arXiv subjects

Smitha Vishveshwara

Publications and source records attributed to Smitha Vishveshwara.

At least 19 recordsLinked to original sources

arXiv2026

From atomic to global connectivity in the structure of the SARS-CoV2-Human ACE2 receptor complex

We investigate connectivity properties of the SARS-CoV2 spike protein-human ACE2-receptor complex employing a protein side chain-based network method that allows us to span a range from atomic to global protein scales. We analyze network topology in terms of clusters and cliques obtained from averaging over snapshots of MD simulations (from D.E. Shaw Research). We demonstrate that SARS-CoV2 forms a more dominant, robust connection with the ACE2-receptor as compared to the less virulent SARS-CoV1. Globally, this stronger connectivity is reflected by our percolation analysis where the interface cluster for the SARS-CoV2-ACE2 complex persists when restricted to stronger and stronger bonds, as compared to the SARSCoV1- ACE2 complex. At the atomic level, interface clique structure reflects a stronger connectivity in the former complex. We pinpoint key functional residues in SARSCoV2 that play important roles in establishing this higher connectivity. Thus, our studies provide an objective method to map spatial connectivity of atomic level non-covalent interactions to global connectivity between any two amino acids in the complex. We also analyze specific snapshots of the MD simulations to highlight prominent variations in network topology that explore diverse conformational landscapes. Finally, we demonstrate that a majority of mutations that occur in the SARSCoV2 spike protein in variants of concern/interest (including the currently circulating JN.1) have been observed at the interface with the ACE2 receptor. Our analyses highlight the importance of interface interactions and provide a rationale for designing receptor-like peptides and proteins to combat immunity-escaping variants.

physics.bio-ph↗

arXiv2026

Quantum critical dynamics and emergent universality in decoherent digital quantum processors

Understanding how noise influences nonequilibrium quantum critical dynamics is essential for both fundamental physics and the development of practical quantum technologies. While the quantum Kibble-Zurek (QKZ) mechanism predicts universal scaling during quenches across a critical point, real quantum systems exhibit complex decoherence that can substantially modify these behaviors, ranging from altering critical scaling to completely suppressing it. By considering a specific case of nondemolishing noise, we first show how decoherence can reshape universal scaling and verify these theoretical predictions using numerical simulations of spin chains across a wide range of noise strengths. Then, we study linear quenches in the transverse-field Ising model on IBM superconducting processors where the noise model is unknown. Using large system sizes of 80-120 qubits, we measure equal-time connected correlations, defect densities, and excess energies across various quench times. Surprisingly, unlike earlier observations where noise-induced defect production masked universal behavior at long times, we observe clear scaling relations, pointing towards persistent universal structure shaped by decoherence. The extracted scaling exponents differ from both ideal QKZ predictions and analytic results for simplified noise models, suggesting the emergence of a distinct noise-influenced universality regime. Our results, therefore, point toward the possibility of using universal dynamical scaling as a high-level descriptor of quantum hardware, complementary to conventional gate-level performance metrics.

quant-ph↗

arXiv2026

Shell-shaped Bose-Einstein condensates: Dynamics, excitations, and thermodynamics

Shell-shaped Bose-Einstein condensates (BECs) represent a paradigmatic instance of quantum fluids in hollow geometries exhibiting phenomena that bridge from ultracold atomic to astrophysical realms. In this work, we present a comprehensive survey of the dynamics, thermodynamics, and collective excitations of shell-shaped BECs, synthesizing two decades of our group's theoretical work in light of recent experimental breakthroughs. We begin by analyzing the evolution of a BEC from filled-sphere to hollow-shell geometries, illustrating the necessity of microgravity conditions to avoid gravitational sag. We then analyze the collective mode structure across this evolution and pinpoint a universal dip in the frequency spectra as well as mode reconfiguration due to inner-surface excitations as robust signatures of the hollowing-out transition. Turning to vortex physics, we show that the closed-surface topology enforces vortex-antivortex configurations in shell-shaped BECs and that the natural annihilation of these pairs can be stabilized by rotation, with the critical rotation rate depending on shell thickness. In the thermodynamic domain, we investigate the interplay between shell inflation and the BEC phase transition, where adiabatic expansions lead to condensate depletion. This behavior motivates a study of the nonequilibrium dynamics of shell-shaped BECs; we perform such a study by constructing a time-dependent dynamic technique that can capture the evolution in both adiabatic and non-adiabatic regimes. Finally, we review recent experimental realizations of shell-shaped BECs, including the landmark creation of ultracold shells aboard the International Space Station, and outline prospects for exploring quantum fluids in curved geometries.

