arXiv subjects

P. K. Panigrahi

Publications and source records attributed to P. K. Panigrahi.

At least 19 recordsLinked to original sources

arXiv2026

Evaporative cooling and deposition patterns of evaporating $Al_2O_3$ nanofluid droplets

The present study examines evaporative cooling and the resulting deposition patterns of a sessile $Al_2O_3$-based nanofluid droplet on a hydrophobic glass substrate at different temperatures. Evaporation predominantly occurs in the pinned contact line mode for both heated and non-heated cases, with only slight recession observed without heating. The droplet height and contact angle decrease linearly with time, and scaling relations are proposed to describe the evolution of droplet geometry and volume. A non-dimensional parameter, $Π_{rel}$, is introduced to characterize transitions in deposition patterns. For $Π_{rel} \leq 1$ ($T_s \leq 26^\circ$C), interconnected irregular polygonal network structures form at the periphery, which are rarely reported in evaporating droplets. With increasing substrate temperature, this structure is suppressed, giving rise to a classical coffee-ring pattern for $1 < Π_{rel} \leq 10$. At higher temperatures ($T_s > 40^\circ$C), dual-ring formation along with central particle deposition is observed for $Π_{rel} > 10$. The interfacial temperature is higher near the contact line and decreases toward the apex, and a universal scaling for the temperature profile is proposed. Internal flow velocity increases with substrate temperature, exhibiting asymmetric multi-vortex structures. Evaporative cooling intensifies with heating, enhancing evaporation flux and capillary flow. Appropriate scaling relations for evaporation flux and capillary velocity are established. Overall, the dynamics are governed by thermocapillary (Marangoni) flow induced by evaporative cooling, which enhances internal circulation and governs nanoparticle deposition morphology.

physics.flu-dyn↗

arXiv2026

Frequency-Dependent Magnetic modulation of deposition morphology

This paper presents a novel approach for magnetic modulation of deposition morphology in an evaporating ferrofluid droplet. The magnetic field strength and ferrofluid concentration are kept unchanged, while the actuation frequencies are varied from 0.016 Hz to 5 Hz. In the absence of a magnetic field, a coffee-ring formation is observed and consistent with previous studies\cite{deegan1997capillary,deegan2000contact,saroj2019drying}. The application of a time-dependent magnetic field significantly modifies the deposition morphology. The periodic magnetic field induces the formation of multiple concentric rings during evaporation. The number of rings initially increases with increasing actuation frequency of the electromagnet. However, beyond a critical actuation frequency ($f_c = 0.2\,\text{Hz}$), the number of rings decreases. At higher actuation frequencies, magnetic particles preferentially deposit in the central region of the droplet, resulting in suppression of the coffee-ring effect. Additionally, the thickness of the inner rings and the ring spacing decrease with increasing actuation frequency up to critical actuation frequency. The transition from multi-ring formation to coffee-ring suppression is governed by the competition among magnetic forcing, capillary flow, and particle diffusion. The underlying physical mechanisms responsible for droplet dynamics and deposition morphology under periodic magnetic fields are evaluated using scaling arguments. The results demonstrate that diffusive particle transport plays a dominant role in determining the deposition pattern. A non-dimensional magnetic switching number, based on the magnetic perturbation timescale, is introduced as a control parameter to characterize the frequency-dependent deposition behavior.

physics.flu-dyn↗

arXiv2025

Ultrafast dynamics of carriers, coherent acoustic phonons and strain pulses in BiSbTe1.5Se1.5 topological insulator thin films

We Investigate the ultrafast carrier, coherent acoustic phonons (CAPs), and acoustic strain pulse dynamics in topological insulator BiSbTe1.5Se1.5 (BSTS) thin films of varying thickness using degenerate pump-probe reflection spectroscopy. Here, Sapphire has been chosen as the main substrate due to its maximum acoustic reflectivity at the BSTS-sapphire interface compared to BSTS-GaAs, BSTS-Si, and BSTS-MgO interfaces. For the films with thickness more than twice the penetration depth, the transient reflectivity data predominantly exhibits travelling acoustic strain pulses (TASP) on the top of single-exponential electronic decay (~ 2 ps). In contrast, films with thickness less than penetration depth are dominated by CAPs and a bi exponential electronic background with decay times of ~ 2 ps and ~ 260-380 ps. The observed TASP dynamics are well-described by a theoretical acoustic strain model. Further, to elucidate the underlying physical mechanisms governing the behavior of photo-excited carriers, CAPs, and strain pulses, we performed carrier density and temperature-dependent (7-294 K) studies on BSTS films with thicknesses of 22 nm and 192 nm. In the 22 nm film, the both fast and slow decay processes increase with carrier density at room temperature but decrease with temperature at a carrier density of 1.7*10^{19} cm^{-3}. A detailed analysis suggests that the faster decay arises from electron-phonon scattering and carrier diffusion, while the slower decay likely results from defect-assisted and phonon-assisted recombination. Furthermore, increasing the sample temperature leads to anharmonic decay induced softening of ~ 14 % in the phonon frequency and an anomalous ~ 48 % decrease in the phonon damping parameter due to reduced Dirac surface electron and acoustic phonon scattering.

