities are traversable in classical cosmology, while the strong big bang and big crunch singularities are not traversable.

Classical and Quantum Big Brake Cosmology for Scalar Field and Tachyonic Models
NASA Astrophysics Data System (ADS)
Kamenshchik, Alexander; Manti, Serena
20150101
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.

Influence of Temperature and Magnetic Field on the First Excited State of a Quantum Pseudodot
NASA Astrophysics Data System (ADS)
Cai, ChunYu; Zhao, CuiLan; Xiao, JingLin
20170201
Investigations on the properties of excited states of complex quantum systems can not only reveal the internal structure and properties of the system but also verify the accuracy of quantum theory. In the case of strong electronlongitudinal optical phonon coupling in a quantum pseudodot with an external magnetic field, the first excited state and transition frequency can be obtained by using the Pekar variational method and quantum statistics theory. Numerical calculations for CsI crystal show that (1) they are increasing functions of the magnetic field, and (2) they will first decrease and then increase as the temperature is increased from a low value.

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.

Quantum transport in carbon nanotube field effect transistors in high magnetic fields
NASA Astrophysics Data System (ADS)
Stephens, Jeffrey Dale
The dissertation is a study of data taken from carbon nanotube field effect transistors (CNTFET). The data presented was taken at two locations, University of Pennsylvania in Philadelphia, PA and at Lehigh University in Bethlehem, PA. The samples are exposed to very low temperature using dilution refrigerator techniques and placed in high magnetic fields using a superconducting magnet. One of the main focuses will be on the effect an external magnetic field can produce on the transport properties of a CNTFET. Particular attention will be paid to the Kondo effect and Coulomb blockade phenomena. Comparisons are drawn between the observed behavior of the samples studied and with published works on carbon nanotube electronics and traditional semiconductor quantum dots.

Entanglement detection in a coupled atomfield system via quantum Fisher information
NASA Astrophysics Data System (ADS)
Mirkhalaf, Safoura Sadat; Smerzi, Augusto
20170201
We consider a system of finite number of particles collectively interacting with a singlemode coherent field inside a cavity. Depending on the strength of the initial field compared to the number of atoms, we consider three regimes of weak, intermediate, and strongfield interaction. The dynamics of multiparticle entanglement detected by quantum Fisher information and spin squeezing are studied in each regime. It is seen that in the weakfield regime, spin squeezing and quantum Fisher information coincide. However, by increasing the initial field population toward the strongfield regime, quantum Fisher information is more effective in detecting entanglement compared to spin squeezing. In addition, in the twoatom system, we also study concurrence. In this case, the quantum Fisher information as a function of time is in good agreement with concurrence in predicting entanglement peaks.

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.

Clustering, randomness and regularity in cloud fields. I  Theoretical considerations. II  Cumulus cloud fields
NASA Technical Reports Server (NTRS)
Weger, R. C.; Lee, J.; Zhu, Tianri; Welch, R. M.
19920101
The current controversy existing in reference to the regularity vs. clustering in cloud fields is examined by means of analysis and simulation studies based upon nearestneighbor cumulative distribution statistics. It is shown that the Poisson representation of random point processes is superior to pseudorandomnumbergenerated models and that pseudorandomnumbergenerated models bias the observed nearestneighbor statistics towards regularity. Interpretation of this nearestneighbor statistics is discussed for many cases of superpositions of clustering, randomness, and regularity. A detailed analysis is carried out of cumulus cloud field spatial distributions based upon Landsat, AVHRR, and Skylab data, showing that, when both large and small clouds are included in the cloud field distributions, the cloud field always has a strong clustering signal.

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.

Constraints on RG flow for four dimensional quantum field theories
NASA Astrophysics Data System (ADS)
Jack, I.; Osborn, H.
20140601
The response of four dimensional quantum field theories to a Weyl rescaling of the metric in the presence of local couplings and which involve a, the coefficient of the Euler density in the energy momentum tensor trace on curved space, is reconsidered. Previous consistency conditions for the anomalous terms, which implicitly define a metric G on the space of couplings and give rise to gradient flow like equations for a, are derived taking into account the role of lower dimension operators. The results for infinitesimal Weyl rescaling are integrated to finite rescalings e2σ to a form which involves running couplings gσ and which interpolates between IR and UV fixed points. The results are also restricted to flat space where they give rise to broken conformal Ward identities. Expressions for the three loop Yukawa βfunctions for a general scalar/fermion theory are obtained and the three loop contribution to the metric G for this theory is also calculated. These results are used to check the gradient flow equations to higher order than previously. It is shown that these are only valid when β→B, a modified βfunction, and that the equations provide strong constraints on the detailed form of the three loop Yukawa βfunction. N=1 supersymmetric WessZumino theories are also considered as a special case. It is shown that the metric for the complex couplings in such theories may be restricted to a hermitian form.

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.

The ontology of quantum field theory: Structural realism vindicated?
PubMed
Glick, David
20161001
In this paper I elicit a prediction from structural realism and compare it, not to a historical case, but to a contemporary scientific theory. If structural realism is correct, then we should expect physics to develop theories that fail to provide an ontology of the sort sought by traditional realists. If structure alone is responsible for instrumental success, we should expect surplus ontology to be eliminated. Quantum field theory (QFT) provides the framework for some of the best confirmed theories in science, but debates over its ontology are vexed. Rather than taking a stand on these matters, the structural realist can embrace QFT as an example of just the kind of theory SR should lead us to expect. Yet, it is not clear that QFT meets the structuralist's positive expectation by providing a structure for the world. In particular, the problem of unitarily inequivalent representations threatens to undermine the possibility of QFT providing a unique structure for the world. In response to this problem, I suggest that the structuralist should endorse pluralism about structure.

