arXiv subjects

Soumya Chakraborty

Publications and source records attributed to Soumya Chakraborty.

13 recordsLinked to original sources

arXiv2026

Viscoelastic dynamics of nanoparticles optically trapped in moving fringe pattern in air-filled hollow-core fiber

We report optical trapping and transport of nanoparticles in a moving interference pattern in hollow-core photonic crystal fiber at atmospheric pressure, when competition between trapping and drag forces causes the particle velocity to oscillate as it is momentarily captured and accelerated by each passing fringe, followed by release and deceleration by viscous forces. As a result the average particle velocity is lower than the fringe velocity. We refer to this phenomenon as drag-trapping. An analytical model of the resulting motion shows excellent agreement with experiment. Additional control is possible by introducing an imbalance in the backward and forward powers. The high precision of this new technique makes it of interest for example in characterizing nanoparticles, exploring viscous drag forces in different gases and liquids, and temperature sensing.

physics.optics↗

arXiv2026

Optomagnetic forces on YIG/YFeO3 microspheres levitated in chiral hollow-core photonic crystal fibre

We explore a magnetooptomechanical system consisting of a single magnetic microparticle optically levitated within the core of a helically twisted single-ring hollow-core photonic crystal fibre. We use newly-developed magnetic particles that have a core of antiferromagnetic yttrium-ortho-ferrite (YFeO3) and a shell of ferrimagnetic YIG (Y3Fe5O12) approximately 50 nm thick. Using a 632.8 nm probe beam, we observe optical-torque-induced rotation of the particle and rotation of the magnetization vector in presence of an external static magnetic field. This one-of-a-kind platform opens a path to novel investigations of optomagnetic physics with levitated magnetic particles.

physics.optics↗

arXiv2025

Quantum Coulomb Blockade in Orbital Resolved Phosphorus Triple-Donor Molecule

Multi-donor architecture in silicon offers a promising direction towards scalable solid-state qubits and quantum technologies operating at practical conditions. However, the overlap of multiple donor wave-functions develops a complex internal electronic configuration with several discrete energy levels. Probing these discrete-correlated states is essential for understanding inter-donor coupling and exchange interactions towards their practical implementations in quantum-technologies. We have experimentally demonstrated quantum Coulomb blockade mediated systematic filling of several electrons into orbital-resolved molecular states within multi-phosphorous-donor molecules accompanied by a correlated decrement in charging energies for higher hybridized orbitals due to expanded Bohr radii and electron delocalization. Corresponding, first-principle density functional theory calculations offer microscopic insight into the orbital configurations, while the rate equation simulations of quantum Coulomb blockade faithfully reproduce the experimental stability diagrams. This comprehensive characterization advances and discusses the role of donor-molecules in silicon in scalable building blocks for quantum technologies operable at elevated temperatures.

cond-mat.mes-hall↗

arXiv2025

A Componentwise Estimation Procedure for Multivariate Location and Scatter: Robustness, Efficiency and Scalability

Covariance matrix estimation is an important problem in multivariate data analysis, both from theoretical as well as applied points of view. Many simple and popular covariance matrix estimators are known to be severely affected by model misspecification and the presence of outliers in the data; on the other hand robust estimators with reasonably high efficiency are often computationally challenging for modern large and complex datasets. In this work, we propose a new, simple, robust and highly efficient method for estimation of the location vector and the scatter matrix for elliptically symmetric distributions. The proposed estimation procedure is designed in the spirit of the minimum density power divergence (DPD) estimation approach with appropriate modifications which makes our proposal (sequential minimum DPD estimation) computationally very economical and scalable to large as well as higher dimensional datasets. Consistency and asymptotic normality of the proposed sequential estimators of the multivariate location and scatter are established along with asymptotic positive definiteness of the estimated scatter matrix. Robustness of our estimators are studied by means of influence functions. All theoretical results are illustrated further under multivariate normality. A large-scale simulation study is presented to assess finite sample performances and scalability of our method in comparison to the usual maximum likelihood estimator (MLE), the ordinary minimum DPD estimator (MDPDE) and other popular non-parametric methods. The applicability of our method is further illustrated with a real dataset on credit card transactions.

stat.ME↗

arXiv2025

Phase-adaptive cooling of fringe-trapped nanoparticles at room temperature in hollow-core photonic crystal fiber

