Interference effects in lossy resonator chains

Abstract

We theoretically study properties of narrow spectral features occurring in chains of coupled optical resonators due to classical optical interference. We compare those properties with the properties of the phenomenon of electro-magnetically induced transparency in quantum systems. Despite the difference in the underlying physics, we show that both types of systems show striking similarities in optical properties and in possible applications.     

Oscillatory interlayer magnetic coupling and induced magnetism in Fe/Nb multilayers

We present an ab initio calculation of interlayer magnetic coupling for Fe/Nb multilayers using the self-consistent full-potential linearized augmented-plane-wave (FLAPW) method. For this calculation, we have constructed supercells consisting of bcc Fe and Nb multilayers in Fe/Nb/Fe sandwich geometry stacked along (001) direction. In the supercells two Fe layers are separated by Nb layers ranging from 1 to 11 layers. We have calculated the total energy of the system as a function of Nb spacer layer thickness. For each spacer layer thickness, we have done three calculations corresponding to para, ferro and antiferromagnetic ordering of Fe atoms. The interlayer magnetic coupling is obtained from the energy difference of the systems in which Fe layers are antiferromagnetically and ferromagnetically ordered. We find that the interlayer magnetic coupling oscillates with increasing Nb spacer thickness in agreement with the experimental results. The induced magnetic moment is also found to be oscillating with increasing Nb spacer layer thickness.     

Simple theory of microwave induced transparency in atomic and molecular systems

Abstract

In recent years the idea of electromagnetically induced transparency in atomic systems using a microwave coupling field has been discussed. We present theoretical work on how this may be achieved in both Doppler systems, and by extension in non-Doppler broadened systems. By considering the specific example of atomic rubidium we demonstrate the feasibility and practical difficulties of such an experiment. By considering systems with appropriate rotational-vibration structure we conclude that microwave induced transparency in gas vapours is more readily achievable in molecular systems.     

Prescription for experimental determination of the dynamics of a quantum black box

Abstract

We give an explicit way to experimentally determine the evolution operators which completely describe the dynamics of a quantum-mechanical black box: an arbitrary open quantum system. We show necessary and sufficient conditions for this to be possible and illustrate the general theory by considering specifically one-and two-quantum-bit systems. These procedures may be useful in the comparative evaluation of experimental quantum measurement, communication and computation systems.     

Experimental detection of entanglement via witness operators and local measurements

Abstract

In this paper we address the problem of detection of entanglement using only few local measurements when some knowledge about the state is given. The idea is based on an optimized decomposition of witness operators into local operators. We discuss two possible ways of optimizing this local decomposition. We present several analytical results and estimates for optimized detection strategies for NPT states of 2 × 2 and N × M systems, entangled states in 3 qubit systems, and bound entangled states in 3 × 3 and 2 × 4 systems.     

Quantum correlations,local interactions and error correction

Abstract

We consider the effects of local interactions upon quantum mechanically entangled systems. In particular we demonstrate that non-local correlations cannot increase through local operations on any of the subsystems, but that through the use of quantum error correction methods, correlations can be maintained. We provide two mathematical proofs that local general measurements cannot increase correlations, and also derive general conditions for quantum error correcting codes. Using these we show that local quantum error correction can preserve non-local features of entangled quantum systems. We also demonstrate these results by use of specific examples employing correlated optical cavities interacting locally with resonant atoms. By way of counter example, we also describe a mechanism by which correlations can be increased, which demonstrates the need for non-local interactions.     

Reconstruction of quantum states of spin systems via the Jaynes principle of maximum entropy

Abstract

We apply the Jaynes principle of maximum entropy for the partial reconstruction of correlated spin states. We determine the minimum set of observables which is necessary for the complete reconstruction of the most correlated states of systems composed of spins 1/2 (e.g. the Bell and the Greenberger-Horne-Zeilinger states). We investigate to what extent an incomplete measurement can reveal non-classical features of correlated spin states.     

Extensions to a lens design program for the ray-optical design of waveguide lenses and prism couplers

Abstract

The design of integrated optical lens systems requires special software because such systems contain both three-dimensional and twodimensional elements (e.g. bulk prisms and planar waveguide lenses), and the waveguides are often anisotropic. We extended the popular optical computer-aided design program OSLO SIX so that it can evaluate and optimize systems that contain coupling prisms and planar waveguide lenses. We describe our software extensions and through examples we demonstrate their usage and benefits. We confirm our computations by measurement results. Finally, we present a ray-optical interpretation of transverse image line inclination and a method for its elimination.     

Squeezing in Correlated Quantum Systems

Abstract

We discuss the connection between quantum correlations and squeezing in simple quantum optical systems. We illustrate this connection by a study of two-mode states of light produced by parametric down-conversion and similar two-photon processes. The intermode correlations in these systems are shown to be responsible for modifications in photon-number sum and difference operators, and for squeezing in the superpositions of the two modes. The disappearance of the diagonal coherent-state quasiprobability function P(α) when non-classical light properties are important is noted, and alternative and better-behaved Wigner functions and coherent-state expectation Q-functions for the two-mode system are developed.     

Rings, chains and planes: Variation ofT g with composition in chalcogenide glasses

We propose a microscopic, phenomenological model for the decrease in the viscosity observed at glass transition. Our model is primarily applicable to chalcogenide glasses. According to this model, the decrease in the viscosity at glass transition is mainly due to the breaking of the Van der Waals bonds in the chalcogenides. Using this model, we derive a relationship between the glass transition temperature,T _g ,and the molar volume V _m.The validity of this relation is checked using experimental data available in the literature for two binary systems (Ge-Se and As-S) and a pseudo-binary system (As ₄₀ Se _x Te _60-x .     