Differential cohomology and locally covariant quantum field theory
NASA Astrophysics Data System (ADS)
Becker, Christian; Schenkel, Alexander; Szabo, Richard J.
We study differential cohomology on categories of globally hyperbolic Lorentzian manifolds. The Lorentzian metric allows us to define a natural transformation whose kernel generalizes Maxwell's equations and fits into a restriction of the fundamental exact sequences of differential cohomology. We consider smooth Pontryagin duals of differential cohomology groups, which are subgroups of the character groups. We prove that these groups fit into smooth duals of the fundamental exact sequences of differential cohomology and equip them with a natural presymplectic structure derived from a generalized Maxwell Lagrangian. The resulting presymplectic Abelian groups are quantized using the CCRfunctor, which yields a covariant functor from our categories of globally hyperbolic Lorentzian manifolds to the category of C∗algebras. We prove that this functor satisfies the causality and timeslice axioms of locally covariant quantum field theory, but that it violates the locality axiom. We show that this violation is precisely due to the fact that our functor has topological subfunctors describing the Pontryagin duals of certain singular cohomology groups. As a byproduct, we develop a FréchetLie group structure on differential cohomology groups.

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...

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.

Dynamic Charge Carrier Trapping in Quantum Dot Field Effect Transistors.
PubMed
Zhang, Yingjie; Chen, Qian; Alivisatos, A Paul; Salmeron, Miquel
20150708
Noncrystalline semiconductor materials often exhibit hysteresis in charge transport measurements whose mechanism is largely unknown. Here we study the dynamics of charge injection and transport in PbS quantum dot (QD) monolayers in a field effect transistor (FET). Using Kelvin probe force microscopy, we measured the temporal response of the QDs as the channel material in a FET following step function changes of gate bias. The measurements reveal an exponential decay of mobile carrier density with time constants of 35 s for holes and ∼10 s for electrons. An Ohmic behavior, with uniform carrier density, was observed along the channel during the injection and transport processes. These slow, uniform carrier trapping processes are reversible, with time constants that depend critically on the gas environment. We propose that the underlying mechanism is some reversible electrochemical process involving dissociation and diffusion of water and/or oxygen related species. These trapping processes are dynamically activated by the injected charges, in contrast with static electronic traps whose presence is independent of the charge state. Understanding and controlling these processes is important for improving the performance of electronic, optoelectronic, and memory devices based on disordered semiconductors.

Quantum Field Energy Sensor based on the Casimir Effect
NASA Astrophysics Data System (ADS)
Ludwig, Thorsten
The Casimir effect converts vacuum fluctuations into a measurable force. Some new energy technologies aim to utilize these vacuum fluctuations in commonly used forms of energy like electricity or mechanical motion. In order to study these energy technologies it is helpful to have sensors for the energy density of vacuum fluctuations. In today's scientific instrumentation and scanning microscope technologies there are several common methods to measure subnano Newton forces. While the commercial atomic force microscopes (AFM) mostly work with silicon cantilevers, there are a large number of reports on the use of quartz tuning forks to get highresolution force measurements or to create new force sensors. Both methods have certain advantages and disadvantages over the other. In this report the two methods are described and compared towards their usability for Casimir force measurements. Furthermore a design for a quantum field energy sensor based on the Casimir force measurement will be described. In addition some general considerations on extracting energy from vacuum fluctuations will be given.

Externalfield effect on quantum features of radiation emitted by a quantum well in a microcavity
SciTech Connect
Sete, Eyob A.; Das, Sumanta; Eleuch, H.
20110215
We consider a semiconductor quantum well in a microcavity driven by coherent light and coupled to a squeezed vacuum reservoir. By systematically solving the pertinent quantum Langevin equations in the strongcoupling and lowexcitation regimes, we study the effect of excitonphoton detuning, external coherent light, and the squeezed vacuum reservoir on vacuum Rabi splitting and on quantum statistical properties of the light emitted by the quantum well. We show that the excitonphoton detuning leads to a shift in polariton resonance frequencies and a decrease in fluorescence intensity. We also show that the fluorescent light exhibits quadrature squeezing, which predominately depends on the excitonphoton detuning and the degree of the squeezing of the input field.

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

Gateinduced carrier delocalization in quantum dot field effect transistors.
PubMed
Turk, Michael E; Choi, JiHyuk; Oh, Soong Ju; Fafarman, Aaron T; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R; Kikkawa, James M
20141008
We study gatecontrolled, lowtemperature resistance and magnetotransport in indiumdoped CdSe quantum dot field effect transistors. We show that using the gate to accumulate electrons in the quantum dot channel increases the "localization product" (localization length times dielectric constant) describing transport at the Fermi level, as expected for Fermi level changes near a mobility edge. Our measurements suggest that the localization length increases to significantly greater than the quantum dot diameter.

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.

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.

The Effect of Magnetic Field Inhomogeneity on the Transverse Relaxation of Quadrupolar Nuclei Measured by Multiple Quantum Filtered NMR
NASA Astrophysics Data System (ADS)
Eliav, U.; Kushnir, T.; Knubovets, T.; Itzchak, Y.; Navon, G.
19970901
The effects of magnetic fieldsB0andB1inhomogeneities on techniques which are commonly used for the measurements of triplequantumfiltered (TQF) NMR spectroscopy of23Na in biological tissues are analyzed. The results of measurements by pulse sequences with and without refocusing ofB0inhomogeneities are compared. It is shown that without refocusing the errors in the measurement of the transverse relaxation times by TQF NMR spectroscopy may be as large as 100%, and thus, refocusing of magnetic field inhomogeneity is mandatory. Theoretical calculations demonstrate that without refocusingB0inhomogeneities the spectral width and phase depend on the interpulse time intervals, thus, leading to errors in the measured relaxation times. It is shown that pulse sequences that were used for the refocusing of the magnetic field (B0) inhomogeneity also reduce the sensitivity of the experimental results to radiofrequency (B1) magnetic field inhomogeneity.

Theoretical study of dynamic electronspinpolarization via the doubletquartet quantummixed state and timeresolved ESR spectra of the quartet highspin state.
PubMed
Teki, Yoshio; Matsumoto, Takafumi
20110407
The mechanism of the unique dynamic electron polarization of the quartet (S = 3/2) highspin state via a doubletquartet quantummixed state and detail theoretical calculations of the population transfer are reported. By the photoinduced electron transfer, the quantummixed chargeseparate state is generated in acceptordonorradical triad (ADR). This mechanism explains well the unique dynamic electron polarization of the quartet state of ADR. The generation of the selectively populated quantummixed state and its transfer to the strongly coupled pure quartet and doublet states have been treated both by a perturbation approach and by exact numerical calculations. The analytical solutions show that generation of the quantummixed states with the selective populations after decoherence and/or accompanying the (complete) dephasing during the chargerecombination are essential for the unique dynamic electron polarization. Thus, the elimination of the quantum coherence (loss of the quantum information) is the key process for the population transfer from the quantummixed state to the quartet state. The generation of highfield polarization on the strongly coupled quartet state by the chargerecombination process can be explained by a polarization transfer from the quantummixed chargeseparate state. Typical timeresolved ESR patterns of the quantummixed state and of the strongly coupled quartet state are simulated based on the generation mechanism of the dynamic electron polarization. The dependence of the spectral pattern of the quartet highspin state has been clarified for the finestructure tensor and the exchange interaction of the quantummixed state. The spectral pattern of the quartet state is not sensitive towards the finestructure tensor of the quantummixed state, because this tensor contributes only as a perturbation in the population transfer to the spinsublevels of the quartet state. Based on the stochastic Liouville equation, it is also

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.