Active feedback cooling of levitated dielectric particles is a pivotal technique for creating ultrasensitive sensors and probing fundamental physics. Here we demonstrate phase-adaptive feedback cooling of silica nanoparticles optically trapped in standing-wave potential formed by two co-linearly polarized counterpropagating diffraction-free guided modes in a hollow-core photonic crystal fiber at room temperature. Unlike standard laser intensity- or Coulomb force-based feedback, our approach modulates the relative optical phase between the counterpropagating fundamental modes proportionally to the particle's axial momentum. This generates a Stokes-like dissipative force which effectively damps the center-of-mass motion without introducing excess heating and can also work with uncharged particles. At 2 mbar air pressure, the axial center-of-mass temperature of a 195 nm silica particle is reduced by half upon application of the feedback and to 58.6 K at 0.5 mbar. The measured mechanical spectra agree well with our analytical model, validating the cooling mechanism. We envision this approach will open up pathways towards long-range, coherent control of mesoscopic particles inside hollow-core fibers, offering a fiber-integrated versatile platform for future quantum manipulation.

physics.optics↗

arXiv2024

A dynamical system analysis of bouncing cosmology with spatial curvature

The present work deals with a FLRW cosmological model with spatial curvature and minimally coupled scalar field as the matter content. The curvature term behaves as a perfect fluid with the equation of state parameter w_K = -1/3 Using suitable transformation of variables, the evolution equations are reduced to an autonomous system for both power law and exponential form of the scalar potential. The critical points are analyzed with center manifold theory and stability has been discussed. Also, critical points at infinity have been studied using the notion of Poincare sphere. Finally, the cosmological implications of the critical points and cosmological bouncing scenarios are discussed. It is found that the cosmological bounce takes place near the points at infinity when the non-isolated critical points on the equator of the Poincare sphere are saddle or saddle-node in nature.

gr-qc↗

arXiv2024

Dynamical system analysis of quintessence dark energy model

Our work deals with the dynamical system analysis of quintessence dark energy scalar field model with exponential potential. A dynamical system analysis has been applied at the background level. Using suitable transformation of variables, the evolution equations are reduced to an autonomous system for exponential form of the scalar potential. The critical points are analyzed with center manifold theory and stability has been discussed by using Schwarzian derivative. Finally, cosmological implications of the critical points are discussed and it is found that the stability of the late-time attractor changes for quintessence dark energy model.

gr-qc↗

arXiv2024

Room Temperature Quantum Control of N-Donor Electrons at Si/SiO2 Interface

The manuscript theoretically discusses various important aspects for donor atom based single qubit operations in silicon (Si) quantum computer architecture at room temperature using a single nitrogen (N) deep-donor close to the Si/SiO2 interface. Quantitative investigation of room temperature single electron shuttling between a single N-donor atom and the interface is the focus of attention under the influence of externally applied electric and magnetic field. To apprehend the realistic experimental configurations, central cell correction along with effective mass approach is adopted throughout the study. Furthermore, a detailed discussion currently explores the significant time scales implicated in the process and their suitability for experimental purposes. Theoretical estimates are also provided for all the external fields required to successfully achieve coherent single electron shuttling and their stable maintenance at the interface as required. The results presented in this work offer practical guidance for quantum electron control using N-donor atoms in Si at room temperature.

cond-mat.mes-hall↗

arXiv2023

Robust Clustering with Normal Mixture Models: A Pseudo $β$-Likelihood Approach

As in other estimation scenarios, likelihood based estimation in the normal mixture set-up is highly non-robust against model misspecification and presence of outliers (apart from being an ill-posed optimization problem). A robust alternative to the ordinary likelihood approach for this estimation problem is proposed which performs simultaneous estimation and data clustering and leads to subsequent anomaly detection. To invoke robustness, the methodology based on the minimization of the density power divergence (or alternatively, the maximization of the $β$-likelihood) is utilized under suitable constraints. An iteratively reweighted least squares approach has been followed in order to compute the proposed estimators for the component means (or equivalently cluster centers) and component dispersion matrices which leads to simultaneous data clustering. Some exploratory techniques are also suggested for anomaly detection, a problem of great importance in the domain of statistics and machine learning. The proposed method is validated with simulation studies under different set-ups; it performs competitively or better compared to the popular existing methods like K-medoids, TCLUST, trimmed K-means and MCLUST, especially when the mixture components (i.e., the clusters) share regions with significant overlap or outlying clusters exist with small but non-negligible weights (particularly in higher dimensions). Two real datasets are also used to illustrate the performance of the newly proposed method in comparison with others along with an application in image processing. The proposed method detects the clusters with lower misclassification rates and successfully points out the outlying (anomalous) observations from these datasets.

