Department of Physics

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Quantum discord is a prominent measure of quantum correlations, playing an important role in expanding its horizon beyond entanglement. Here we provide an operational meaning of (geometric) discord, which quantifies the amount of nonclassical correlations of an arbitrary quantum system based on its minimal distance from the set of classical states, in terms of teleportation fidelity for general two-qubit and (dâŠ-d)-dimensional isotropic and Werner states. A critical value of the discord is found beyond which the two-qubit state must violate Bell's inequality. This is illustrated by an open-system model of a dissipative two-qubit state. For the (dâŠ-d)-dimensional states the lower bound of discord is shown to be obtainable from an experimentally measurable witness operator. © 2012 American Physical Society.

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Physical Review A - Atomic, Molecular, and Optical Physics

Operational meaning of discord in terms of teleportation fidelity

First principle calculations are carried out to investigate the ground state electronic and magnetic properties of G-type antiferromagnetic (AFM) LaCrO3 compound in orthorhombic phase. The orthorhombic LaCrO3, a distorted GdFeO3 - type perovskite exhibits AFM transition at ~290 K. Additionally; this system shows weak ferromagnetism at room temperature, in conjugation with its semiconducting properties. In this paper, we will discuss the onset of weak ferromagnetism and electronic properties of LaCrO3, implementing generalized gradient approximation for exchange correlation potential. We present results for electronic structure and density of states, including the effect of onsite Coulomb interaction and non-collinear arrangement of Cr&lt;sup&gt;3+&lt;/sup&gt; magnetic ions in G-type AFM geometry. © (2012) Trans Tech Publications, Switzerland.

Advanced Materials Research

Ground state electronic and magnetic properties of LaCrO3 system

The effect of a number of mechanisms designed to suppress decoherence in open quantum systems are studied with respect to their effectiveness at slowing down the loss of entanglement. The effect of photonic band-gap materials and frequency modulation of the system-bath coupling are along expected lines in this regard. However, other control schemes, like resonance fluorescence, achieve quite the contrary: increasing the strength of the control leads to a faster decay of entanglement. The effect of dynamic decoupling schemes on two qualitatively different system-bath interactions are studied in depth. Dynamic decoupling control has the expected effect of slowing down the decay of entanglement in a two-qubit system coupled to a harmonic oscillator bath under a nondemolition interaction. However, nontrivial phenomena are observed when a Josephson charge qubit, strongly coupled to a random telegraph noise bath, is subject to decoupling pulses. The most striking of these reflects the resonance fluorescence scenario, in that an increase in the pulse strength decreases decoherence but also speeds up the sudden death of entanglement. This demonstrates that the behavior of decoherence and entanglement in time can be qualitatively different in the strong-coupling non-Markovian regime. © 2012 American Physical Society.

Effect of control procedures on the evolution of entanglement in open quantum systems

Enhancement of nonlinear absorption of polystyrene (PS) was investigated using 3D PS photonic crystals (PCs) with Z-scan technique. The Z-scan experiment was carried out at 532 nm in the picosecond (ps) regime. The transmittance of the PC was found to get modified because of the nonlinear absorption of PS particularly when 532 nm is near the photonic stop band (PSB) edge of PC. Calculations show that the field gets enhanced by 1.4 times the input field intensity within the crystal when the 532 nm wavelength falls at the PSB edge while keeping the crystal at an angle of 35°. © 2012 Elsevier B.V. All rights reserved.

Photonics and Nanostructures - Fundamentals and Applications

Experimental verification of enhanced electromagnetic field intensities at the photonic stop band edge of 3D polystyrene photonic crystals using Z-Scan technique

Large enhancement in nonlinear absorption (NLA) was observed in 1-D photonic crystal containing ZnO defect fabricated by rf sputtering. The enhancement in NLA is due to the strong confinement of the optical field around the defect layer. © 2012 OSA.

2012 International Conference on Fiber Optics and Photonics, PHOTONICS 2012

Nonlinear enhancement in 1-D photonic crystal with ZnO defect fabricated by rf sputtering

Graphene oxide-ZnO/TiO2 nanoparticles are synthesized for optical limiting. Micro Raman studies reveal that GO sheets are limited to 6-8 layers. UV-Vis and FTIR results demonstrated that GO with ZnO/TiO2 nanoparticles are successfully conjugated. © 2012 OSA.