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.

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.

Causal signal transmission by quantum fields. VI: The Lorentz condition and Maxwell's equations for fluctuations of the electromagnetic field
NASA Astrophysics Data System (ADS)
Plimak, L. I.; Stenholm, S.
20131101
The general structure of electromagnetic interactions in the socalled response representation of quantum electrodynamics (QED) is analysed. A formal solution to the general quantum problem of the electromagnetic field interacting with matter is found. Independently, a formal solution to the corresponding problem in classical stochastic electrodynamics (CSED) is constructed. CSED and QED differ only in the replacement of stochastic averages of cnumber fields and currents by timenormal averages of the corresponding Heisenberg operators. All relations of QED connecting quantum field to quantum current lack Planck's constant, and thus coincide with their counterparts in CSED. In Feynman's terms, one encounters complete disentanglement of the potential and current operators in response picture.

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.

The effect of the intense laser field on the electronic states and optical properties of ntype double δdoped GaAs quantum wells
NASA Astrophysics Data System (ADS)
Kasapoglu, E.; Yesilgul, U.; Ungan, F.; Sökmen, I.; Sari, H.
20170201
In this work, within the effective mass approximation we have performed a theoretical study of electronic states, the intersubbandrelated optical absorption coefficient and relative refractive index change properties in the GaAsbased double δdoped quantum well under nonresonant intense laser field. By solving the Schrödinger equation in the laserdressed confinement potential, we calculated eigenvalues and corresponding eigenfunctions as an intense laser parameter. We concluded that the separation between ground and first excited energy levels in the double δdoped quantum well increases in energy by the increase of the laser field intensity and this effect leads to an optical blueshift in intersubband transitions. Therefore a significant tunability of the optical transitions in double δdoped quantum well can be achieved by modulating the intensity of the intense laser field.

Resonance fluorescence from an asymmetric quantum dot dressed by a bichromatic electromagnetic field
NASA Astrophysics Data System (ADS)
Kryuchkyan, G. Yu.; Shahnazaryan, V.; Kibis, O. V.; Shelykh, I. A.
20170101
We present the theory of resonance fluorescence from an asymmetric quantum dot driven by a twocomponent electromagnetic field with two different frequencies, polarizations, and amplitudes (bichromatic field) in the regime of strong lightmatter coupling. It follows from the elaborated theory that the broken inversion symmetry of the driven quantum system and the bichromatic structure of the driving field result in unexpected features of the resonance fluorescence, including the infinite set of Mollow triplets, the quench of fluorescence peaks induced by the dressing field, and the oscillating behavior of the fluorescence intensity as a function of the dressing field amplitude. These quantum phenomena are of general physical nature and, therefore, can take place in various doubledriven quantum systems with broken inversion symmetry.

Magnetic field dependence of a chargefrustrated state in a triangular triple quantum dot
NASA Astrophysics Data System (ADS)
Seo, M.; Chung, Y.
20131101
We studied the magnetic field dependence of a chargefrustrated state formed in a triangular triple quantum dot. Stability diagrams at various magnetic fields were measured by using twoterminal and threeterminal conductance measurement schemes. We found that the frustrated state broke down at an external magnetic field of around 0.1 T. This result is due to the confinement energy shifts in quantum dots under external magnetic fields. A similar breakdown of the frustrated state was observed when the confinement energy of a quantum dot was intentionally shifted by the plunger gate of the dot, which confirm the reason for the breakdown of the frustrated state under on applied magnetic field. Our measured stability diagrams differed depending on the measurement schemes, which could not be explained by the capacitive interaction model based on an independent particle picture. We believe that the discrepancy is related to the closed electron and hole trajectories inside a triple quantum dot.

Influence of confined acoustic phonons on the Radioelectric field in a Quantum well
NASA Astrophysics Data System (ADS)
Long, Do Tuan; Quang Bau, Nguyen
20150601
The influence of confined acoustic phonons on the Radioelectric field in a quantum well has been studied in the presence of a linearly polarized electromagnetic wave and a laser radiation. By using the quantum kinetic equation for electrons with confined electrons  confined acoustic phonons interaction, the analytical expression for the Radio electric field is obtained. The formula of the Radio electric field contains the quantum number m characterizing the phonons confinement and comes back to the case of unconfined phonons when m reaches to zero. The dependence of the Radio electric field on the frequency of the laser radiation, in case of confined acoustic phonons, is also achieved by numerical method for a specific quantum well AlGaAs/GaAs/AlGaAs. Results show that the Radio electric field has a peak and reaches saturation as the frequency of the laser radiation increases.

Coherent confinement of plasmonic field in quantum dotmetallic nanoparticle molecules
NASA Astrophysics Data System (ADS)
Sadeghi, S. M.; Hatef, A.; FortinDeschenes, Simon; Meunier, Michel
20130501
Interaction of a hybrid system consisting of a semiconductor quantum dot and a metallic nanoparticle (MNP) with a laser beam can replace the intrinsic plasmonic field of the MNP with a coherently normalized field (coherentplasmonic or CP field). In this paper we show how quantum coherence effects in such a hybrid system can form a coherent barrier (quantum cage) that spatially confines the CP field. This allows us to coherently control the modal volume of this field, making it significantly smaller or larger than that of the intrinsic plasmonic field of the MNP. We investigate the spatial profiles of the CP field and discuss how the field barrier depends on the collective states of the hybrid system.

