Department of Physics

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IIT Jodhpur

We propose a three-qubit partially entangled set of states as a shared resource for optimal and faithful quantum information processing. We show that our states always violate the Svetlichny inequality, which is a Bell-type inequality whose violation is a sufficient condition for the confirmation of genuine three-qubit nonlocality. Although our states can be physically realized from the generalized Greenberger-Horne-Zeilinger (GGHZ) states using a simple quantum circuit, the nonlocal properties of the set are quite different from the GGHZ states. Instead, they are similar to the maximal slice (MS) states, even though our states are not locally equivalent to the MS states. Unlike other two- and three-qubit partially entangled states, quantum teleportation using our states results in faithful transmission of information with unit probability and unit fidelity by performing only standard measurements for the sender, controller, and receiver. We further demonstrate that dense coding also leads to the deterministic transfer of a maximum number of bits from the sender to the receiver. We also introduce witness operators able to experimentally detect the family of states introduced. This work highlights the importance of both the local as well as nonlocal aspects of quantum correlations in multiqubit systems. © 2013 American Physical Society.

World University root node

Physical Review A - Atomic, Molecular, and Optical Physics

Optimal quantum communication using multiparticle partially entangled states

Geometric phase plays an important role in evolution of pure or mixed quantum states. However, when a system undergoes decoherence the development of geometric phase may be inhibited. Here we show that when a quantum system interacts with two competing environments there can be enhancement of geometric phase. This effect is akin to a Parrondo-like effect on the geometric phase which results from quantum frustration of decoherence. Our result suggests that the mechanism of two competing decoherence can be useful in fault-tolerant holonomic quantum computation. © 2013 American Physical Society.

Fulltext

Enhancement of geometric phase by frustration of decoherence: A Parrondo-like effect

Low energy optical modes of MBE-grown In1-xGaxN thin films with different values of x are investigated using Raman spectroscopy. We also studied the influence of Raman excitation frequency using red and green lasers on scattering intensity of various Raman modes. For those In1-xGaxN alloys whose bandgap energy is close to the red laser, a huge enhancement in the intensities of ALO) mode and its 2ALO) replica is observed when excited with red laser as compared to the green laser excitation. We found that the energies of longitudinal optical modes (ALO) and 2ALO)) vary nonlinearly unlike the Emode with increasing Ga atomic fraction. A Raman mode 540 cm-1 was observed in all In1-xGaxN films with low energy red laser excitation but was absent with green laser excitation. We attribute this mode to ATO) mode of the underneath GaN buffer layer. © 2013 A. Dixit et al.

Advances in Condensed Matter Physics

Influence of excitation frequency on raman modes of In1-xGaxN thin films

Third order optical nonlinearities of various solvents such as Dimethylformamide (DMF), ethanol, chloroform, CCl4, acetone, toluene, Tetrahydrofuran (THF), and CS2 are studied in picosecond (ps) and femtosecond (fs) time scales using Z-scan technique. All the solvents show reverse saturable absorption behavior which is attributed to significant two-photon absorption and three-photon absorption processes in ps and fs time scale regimes, respectively. Nonlinear refraction studies reveal the positive signature of nonlinearity of solvents in both pulse regimes. We have investigated the effect of solvents on observed nonlinearities of near infra-red absorbing squaraine and croconate dye samples. Interestingly, a change in the sign of nonlinearity of molecules (phe cro, ptbu cro, phe squ, and ptbu squ) is observed in the ps regime when the solvent contribution is removed. Further, we also observed a change in magnitude of the nonlinearity for all the molecules under both pulse regimes. This gives clear evidence on the role of the solvents in the measurement of optical nonlinearities and that the true nonlinearities of the solute in fs/ps time domain can only be obtained when the measurements account for the solvent. © 2013 AIP Publishing LLC.

Journal of Applied Physics

Influence of solvent contribution on nonlinearities of near infra-red absorbing croconate and squaraine dyes with ultrafast laser excitation

Two types of rapidly solidified filler alloys of nominal composition Cu-40Mn-10Ni (C50) and Ni-7Cr-3·2B-4·5Si-3Fe (N82) were used for stainless steel (SS304) brazing joints. The C50 foil is crystalline in nature, whereas N82 foil shows amorphous structure. The SS304/C50/SS304 joint shows solid solution phases at interfacial area, with maximum bond strength of 500 MPa, which qualifies to 80% of base metal strength. Conversely, the SS304/N82/SS304 joint develops brittle CrxBy intermetallic phases, which lowers bond strength to 330 MPa. © 2013 Institute of Materials, Minerals and Mining.