cond-mat.quant-gas↗

arXiv2026

Quantum statistics and self-interference in extended colliders

Collision of quantum particles remains an effective way of probing their mutual statistics. Colliders based on quantum point contacts in quantum Hall edge states have been successfully used to probe the statistics of the underlying quantum particles. Notwithstanding the extensive theoretical work focusing on point-like colliders, when it comes to experiment, the colliders are rarely point-like objects and can support a resonant level or multiple tunneling points. We present a study of a paradigmatic extended (non-point-like) fermionic collider (and an extension to bosonic colliders). As with particle interferometers, in an extended collider there is an infinite number of trajectories for any single or multi-particle event. Self-interference of the former can lead to an apparent bunching of fermions when we compare the cross-current correlator with a classical benchmark representing two colliding beams. In view of this apparent bunching behavior of fermions, we identify an experimentally accessible current correlator which reveals the true mutual statistics of fermions.

cond-mat.mes-hall↗

arXiv2026

Observing quantum many-body dynamics in emergent curved spacetime using programmable quantum processors

We digitally simulate quantum many-body dynamics in emergent curved backgrounds using 80 superconducting qubits on IBM Heron processors. By engineering spatially varying couplings in the spin-$\frac12$ XXZ chain, consistent with the low-energy description of the model in terms of an inhomogeneous Tomonaga-Luttinger liquid, we realize excitations that follow geodesics of an effective metric inherited from the underlying spatial deformation. Following quenches from Néel and few-spin-flip states, we observe curved light-cone propagation, horizon-induced freezing in the local magnetization, and position-dependent oscillation frequencies set by the engineered spatial deformation. Despite strong spatial inhomogeneity, unequal-time correlators reveal ballistic quasiparticle propagation in the spin chain. These results establish large-scale digital quantum processors as a flexible platform for detailed and controlled exploration of many-body dynamics in tunable and synthetic curved spacetimes.

quant-ph↗

arXiv2025

Dynamics of "Classical" Bosons, Fermions, and beyond

We study the classical mechanics and dynamics of particles that retains some memory of quantum statistics. Our work builds on earlier work on the statistical mechanics and thermodynamics of such particles. Starting from the effective classical manifold associated with two-particle bosonic and fermionic coherent states, we show how their exchange statistics is reflected in the symplectic form of the manifold. We demonstrate the classical analogues of exclusion or bunching behavior expected in such states by studying their trajectories in various quadratic potentials. Our examples are two-particle coherent states in one dimension and two-particle vortex motion in the lowest Landau level. We finally compare and contrast our results with previous simulations of the full quantum system, and with existing results on the geometric interpretations of quantum mechanics.

quant-ph↗

arXiv2025

Anyonic analogue of optical Mach-Zehnder interferometer

Anyonic interferometry is a direct probe of fractional statistics. We propose an interferometry geometry that parallels an optical Mach-Zehnder interferometer and offers several advantages over existing interferometry schemes. In contrast to the currently studied electronic Mach-Zehnder interferometer, our setup has no drain inside the device so that the trapped topological charge is time-independent. In contrast to electronic Fabry-Pérot interferometry, anyons cannot go around the device more than once. Thus, the interference signal has a straightforward interpretation in terms of anyonic statistical phases. The proposed geometry suppresses the undesirable effects of bulk-edge coupling. Moreover, the setup allows for simple exact solutions for the electric current and noise for an arbitrary quasiparticle tunneling strength in a broad range of conditions. The structure of the solutions is similar to that for non-interacting electrons but reflects fractional charge and statistics. We present results for electric current and noise in Jain states and address thermal interferometry at zero voltage bias.