Coherent confinement of plasmonic field in quantum dotmetallic nanoparticle molecules.
PubMed
Sadeghi, S M; Hatef, A; FortinDeschenes, Simon; Meunier, Michel
20130524
Interaction of a hybrid system consisting of a semiconductor quantum dot and a metallic nanoparticle (MNP) with a laser beam can replace the intrinsic plasmonic field of the MNP with a coherently normalized field (coherentplasmonic or CP field). In this paper we show how quantum coherence effects in such a hybrid system can form a coherent barrier (quantum cage) that spatially confines the CP field. This allows us to coherently control the modal volume of this field, making it significantly smaller or larger than that of the intrinsic plasmonic field of the MNP. We investigate the spatial profiles of the CP field and discuss how the field barrier depends on the collective states of the hybrid system.

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.

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.

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.

Margins of freedom: a fieldtheoretic approach to classbased health dispositions and practices.
PubMed
Burnett, Patrick John; Veenstra, Gerry
20170323
Pierre Bourdieu's theory of practice situates social practices in the relational interplay between experiential mental phenomena (habitus), resources (capitals) and objective social structures (fields). When applied to classbased practices in particular, the overarching field of power within which social classes are potentially made manifest is the primary field of interest. Applying relational statistical techniques to original survey data from Toronto and Vancouver, Canada, we investigated whether smoking, engaging in physical activity and consuming fruit and vegetables are dispersed in a threedimensional field of power shaped by economic and cultural capitals and cultural dispositions and practices. We find that aesthetic dispositions and flexibility of developing and established dispositions are associated with positioning in the Canadian field of power and embedded in the logics of the health practices dispersed in the field. From this fieldtheoretic perspective, behavioural change requires the disruption of existing relations of harmony between the habitus of agents, the fields within which the practices are enacted and the capitals that inform and enforce the mores and regularities of the fields. The threedimensional model can be explored at: http://relationalhealth.ca/marginsfreedom.

Multipartite nonlocality and entanglement signatures of a fieldinduced quantum phase transition
NASA Astrophysics Data System (ADS)
Batle, Josep; Alkhambashi, Majid; Farouk, Ahmed; Naseri, Mosayeb; Ghoranneviss, Mahmood
20170201
Quantum correlation measures are limited in practice to a few number of parties, since no general theory is still capable of reaching the thermodynamic limit. In the present work we study entanglement and nonlocality for a cluster of spins belonging to a compound that displays a magnetocaloric effect. A quantum phase transition (QPT) is induced by an external magnetic field B, in such a way that the corresponding quantum fluctuations are reproduced at a much smaller scale than the experimental outcomes, and then described by means of the aforementioned quantum measures.

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.

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.

Theoretical study of nanophotonic directional couplers comprising nearfieldcoupled metal nanoparticles.
PubMed
Holmström, Petter; Yuan, Jun; Qiu, Min; Thylén, Lars; Bratkovsky, Alexander M
20110411
The properties of integratedphotonics directional couplers composed of nearfieldcoupled arrays of metal nanoparticles are analyzed theoretically. It is found that it is possible to generate very compact, submicron length, high fieldconfinement and functionality devices with very low switch energies. The analysis is carried out for a hypothetical lossless silver to demonstrate the potential of this type of circuits for applications in telecom and interconnects. Employing losses of real silver, standalone devices with the above properties are still feasible in optimized metal nanoparticle structures.

Fieldtheoretical approach to a dense polymer with an ideal binary mixture of clustering centers.
PubMed
Fantoni, Riccardo; MüllerNedebock, Kristian K
20110701
We propose a fieldtheoretical approach to a polymer system immersed in an ideal mixture of clustering centers. The system contains several species of these clustering centers with different functionality, each of which connects a fixed number segments of the chain to each other. The field theory is solved using the saddle point approximation and evaluated for dense polymer melts using the random phase approximation. We find a shortranged effective intersegment interaction with strength dependent on the average segment density and discuss the structure factor within this approximation. We also determine the fractions of linkers of the different functionalities.

Smooth and fast versus instantaneous quenches in quantum field theory
NASA Astrophysics Data System (ADS)
Das, Sumit R.; Galante, Damián A.; Myers, Robert C.
20150801
We examine in detail the relationship between smooth fast quantum quenches, characterized by a time scale δ t, and instantaneous quenches, within the framework of exactly solvable mass quenches in free scalar field theory. Our earlier studies [1, 2] highlighted that the two protocols remain distinct in the limit δ t → 0 because of the relation of the quench rate to the UV cutoff, i.e., 1 /δ t ≪ Λ always holds in the fast smooth quenches while 1 /δ t ˜ Λ for instantaneous quenches. Here we study UV finite quantities like correlators at finite spatial distances and the excess energy produced above the final ground state energy. We show that at late times and large distances (compared to the quench time scale) the smooth quench correlator approaches that for the instantaneous quench. At early times, we find that for small spatial separation and small δ t, the correlator scales universally with δ t, exactly as in the scaling of renormalized one point functions found in earlier work. At larger separation, the dependence on δ t drops out. The excess energy density is finite (for finite mδ t) and scales in a universal fashion for all d. However, the scaling behaviour produces a divergent result in the limit mδ t → 0 for d ≥ 4, just as in an instantaneous quench, where it is UV divergent for d ≥ 4. We argue that similar results hold for arbitrary interacting theories: the excess energy density produced is expected to diverge for scaling dimensions Δ > d/2.

Combinatorial Hopf Algebras in Quantum Field Theory I
NASA Astrophysics Data System (ADS)
Figueroa, Héctor; GraciaBondía, José M.
This paper stands at the interface between combinatorial Hopf algebra theory and renormalization theory. Its plan is as follows: Sec. 1.1 is the introduction, and contains an elementary invitation to the subject as well. The rest of Sec. 1 is devoted to the basics of Hopf algebra theory and examples in ascending level of complexity. Section 2 turns around the allimportant Faà di Bruno Hopf algebra. Section 2.1 contains a first, direct approach to it. Section 2.2 gives applications of the Faà di Bruno algebra to quantum field theory and Lagrange reversion. Section 2.3 rederives the related ConnesMoscovici algebras. In Sec. 3, we turn to the ConnesKreimer Hopf algebras of Feynman graphs and, more generally, to incidence bialgebras. In Sec. 3.1, we describe the first. Then in Sec. 3.2, we give a simple derivation of (the properly combinatorial part of) Zimmermann's cancellationfree method, in its original diagrammatic form. In Sec. 3.3, general incidence algebras are introduced, and the Faà di Bruno bialgebras are described as incidence bialgebras. In Sec. 3.4, deeper lore on Rota's incidence algebras allows us to reinterpret ConnesKreimer algebras in terms of distributive lattices. Next, the general algebraiccombinatorial proof of the cancellationfree formula for antipodes is ascertained. The structure results for commutative Hopf algebras are found in Sec. 4. An outlook section very briefly reviews the coalgebraic aspects of quantization and the RotaBaxter map in renormalization.

