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"Gyawali, Gaurav"
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Simulating Dynamics of Quantum Information in Strongly Correlated Electron Systems
Recent advances in probing and controlling quantum systems have brought us closer to Feynman’s vision of simulating nature using quantum mechanics. Quantum processors promise efficient simulation of strongly correlated electrons, which suffer from the exponential scaling of classical simulation resources. Additionally, quantum processors provide access to quantum information properties that are not easily accessible in conventional condensed matter experiments. In this dissertation, I explore three distinct approaches to studying the dynamics of quantum information in the context of many-body physics simulations.First, I present an information theoretic study of the dynamics of monitored variational circuits that prepare the ground states of strongly correlated Hamiltonians (Chapter 3). Viewing the optimization as a communication problem reveals “coding barren plateaus”, where a finite communication rate can be achieved between the sender and the receiver despite vanishing gradients. In a parallel study (Chapter 4), I present an adaptive variational algorithm to prepare the eigenstates of the Fermi-Hubbard model by building entanglement one gate at a time. This approach results in shallower circuits and circumvents barren plateaus, potentially enabling more efficient ground state preparation on near-term devices.Second, I focus on quantum information dynamics in strongly correlated electron systems, both clean and disordered. I present a real-device implementation for efficient disorder averaging, one of the central challenges in the computational study of many-body localization due to rare events, by leveraging quantum parallelism (Chapter 5). I examine the signature of localization in the dynamics of the second Renyi ´ entropy, which can be extended to measure mutual information and detect rare events to determine the stability of the many-body localization phase. I also explore learning thermodynamics from the simulation of quantum dynamics by employing diffusion maps—an unsupervised machine learning method—to uncover the quantum phase diagram of the transverse field Ising model and map entropy across the phase diagram with only 500 shots per data point (Chapter 6). I do so by developing time average classical shadows (TACS), an efficient classical representation of the microcanonical ensemble. Additionally, I discuss a novel shadow tomographic technique called the valence bond shadows that offers intuitive and efficient method to estimate observables of quantum spin liquids prepared on quantum processors (Chapter 7).Third, simulating long-time dynamics of strongly correlated electrons on quantum processors will likely require fault-tolerant quantum computing using error-correcting codes. By studying the channel capacity of realistic quantum device models, I find emergent coding phases tailored to specific noise characteristics (Chapter 8). Carrying out this approach on current noisy devices could provide a systematic way to construct quantum codes for robust computation and communication.Although access to quantum information properties is challenging using conventional analytical and numerical methods, the same challenge provides a promising path to quantum advantage in near-term devices. My studies highlight the potential of near-term quantum simulations to deepen our understanding of strongly correlated electrons by enabling the direct probing of quantum information-theoretic quantities in their dynamics.
Dissertation
Coarse-Grained Simulations of Aqueous Thermoresponsive Polyethers
Thermoresponsive polymers can change structure or solubility as a function of temperature. Block co-polymers of polyethers have a response that depends on polymer molecular weight and co-polymer composition. A coarse-grained model for aqueous polyethers is developed and applied to polyethylene oxide and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock co-polymers. In this model, no interaction sites on hydrogen atoms are included, no Coulombic interactions are present, and all interactions are short-ranged, treated with a combination of two- and three-body terms. Our simulations find that The triblock co-polymers tend to associate at temperatures above 350 K. The aggregation is stabilized by contact between The hydrophobic methyl groups on The propylene oxide monomers and involves a large, favorable change in entropy.