cond-mat.mes-hall↗

arXiv2025

Symmetries and dynamics of quantum Hall bulk anyons in quadratic potentials

We study two-particle coherent states and their dynamics in the lowest Landau level (LLL) under the influence of quadratic potentials. We focus on generalized coherent states that describe Abelian anyons in the LLL and are associated with the $\mathfrak{su}(1,1)$ Lie algebra. We draw on parallels with quantum optics and symmetry properties of the coherent states considered here to analytically calculate quantities such as a bunching parameter, which depends on quantum statistics, as well as coherent state trajectories under the influence of generic quadratic potentials. Our results show that in unbounded saddle potentials, the bunching parameter governs the trajectories which show exponentially diverging behavior in a manner that depends on quantum statistics. In bounded elliptical potentials, the bunching parameter is oscillatory and its maximum magnitude depends on the eccentricity of the applied potential. We draw connections between our analyses and the key concepts that underlie anyon detection in recent experiments.

cond-mat.mes-hall↗

arXiv2025

Mechanical cosmology: simulating scalar fluctuations in expanding Universes using synthetic mechanical lattices

Inspired by recent advances in observational astrophysics and continued explorations in the field of analog gravity, we discuss the prospect of simulating models of cosmology within the context of synthetic mechanical lattice experiments. We focus on the physics of expanding Universe scenarios described by the Friedmann-Lemaître-Robertson-Walker (FLRW) metric. Specifically, quantizing scalar fluctuations in a background FLRW spacetime leads to a quadratic bosonic Hamiltonian with temporally varying pair production terms. Here we present a mapping that provides a one-to-one correspondence between these classes of cosmology models and feedback-coupled mechanical oscillators. As proof-of-principle, we then perform experiments on a synthetic mechanical lattice composed of such oscillators. We simulate two different FLRW expansion scenarios with Universes dominated by vacuum energy and matter and discuss our experimental results.

cond-mat.mes-hall↗

arXiv2024

Majorana bound state parity exchanges in planar Josephson junctions

We describe a scheme to exchange fermion parity between two pairs of Majorana bound states mediated by coupling with a centralized quantum dot. We specifically formulate such a scheme for Majorana bound states nucleated in the Josephson vortices formed in a four-fold crossroads junction of planar topological superconductors in the presence of a perpendicular magnetic field. This platform yields several advantages to the execution of our scheme as compared to similar ideas proposed in wire geometries, including control over the positions of the MBS and hence, a tunable coupling with the quantum dot. We show that moving the MBS along the junctions through voltage pulses can facilitate parity exchange via a two-step process, with intermediate projective measurements of the quantum dot charge. Thus, we formulate a way to achieve single qubit operations for MBS in extended Josephson junctions through projective measurements of quantum dot charge. We also discuss the physical viability of our scheme with a particular focus on changes in quantum dot energy levels as a measurable indicator of the success of the scheme.

cond-mat.mes-hall↗

arXiv2023

Anyonic Mach-Zehnder interferometer on a single edge of a 2D electron gas

Anyonic Fabry-Pérot and Mach-Zehnder interferometers have been proposed theoretically and implemented experimentally as tools to probe electric charges and statistics of anyons. The experimentally observed visibility of Aharonov-Bohm oscillations is maximal at a high transmission through an interferometer but simple theoretical expressions for the electric currents and noises are only available at low visibility. We consider an alternative version of a Mach-Zehnder interferometer, in which anyons tunnel between co-propagating chiral channels on the edges of quantum Hall liquids at the filling factors $n/(2n+1)$. We find simple exact solutions for any transmission. The solutions allow a straight-forward interpretation in terms of fractional charges and statistics.

cond-mat.mes-hall↗

arXiv2023

Interacting bosons on a Su-Schrieffer-Heeger ladder: Topological phases and Thouless pumping

