arXiv subjects

S. Pradhan

Publications and source records attributed to S. Pradhan.

At least 19 recordsLinked to original sources

arXiv2026

Compact U(1) Lattice Gauge Theory in Superconducting Circuits with Infinite-Dimensional Local Hilbert Spaces

We propose a superconducting-circuit architecture that realizes a compact U(1) lattice gauge theory using the intrinsic infinite-dimensional Hilbert space of phase and charge variables. The gauge and matter fields are encoded directly in the degrees of freedom of the rotor variables associated with the circuit nodes, and Gauss's law emerges exactly from the conservation of local charge, without auxiliary stabilizers, penalty terms, or Hilbert-space truncation. A minimal gauge-matter coupling arises microscopically from Josephson nonlinearities, whereas the magnetic plaquette interaction is generated perturbatively via virtual matter excitations. Numerical diagonalization confirms the emergence of compact electrodynamics and coherent vortex excitations, underscoring the need for large local Hilbert spaces in the continuum regime. The required circuit parameters are within the current experimental capabilities. Our results establish superconducting circuits as a scalable, continuous-variable platform for analog quantum simulation of non-perturbative gauge dynamics.

quant-ph↗

arXiv2023

Beyond equivalent circuit representations in nonlinear systems with inherent memory

Basic multimode impedance analysis grounded in the availability of nonequilibrium charge carriers and their retarded path towards equilibrium is used to access the inadequacy of equivalent circuits in nonlinear systems with inherent memory. On the basic grounds of generation and recombination (or trapping) of nonequilibrium carriers and their relaxation times, we show how seeming complexity of frequency-dependent impedance that matches a vast universe of experimental evidences can be reduced to simple combinations of basic microscopic ingredients. Counterintuitive features such as a negative capacitances or unexpected inductances become a metaphoric construction with poor physical meaning, pointing to the limitations and ambiguities of the symbolic nature of "equivalent" circuits. Our approach further provides a microscopic perspective that exposes the linkage of an apparent flux with an apparent inductance dismissing any magnetic essence.

physics.app-ph↗

arXiv2023

Hamiltonians and gauge-invariant Hilbert space for lattice Yang-Mills-like theories with finite gauge group

Motivated by quantum simulation, we consider lattice Hamiltonians for Yang-Mills gauge theories with finite gauge group, for example a finite subgroup of a compact Lie group. We show that the electric Hamiltonian admits an interpretation as a certain natural, non-unique Laplacian operator on the finite Abelian or non-Abelian group, and derive some consequences from this fact. Independently of the chosen Hamiltonian, we provide a full explicit description of the physical, gauge-invariant Hilbert space for pure gauge theories and derive a simple formula to compute its dimension. We illustrate the use of the gauge-invariant basis to diagonalize a dihedral gauge theory on a small periodic lattice.

quant-ph↗

arXiv2020

Analysis of an infinite-buffer batch-size-dependent service queue with discrete-time Markovian arrival process: D-$MAP/G_n^{(a,b)}/1$

Discrete-time queueing models find huge applications as they are used in modeling queueing systems arising in digital platforms like telecommunication systems, computer networks, etc. In this paper, we analyze an infinite-buffer queueing model with discrete Markovian arrival process. The units on arrival are served in batches by a single server according to the general bulk-service rule, and the service time follows general distribution with service rate depending on the size of the batch being served. We mathematically formulate the model using the supplementary variable technique and obtain the vector generating function at the departure epoch. The generating function is in turn used to extract the joint distribution of queue and server content in terms of the roots of the characteristic equation. Further, we develop the relationship between the distribution at the departure epoch and the distribution at arbitrary, pre-arrival and outside observer's epoch, which is used to obtain the latter ones. We evaluate some essential performance measures of the system and also discuss the computing process extensively which is demonstrated by a few numerical examples.

math.PR↗

arXiv2020

Stationary queue and server content distribution of a batch-size-dependent service queue with batch Markovian arrival process: BMAP/G^{(a,b)}_n/1