Journal Article
Adaptive variational preparation of the Fermi-Hubbard eigenstates
Approximating the ground states of strongly interacting electron systems in quantum chemistry and condensed matter physics is expected to be one of the earliest applications of quantum computers. In this paper, we prepare highly accurate ground states of the Fermi-Hubbard model for small grids up to 6 sites (12 qubits) by using an interpretable, adaptive variational quantum eigensolver(VQE) called ADAPT-VQE. In contrast with non-adaptive VQE, this algorithm builds a system-specific ansatz by adding an optimal gate built from one-body or two-body fermionic operators at each step. We show this adaptive method outperforms the non-adaptive counterpart in terms of fewer variational parameters, short gate depth, and scaling with the system size. The fidelity and energy of the prepared state appear to improve asymptotically with ansatz depth. We also demonstrate the application of adaptive variational methods by preparing excited states and Green functions using a proposed ADAPT-SSVQE algorithm. Lower depth, asymptotic convergence, noise tolerance of a variational approach, and a highly controllable, system-specific ansatz make the adaptive variational methods particularly well-suited for NISQ devices.
Paper
Measurement-Induced Landscape Transitions and Coding Barren Plateaus in Hybrid Variational Quantum Circuits
The entanglement-induced barren plateau is an exponential vanishing of the parameter gradients with system size that limits the practical application of variational quantum algorithms(VQA). A landscape transition from barren plateau to no-barren plateau was recently observed in monitored quantum circuits, hypothesized to coincide with the measurement-induced phase transition (MIPT) that separates the area-law states from the volume-law states. We argue from an information theory perspective that these are different transitions. This hypothesis is supported by a numerical study that includes cost-gradient variances, visualizations of the optimization runs and cost-landscape, and a quantum-classical channel mutual information measure. The results are evidence for a universal measurement-induced landscape transition (MILT) at \\(p_c^{\\text{MILT}} \\approx 0.2 < p_c^{\\text{MIPT}}\\) and that throughout \\(0
Paper
Revealing microcanonical phases and phase transitions of strongly correlated electrons via time-averaged classical shadows
Quantum computers and simulators promise to enable the study of strongly correlated quantum systems. Yet, surprisingly, it is hard for them to compute ground states. They can, however, efficiently compute the dynamics of closed quantum systems. We propose a method to study the quantum thermodynamics of strongly correlated electrons from quantum dynamics. We define time-averaged classical shadows (TACS) and prove it is a classical shadow(CS) of the von Neumann ensemble, the time-averaged density matrix. We then show that the diffusion maps, an unsupervised machine learning algorithm, can efficiently learn the phase diagram and phase transition of the one-dimensional transverse field Ising model both for ground states using CS \\emph{and state trajectories} using TACS. It does so from state trajectories by learning features that appear to be susceptibility and entropy from a total of 90,000 shots taken along a path in the microcanonical phase diagram. Our results suggest a low number of shots from quantum simulators can produce quantum thermodynamic data with a quantum advantage.
Paper
Visualizing Dynamics of Charges and Strings in (2+1)D Lattice Gauge Theories
Lattice gauge theories (LGTs) can be employed to understand a wide range of phenomena, from elementary particle scattering in high-energy physics to effective descriptions of many-body interactions in materials. Studying dynamical properties of emergent phases can be challenging as it requires solving many-body problems that are generally beyond perturbative limits. We investigate the dynamics of local excitations in a \\(\\mathbb{Z}_2\\) LGT using a two-dimensional lattice of superconducting qubits. We first construct a simple variational circuit which prepares low-energy states that have a large overlap with the ground state; then we create particles with local gates and simulate their quantum dynamics via a discretized time evolution. As the effective magnetic field is increased, our measurements show signatures of transitioning from deconfined to confined dynamics. For confined excitations, the magnetic field induces a tension in the string connecting them. Our method allows us to experimentally image string dynamics in a (2+1)D LGT from which we uncover two distinct regimes inside the confining phase: for weak confinement the string fluctuates strongly in the transverse direction, while for strong confinement transverse fluctuations are effectively frozen. In addition, we demonstrate a resonance condition at which dynamical string breaking is facilitated. Our LGT implementation on a quantum processor presents a novel set of techniques for investigating emergent particle and string dynamics.