Graphene oxide (GO)-semiconductor (ZnO, TiO2) nanoparticles for broadband optical limiting

Synthesis and measurements of third order nonlinear optical (NLO) coefficients of water soluble zinc octacarboxy phthalocyanine (ZnOCPc) are reported here using different laser pulse durations. Nonlinear absorption and refraction behaviour in the nanosecond (ns), picosecond (ps) and femtosecond (fs) time domains were studied in detail. Three-photon absorption was the prevalent mechanism with femtosecond laser excitation whereas strong reverse saturable absorption due to dominant two-photon absorption (TPA) was observed with picosecond and nanosecond excitations. We have evaluated the sign and magnitude of the third order nonlinearity in fs, ps, and ns regimes. We observed large off-resonant second order hyperpolarizability (γ) with ultrafast nonlinear optical response in the femtosecond domain using degenerate four wave mixing (DFWM) technique. We also report the optical limiting characteristics and figure of merit (FOM) of ZnOCPc for optical switching. © 2012 World Scientific Publishing Company.

Journal of Porphyrins and Phthalocyanines

Ultrafast third order nonlinear optical properties of water soluble zinc-octacarboxy-phthalocyanine

Rapidly quenched microwires with a nominal composition of Fe 39Co 39Si 8B 14 (#A O), Fe 37Co 37Nb 4Si 8B 14 (#A N) and Fe 36Co 36Nb 4Cr 2Si 8B 14 (#A NC) have been investigated. Devitrification of as-quenched microwires showed that crystallization temperatures increased with simultaneous incorporation of Nb and Cr as in #A NC alloy. Addition of these elements also contributed to an increase in activation energy in #A N and #A NC alloys. Nb addition reduced the particle size, which became much finer in the case of the Cr-containing alloy. Although Nb addition did not have much effect on lowering the Curie temperature T C of the amorphous phase, Cr substitution lowered T C to 698 K from high values of 785 K and 787 K observed in the #A O and #A NC alloys, respectively. However, the Cr addition revealed a better Giant magneto-impedance (GMI) response compared to the other alloys. Such improved GMI properties in the Cr-containing alloy are attributed to lower values of the coercivity and magnetostriction in the alloy containing both Nb and Cr. © 2012 Elsevier B.V. All rights reserved.

Journal of Magnetism and Magnetic Materials

Effect of Nb and Cr incorporation on the structural and magnetic properties of rapidly quenched FeCoSiB microwires

Surface plastic deformation processes like shot peening (SP) have been extensively used by engineering industries to introduce compressive stresses at the surface to achieve superior mechanical properties (especially fatigue and wear resistance). A new family of surface severe plastic deformation processes S2 PD using high-energy balls, widely known as the Surface Mechanical Attrition Treatment (SMAT), is gaining prominence. The investigation addresses the analysis of residual stresses in SMAT-exposed pure iron and SA 516 Grade 70 pressure vessel steel components by Magnetic Barkhausen emission (MBE) technique which is a potential nondestructive evaluation tool. The stresses corresponding to optimized band filter frequencies in MBE technique exhibit good correlation with the X-ray-diffraction based residual stress measurement data. The stresses correlate at a filter frequency of 100-250 kHz in the case of pure iron and 100-300 kHz in the case of SA 516 Grade 70 pressure vessel steel. Depth profiling by chemical etching showed that the nature of stresses changed from compressive to tensile. Microhardness measurements revealed an exponential decrease of hardness with depth. © 2012 IEEE.

IEEE Transactions on Magnetics

Residual stress analysis in surface mechanical attrition treated (SMAT) iron and steel component materials by magnetic barkhausen emission technique

A simple EDTA precursor based chemical method has been reported for preparation of Mn0.2NixZn(0.8-x)Fe2O4 nanopowders. The influences of microstructure, composition, and measurement temperature on the DC resistivity of the synthesized nanopowders have been investigated. Room temperature resistivity values (ρRT) of the as-synthesized samples were in the order of ~107 Ωcm, Variation of room temperature magnetic parameters, such as saturation magnetization and coercivity, has also been reported with respect to change in Zn2+ concentration.

Optoelectronics and Advanced Materials, Rapid Communications

Preparation of Mn0.2NixZn(0.8-x)Fe2O4 nanopowders by using a novel EDTA precursor method and their microstructute, DC resistivity and magnetic properties