Searcharxiv⌕ Search

arXiv subjects

Sutapa Ghosh

Publications and source records attributed to Sutapa Ghosh.

At least 19 recordsLinked to original sources
arXiv2026

RCSB PDB AI Help Desk: retrieval-augmented generation for protein structure deposition support

Motivation: Structural Biologists have contributed more than 245,000 experimentally determined three-dimensional structures of biological macromolecules to the Protein Data Bank (PDB). Incoming data are validated and biocurated by ~20 expert biocurators across the wwPDB. RCSB PDB biocurators who process more than 40% of global depositions face increasing challenges in maintaining efficient Help Desk operations, with approximately 19,000 messages in approximately 8,000 entries received from depositors in 2025. Results: We developed an AI-powered Help Desk using Retrieval-Augmented Generation (RAG) built on LangChain with a pgvector store (PostgreSQL) and GPT-4.1-mini. The system employs pymupdf4llm for Markdown-preserving PDF extraction, two-stage document chunking, Maximal Marginal Relevance retrieval, a topical guardrail that filters off-topic queries, and a specialized system prompt that prevents exposure of internal terminology. A dual-LLM architecture uses separate model configurations for question condensing and response generation. Deployed in production on Kubernetes with PostgreSQL (pgvector), it provides around-the-clock depositor assistance with citation-backed, streaming responses. Availability and implementation: Freely available at https://rcsb-deposit-help.rcsb.org.

cs.IR↗
arXiv2025

Tunable N-level EIT: Deterministic Generation of Optical States with Negative Wigner Function

Strong optical nonlinearities are key to a range of technologies, particularly in the generation of photonic quantum states. The strongest nonlinearity in hot atomic vapors originates from electromagnetically induced transparency (EIT), which, while effective, often lacks tunability and suffers from significant losses due to atomic absorption. We propose and demonstrate an N-level EIT scheme, created by an optical frequency comb that excites a warm rubidium vapor. The massive number of comb lines simultaneously drive numerous transitions that interfere constructively to induce a giant and highly tunable cross-Kerr optical nonlinearity. The obtained third-order nonlinearity values range from $1.2 \times 10^{-7}$ to $7.7 \times 10^{-7}$ $m^2 V^{-2}$. Above and beyond that, the collective N-level interference can be optimized by phase shaping the comb lines using a spectral phase mask. Each nonlinearity value can then be tuned over a wide range, from 40\% to 250\% of the initial strength. We utilize the nonlinearity to demonstrate squeezing by self polarization rotation of CW signals that co-propagate with the pump and are tuned to one of the EIT transparent regions. Homodyne measurements reveal a quadrature squeezing level of 3.5 dB at a detuning of 640 MHz. When tuned closer to an atomic resonance, the nonlinearity is significantly enhanced while maintaining low losses, resulting in the generation of non-Gaussian cubic phase states. These states exhibit negative regions in their Wigner functions, a hallmark of quantum behavior. Consequently, N-level EIT enables the direct generation of photonic quantum states without requiring postselection.

quant-ph↗
arXiv2022

Combined time and frequency spectroscopy with engineered dual comb spectrometer

Dual comb spectroscopy (DCS) is a powerful technique for broadband spectroscopy with high precision and fast data acquisition. High-frequency resolution requires long data acquisition times, limiting the temporal resolution in time-resolved measurements. Here we overcome this limitation by engineering the DCS pulse train that interacts with the sample. The measurement is performed in steps where the number of pulses interacting with the sample varies in each step. The DCS spectrum is recorded in each stage, and a multi-dimensional spectrum is generated from which the system time evolution is deduced. We demonstrate this method by measuring the absorption spectrum of a room temperature rubidium vapor. The measured population dynamics of the excited state show a square dependence on the number of interacting pulses due to the coherent accumulation of population. Rabi oscillations are also observed under intense excitation conditions. This is the first demonstration of DCS with high frequency and time resolutions without invoking pump-probe spectroscopy, uniting the pulsed laser spectral and temporal properties. This method can simultaneously detect the kinetics of different chemical species and the pathway for the chemical reaction.

