Department of Physics

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The classicalization of a decoherent discrete-time quantum walk on a line or an n-cycle can be demonstrated in various ways that do not necessarily provide a geometry-independent description. For example, the position probability distribution becomes increasingly Gaussian, with a concomitant fall in the standard deviation, in the former case, but not in the latter. As another example, each step of the quantum walk on a line may be subjected to an arbitrary phase gate, without affecting the position probability distribution, no matter whether the walk is noiseless or noisy. This symmetry, which is absent in the case of noiseless cyclic walk, but is restored in the presence of sufficient noise, serves as an indicator of classicalization, but only in the cyclic case. Here we show that the degree of quantum correlations between the coin and position degrees of freedom, quantified by a measure based on the disturbance induced by local measurements, provides a suitable measure of classicalization across both type of walks. Applying this measure to compare the two walks, we find that cyclic quantum walks tend to classicalize faster than quantum walks on a line because of more efficient phase randomization due to the self-interference of the two counter-rotating waves. We model noise as acting on the coin, and given by the squeezed generalized amplitude damping (SGAD) channel, which generalizes the generalized amplitude damping channel. © 2010 The American Physical Society.

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Physical Review A - Atomic, Molecular, and Optical Physics

Quantumness in a decoherent quantum walk using measurement-induced disturbance

Magnetic Γ-Fe 2O 3 nanoparticles with a mean diameter of 20 nm and size distribution of 7% were chemically synthesized and spin-coated on top of a Si-substrate. As a result, the particles self-assembled into a mono layer with hexagonal close-packed order. Subsequently, the nanoparticle array was coated with a Co layer of 20 nm thickness. The magnetic properties of this composite nanopar-ticle/thin film system were investigated by magnetometry and related to high-resolution transmission electron microscopy studies. Herein three systems were compared: i.e. a reference sample with only the particle monolayer, a composite system where the particle array was ion-milled prior to the deposition of a thin Co film on top, and a similar composite system but without ion-milling. The nanoparticle array showed a collective super-spin behavior due to dipolar interparticle coupling. In the composite system, we observed a decoupling into two nanoparticle subsystems. In the ion-milled system, the nanoparticle layer served as a magnetic flux guide as observed by magnetic force microscopy. Moreover, an exchange bias effect was found, which is likely to be due to oxygen exchange between the iron oxide and the Co layer, and thus forming of an antiferromagnetic CoO layer at the Γ-Fe 2O 3/Co interface. © 2010 Confalonieri et al.

Beilstein Journal of Nanotechnology

Magnetic coupling mechanisms in particle/thin film composite systems

CoNiAl system is a potential candidate for engineering applications because of its improved ductility over other ferromagnetic shape memory alloys. We have made a sample of CoNiAl alloy (Co37Ni35Al28) by arc melting and characterized it by X-ray diffraction, resistivity, susceptibility and magnetization measurements. The martensitic phase transitions have been investigated in both the as-prepared and annealed CoNiAl alloys. We show how the metallurgical modifications progress in the system from the as-prepared to the annealed state and how they modify the transformation temperatures. © 2009 Elsevier B.V. All rights reserved.

Journal of Alloys and Compounds

Effect of annealing on the martensitic transformation of a CoNiAl ferromagnetic shape memory alloy

We report a numerical investigation on the transverse localization of light in a lattice of disordered coupled waveguides. The interplay of disorder with medium's nonlinearity in localization from application point of view is studied. © 2010 Optical Society of America.

Optics InfoBase Conference Papers

Role of nonlinearity and transverse localization of light in a disordered coupled optical waveguide lattice

Chirped cladding is proposed as a novel tailoring tool to simultaneously attain wider transmission window and reduced temporal dispersion in an all-solid Bragg-like microstructured optical fiber as compared to its perfectly periodic cladding counterpart. This design route for photonic bandgap microstructured fibers could be exploited as an additional degree of freedom for bandgap engineering. A suitably chirped clad fiber could be gainfully exploited to deliver femto-second pulse with ultra wide bandwidth. Further, generation of self-similar parabolic profile pulse is demonstrated by simulating propagation of an input Gaussian pulse through a 2 m long sample of such a linearly tapered Bragg like fiber. © 2010 Springer Science+Business Media, LLC.