Paper
System Pharmacological Approach to Investigate and Validate Multitargeted and Therapeutic Effect of Furocoumarins of Apium graveolens L. for Treatment of Kidney Disease
Background. System pharmacological approaches play important roles in drug discovery and development and in biomolecular exploration to investigate the multitarget therapeutic effects of phytochemicals for the treatment of acute and chronic ailments. Objectives. The aim of the study was to apply a system pharmacological approach to investigate the multitarget therapeutic effects of furocoumarins of Apium graveolens L. for the treatment of kidney disease. Methods. Several furocoumarins of Apium graveolens were screened from online databases. Network biology and poly-pharmacology analyses were performed to investigate the multitarget therapeutic effect of furocoumarins. The potential metabolites that showed significant interactions with various genes were selected for in silico docking analysis with CASP-3 and SOD proteins. In silico ADME analysis was also performed to investigate the pharmacokinetic behavior of targeted furocoumarins. Results. Out of thirteen furocoumarins selected for analysis, six showed partial or significant interaction with SOD and CASP-3 proteins. These metabolites may alleviate kidney dysfunction by reducing oxidative and inflammatory stress, regulating apoptosis, slowing down the progression of diabetic nephropathy, and reducing hypertension and glomerular vascular rigidity. In silico docking analysis revealed bergapten as a potential therapeutic agent for kidney disease treatment. In silico docking analysis showed anglicine, imperatorin, and sphondin exhibited strong interaction with CASP-3 and SOD with binding energy −6.5, −7.2, −6.5 and −6.8, −6.2 −5.7 kcal/mol, respectively. These components exhibited greater conventional hydrogen bonding with CASP-3 and SOD than other furocoumarins. Furthermore, in silico ADME analysis of metabolites showed that all furocoumarins have a highly lipophilic nature, good skin permeability, and GI absorption, as well as good blood-brain permeability (BBB). Conclusion. Furocoumarins reduce kidney dysfunction and associated pathophysiological complications via the reduction of glomerular vascular rigidity, diabetic nephropathy, and oxidative and inflammatory stress. However, further biomolecular and clinical examinations are necessary to validate and enhance the credibility of present findings.
Journal Article
Missed Wooden Perineum Foreign Body Leading to Extensive Necrotizing Soft Tissue Infection: A Case Report
Penetrating perineal trauma is rare but carries a high risk due to contamination, hidden tracts, and proximity to major vessels and viscera. Retained organic foreign bodies, particularly wood, are often radiolucent and can perpetuate infection or erode into vascular structures. Necrotizing soft tissue infection (NSTI) is a devastating complication with significant mortality. A 53‐year‐old woman from rural Nepal presented 8 days after falling onto a tree branch, sustaining a perineal impalement. Her wound had been sutured primarily at a local center. She developed severe pain, swelling, foul discharge, and rectal bleeding. On exploration, extensive necrotic tissue and foul collections were found. MRI revealed a pelvic extension of infection but missed the wooden fragments. During subsequent staged debridements, two retained wooden pieces were discovered. Their removal precipitated massive pelvic hemorrhage requiring ligation of the right internal iliac artery. A loop colostomy was fashioned to prevent fecal contamination. After multiple surgeries and 53 days of inpatient care, she was discharged in stable condition. Key Clinical Message Penetrating perineal injuries carry a high risk of occult infection and vascular damage, especially when contaminated wounds are closed primarily. Wooden fragments may be missed on imaging and cause necrotizing soft‐tissue infection. Avoid primary closure in contaminated perineal wounds, and early referral when deeper injury or contamination is suspected.
Journal Article
Schizencephaly diagnosed after an episode of seizure during labor: A case report
Schizencephaly, an extremely rare anomaly of the cortex, is characterized by abnormal clefts in the cerebral cortex. Very often, this condition is diagnosed early in the childhood period but few instances exist in literature where schizencephaly‐associated seizures and hemiparesis have presented later in life too. Here, we report a rare case scenario of a lady in her late 30s who initially presented to us with obstetric concerns wherein schizencephaly remained an incidental finding despite the significantly large cortical cleft along with lobar holoprosencephaly and lissencephaly.
Journal Article