physics.optics↗
arXiv2022

A phase stable hybrid dual comb spectrometer

Dual comb spectroscopy (DCS) is a broadband technique offering high resolution and fast data acquisition. We describe a hybrid dual comb spectrometer comprising a broadband commercial fiber laser system offering a wide range of sample interrogation, and an actively mode locked semiconductor laser (MLL) having a widely tunable, relatively narrow spectrum. The mutual coherence over 100 seconds has been realized between the two combs. We employed the DCS system to characterize the absorption spectrum of rubidium atoms at 313 K with a high signal to noise ratio. The broadband laser is directly locked on a high finesse cavity, providing long-term stability, while the semiconductor laser is locked to it. To characterize the absolute stability of the DCS system, the linewidth of the MLL comb line is measured and shown to reduce from 880 kHz to $17$ kHz when the system is fully locked. The long-term stability was measured to be $5 \times 10^{-12}$ at $1$ second and $5 \times 10^{-14}$ at $350$ seconds. The measured timing jitter of the MLL is ten times smaller due to the overall locking. In addition, we have addressed the effect of dispersion on the locking quality, which is significant for broadband comb lasers.

physics.optics↗
arXiv2017

Fast non-destructive parallel readout of neutral atom registers in optical potentials

We demonstrate the parallel and non-destructive readout of the hyperfine state for optically trapped $^{87}$Rb atoms. The scheme is based on state-selective fluorescence imaging and achieves detection fidelities $>$98% within 10$\,$ms, while keeping 99% of the atoms trapped. For the read-out of dense arrays of neutral atoms in optical lattices, where the fluorescence images of neighboring atoms overlap, we apply a novel image analysis technique using Bayesian inference to determine the internal state of multiple atoms. Our method is scalable to large neutral atom registers relevant for future quantum information processing tasks requiring fast and non-destructive readout and can also be used for the simultaneous read-out of quantum information stored in internal qubit states and in the atoms' positions.

physics.atom-ph↗
arXiv2017

State-dependent fluorescence of neutral atoms in optical potentials

Recently we have demonstrated scalable, non-destructive, and high-fidelity detection of the internal state of $^{87}$Rb neutral atoms in optical dipole traps using state-dependent fluorescence imaging [M. Martinez-Dorantes et al., PRL, 2017]. In this article we provide experimental procedures and interpretations to overcome the detrimental effects of heating-induced trap losses and state leakage. We present models for the dynamics of optically trapped atoms during state-dependent fluorescence imaging and verify our results by comparing Monte Carlo simulations with experimental data. Our systematic study of dipole force fluctuations heating in optical traps during near-resonant illumination shows that off-resonant light is preferable for state detection in tightly confining optical potentials.

physics.atom-ph↗
arXiv2017

Thomas-Fermi Model in Rindler Space

In this article we have investigated the Thomas-Fermi model for the electron gas in Rindler space. We have found that if the uniform acceleration is along $+x$-direction, then there is $y-z$-symmetry in space. For the sake of mathematical simplicity, we have assumed two dimensional spatial structure ($x-y$) in Rindler space. It has been observed that in two dimensional spatial coordinates the electrons are distributed discontinuously but in a periodic manner in a number of rectangular strips like domain along $\pm y$-direction. Some of them are having void structure, with no electrons inside such rectangular strips, while some are filled with electrons. We call the later type domain as the normal zone. We have also given physical interpretation for such exotic type electron distribution in Rindler space.

gr-qc↗
arXiv2016

High Finesse Fiber Fabry-Perot Cavities: Stabilization and Mode Matching Analysis