Queueing systems with batch Markovian arrival process (BMAP) have paramount applications in the domain of wireless communication. The BMAP has been used to model the superposition of video sources and to approximate the super-position of data, voice and video traffic. This paper analyzes an infinite-buffer generally distributed batch-service queue with BMAP, general bulk service ($a,b$) rule and batch-size-dependent service time. In this proposed analysis, we mainly focus on deriving the bivariate vector generating function of queue and server content distribution together at departure epoch using supplementary variable technique. The mathematical procedure for the complete extraction of distribution at departure epoch has been discussed and using those extracted probabilities, we achieve the queue and server content distribution at arbitrary epoch. Finally, numerical illustrations have been carried out in order to make a deep insight to the readers which contains deterministic as well as phase-type service time distributions.

math.PR↗

arXiv2019

Investigation of the Yu-Shiba-Rusinov states of a multi-impurity Kondo system

Recent studies of mutually interacting magnetic atoms coupled to a superconductor have gained enormous interest due to the potential realization of topological superconductivity. The Kondo exchange coupling J_K of such atoms with the electrons in the superconductor has a pair-breaking effect which produces so-called Yu-Shiba-Rusinov (YSR) states within the superconducting energy gap, whose energetic positions are intimately connected with the requirements for topological superconductivity. Here, using the tip of a scanning tunneling microscope, we artificially craft a multi-impurity Kondo system coupled to a superconducting host consisting of an Fe adatom interacting with an assembly of interstitial Fe atoms on an oxygen-reconstructed Ta(100) surface and we experimentally investigate the signatures of Kondo screening and the YSR states. With the help of numerical renormalization group (NRG) calculations, we show that the observed behavior can be qualitatively reproduced by a two-impurity Kondo system whose inter-impurity antiferromagnetic interaction J is adjusted by the number of interstitial Fe atoms in the assembly. When driving the system from the regime of two decoupled Kondo singlets (small J) to that of an antiferromagnetic dimer (large J), the YSR state shows a characteristic cross-over in its energetic position and particle-hole asymmetry.

cond-mat.supr-con↗

arXiv2019

Sum of two maximal monotone operators in a general Banach space is maximal

In a real Banach space, we first prove that the sum of a monotone operator of type (FPV) and maximal monotone operator Rockafellar's constraint qualification is maximal. This prove leads to the solution of most interesting long-time outstanding problem in monotone operator theory is the sum problem.

math.FA↗

arXiv2018

Development of Precise Low Value Capacitance Measurement System for Cryogenics Two Phase Flow Application

In cryogenic two phase flow, it is always challenging to measure the quality and void fraction. In this regard, an effort has been made to indigenously develop an electronic circuit to measure the void fraction by measuring the capacitance of the order of picofarads accurately depending upon the dielectric constant of nitrogen in vapor and liquid phase. The state-of-art electronics card has been developed and tested successfully for its performance and validation. Using this card, an experiment has been conducted using liquid nitrogen cryo transfer line to study the two phase void fraction. In this paper, the design basis and working principle of the designed electronics card along with the performance results are discussed. A/D conversion and DAQ system has been implemented to display the direct measurement data in a computer.

physics.ins-det↗

arXiv2018

Prediction of helium vapor quality in steady state Two-phase operation for SST-1 Toroidal field magnets

Steady State Superconducting Tokamak (SST-1) at the Institute for Plasma Research (IPR) is an operational device and is the first superconducting Tokamak in India. Superconducting Magnets System (SCMS) in SST-1 comprises of sixteen Toroidal field (TF) magnets and nine Poloidal Field (PF) magnets manufactured using NbTi/Cu based cable-in-conduit-conductor (CICC) concept. SST-1, superconducting TF magnets are operated in a Cryo-stable manner being cooled with two-phase (TP) flow helium. The typical operating pressure of the TP helium is 1.6 bar (a) at corresponding saturation temperature. The SCMS has a typical cool-down time of about 14 days from 300 K down to 4.5 K using Helium plant of equivalent cooling capacity of 1350 W at 4.5 K. Using the onset of experimental data from the HRL, we estimated the vapor quality for the input heat load on to the TF magnets system. In this paper, we report the characteristics of two-phase flow for given thermo-hydraulic conditions during long steady state operation of the SST-1 TF magnets. Finally, the experimentally obtained results have been compared with the well-known correlations of two-phase flow.