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.

Theoretical analysis of the coupling effect for the seepage field, stress field, and temperature field in underground coal gasification
SciTech Connect
Yang, L.H.
20051001
In this article, the derivative control equations of the simultaneous mathematical models on the temperature field, stress field of coal and rock mass, and the seepage field of retort gases in the gasification panel were established. The finite element form of the threefields coupling problem for gassolid solutions by means of a sixnode triangular element was deduced. The numerical analysis software for threefields coupling was developed. Combined with the calculation example, the mechanism of the thermodynamic effect was illustrated. The impact of the heating effect on the measured value and the simulated value of the seepage field, stress field, and displacement field was discussed and analyzed at length.

Evolution of quantum field, particle content, and classicality in the three stage universe
NASA Astrophysics Data System (ADS)
Singh, Suprit; Modak, Sujoy Kumar; Padmanabhan, T.
20131201
We study the evolution of a quantum scalar field in a toy universe which has three stages of evolution, viz., (i) an early (inflationary) de Sitter phase (ii) radiationdominated phase and (iii) latetime (cosmological constant dominated) de Sitter phase. Using the Schrödinger picture, the scalar field equations are solved separately for the three stages and matched at the transition points. The boundary conditions are chosen so that field modes in the early de Sitter evolves from the BunchDavies vacuum state. We determine the (timedependent) particle content of this quantum state for the entire evolution of the universe and describe the various features both numerically and analytically. We also describe the quantum to classical transition in terms of a classicality parameter which tracks the particle creation and its effect on phase space correlation of the quantum field.

Protecting quantum coherence of twolevel atoms from vacuum fluctuations of electromagnetic field
SciTech Connect
Liu, Xiaobao; Tian, Zehua; Wang, Jieci; Jing, Jiliang
20160315
In the framework of open quantum systems, we study the dynamics of a static polarizable twolevel atom interacting with a bath of fluctuating vacuum electromagnetic field and explore under which conditions the coherence of the open quantum system is unaffected by the environment. For both a singlequbit and twoqubit systems, we find that the quantum coherence cannot be protected from noise when the atom interacts with a nonboundary electromagnetic field. However, with the presence of a boundary, the dynamical conditions for the insusceptible of quantum coherence are fulfilled only when the atom is close to the boundary and is transversely polarizable. Otherwise, the quantum coherence can only be protected in some degree in other polarizable direction.  Highlights: •We study the dynamics of a twolevel atom interacting with a bath of fluctuating vacuum electromagnetic field. •For both a single and twoqubit systems, the quantum coherence cannot be protected from noise without a boundary. •The insusceptible of the quantum coherence can be fulfilled only when the atom is close to the boundary and is transversely polarizable. •Otherwise, the quantum coherence can only be protected in some degree in other polarizable direction.

THEORETICAL LIMITS ON MAGNETIC FIELD STRENGTHS IN LOWMASS STARS
SciTech Connect
Browning, Matthew K.; Weber, Maria A.; Chabrier, Gilles; Massey, Angela P.
20160220
Observations have suggested that some lowmass stars have larger radii than predicted by 1D structure models. Some theoretical models have invoked very strong interior magnetic fields (of order 1 MG or more) as a possible cause of such large radii. Whether fields of that strength could in principle be generated by dynamo action in these objects is unclear, and we do not address the matter directly. Instead, we examine whether such fields could remain in the interior of a lowmass object for a significant amount of time, and whether they would have any other obvious signatures. First, we estimate the timescales for the loss of strong fields by magnetic buoyancy instabilities. We consider a range of field strengths and simple morphologies, including both idealized flux tubes and smooth layers of field. We confirm some of our analytical estimates using thin flux tube magnetohydrodynamic simulations of the rise of buoyant fields in a fully convective Mdwarf. Separately, we consider the Ohmic dissipation of such fields. We find that dissipation provides a complementary constraint to buoyancy: while smallscale, fibril fields might be regenerated faster than they rise, the dissipative heating associated with such fields would in some cases greatly exceed the luminosity of the star. We show how these constraints combine to yield limits on the internal field strength and morphology in lowmass stars. In particular, we find that for stars of 0.3 solar masses, no fields in flux tubes stronger than about 800 kG are simultaneously consistent with both constraints.

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.

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.

IIVI colloidal quantumdot/quantumrod heterostructures under electric field effect and their energy transfer rate to graphene
NASA Astrophysics Data System (ADS)
Zahra, H.; Elmaghroui, D.; Fezai, I.; Jaziri, S.
20161101
We theoretically investigate the energy transfer between a CdSe/CdS Quantumdot/Quantumrod (QD/QR) core/shell structure and a weakly doped graphene layer, separated by a dielectric spacer. A numerical method assuming the realistic shape of the type I and quasitype II CdSe/CdS QD/QR is developed in order to calculate their energy structure. An electric field is applied for both types to manipulate the carriers localization and the exciton energy. Our evaluation for the isolated QD/QR shows that a quantum confined Stark effect can be obtained with large negative electric filed while a small effect is observed with positive ones. Owing to the evolution of the carriers delocalization and their excitonic energy versus the electric field, both type I and quasitype II QD/QR donors are suitable as sources of charge and energy. With a view to improve its absorption, the graphene sheet (acceptor) is placed at different distances from the QD/QR (donor). Using the random phase approximation and the massless Dirac Fermi approximation, the quenching rate integral is exactly evaluated. That reveals a high transfer rate that can be obtained with type I QD/QR with no dependence on the electric field. On the contrary, a high dependence is obtained for the quasitype II donor and a high fluorescence rate from F = 80 kV/cm. Rather than the exciton energy, the transition dipole is found to be responsible for the evolution of the fluorescence rate. We find also that the fluorescence rate decreases with increasing the spacer thickness and shows a power low dependence. The QD/QR fluorescence quenching can be observed up to large distance which is estimated to be dependent only on the donor exciton energy.