cond-mat.mtrl-sci↗

arXiv2023

Electro optic effect measurements for waveguide inscribed in X-cut LiNbO3 substrate using femtosecond laser direct writing process

This work represents a particular application of waveguide fabricated by femtosecond laser micromachining technology. More specifically, we report the development of an optical modulator based on the fabrication of single-mode optical waveguide structures buried in X-cut lithium niobate crystal with the femtosecond laser direct writing method. Here, change in refractive index profile is measured using near field intensity profile measurement method at optimized writing conditions. It has been observed that the change refractive index (Δn) is in the range of 10-4. Finally, the behavior of femtosecond written waveguides as an intensity modulator at 632.8 nm and 1550 nm under the influence of an external electric field is analyzed by pattering electrode structures on the substrate respectively.

physics.optics↗

arXiv2023

Femtosecond Laser Engraved 2D Tunable Optofluidic Liquid Core/Air Cladding Channel Waveguides on PDMS

We have demonstrated the fabrication and characterization of 2D liquid-based multimode optical waveguide structures over a Polydimethylsiloxane (PDMS) material-based chip. Fabrication of two separate microstructures, one with a width of 14 microns and a depth of 27 microns while the other with a width as well as depth of 110 microns, was achieved by the femtosecond laser micromachining process. The dye solution is passed through the microstructure from one end to the other; wherein the dye solution acts as the core while PDMS and air act as the cladding medium. The femtosecond laser micromachining parameters are optimized in terms of laser power, pulse width, writing speed, focused beam size, etc. The quality of fabricated microstructures is confirmed by microscopic analysis. The confirmation of liquid-core/air cladding-based waveguide is obtained through spectral and modal analysis. The optical analysis has been done by using fluorescence light coupled out from waveguide structures filled with different dye solutions. These waveguide structures give strong light confinement and intense interaction between dye solution and pump light. The developed microstructures are tunable in terms of intensity, wavelength, and beam size. Such microstructures can be implemented in the design and development of lab-on-chip microlasers and sensing applications in any multifunction lab-on-chip devices.

physics.optics↗

arXiv2022

Quantum Blockchain Based on Dimensional Lifting Generalized Gram-Schmidt Procedure

The advancement of quantum computers undermines the security of classical blockchain, necessitating either a post-quantum upgrade of the existing architecture or creation of an inherently quantum blockchain. Here we propose a practically realizable model of a fully quantum blockchain based on a generalized Gram-Schmidt procedure utilizing dimensional lifting. In this model, information of transactions stored in a multi-qubit state are subsequently encoded using the generalized Gram-Schmidt process. The chain is generated as a result of the reliance of orthogonalized state on the sequence of states preceding it. Various forking scenarios and their countermeasures are considered for the proposed model. It is shown to be secure even against quantum computing attacks using the no-cloning theorem and non-democratic nature of Generalized Gram-Schmidt orthogonalization. Finally, we outline a framework for a quantum token built on the same architecture as our blockchain.

quant-ph↗

arXiv2022

Control of $^{164}$Dy Bose-Einstein condensate phases and dynamics with dipolar anisotropy

We investigate the quench dynamics of quasi-one and two dimensional dipolar Bose-Einstein condensates (dBEC) of $^{164}$Dy atoms under the influence of a fast rotating magnetic field. The magnetic field thus controls both the magnitude and sign of the dipolar potential. We account for quantum fluctuations, critical to formation of exotic quantum droplet and supersolid phases in the extended Gross-Pitaevskii formalism, which includes the so-called Lee-Huang-Yang (LHY) correction. An analytical variational ansatz allows us to obtain the phase diagrams of the superfluid and droplet phases. The crossover from the superfluid to the supersolid phase and to single and droplet arrays is probed with particle number and dipolar interaction. The dipolar strength is tuned by rotating the magnetic field with subsequent effects on phase boundaries. Following interaction quenches across the aforementioned phases, we monitor the dynamical formation of supersolid clusters or droplet lattices. We include losses due to three-body recombination over the crossover regime, where the three-body recombination rate coefficient scales with the fourth power of the scattering length ($a_s$) or the dipole length ($a_{dd}$). For fixed values of the dimensionless parameter, $ε_{dd} = a_{dd}/a_s$, tuning the dipolar anisotropy leads to an enhancement of the droplet lifetimes.