physics.ins-det↗

arXiv2018

Shot noise as a probe of spin-correlated transport through single atoms

We address the shot noise in the tunneling current through a localized spin, pertaining to recent experiments on magnetic adatoms and single molecular magnets. We show that both uncorrelated and spin-correlated scattering processes contribute vitally to the noise spectrum. The spin-correlated scattering processes provide an additional contribution to the Landauer-Büttiker shot noise expression, accounting for correlations between the tunneling electrons and the localized spin moment. By calculating the Fano factor, we show that both super- and sub-Poissonian shot noise can be described within our approach. Our theory provides transparent insights to noise spectroscopy, consistent with recent experiments using local probing techniques on magnetic atoms.

cond-mat.mes-hall↗

arXiv2017

Two phase helium cooling characteristics in Cable-in Conduit Conductors

Cable-in-Conduit Conductors (CICCs) are used in the fabrication of superconducting fusion grade magnets. It acts as a narrow cryostat to provide cryo-stability with direct contact of coolant fluid to conductor. The superconducting magnets are cooled using forced flow (FF), supercritical helium or two phase (TP) cooling through void space in the CICC. Thermo-hydraulics using supercritical helium single phase flow is well-known and established. Research topic of behavior of forced flow, two phase (TP) helium cooling in CICC involves perceived risks of the CICC running into flow chocking and possible thermo-acoustic oscillations leading to flow instabilities. This research work involves study of forced flow two phase helium cooling in CICC wound superconducting magnets. The TP flow provides cryo-stability by the latent heat of helium not by enthalpy as in case of CICC being cooled with supercritical helium. Study reveals some attractive regimes in the case of TP cooling, at a given mass flow rate of single phase helium at the inlet and a heat flux acting on the CICC. Analysis carried out predicts significant gains with TP cooling on a prototype CICC, which is circular in cross section and appropriate for fusion devices for high magnetic field applications. These general formalisms may be extended to specific magnets wound with CICC. This paper describes analysis of TP cooling of a CICC.

physics.flu-dyn↗

arXiv2015

Exciton condensation in an extended spinless Falicov Kimball model in the presence of orbital magnetic fields

An extended, spinless Falicov-Kimball model in the presence of perpendicular magnetic field is investigated employing Hartree-Fock self-consistent mean-field theory in two dimensions. In the presence of an orbital field the hybridization-dependence of the excitonic average ${ Δ=<{{d_i}^\dagger} {f_i}>}$ is modified. The exciton responses in subtle different ways for different chosen values of the magnetic flux consistent with Hofstadter's well-known spectrum. The excitonic average is suppressed by the application of magnetic field. We further examine the effect of Coulomb interaction and $f$-electron hopping on the condensation of exciton for some rational values of the applied magnetic field. The interband Coulomb interaction enhances the $Δ$ exponentially, while a non-zero $f$-electron hopping reduces it. A strong commensurability effect of the magnetic flux on the behaviour of the excitons is observed.

cond-mat.str-el↗

arXiv2015

Fracturing tests on reservoir rocks: Analysis of AE events and radial strain evolution