We study the topological properties of hardcore bosons on a two-leg ladder consisting of two Su-Schrieffer-Heeger (SSH) chains that are coupled via hopping and interaction. We chart out the phase diagram for the system and show that based on the relative hopping dimerization pattern along the legs, distinctly different topological phases and phase transitions can occur. When the dimerization along the legs are uniform, we find that the topological nature vanishes for even the slightest rung hopping. For staggered dimerization, the system exhibits a well defined topological character and a topological phase transition as a function of rung hopping. While the topological phase shows bond order character, the trivial phase shows the behavior of a rung-Mott insulator. For this case, the topological nature is found to survive even in the presence of finite inter-leg interactions. Moreover, we find that the critical point of the topological phase transition shifts to a higher or a lower rung hopping strength depending on the attractive or repulsive nature of the interaction. To highlight the marked effects of interactions, we propose a scheme involving a Thouless charge pump that provides insights for the topological phases characterized by a quantised particle transport through a periodic modulation of appropriate system parameters. In our studies, we show an interaction induced charge pumping following specific pumping protocols in the case of staggered dimerization.

cond-mat.quant-gas↗

arXiv2022

Perspective on Quantum Bubbles in Microgravity

Progress in understanding quantum systems has been driven by the exploration of the geometry, topology, and dimensionality of ultracold atomic systems. The NASA Cold Atom Laboratory (CAL) aboard the International Space Station has enabled the study of ultracold atomic bubbles, a terrestrially-inaccessible topology. Proof-of-principle bubble experiments have been performed on CAL with an rf-dressing technique; an alternate technique (dual-species interaction-driven bubbles) has also been proposed. Both techniques can drive discovery in the next decade of fundamental physics research in microgravity.

cond-mat.quant-gas↗

arXiv2022

Signatures of Majorana bound states and parity effects in two-dimensional chiral p-wave Josephson junctions

We characterize topological features of Josephson junctions formed by coupled mesoscopic chiral $p$-wave superconducting islands. Through analytic and numerical studies of the low-lying BdG (Bogoliubov-de Gennes) spectrum, we identify localized MBS (Majorana bound states) nucleated in Josephson vortices by the application of a perpendicular magnetic field. Additionally, we demonstrate the existence of an extended MBS that is delocalized around the outer perimeter of the coupled islands, which has measurable consequences on the Josephson supercurrent and phase dynamics of the junction. In particular, we predict a change in the critical current diffraction pattern in which the odd integer-flux nodes are lifted in a fermion parity-dependent fashion. We model the competing stochastic effects of thermal noise and macroscopic quantum tunneling within the RCSJ framework and show the emergence of a bimodal critical current distribution. We demonstrate that increasing the parity transition rate suppresses the bimodal nature of the distribution, thus strongly emphasizing the non-trivial parity dependent nature of the many-body ground state. Finally, we consider a trijunction geometry with three islands and discuss possible schemes to braid Majorana bound states by moving the Josephson vortices to which they are bound.

cond-mat.supr-con↗

arXiv2022

Observation of Phase Controllable Majorana-like Bound States in Metamaterial-based Kitaev Chain Analogues

We experimentally demonstrate that Majorana-like bound states (MLBSs) can occur in quasi-one-dimensional metamaterials, analogous to Majorana zero modes (MZM) in the Kitaev chain. In a mechanical spinner ladder system, we observe a topological phase transition and spectral-gap-protected edge MLBSs. We characterize the decaying and oscillatory nature of these MLBS pairs and their phase-dependent hybridization. It is shown that the hybridization can be tuned to yield the analogue of parity switching in MZMs, a key element of topological qubits. We find strong agreements with theory.