cond-mat.quant-gas↗

arXiv2018

Sub-Planck structure in a mixed state

The persistence of sub-Planck structure in phase space with loss of coherence is demonstrated in a mixed state, which comprises two terms in the density matrix. Its utility in carrying out Heisenberg-limited measurement and quantum parameter estimation have been shown. It is also shown that the mixed state performs equally well as the compass state for carrying out precision measurements. The advantage of using mixed state relies on the fact that such a state can be easier to prepare and may appear from pure states after partial loss of coherence. We explicate the effect of environment on these sub-Planck structures in the mixed state and estimates the time scale of complete decoherence.

quant-ph↗

arXiv2018

An educational website on interferometry

The present work describes a website designed for remote teaching of optical measurements using lasers. It enables senior undergraduate and postgraduate students to learn theoretical aspects of the subject and also have a means to perform experiments for better understanding of the application at hand. At this stage of web development, optical methods considered are those based on refractive index changes in the material medium. The website is specially designed in order to provide remote access of expensive lasers, cameras, and other laboratory instruments by employing a commercially available web browser. The web suite integrates remote experiments, hands-on experiments and life-like optical images generated by using numerical simulation techniques based on Open Foam software package. The remote experiments are real time experiments running in the physical laboratory but can be accessed remotely from anywhere in the world and at any time. Numerical simulation of problems enhances learning, visualization of problems and interpretation of results. In the present work hand-on experimental results are discussed with respect to simulated results. A reasonable amount of resource material, specifically theoretical background of interferometry is available on the website along with computer programs image processing and analysis of results obtained in an experiment.

physics.ed-ph↗

arXiv2017

Joint weak value for all order coupling using continuous variable and qubit probe

The notion of weak measurement in quantum mechanics has gained a significant and wide interest in realizing apparently counterintuitive quantum effects. In recent times, several theoretical and experimental works have been reported for demonstrating the joint weak value of two observables where the coupling strength is restricted to the second order. In this paper, we extend such a formulation by providing a complete treatment of joint weak measurement scenario for all-order-coupling for the observable satisfying $A^2=\mathbb{I}$ and $A^2=A$, which allows us to reveal several hitherto unexplored features. By considering the probe state to be discrete as well as continuous variable, we demonstrate how the joint weak value can be inferred for any given strength of the coupling. A particularly interesting result we pointed out that even if the initial pointer state is uncorrelated, the single pointer displacement can provide the information about the joint weak value, if at least third order of the coupling is taken into account. As an application of our scheme, we provide an all-order-coupling treatment of the well-known Hardy paradox by considering the continuous as well as discrete meter states and show how the negative joint weak probabilities emerge in the quantum paradoxes at the weak coupling limit.

quant-ph↗

arXiv2017

Submicron scale tissue multifractal anisotropy in polarized light scattering

A number of disordered systems exhibit local anisotropy in the fractal or multifractal correlation and in the resulting scaling behavior, which contain wealth of information on the system. Here, we demonstrate that the spatial dielectric fluctuations in a random medium like biological tissue exhibit such multifractal anisotropy, leaving its unique signature in the wavelength variation of the light scattering Mueller matrix and manifesting as an intriguing spectral diattenuation effect. We have thus developed an inverse analysis method for the quantification of the multifractal anisotropy from the scattering Mueller matrix. The method is based on processing the relevant Mueller matrix elements in Fourier domain using Born approximation followed by multifractal analysis. Application of this technique on tissues of human cervix ex vivo demonstrate the potential of the multifractal anisotropy parameters as novel biomarkers for screening subtle micro-structural changes associated with precancers. Sensing structural anisotropy in the sub-micron length scale via the multifractal anisotropy parameters may prove valuable for non-invasive characterization of a wide class of complex materials and disordered scattering media.

physics.optics↗

arXiv2016

Efimov-like Resonances in Planar QED

It is shown that planar topological effective gauge theory with dynamics, acquires corrections to angular momentum beyond the well-known topological photon spin, the latter arising from interactions with parity-breaking massive fermions. In the non-relativistic limit, a first quantized Schroedinger representation is possible where the topological and kinetic terms decouple, the latter contributing to angular momentum and compete with the centrifugal barrier. This results in shallow resonances of Efimov kind, which may be verified in planar physical systems.