Fracturing in reservoir rocks is an important issue for the petroleum industry - as productivity can be enhanced by a controlled fracturing operation. Fracturing also has a big impact on CO2 storage, geothermal installation and gas production at and from the reservoir rocks. Therefore, understanding the fracturing behavior of different types of reservoir rocks is a basic need for planning field operations towards these activities. In our study, the fracturing of rock sample is monitored by Acoustic Emission (AE) and post-experiment Computer Tomography (CT) scans. The fracturing experiments have been performed on hollow cylinder cores of different rocks - sandstones and chalks. Our analysis show that the amplitudes and energies of acoustic events clearly indicate initiation and propagation of the main fractures. The amplitudes of AE events follow an exponential distribution while the energies follow a power law distribution. Time-evolution of the radial strain measured in the fracturing-test will later be compared to model predictions of fracture size.

physics.geo-ph↗

arXiv2015

Orbital Effects of Strong Magnetic Field on a 2-D Holstein Polaron

We investigate the orbital effects of strong external magnetic field on the ground state properties of a two dimensional holstein polaron, employing variational approaches based on the exact diagonalization (VAED). From the ground state energy and the wave function we calculate electron-phonon correlation function, the average phonon number and the Drude weight and investigate the evolution of a 2D holstein polaron as a function of the magnetic flux. Although the external magnetic field affects the polaron throughout the parameter regime, we show that the magnetic field has a stronger effect on a loosely bound (spatially extended) polaron. We also find that the magnetic field can be used as a tuning parameter, particularly for weakly coupled polaron, to reduce the spatial extent of a large polaron.

cond-mat.str-el↗

arXiv2014

Resonant magneto-optic rotation for magnetometry using autonomous frequency stabilization

The operation of a high sensitive atomic magnetometer using resonant elliptically polarized light is demonstrated. The experimental geometry allows autonomous frequency stabilization of the laser, thereby offers compact operation of the overall device. The magnetometry is based on measurement of the zero magnetic field resonance in degenerate two level system using polarimetric detection and has a preliminary sensitivity of <10 pT/Hz1/2 @ 1 Hz.

physics.atom-ph↗

arXiv2013

A non-scanning atomic magnetometer based on coherent population trapping

The method of operation of an atomic magnetometer based on coherent population trapping (CPT) without any requirement of radio frequency scanning is demonstrated. Using a hybrid approach comprising of polarization rotation and tailored transmission due to CPT states, the simultaneous operation of the device as atomic frequency standard as well as atomic magnetometer is investigated. The magnetometer sensitivity can be further improved by utilizing the inherent option of magnetic field assisted synchronized radio frequency scanning.

physics.atom-ph↗

arXiv2012

Non-linear magneto-optic and self polarization rotation by superposition of states

We report the observation of enhanced magneto-optic rotation as the coherent superposition of different hyperfine states is established in an atomic sample. The polarization rotation near the two photon Raman resonance condition appears to have an analogous characteristic to the well established Faraday rotation observed in the vicinity of a single photon resonance, however it contains sharp features arising from coherent population trapping state. The profile of the two photon rotation signal exhibits interesting features for slightly imbalanced circular polarization component of the laser field as well as for on and away from the single photon resonance. The investigation can be used to explore the effect of superposition states generated by coherent population trapping on optical activity. A complete density matrix based numerical simulation that consistently captures all the relevant features of the experiment is presented.

physics.optics↗

arXiv2008

A student designed experiment measuring the speed of sound as a function of altitude

Relatively inexpensive and readily commercially available equipment (such as digital recorders, MP3 portable speakers and tie-pin microphones), allowed a team of students from McNeese State University to measure the speed of sound in the atmosphere as a function of altitude. The experiment was carried as a payload (in the context of a NASA funded student program called La-ACES) on a high altitude balloon that reached a maximum altitude of 101,000 feet. Not withstanding substantial environmental noise, our particular experimental design allowed for the filtering of the signal out of the noise, thus achieving remarkable accuracy and precision. The speed of sound measurement was then used to set limits on the abundances of the main molecular components of the atmosphere (diatomic nitrogen and oxygen). Bayesian analysis was used to set meaningful values on the uncertainty of our limits. It is our experience that students find intutive and appealing this type of probability method.

physics.ed-ph↗