Optical and Quantum Electronics

A Bragg-like chirped clad all-solid microstructured optical fiber with ultra-wide bandwidth for short pulse delivery and pulse reshaping

Ni1-xZnxFe2O4 (0 ≤ x ≤1) nanopowders (average particle size ∼ 30 nm) have been synthesized by using a ethylenediamine tetraacetic acid precursor based method. The synthesized nanopowders were obtained by calcining the precursors in air at 450°C. Microstructures of the nanopowders and samples obtained on sintering have been studied by using Scanning Electron Microscopy. DC electrical resistivity was found to be ∼107Ωcm for the as-synthesized nanopowders and ∼106.cm for sintered samples. Room temperature magnetization has also been measured for all compositions and it exhibits a decrease with increasing Zn content in the samples.

Journal of Optoelectronics and Advanced Materials

Microstructure DC resistivity and magnetic property of Ni-Zn ferrite nano-powders synthesized by edta precursor based method

CoSe2 O5 has a crystal structure consisting of zigzag chains of edge shared CoO6 octahedra running along the c axis with the chains separated by Se2 O5 2- units. Magnetic-susceptibility measurements indicate a transition at 8.5 K to an ordered state. We investigate the nature of this magnetic order using magnetization and specific-heat measurements, in addition to powder neutron diffraction. A transition to long-range antiferromagnetic order is found below TN =8.5 K as identified by magnetic-susceptibility and heat-capacity measurements, and the emergence of magnetic Bragg reflections with a propagation vector k=0. The low-field magnetic-susceptibility data indicate the presence of weak ferromagnetism in the antiferromagnetic ordered state which saturates in very small fields. Heat-capacity measurements at low temperatures indicate that only about half the configurational entropy is released at TN. The functional form of the heat capacity below TN suggests the presence of a gap of 6.5 K in the magnon dispersion. The refined magnetic structure shows that the moments align perpendicular to the c axis, and tilting alternately by +14°and -14°with respect to the a axis. © 2010 The American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Magnetic structure and susceptibility of CoSe2 O5: An antiferromagnetic chain compound

We study the forward-backward asymmetry (AFB) and the differential branching ratio (DBR) in B → K*μ+μ- in the presence of new physics (NP) with different Lorentz structures. We consider NP contributions from vector-axial vector (VA), scalarpseudoscalar (SP), and tensor (T) operators, as well as their combinations. We calculate the effects of these new Lorentz structures in the low-q2 and high-q2 regions, and explain their features through analytic approximations. We find two mechanisms that can give a significant deviation from the standard-model predictions, in the direction indicated by the recent measurement of AFB by the Belle experiment. They involve the addition of the following NP operators: (i) VA, or (ii) a combination of SP and T (slightly better than T alone). These two mechanisms can be distinguished through measurements of DBR in B → K*μ+μ- and AFB in B → Kμ+μ-. © 2010 SISSA.

Journal of High Energy Physics

New-physics contributions to the forward-backward asymmetry in B → K*μ+μ-

Cellular Automata (CA) have a long history as computation models, but only in the last few years have serious attempts started to implement them in terms of molecules. Such nano-technological innovations promise very cost-effective fabrication because of the regular structure of CA, which allows assembly through molecular self-organization. The small sizes of molecules combined with their availability in Avogadro-scale numbers promises a huge computational power, in which the massive parallelism inherent in CA can be effectively exploited. This paper discusses critical background aspects of our recent results on the implementation of a CA by a molecular assembly (Bandyopadhyay et al., Nature Physics 2010). © 2010 Springer-Verlag.

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

Molecular implementations of cellular automata

The synthesis of a new type, high performance polybenzoxazine-ferrite nanocomposite has been reported. A simple aqueous solution based method was developed for preparation of several compositions of Ni1-xZn xFe2O4 (x=0.20-0.60) nanopowders using metal nitrates and EDTA. Benzoxazine monomer was prepared by employing a solvent less method using aniline, paraformaldehyde and bisphenol A as starting materials. Polybenzoxazine-ferrite nanocomposites were prepared by using a solvent casting method followed by thermal curing. The synthesised powders, monomer, polymer and the resultant composites were characterised by using thermogravimetric analysis and differential scanning calorimeter, surface area and pore size analyser, scanning electron microscope (SEM) and transmission electron microscope. X-ray diffraction spectra of the powders revealed the formation of single phase Ni-Zn ferrite, with average crystallite size of about 20-30 nm. Transmission electron microscopy micrographs confirmed the average ferrite particle size as ∼ 30 nm while SEM morphology showed a uniform dispersion of nanoferrite particles in the polybenzoxazine matrix. Room temperature magnetic properties of pure ferrite nanopowders as well as polybenzoxazine-ferrite nanocomposites were measured with a vibrating sample magnetometer. © 2010 W. S. Maney &amp; Son Ltd.