Electronic structures in a CdSe spherical quantum dot in a magnetic field: Diagonalization method and variational method
NASA Astrophysics Data System (ADS)
Wu, Shudong; Wan, Li
20120301
The electronic structures of a CdSe spherical quantum dot in a magnetic field are obtained by using an exact diagonalization method and a variational method within the effectivemass approximation. The dependences of the energies and wave functions of electron states, exciton binding energy, exciton transition energy, and exciton diamagnetic shift on the applied magnetic field are investigated theoretically in detail. It is observed that the degeneracy of magnetic quantum number m is removed due to the Zeeman effect when the magnetic field is present. For the states with m ≥ 0, the electron energies increase as the magnetic field increases. However, for the states with m < 0, the electron energies decrease to a minimum, and then increase with increasing the magnetic field. The energies and wave functions of electron states obtained from the variational method based on the variational functions we proposed are in excellent agreement with the results obtained from the exact diagonalization method we presented. A comparison between the results obtained from the variational functions proposed by us and Xiao is also verified.

Donor impurityrelated intraband optical absorption in a single quantum ring: Hydrostatic pressure and intense laser field effects
NASA Astrophysics Data System (ADS)
Barseghyan, M. G.
20161001
The simultaneous influence of hydrostatic pressure and intense laser field on hydrogenic donor impurity states and intraband optical absorption has been investigated in GaAs/Ga_{1tilde{x}}Al_{tilde{x}}As quantum ring. The oneelectron energy spectrum and wave functions have been found using the effective mass approximation and exact diagonalization technique. The intraband absorption coefficient is calculated for different values of the hydrostatic pressure, intense laser field parameter and different locations of hydrogenic donor impurity. The simultaneous influence of hydrostatic pressure and intense laser field shows that while the increment of the first one leads only to the blueshift of the absorption spectrum, the augmentation of the second one makes the redshift. In addition, both blueshift and redshift of the spectrum have been obtained with the changes of impurity location. The obtained theoretical results indicate good controlling means of the optical spectrum of ringlike structures by the combined influence of the considered factors.

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

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.

Electron emission from selfassembled quantum dots in strong magnetic fields
NASA Astrophysics Data System (ADS)
Schramm, A.; Schulz, S.; Schaefer, J.; Zander, T.; Heyn, Ch.; Hansen, W.
20060501
We probe with deep level transient spectroscopy electron states in selfassembled InAs quantum dots. Two pronounced maxima are observed that we associate with emission from different quantumdot orbital states. Fine structure clearly establishes distinct emission rates for quantum dots with one or two electrons in the s state and up to four electrons in the plike states. In order to confirm these assignments spectra have been recorded in strong magnetic fields. The observed magnetic field dispersion of the emission energies is described with a harmonic oscillator model using an effective electron mass of m*=0.03me.

Effects of external fields, dimension and polarization on the resonance fluorescence of quantum dots
NASA Astrophysics Data System (ADS)
Vaseghi, B.; Razavi, S. M.
20170201
In this paper simultaneous effects of external electric and magnetic fields, dimension and polarization on the resonance fluorescence spectrum and photon statistics of a spherical quantum dot with parabolic confinement are investigated. With special attention to the optical scattering processes resonance fluorescence spectrum and secondorder correlation function are calculated and plotted for different external parameters. Our results show the occurrence of resonance fluorescence similar to atomic systems and considerable effects of external fields, quantum confinement and light polarization on the resonance fluorescence spectrum and secondorder correlation function in the quantum dot systems. The existence of Mollow triplets and photon antibunching are strongly depend on these external agents.

Noncollinear SpinOrbit Magnetic Fields in a Carbon Nanotube Double Quantum Dot.
PubMed
Hels, M C; Braunecker, B; GroveRasmussen, K; Nygård, J
20161230
We demonstrate experimentally that noncollinear intrinsic spinorbit magnetic fields can be realized in a curved carbon nanotube twosegment device. Each segment, analyzed in the quantum dot regime, shows near fourfold degenerate shell structure allowing for identification of the spinorbit coupling and the angle between the two segments. Furthermore, we determine the four unique spin directions of the quantum states for specific shells and magnetic fields. This class of quantum dot systems is particularly interesting when combined with induced superconducting correlations as it may facilitate unconventional superconductivity and detection of Cooper pair entanglement. Our device comprises the necessary elements.

Quantum field theory and classical optics: determining the fine structure constant
NASA Astrophysics Data System (ADS)
Leuchs, Gerd; Hawton, Margaret; SánchezSoto, Luis L.
20170101
The properties of the vacuum are described by quantum physics including the response to external fields such as electromagnetic radiation. Of the two parameters that govern the details of the electromagnetic field dynamics in vacuum, one is fixed by the requirement of Lorentz invariance c = 1/\\sqrt {ε 0 μ 0 } . The other one, Z0 = \\sqrt {μ 0 /ε 0 } = 1/(cε 0 ) and its relation to the quantum vacuum, is discussed in this contribution. Deriving ε 0 from the properties of the quantum vacuum implies the derivation of the fine structure constant.

EnvironmentAssisted Speedup of the Field Evolution in Cavity Quantum Electrodynamics
DOE PAGES
Cimmarusti, A. D.; Yan, Z.; Patterson, B. D.; ...
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).

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).

Transport of electrons in a GaAs quantum well in high electric fields
SciTech Connect
Pozela, J. Pozela, K.; Raguotis, R.; Juciene, V.
20090915
The rates of intrasubband and intersubband scattering of electrons by polar optical and intervalley phonons are determined in relation to the electron energy and width of a deep rectangular quantum well in GaAs. The Monte Carlo method was used to calculate the field dependences of the electron's drift velocity in quantum wells with the width of 10, 20, and 30 nm. It is shown that the drift velocity in high electric fields in a quantum well vastly exceeds the maximum drift's saturation velocity in the bulk material.