Fiber Fabry-Perot cavities, formed by micro-machined mirrors on the end-facets of optical fibers, are used in an increasing number of technical and scientific applications, where they typically require precise stabilization of their optical resonances. Here, we study two different approaches to construct fiber Fabry-Perot resonators and stabilize their length for experiments in cavity quantum electrodynamics with neutral atoms. A piezo-mechanically actuated cavity with feedback based on the Pound-Drever-Hall locking technique is compared to a novel rigid cavity design that makes use of the high passive stability of a monolithic cavity spacer and employs thermal self-locking and external temperature tuning. Furthermore, we present a general analysis of the mode matching problem in fiber Fabry-Perot cavities, which explains the asymmetry in their reflective line shapes and has important implications for the optimal alignment of the fiber resonators. Finally, we discuss the issue of fiber-generated background photons. We expect that our results contribute towards the integration of high-finesse fiber Fabry-Perot cavities into compact and robust quantum-enabled devices in the future.

physics.atom-ph↗
arXiv2015

The Hawking Radiation as Gravitational Fowler-Nordheim Emission in Uniformly Accelerated Frame, in The Non-Relativistic Scenario

In the conventional scenario, the Hawking radiation is believed to be a tunneling process at the event horizon of the black hole. In the quantum field theoretic approach the Schwinger's mechanism is generally used to give an explanation of this tunneling process. It is the decay of quantum vacuum into particle anti-particle pairs near the black hole surface. However, in a reference frame undergoing an uniform accelerated motion in an otherwise flat Minkowski space-time geometry, in the non-relativistic approximation, the particle production near the event horizon of a black hole may be treated as a kind of Fowler-Nordheim field emission, which is the typical electron emission process from a metal surface under the action of an external electrostatic field. This type of emission from metal surface is allowed even at extremely low temperature. It has been noticed that in one-dimensional scenario, the Schr$\ddot{\rm{o}}$dinger equation satisfied by the created particle (anti-particle) near the event horizon, can be reduced to a differential form which is exactly identical with that obeyed by an electron immediately after the emission from the metal surface under the action of a strong electrostatic field. The mechanism of particle production near the event horizon of a black hole is therefore identified with Schwinger process in relativistic quantum field theory, whereas in the non-relativistic scenario it may be interpreted as Fowler-Nordheim emission process, when observed from an uniformly accelerated frame.

astro-ph.HE↗
arXiv2010

A Theoretical Study of the Equation of States for Crustal Matter of Strongly Magnetized Neutron Stars

We have investigated some of the properties of dense sub-nuclear matter at the crustal region (both the outer crust and the inner crust region) of a magnetar. The relativistic version of Thomas-Fermi (TF) model is used in presence of strong quantizing magnetic field for the outer crust matter. The compressed matter in the outer crust, which is a crystal of metallic iron, is replaced by a regular array of spherically symmetric Wigner-Seitz (WS) cells. In the inner crust region, a mixture of iron and heavier neutron rich nuclei along with electrons and free neutrons has been considered. Conventional Harrison-Wheeler (HW) and Bethe-Baym-Pethick (BBP) equation of states are used for the nuclear mass formula. A lot of significant changes in the characteristic properties of dense crustal matter, both at the outer crust and the inner crust, have been observed.

astro-ph.SR↗
arXiv2008

The Study of Relatively Low Density Stellar Matter in Presence of Strong Quantizing Magnetic Field

The effect of strong quantizing magnetic field on the equation of state of matter at the outer crust region of magnetars is studied. The density of such matter is low enough compared to the matter density at the inner crust or outer core region. Based on the relativistic version of semi-classical Thomas-Fermi-Dirac model in presence of strong quantizing magnetic field a formalism is developed to investigate this specific problem. The equation of state of such low density crustal matter is obtained by replacing the compressed atoms/ions by Wigner-Seitz cells with nonuniform electron density. The results are compared with other possible scenarios. The appearance of Thomas-Fermi induced electric charge within each Wigner-Seitz cell is also discussed.

