arXiv subjects

P. Gupta

Publications and source records attributed to P. Gupta.

12 recordsLinked to original sources

arXiv2023

Studies on the proximity effect in Bi-based high-temperature superconductor/manganite heterostructures

The effect of proximity of the magnetism of the Pr-based manganite (Pr0.6Sr0.4MnO3) on the superconductivity of Bi-based high-temperature superconductor (Bi1.75Pb0.25Sr2Ca2Cu3O10+d) was studied based on the results obtained from the magnetotransport and magnetization measurements. Decrease in the values of the upper critical field (HC2(0)) and an increase in the width of the superconducting transition (Delta TC) of Bi1.75Pb0.25Sr2Ca2Cu3O10+d were observed in proximity with the manganite. The combined effect of magnetic exchange interaction arising from the manganite, the leakage of Cooper-pairs from the superconductor into the manganite, and the diffusion and transport of spin-polarized electrons from the manganite into the superconductor were found to modify the superconducting properties of Bi1.75Pb0.25Sr2Ca2Cu3O10+d. The stacking sequence of the individual layers in these heterostructures was found to dictate the ground state properties of the heterostructure. As a consequence of the proximity effect, the colossal-magnetoresistance (CMR) ratio as high as ~ 99 % observed in the heterostructure makes the thin film heterostructures promising candidates for potential technological applications.

cond-mat.supr-con↗

arXiv2019

A Decentralized IoT Data Marketplace

This paper proposes an architecture for dynamic decentralized marketplace for trading of Internet of Things data. To this end, we introduce a 3-tier framework which consists of provider, consumer and broker. The framework is realized using multiple trustless broker which matches and selects potential data provider based on the consumers requirements. Rather than using a centralized server to manage the contract between provider and consumer, the framework leverages smart contract-based agreement for automatically enforcing the terms of the contract to the involved parties.

cs.NI↗

arXiv2017

Understanding `galaxy groups' as a unique structure in the universe

`Galaxy groups' have hardly been realised as a separate class of objects with specific characteristics in the structural hierarchy. The presumption that the self-similarity of dark matter structures is a valid prescription for the baryonic universe at all scales has rendered smaller structures undetectable by current observational facilities, leading to lesser dedicated studies on them. Some recent reports that indicate a deviation from $\rm{L_x}$-T scaling in groups compared to clusters have motivated us to study their physical properties in depth. In this article, we report the extensive study on physical properties of groups in comparison to the clusters through cosmological hydrodynamic plus N-body simulations using ENZO 2.2 code. As additional physics, radiative cooling, heating due to supernova and star motions, star formation and stellar feedback has been implemented. We have produced a mock sample of 362 objects with mass ranging from $5\times10^{12}\; \rm{M_{\odot}}$ to 2.5$\times 10^{15}\; \rm{M_{\odot}}$. Strikingly, we have found that objects with mass below $\sim$ $8\times 10^{13}\;\rm{M_{\odot}}$ do not follow any of the cluster self-similar laws in hydrostatics, not even in thermal and non-thermal energies. Two distinct scaling laws are observed to be followed with breaks at $\sim$ $8\times 10^{13}\;\rm{M_{\odot}}$ for mass, $\sim$1 keV for temperature and $\sim$1 Mpc for radius. This places groups as a distinct entity in the hierarchical structures, well demarcated from clusters. This study reveals that groups are mostly far away from virialization, suggesting the need for formulating new models for deciphering their physical parameters. They are also shown to have high turbulence and more non-thermal energy stored, indicating better visibility in the non-thermal regime.

astro-ph.CO↗

arXiv2017

Optimal phase measurements with bright and vacuum-seeded SU(1,1) interferometers

The SU(1,1) interferometer can be thought of as a Mach-Zehnder interferometer with its linear beamsplitters replaced with parametric nonlinear optical processes. We consider the cases of bright and vacuum-seeded SU(1,1) interferometers using intensity or homodyne detectors. A simplified, truncated scheme with only one nonlinear interaction is introduced, which not only beats conventional intensity detection with a bright seed, but can saturate the phase sensitivity bound set by the quantum Fisher information. We also show that the truncated scheme achieves a sub-shot-noise phase sensitivity in the vacuum-seeded case, despite the phase-sensing optical beams having no well-defined phase.

quant-ph↗

arXiv2014

X-ray absorption spectroscopy characterization of iron-oxide nanoparticles synthesized by high temperature plasma processing

Iron-oxide nanoparticles have been synthesized by high temperature arc plasma route with different plasma currents and characterized for their structure, morphology and local atomic order. Fe K-edge x-ray absorption spectra reveal distinct local structure of the samples grown with different plasma currents. We have shown that the local disorder is higher for the higher plasma current grown samples that also have a larger average particle-size. The results provide useful information to control structural and morphological properties of nanoparticles grown by high temperature plasma synthesis process.