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

Noncollinear SpinOrbit Magnetic Fields in a Carbon Nanotube Double Quantum Dot
NASA Astrophysics Data System (ADS)
Hels, M. C.; Braunecker, B.; GroveRasmussen, K.; Nygârd, J.
20161201
We demonstrate experimentally that noncollinear intrinsic spinorbit magnetic fields can be realized in a curved carbon nanotube twosegment device. Each segment, analyzed in the quantum dot regime, shows near fourfold degenerate shell structure allowing for identification of the spinorbit coupling and the angle between the two segments. Furthermore, we determine the four unique spin directions of the quantum states for specific shells and magnetic fields. This class of quantum dot systems is particularly interesting when combined with induced superconducting correlations as it may facilitate unconventional superconductivity and detection of Cooper pair entanglement. Our device comprises the necessary elements.

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
20150504
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.

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.

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.

Theoretical foundation for realtime prostate localization using an inductively coupled transmitter and a superconducting quantum interference device (SQUID) magnetometer system.
PubMed
McGary, John E
20040101
Realtime, 3D localization of the prostate for intensitymodulated radiotherapy can be accomplished with passively charged radio frequency transmitters and superconducting quantum interference device (SQUID) magnetometers. The overall system design consists of an external dipole antenna as a power source for charging a microchip implant transmitter and SQUID magnetometers for signal detection. An external dipole antenna charges an onchip capacitor through inductive coupling in the near field region through a small implant inductor. The charge and discharge sequence between the external antenna and the implant circuit can be defined by half duplex, full duplex, or sequential operations. The resulting implant discharge current creates an alternating magnetic field through the inductor. The field is detected by the surrounding magnetometers, and the location of the implant transmitter can be calculated. Problems associated with this system design are interrelated with the signal strength at the detectors, detector sensitivity, and charge time of the implant capacitor. The physical parameters required for optimizing the system for realtime applications are the operating frequency, implant inductance and capacitance, the external dipole current and loop radius, the detector distance, and mutual inductance. Consequently, the sequential operating mode is the best choice for realtime localization for constraints requiring positioning within 1 s due to the mutual inductance and detector sensitivity. We present the theoretical foundation for designing a realtime, 3D prostate localization system including the associated physical parameters and demonstrate the feasibility and physical limitations for such a system.

Impacts of noise on a field theoretical model of the human brain
NASA Astrophysics Data System (ADS)
Frank, T. D.; Daffertshofer, A.; Beek, P. J.; Haken, H.
19990301
Salient properties of the spatiotemporal patterns in MEG recordings of human brain activity, such as macroscopic coherence of a limited number of modes and the occurrence of phase transitions, have been successfully described with the help of field theoretical models for the dendritic currents in the cortex. So far, however, these models have ignored the effects of noise which play an important role in the emergence of such properties. The present article provides a formal treatment of the effects of stochastic fluctuations in the vicinity of the phase transitions that were observed by Kelso in his socalled Julliard experiment [Fuchs et al., Phase transition in the human brain: spatial mode dynamics, Int. J. Bifurcation and Chaos 2 (1992) 917939; H. Haken, Principles of Brain Functioning, Springer, Berlin, 1996; J.A.S. Kelso, Dynamic Patterns  The Selforganization of Brain and Behavior, MIT Press, Cambridge, 1995]. To describe and examine these effects, the field theoretical model proposed by Jirsa and Haken [A field theory of electromagnetic brain activity, Phys. Rev. Lett. 77 (1996) 960963; A derivation of a macroscopic field theory of the brain from the quasimicroscopic neural dynamics, Physica D 99 (1997) 503526] was extended by incorporating Gaussian white noise. The extended model describes the stochastic properties of the most dominant spatiotemporal components, including stochastic variations of the amplitudes of the extracted spatial modes. Furthermore, the model captures critical phenomena such as critical slowing down and critical fluctuations, which are derived analytically. These theoretical results are generalized by means of numerical simulations of amplitude and phase dynamics.

Mirrorfield entanglement in a microscopic model for quantum optomechanics
NASA Astrophysics Data System (ADS)
Sinha, Kanupriya; Lin, ShihYuin; Hu, B. L.
20150801
We use a microscopic model, the mirroroscillatorfield (MOF) model proposed by C. R. Galley, R. O. Behunin, and B. L. Hu [Phys. Rev. A 87, 043832 (2013), 10.1103/PhysRevA.87.043832], to describe the quantum entanglement between a mirror's centerofmass (c.m.) motion and a field. In contrast with the conventional approach where the mirrorfield entanglement is understood as arising from the radiation pressure of an optical field inducing the motion of the mirror's c.m., the MOF model incorporates the dynamics of the internal degrees of freedom of the mirror that couple to the optical field directly. The major advantage in this approach is that it provides a selfconsistent treatment of the three pertinent subsystems (the mirror's c.m. motion, its internal degrees of freedom, and the field) including their backactions on each other, thereby giving a more accurate account of the quantum correlations between the individual subsystems. The optical and the mechanical properties of a mirror arising from its dynamical interaction with a quantum field are obtained without imposing any boundary conditions on the field additionally, as is done in the conventional way. As one of the new physical features that arise from this selfconsistent treatment of the coupled optics and mechanics behavior we observe a coherent transfer of quantum correlations from the field to the mirror via its internal degrees of freedom. We find the quantum entanglement between the optical field and the mirror's centerofmass motion upon coarsegraining over the internal degree of freedom. Further, we show that in certain parameter regimes the mirrorfield entanglement is enhanced when the field interacts resonantly with the mirror's internal degree of freedom, a result which highlights the importance of including the internal structure of the mirror in quantum optomechanical considerations.

Theoretical Study of UltraRelativistic Laser Electron Interaction with Radiation Reaction by Quantum Description
NASA Astrophysics Data System (ADS)
Seto, Keita; Nagatomo, Hideo; Koga, James; Mima, Kunioki
In the near future, the intensity of the ultrashort pulse laser will reach to 1022 W/cm2. When an electron is irradiated by this laser, the electron's behavior is relativistic with significant bremsstrahlung. This radiation from the electron is regarded as the energy loss of electron. Therefore, the electron's motion changes because of the kinetic energy changing. This radiation effect on the charged particle is the selfinteraction, called the “radiation reaction” or the “radiation damping”. For this reason, the radiation reaction appears in laser electron interactions with an ultrashort pulse laser whose intensity becomes larger than 1022 W/cm2. In the classical theory, it is described by the LorentzAbrahamDirac (LAD) equation. But, this equation has a mathematical difficulty, which we call the “runaway”. Therefore, there are many methods for avoiding this problem. However, Dirac's viewpoint is brilliant, based on the idea of quantum electrodynamics. We propose a new equation of motion in the quantum theory with radiation reaction in this paper.