Ageing Influence on the Absorption and Laser Damage Resistance of Ta2O5 Thin Films

Abstract

We present results from experiments on the ageing influence of laser-induced damage of evaporated Ta₂O₅ quarter-wave single-layer films and coating systems of Ta₂O₅-SiO₂ at λ = 1060 nm. With Ta₂O₅ films emphasis is placed on the correlation between increase in damage threshold and decrease in absorption with the storage time.     

The Use of Annular Pupil Plane Filters to Tune the Imaging Properties in Confocal Microscopy

Abstract

We consider the use of pupil plane filters to modify the imaging properties of confocal optical systems. We specialize to the annular filter as it is useful in itself and as part of a more complex filter. We show, inter alia, that by changing the size of the annular obscuration we can tune the strength of the optical sectioning. The question of spherical aberration is considered and it is found both theoretically and experimentally that the effects are reduced in the annular case. We also discuss the problem of where best to place the filters in reflection systems where different filter functions are required for the two imaging lenses. The use of filters in both bright-field and fluorescence imaging modes is considered.     

Frontiers and symmetries of dynamical systems

The frontiers of boundedness ? _b of the orbits of dynamical systems X defined on ? ⁿ are studied. When X is completely integrable some topological properties of ? _b are found and, in certain cases, ? _b is localized with the help of symmetries of X. Several examples in dimensions 2 and 3 are provided. In case the number of known first integrals of the vector field X is less than n ? 1, an interesting connection of ? _b with the frontier of boundedness of the level-sets of the first integrals of X is proved. This result also applies to Hamiltonian systems.     

Eavesdropping on practical quantum cryptography

Abstract

Practical implementations of quantum cryptography use attenuated laser pulses as the signal source rather than single photons. The channels used to transmit are also lossy. Here we give a simple derivation of two beamsplitting attacks on quantum cryptographic systems using laser pulses, either coherent or mixed states with any mean photon number. We also give a simple derivation of a photon-number splitting attack, the most advanced, both in terms of performance and technology required. We find bounds on the maximum disturbance for a given mean photon number and observed channel transmission efficiency for which a secret key can be distilled. We start by reviewing two incoherent attacks that can be used on single photon quantum cryptographic systems. These results are then adapted to systems that use laser pulses and lossy channels.     

Addressing Challenges of Transferring Explicit Knowledge,Information, and Data in Large Heterogeneous Organizations: A Case Example from a Data-Rich Integration Project at the U.S. Army Test and Evaluation Command

Abstract:

We contribute reflective case studies on development and implementation of common data engineering architectures addressing the engineering and technology management challenge of integrating heterogeneous information systems. In data-rich integration projects, the role of data as a critical resource requires applying managed data engineering addressing the aligned information exchange between systems in support of business/operational processes in organizations and the enterprise. The recommended data engineering architecture comprises standards, methods, and tools that contribute part-solution for process modeling, data resources documentation, metadata modeling, and data modeling. We show how alignment by engineering and project managers ensures efficient and effective solutions.     

Quantum entanglement criteria

Abstract

We review the main criteria used to detect entanglement in quantum systems. The main properties of each criteria are summarized depending on whether the criteria provides a sufficient or necessary condition, whether it involves density matrix or operators, or if the criteria is phase sensitive. We show that several criteria have much in common and they could be related mathematically. We also discuss the features of entanglement which are useful in quantum information technology.     

Quantum Random-number Generation and Key Sharing

Abstract

We review the status of interferometry-based quantum cryptography and compare photon-pair and faint-pulse schemes. The key technical limitations in both cases are the propagation losses and detector performance. We also discuss a simple approach to generating the random measurement bases used in quantum cryptography systems which exploits random partition at a beam splitter. This removes the need for active components in the receiver, reducing system complexity and losses.     

Managing object schemas in a distributed database architecture for concurrent engineering

Abstract

In recent years, object database systems have emerged as a new technology, integrating object‐oriented paradigms with transaction and query capabilities of conventional database systems. The strength of distributed object database systems is further enhanced by new generations of powerful workstations. The synergy between object databases and the networked workstation environment, however, brings forth a new set of challenges. In this paper, we address the issues of managing object schemas in a cooperative network environment. After reviewing existing solutions, we present a more dynamic approach to the problem of distributed schema management. We also show how this approach can serve as a general framework for supporting various schema management policies.     

Stability of schur polynomials under coefficient perturbation

Abstract

In this paper, we are concerned with the stability robustness of characteristic polynomials with perturbed coefficients for linear discrete‐time systems. An upper bound on the allowable coefficient perturbation of a Schur polynomial with retaining stability is obtained. The proposed upper bound is directly formulated in terms of the polynomial under consideration and its value can be determined by numerical computation. We also provide a sufficient condition for the stability of interval polynomials.     

Counteracting quantum decoherence with optimized disorder in discrete-time quantum walks

ABSTRACT

Decoherence and disorder are two major difficulties limiting the performance of quantum systems in practical settings. Yet they can potentially counteract each other to partially restore the systems' quantum signatures. We adopt the particle swarm optimization method to find the optimal disorder for mitigating the effects of decoherence in one- and two-dimensional quantum random walks, achieving substantial increase in the mean walking distance for a wide range of decoherence strength. This result suggests a viable approach to constructing practical quantum systems robust against decoherence and disorder.