hep-th↗

arXiv2016

Novel symmetries in Weyl-invariant gravity with massive gauge field

The background field method is used to linearize the Weyl invariant scalar-tensor gravity, coupled with a Stueckelberg field. For a generic background metric, this action is found to be not invariant, under both diffeomorphism and generalized Weyl symmetry, the latter being a combination of gauge and Weyl transformations. Interestingly, the quadratic Lagrangian, emerging from a background of Minkowski metric, respects both the transformations, independently. Becchi-Rouet-Stora-Tyutin (BRST) symmetry of scalar-tensor gravity coupled with a Stueckelberg-like massive gauge particle, possessing diffeomorphism and generalized Weyl symmetry, reveals that in both the cases, negative norm states with unphysical degrees of freedom do exist. We then show that, by combining diffeomorphism and generalized Weyl symmetries, all the ghost states decouple, thereby removing the unphysical redundancies of the theory. During this process, the scalar field does not represent any dynamic mode, yet modifies the usual harmonic gauge condition through non-minimal coupling with gravity.

hep-th↗

arXiv2015

Selective observation of Goos-Hänchen and Imbert-Federov shifts in partial reflection via optimized weak measurements in linear and elliptical polarization basis

The spatial and the angular variants of the Goos-Hänchen (GH) and the Imbert-Federov (IF) beam shifts contribute in a complex interrelated way to the resultant beam shift in partial reflection at planar dielectric interfaces. Here, we show that the angular GH and the two variants of the IF effects can be decoupled, amplified and separately observed by weak value amplification and subsequent conversion of spatial$\leftrightarrow$angular nature of the beam shifts using appropriate pre and post selection of polarization states. We experimentally demonstrate such decoupling and illustrate various other intriguing manifestations of weak measurements by employing optimized pre and post selections (based on the eigen polarization states of the shifts) elliptical and / or linear polarization basis. The demonstrated ability to amplify, controllably decouple or combine the beam shifts via weak measurements may prove to be valuable for understanding the different physical contributions of the effects and for their applications in sensing and precision metrology

physics.optics↗

arXiv2015

Complex Solitary Waves and Soliton Trains in KdV and mKdV Equations

We demonstrate the existence of complex solitary wave and periodic solutions of the Kortweg de-vries (KdV) and modified Kortweg de-Vries (mKdV) equations. The solutions of the KdV (mKdV) equation appear in complex-conjugate pairs and are even (odd) under the simultaneous actions of parity ($\cal{P}$) and time-reversal ($\cal{T}$) operations. The corresponding localized solitons are hydrodynamic analogs of Bloch soliton in magnetic system, with asymptotically vanishing intensity. The $\cal{PT}$-odd complex soliton solution is shown to be iso-spectrally connected to the fundamental $sech^2$ solution through supersymmetry.

math-ph↗

arXiv2014

Effect of high frequency modes of medium on an open quantum system

We present a method to calculate the real time effective propagator of a generic open quantum system, immersed in a medium using a wave function based framework. The medium is characterised by a set of harmonic oscillators having a continuous span of frequencies. This technique has been applied to the Caldeira-Leggett model showing that high frequency modes of the medium do not contribute towards decay of the population of states of the open system. In fact, they cause a Rabi type oscillation. Moreover, our wave function based approach provides an excellent alternative to conventional formalisms involving the density matrix.

nucl-th↗

arXiv2013

Comment on "Weak Measurements with Orbital-Angular-Momentum Pointer states"

In a recent Letter (Phys. Rev. Lett. 109, 040401 (2012)), G. Puentes, N. Hermosa and J. P. Torres report a scheme for extracting higher-order weak values by using orbital-angular momentum states as pointer states. They claim that such weak values are inaccessible with a Gaussian pointer state only. In this Comment, we show that the Gaussian pointer state by itself can provide access to the higher-order weak value, if suitable pointer displacement is observed.

quant-ph↗

arXiv2013

Cat state, sub-Planck structure and weak measurement

Heisenberg-limited and weak measurements are the two intriguing notions, used in recent times for enhancing the sensitivity of measurements in quantum metrology. Using a quantum cat state, endowed with sub-Planck structure, we connect these two novel concepts. It is demonstrated that these two phenomena manifest in complementary regimes, depending upon the degree of overlap between the mesoscopic states constituting the cat state under consideration. In particular, we find that when sub-Planck structure manifests, the imaginary weak value is obscured and vice-versa.

quant-ph↗