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
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

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.

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

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.

Linear and nonlinear optical properties of anisotropic quantum dots in a magnetic field
NASA Astrophysics Data System (ADS)
Xie, Wenfang
20130501
We have investigated the linear and nonlinear optical properties of a twodimensional anisotropic quantum dot in a magnetic field. Based on the computed energies and wave functions, the linear, thirdorder nonlinear and total optical absorption coefficients as well as the refractive index changes have been examined. The results are presented as a function of the incident photon energy for the different cases of anisotropy, dot size and external magnetic field. The results show that the linear and nonlinear optical properties of anisotropic quantum dots are strongly affected by the degree of anisotropy, the dot size, the external magnetic field and the polarized direction of the incident electromagnetic wave. The result also shows that the size effect of anisotropy quantum dots on the optical absorptions is different from that of isotropic quantum dots.

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 nondemolition measurement of parity and generation of parity eigenstates in optical fields
SciTech Connect
Gerry, Christopher C.; Benmoussa, A.; Campos, R. A.
20051115
The parity of photonic number states is known to be an important observable for quantized electromagnetic fields with applications to quantum information processing and to Heisenberglimited measurement of phase shifts in quantum interferometry performed with maximally entangled states and with twin number states. In this paper we describe an approach to the quantum nondemolition measurement of parity for quantized optical fields. The method proposed involves the use of a crossKerr interaction where we assume a large Kerr nonlinearity is available through the techniques of electromagnetically induced transparency. Our proposed method does not require the measurement of photon number but rather measures parity directly. The method not only allows for the quantum nondemolition measurement of parity but also allows for the von Neumann projection of parity eigenstates from an arbitrary field state. The generation and detection of higherorder parity eigenstates is also discussed. Losses from dissipation and the effects of detector efficiency are considered.

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.

Theoretical and Experimental Study of LowerDimensional OneDimensional and ZeroDimensional Strained Quantum System.
NASA Astrophysics Data System (ADS)
Tan, I.Hsing
19920101
With the success of the optoelectronic devices based on the twodimensional (2D) quantum well, it is a natural trend to continue to reduce system's dimensionality to 1D and 0D systems. However, extrinsic fabrication defects such as processinduced damage and pattern nonuniformity and intrinsic defects such as a slower hot carrier cooling rate can render the luminescence of the wires and dots extremely poor. In this dissertation, I will show that strain modulation and lowdamage dry/wet etching techniques allow one to obtain high luminescence straininduced quantum wires (SIQWs) and dots (SIQDs) with lateral dimensions less than 100 nm. The reduction of the fabricationinduced defects has allowed us to examine the intrinsic optical properties of the SIQWs and SIQDs through the photoluminescence (PL), PL excitation (PLE), and PL decay spectroscopy. Using epitaxial InGaAs layer as a stressor, we have achieved a ~20 meV of strain modulation and a ~7 meV of subband spacing in the SIQW structures having a lateral dimension of 75 nm and have observed an increase of FL decay time in the SIQD structures. The energy shifts, subband spacing, and increased PL decay time observed in the SIQWs and SIQDs can be well interpreted by our theoretical model, based on solving both the elasticity equation as well as the LuttingerKohn fourband Hamiltonian including strain.

Theoretical investigation of the effect of asymmetry on optical anisotropy and electronic structure of StranskiKrastanov quantum dots
NASA Astrophysics Data System (ADS)
Kumar, Jitendra; Kapoor, Sheetal; Gupta, Saral K.; Sen, Pranay K.
20060901
The effect of size and shape anisotropy on the optical properties of StranskiKrastanov quantum dots (QDs) is theoretically investigated. The QD is modeled using anisotropic parabolic confinement potential. The complex structure of the valence band is described by Luttinger Hamiltonian. The energy spectra and eigenfunctions of hole states are calculated by numerical diagonalization of the Hamiltonian. The dipole matrix elements are obtained for the interband transitions and hence the degree of linear polarization is calculated. The formulation is applied to selfassembled CdSe quantum dots for numerical analysis. The variation of energy eigenvalues with the QD shape anisotropy parameter is studied and the effect of valence subband mixing is clearly identified. The crossings and anticrossings of the valence subbands have been explained in terms of the symmetries of the corresponding eigenstates. It is worthy to note that these symmetry properties of the energy states are responsible for the specific types of dipole selection rules for the anisotropic QDs. The degree of linear polarization is found to increase almost linearly with anisotropy parameter for the transitions from heavyhole ground states. On the contrary, for the excited hole states, the change is nonmonotonic due to strong anisotropydependent mixing effects.

Theoretical estimates of maximum fields in superconducting resonant radio frequency cavities: stability theory, disorder, and laminates
NASA Astrophysics Data System (ADS)
Liarte, Danilo B.; Posen, Sam; Transtrum, Mark K.; Catelani, Gianluigi; Liepe, Matthias; Sethna, James P.
20170301
Theoretical limits to the performance of superconductors in high magnetic fields parallel to their surfaces are of key relevance to current and future accelerating cavities, especially those made of new higherT c materials such as Nb3Sn, NbN, and MgB2. Indeed, beyond the socalled superheating field {H}{sh}, flux will spontaneously penetrate even a perfect superconducting surface and ruin the performance. We present intuitive arguments and simple estimates for {H}{sh}, and combine them with our previous rigorous calculations, which we summarize. We briefly discuss experimental measurements of the superheating field, comparing to our estimates. We explore the effects of materials anisotropy and the danger of disorder in nucleating vortex entry. Will we need to control surface orientation in the layered compound MgB2? Can we estimate theoretically whether dirt and defects make these new materials fundamentally more challenging to optimize than niobium? Finally, we discuss and analyze recent proposals to use thin superconducting layers or laminates to enhance the performance of superconducting cavities. Flux entering a laminate can lead to socalled pancake vortices; we consider the physics of the dislocation motion and potential reannihilation or stabilization of these vortices after their entry.
