Sajag Kumar

I graduated with an Integrated Master's in Physical Sciences with a minor in Computer Sciences from NISER Bhubaneswar. I am broadly interested in theoretical condensed matter physics. In particular, I enjoy working on problems in many-body physics that involve ideas from quantum information and quantum field theory.

I worked on my master's thesis, advised by Dr. Shamik Banerjee, on the applications of Chern-Simons theories. In the past, I have worked in the Theoretical Quantum Technology group of Prof. Markus Müller at the Institute of Quantum Information, at RWTH Aachen University, on neural networks-based decoding of sparse quantum codes, and in the Theory of Quantum and Ultracold Matter group of Prof. Sayan Choudhury at HRI Prayagraj on prethermalization in classical spin systems.

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Research

thesis

Aspects and Applications of Chern-Simons Theories

We studied the geometrical setting of Chern-Simons theories and their quantization on various interesting manifolds in three dimensions. We calculated the Feynman diagrams of Chern-Simons theories coupled to bosons in the fundamental representation and discussed the applications of Chern-Simons matter theories in the quantum mechanics of non-Abelian anyons and as effective field theories of quantum Hall effects.

[Thesis]

thesis

Neural Belief Propagation Decoding of Sparse Quantum Codes

We extended the Neural Belief Propagation algorithm to decode quantum error correcting codes under experimentally relevant noise models. We implemented the neural networks in PyTorch and simulated stabilizer circuits using Stim.

[Report]

thesis

Prethermalization in Aperiodically Driven Classical Spin Systems

We discover a novel thermalization time scaling law for classical spin systems subject to random multipolar drives. We also establish the presence of classical discrete time-crystalline phases of matter in the prethermal plateau. The thermalization process in the classical systems we study is parametrically slower than their quantum counterparts.

[Phys. Rev. E 110, 064150] [arXiv]

thesis

Geometric Phases in Optics

We explored the possibility of demonstrating the geometric phase of light in angular momentum space using Laguerre-Gaussian beams. We also built an experimental setup to demonstrate the Panchratnam-Berry phase.

Course Projects

thesis

RIXS Spectrum of the Kitaev Chain

We computed the resonant inelastic X-ray scattering (RIXS) spectrum of the Kitaev chain in the spin conserving channel using tensor network methods.

[Report]

thesis

Scrambling Dynamics in Classical and Quantum Systems

We used time evolving block decimation and time-dependent variational principle algorithms to compute the out-of-time ordered correlators for interacting quantum systems. We also compute the decorrelator for classical systems.

[Report] [Presentation]

thesis

Gamma Matrix Model for Algebraic Spin Liquid

We studied an exactly solvable model for algebraic spin liquid using Kitaev's fermionization technique.

[Report] [Presentation]

thesis

Pruned-Enriched Rosenbluth Method for Simulating Polymers on Lattices

We simulate polymers as self-avoiding random walks on two and three-dimensional lattices and compute the average end-to-end distance using Monte Carlo methods.

[Report]

thesis

Topological Quantum Error Correction

We studied the stabilizer formalism and braiding of anyons in the toric code for quantum error correction. We also implement the repetition code in Qiskit.

[Presentation]

thesis

Divergences in Perturbation Theory

We studied Dyson's argument for divergence of the perturbation series in quantum electrodynamics and learned techniques for resummation of divergent series.

thesis

Estimation of Electronic Band Gap Energy From Material Properties Using Machine Learning

We implemented a novel ensemble learning algorithm in scikit-learn to estimate the electric band gap. We trained the machine learning model on the AFLOW dataset.

[IEEE Xplore]

Miscellaneous

The video of my talk titled "Spontaneously Broken Time Translation Symmetry: Time Crystals" in Vikiran, the Physics club of NISER.


Design and source code from Jon Barron's website.