stat.ME↗

arXiv2023

A study of interacting scalar field model from the perspective of the dynamical systems theory

In this work, considering the background dynamics of flat Friedmann-Lemaitre-Robertson-Walker(FLRW) model of the universe, we investigate a scalar field model as dark energy candidate which interacting with the pressure-less dust as dark matter from dynamical systems perspective. From phenomenological vantage point two interaction terms are chosen: one depends on Hubble parameter $H$ and other is local, independent of Hubble parameter. In interaction model 1, the scalar field potential as well as the coupling are considered to be in the form of inverse square and accordingly a two-dimensional autonomous system is obtained. On the other hand, Interaction model 2 comprises with the potential as well as coupling of scalar field which are considered in form of exponential function of scalar field ($ϕ$) and as a result of which a four-dimensional autonomous system is achieved. We study two systems separately and come by several critical points in 2D system as well as in 4D system. We have derived sound speed and the classical stability conditions. Furthermore, for 2D autonomous system we analyzed the stability of some critical points at infinity. From this autonomous system, we obtain scalar field dominated solutions representing late time accelerated evolution of the universe that does not elucidate the coincidence problem. Late time scaling solutions are also realized by the accelerated expansion of the universe which evolves in quintessence era that alleviates the coincidence problem successfully. From the analysis of 4D system, we obtain non-hyperbolic sets of critical points which are analyzed by the center manifold theory. In this model, the de Sitter like solutions represent the transient evolution of the universe.

gr-qc↗

arXiv2023

Existence and Consistency of the Maximum Pseudo \b{eta}-Likelihood Estimators for Multivariate Normal Mixture Models

Robust estimation under multivariate normal (MVN) mixture model is always a computational challenge. A recently proposed maximum pseudo \b{eta}-likelihood estimator aims to estimate the unknown parameters of a MVN mixture model in the spirit of minimum density power divergence (DPD) methodology but with a relatively simpler and tractable computational algorithm even for larger dimensions. In this letter, we will rigorously derive the existence and weak consistency of the maximum pseudo \b{eta}-likelihood estimator in case of MVN mixture models under a reasonable set of assumptions.

math.ST↗

arXiv2022

Inelastic Cotunneling Resonances in the Coulomb-Blockade Transport in Donor-Atom Transistors

We report finite-bias characteristics of electrical transport through phosphorus donors in silicon nanoscale transistors, in which we observe inelastic-cotunneling current in the Coulomb blockade region. The cotunneling current appears like a resonant-tunneling current peak emerging from the excited state at the crossover between blockade and non-blockade regions. These cotunneling features are unique, since the inelastic-cotunneling currents have so far been reported either as a broader hump or as a continuous increment of current. This finding is ascribed purely due to excitation-related inelastic cotunneling involving the ground and excited states. Theoretical calculations were performed for a two-level quantum dot, supporting our experimental observation.

cond-mat.mes-hall↗

arXiv2020

A Dynamical System Analysis of cosmic evolution with coupled phantom dark energy with dark matter

The present work is an example of the application of the dynamical system analysis in the context of cosmology. Here cosmic evolution is considered in the background of homogeneous and isotropic flat Friedmann-Lemaître-Robertson-Walker space-time with interacting dark energy and varying mass dark matter as the matter content. The Dark Energy (DE) is chosen as phantom scalar field with self-interacting potential while the Dark Matter (DM) is in the form of dust. The potential of the scalar field and the mass function of dark matter are chosen as exponential or power-law form or in their product form. Using suitable dimensionless variables the Einstein field equations and the conservation equations constitute an autonomous system. The stability of the non-hyperbolic critical points are analyzed by using center manifold theory. Finally, cosmological phase transitions have been detected through bifurcation analysis which has been done by Poincaré index theory.

gr-qc↗