cond-mat.mtrl-sci↗

arXiv2011

The 2010 Interim Report of the Long-Baseline Neutrino Experiment Collaboration Physics Working Groups

In early 2010, the Long-Baseline Neutrino Experiment (LBNE) science collaboration initiated a study to investigate the physics potential of the experiment with a broad set of different beam, near- and far-detector configurations. Nine initial topics were identified as scientific areas that motivate construction of a long-baseline neutrino experiment with a very large far detector. We summarize the scientific justification for each topic and the estimated performance for a set of far detector reference configurations. We report also on a study of optimized beam parameters and the physics capability of proposed Near Detector configurations. This document was presented to the collaboration in fall 2010 and updated with minor modifications in early 2011.

hep-ex↗

arXiv2007

Electron Temperature Evolution in Expanding Ultracold Neutral Plasmas

We have used the free expansion of ultracold neutral plasmas as a time-resolved probe of electron temperature. A combination of experimental measurements of the ion expansion velocity and numerical simulations characterize the crossover from an elastic-collision regime at low initial Gamma_e, which is dominated by adiabatic cooling of the electrons, to the regime of high Gamma_e in which inelastic processes drastically heat the electrons. We identify the time scales and relative contributions of various processes, and experimentally show the importance of radiative decay and disorder-induced electron heating for the first time in ultracold neutral plasmas.

physics.atom-ph↗

arXiv2007

Experimental Realization of an Exact Solution to the Vlasov Equations for an Expanding Plasma

We study the expansion of ultracold neutral plasmas in the regime in which inelastic collisions are negligible. The plasma expands due to the thermal pressure of the electrons, and for an initial spherically symmetric Gaussian density profle, the expansion is self-similar. Measurements of the plasma size and ion kinetic energy using fluorescence imaging and spectroscopy show that the expansion follows an analytic solution of the Vlasov equations for an adiabatically expanding plasma.

physics.plasm-ph↗

arXiv2004

Ultracold Neutral Plasmas

Ultracold neutral plasmas are formed by photoionizing laser-cooled atoms near the ionization threshold. Through the application of atomic physics techniques and diagnostics, these experiments stretch the boundaries of traditional neutral plasma physics. The electron temperature in these plasmas ranges from 1-1000 K and the ion temperature is around 1 K. The density can approach $10^{11}$ cm$^{-3}$. Fundamental interest stems from the possibility of creating strongly-coupled plasmas, but recombination, collective modes, and thermalization in these systems have also been studied. Optical absorption images of a strontium plasma, using the Sr$^+$ ${^2S\_{1/2}} -> {^2P\_{1/2}}$ transition at 422 nm, depict the density profile of the plasma, and probe kinetics on a 50 ns time-scale. The Doppler-broadened ion absorption spectrum measures the ion velocity distribution, which gives an accurate measure of the ion dynamics in the first microsecond after photoionization.

physics.plasm-ph↗

arXiv2004

Absorption Imaging and Spectroscopy of Ultracold Neutral Plasmas

Absorption imaging and spectroscopy can probe the dynamics of an ultracold neutral plasma during the first few microseconds after its creation. Quantitative analysis of the data, however, is complicated by the inhomogeneous density distribution, expansion of the plasma, and possible lack of global thermal equilibrium for the ions. In this article we describe methods for addressing these issues. Using simple assumptions about the underlying temperature distribution and ion motion, the Doppler-broadened absorption spectrum obtained from plasma images can be related to the average temperature in the plasma.

physics.atom-ph↗

arXiv2003

Using Absorption Imaging to Study Ion Dynamics in an Ultracold Neutral Plasma

We report optical absorption imaging of ultracold neutral plasmas.Images are used to measure the ion absorption spectrum, which is Doppler-broadened. Through the spectral width, we monitor ion equilibration in the first 250ns after plasma formation. The equilibration leaves ions on the border between the weakly coupled gaseous and strongly coupled liquid states. On a longer timescale of microseconds, we observe radial acceleration of ions resulting from pressure exerted by the trapped electron gas.

physics.atom-ph↗

arXiv2002

Magnetic trapping of metastable $^3P_2$ atomic strontium

We report the magnetic trapping of metastable $^3P_2$ atomic strontium. Atoms are cooled in a magneto-optical trap (MOT) operating on the dipole allowed $^1S_0-^1P_1$ transition at 461 nm. Decay via $^1P_1\to {^1D_2}\to {^3P_2}$ continuously loads a magnetic trap formed by the quadrupole magnetic field of the MOT. Over $10^8$ atoms at a density of $8 \times 10^9$ cm$^{-3}$ and temperature of 1 mK are trapped. The atom temperature is significantly lower than what would be expected from the kinetic and potential energy of atoms as they are transferred from the MOT. This suggests that thermalization and evaporative cooling are occurring in the magnetic trap.

physics.atom-ph↗