Science and Technology of Welding and Joining

Development of high strength stainless steel brazed joints using rapidly solidified filler alloys

A simple wet chemical route has been employed to synthesize multifunctional core-shell nanoparticles of Fe3O4@Y2O 3:Eu3+ showing an interesting combination of magnetic and luminescent properties having potential for medical applications. The core-shell nanoparticles were synthesized in a two-step process wherein first step, the Fe3O4 nanoparticles were synthesized and subsequently they are coated with Y2O3:Eu3+. XRD and magnetization curves were successfully used to retrieve the particle size of Fe3O4 nanoparticles. Particle size (∼10 nm) extracted from XRD and magnetization curves have been found to be consistent with the measured size from AFM and TEM. Further, the XRD analysis reveals formation of pure cubic phases of magnetite as well as of Y2O3:Eu 3+. It has been shown here that through simple chemistry it is possible to change the thickness of Y2O3:Eu3+ shell. From SEM and TEM studies, the size of core shell nanoparticles seen as ∼30 nm. In addition to bright red (612 nm) emission, these materials also show superparamagnetic behavior at room temperature. Emission intensity has been found to significantly increase with increase in annealing temperature. The synthesized materials have extensive for applications in the area of drug delivery and bio-imaging. © 2013 Elsevier B.V. All rights reserved.

Optical Materials

Synthesis of Fe3O4@Y2O3:Eu 3+ core-shell multifunctional nanoparticles and their magnetic and luminescence properties

We numerically report the feasibility of generating broadband low divergent supercontinuum covering the entire wavelength window of 1.5-3.5 μm from a 2.25 m long effectively single mode all solid, soft glass based, photonic bandgap fiber with mode area as large as 1100 μm2. Owing to its chosen fabrication, friendly geometry, and the chosen material composition, the proposed fiber-based light source should be useful as a mid-wave IR pulsed broadband light source for applications such as high power delivery, optical coherence tomography and mid-IR spectroscopy. © 2013 Astro Ltd.

Laser Physics

Generation of a low divergent supercontinuum for mid-IR high power delivery through a large mode area photonic bandgap fiber

An efficient compact ~ 80 cm long microstructured optical fiber-based broad-band (5.0- 6.3 μm) mid-IR light source with power conversion efficiency > 40% has been designed by exploiting FWM with commercially available CO laser as pump. © OSA 2013.

Optics InfoBase Conference Papers

Design tailored efficient broad-band fiber optic light source for Mid-IR molecular spectroscopy

We study the phase-separation kinetics of a binary (AB) mixture confined in a thin film of thickness D with a temperature gradient. Starting from a Kawasaki-exchange kinetic Ising model, we use a master-equation approach to systematically derive an extension of the Cahn-Hilliard model for this system. We study the effect of temperature gradients perpendicular to the film with "neutral" (no preference for either A or B) surfaces. We highlight the rich phenomenology and pattern dynamics which arises from the interplay of phase separation and the temperature gradient. © Copyright EPLA, 2013.

Phase separation in thin films: Effect of temperature gradients

We report spontaneous translocation of small interfering RNA (siRNA) inside carbon nanotubes (CNTs) of various diameters and chirality using all atom molecular dynamics simulations with explicit solvent. We use umbrella sampling method to calculate the free energy landscape of the siRNA entry and translocation event. Free energy profiles show that siRNA gains free energy while translocating inside CNT, and barrier for siRNA exit from CNT ranges from 40 to 110 kcal/mol depending on CNT chirality and salt concentration. The translocation time τ decreases with the increase of CNT diameter with a critical diameter of 24 Å for the translocation. In contrast, double strand DNA of the same sequence does not translocate inside CNT due to large free energy barrier for the translocation. This study helps in understanding the nucleic acid transport through nanopores at microscopic level and may help designing carbon nanotube based sensor for siRNA. © 2013 American Institute of Physics.