astro-ph↗
arXiv2008

On the Low Surface Magnetic Field Structure of Quark Stars

Following some of the recent articles on hole super-conductivity and related phenomena by Hirsch \cite{H1,H2,H3}, a simple model is proposed to explain the observed low surface magnetic field of the expected quark stars. It is argued that the diamagnetic moments of the electrons circulating in the electro-sphere induce a magnetic field, which forces the existing quark star magnetic flux density to become dilute. We have also analysed the instability of normal-superconducting interface due to excess accumulation of magnetic flux lines, assuming an extremely slow growth of superconducting phase through a first order bubble nucleation type transition.

astro-ph↗
arXiv2006

On The Problem with Only Zeroth Landau Level Occupancy of Electrons / Protons in Strongly Magnetized Neutron Star Matter in $β$-equilibrium Condition- The Role of Anomalous Magnetic Moments

It is shown explicitly that if only the zeroth Landau level is occupied by electrons in strongly magnetized neutron star matter in $β$-equilibrium condition, then both the proton and neutron matter sectors become spin symmetric. Whereas, the study of Pauli para-magnetism of neutron matter sector shows that such a scenario is physically impossible. It is also shown that in dense stellar hadronic matter in $β$-equilibrium in presence of strong quantizing magnetic field, with $σ-ω-ρ$ exchange type mean field interaction and with the inclusion of magnetic dipole moments does not allow electrons to occupy only the zeroth Landau level.

astro-ph↗
arXiv2006

Neutron Star Equation of State and the Possibility of Complex Self-Energy in Landau Theory of Fermi Liquid in Presence of Strong Quantizing Magnetic Field

Using a relativistic version of Landau theory of Fermi liquid with $σ-ω$ and $ρ$ mesons exchange, we have obtained an equation of state for dense neutron star matter in presence of strong quantizing magnetic field. It is found that in this scenario the self energies of both neutron and proton components of dense neutron star matter become complex under certain physical conditions. To be more specific, it is observed that in the exchange diagrams of $σ$, $ω$ and neutral $ρ$ transfer processes and in the direct interaction diagram with $ρ_\pm$ transfer reactions, the nucleon self-energies become complex in nature.

astro-ph↗
arXiv2005

Chiral Properties of QCD Vacuum in Magnetars- A Nambu-Jona-Lasinio Model with Semi-Classical Approximation

The breaking of chiral symmetry of light quarks at zero temperature in presence of strong quantizing magnetic fiels is studied using Nambu-Jona-Lasinio (NJL) model with Thomas-Fermi type semi-classical formalism. It is found that the dynamically generated light quark mass can never become zero if the Landau levels are populated and the mass increases with the increase of magnetic field strength.

astro-ph↗
arXiv2004

Chiral Symmetry Breaking in Presence of Strong Quantizing Magnetic Fields- A Nambu-Jona-Lasino Model with Semi-Classical Approximation

The breaking of chiral symmetry of light quarks at zero temperature in presence of strong quantizing magnetic field is studied using Nambu-Jona-Lasinio (NJL) model with Thomas-Fermi type semi-classical formalism. It is found that the dynamically generated light quark mass can never become zero if the Landau levels are populated and increases with the increase of magnetic field strength.

astro-ph↗
arXiv2003

Impossibility of Spin Polarized States for Neutron Star / Proto-neutron Star Matter in $β$-Equilibrium Condition

It is shown explicitly that a ferromagnetic transition of neutron star (NS) / proto-neutron star (PNS) matter in the $β$-equilibrium condition with $σ-ω-ρ$ exchange type of mean field approximation can actually occur if and only if the neutrinos remain trapped within the system, and perhaps it is also necessary for the neutrinos / anti-neutrinos to carry some finite non-zero mass. It is further shown that the electrons also play a significant role in this transition process. It is therefore, very much unlikely that such a transition of spin polarization can really take place in old neutron stars of very low temperature, whereas, the possibility of spontaneous ferromagnetic transition cannot be ruled out in a newly born PNS.

astro-ph↗