cond-mat.mtrl-sci↗

arXiv2021

Microtubules as electron-based topological insulators

The microtubule is a cylindrical biological polymer that plays key roles in cellular structure, transport, and signalling. In this work, based on studies of electronic properties of polyacetelene and mechanical properties of microtubules themselves (see Phys. Rev. Lett. 103, 248101), we explore the possibility that microtubules could act as topological insulators that are gapped to electronic excitations in the bulk but possess robust electronic bounds states at the tube ends. Through analyses of structural and electronic properties, we model the microtubule as a cylindrical stack of Su-Schrieffer-Heeger chains (originally proposed in the context of polyacetylene) describing electron hopping between the underlying dimerized tubulin lattice sites. We postulate that the microtubule is mostly uniform, dominated purely by GDP-bound dimers, and is capped by a disordered regime due to the presence of GTP-bound dimers as well. In the uniform region, we identify the electron hopping parameter regime in which the microtubule is a topological insulator. We then show the manner in which these topological features remain robust when the hopping parameters are disordered. We briefly mention possible biological implications for these microtubules to possess topologically robust electronic bound states.

cond-mat.mes-hall↗

arXiv2021

Thermodynamics in expanding shell-shaped Bose-Einstein condensates

Inspired by investigations of Bose-Einstein condensates (BECs) produced in the Cold Atom Laboratory (CAL) aboard the International Space Station, we present a study of thermodynamic properties of shell-shaped BECs. Within the context of a spherically symmetric `bubble trap' potential, we study the evolution of the system from small filled spheres to hollow, large, thin shells via the tuning of trap parameters. We analyze the bubble trap spectrum and states, and track the distinct changes in spectra between radial and angular modes across the evolution. This separation of the excitation spectrum provides a basis for quantifying dimensional cross-over to quasi-2D physics at a given temperature. Using the spectral data, for a range of trap parameters, we compute the critical temperature for a fixed number of particles to form a BEC. For a set of initial temperatures, we also evaluate the change in temperature that would occur in adiabatic expansion from small filled sphere to large thin shell were the trap to be dynamically tuned. We show that the system cools during this expansion but that the decrease in critical temperature occurs more rapidly, thus resulting in depletion of any initial condensate. We contrast our spectral methods with standard semiclassical treatments, which we find must be used with caution in the thin-shell limit. With regards to interactions, using energetic considerations and corroborated through Bogoliubov treatments, we demonstrate that they would be less important for thin shells due to reduced density but vortex physics would become more predominant. Finally, we apply our treatments to traps that realistically model CAL experiments and borrow from the thermodynamic insights found in the idealized bubble case during adiabatic expansion.

cond-mat.quant-gas↗

arXiv2021

Observation of ultracold atomic bubbles in orbital microgravity

Significant leaps in the understanding of quantum systems have been driven by the exploration of geometry, topology, dimensionality, and interactions with ultracold atomic ensembles. A system where atoms evolve while confined on an ellipsoidal surface represents a heretofore unexplored geometry and topology. Realizing such an ultracold bubble system (potentially Bose-Einstein condensed) has areas of interest including quantized-vortex flow respecting topological constraints imposed by closed surfaces, new collective modes, and self-interference via free bubble expansion. Large ultracold bubbles, created by inflating smaller condensates, directly tie into Hubble-analog expansion physics. Here, we report observations from the NASA Cold Atom Lab facility aboard the International Space Station of bubbles of ultracold atoms created using a radiofrequency-dressing protocol. We observe a variety of bubble configurations of differing sizes and initial temperature, and explore bubble thermodynamics, demonstrating significant cooling associated with inflation. Additionally, we achieve partial coverings of bubble traps greater than 1 mm in size with ultracold films of inferred few-$μ$m thickness, and we observe the dynamics of shell structures projected into free-evolving harmonic confinement. The observations are part of the first generation of scientific measurements made with ultracold atoms in space, exploiting the benefits of perpetual free-fall to explore gravity-free evolution of quantum systems that are prohibitively difficult to create on Earth. This work points the way to experiments focused on the nature of the Bose-Einstein condensed bubble, the character of its excitations, and the role of topology in its evolution; it also ushers in an era of orbital microgravity quantum-gas physics.

cond-mat.quant-gas↗