Hersh Singh
Postdoctoral researcher and Quantum Theory Fellow, Fermilab
I’m a theoretical physicist working out how to simulate the fundamental laws of nature, using quantum field theory, lattice methods and quantum computers. I’m especially fascinated by chiral gauge theories, like the Standard Model itself, because no one yet knows how to put them on a computer. My work mixes pen-and-paper theory with large-scale computer simulations.
My papers are on iNSPIRE and Google Scholar; my talks are here.
I love teaching, and I always seem to find a reason to talk about whatever I’m excited about. At Fermilab I lecture at a summer quantum computing internship for undergraduates. At Duke I won the Mary Creason Memorial Award for Undergraduate Teaching and taught a graduate mini-course on the renormalization group.
Recent Activity
- Sep 2026TalkSimulating a chiral gauge theoryUniversity of Illinois Urbana-Champaign, HEP Seminar
- Jul 2026TalkLattice Hamiltonian Formulations of Chiral Fermions and Chiral Gauge Theories"Lattice 2026" (plenary), University of Maryland, College Park, MD, USA
- Jul 2026TalkExact Chiral Symmetry with Quantum Signal ProcessingUniversity of Tokyo, Japan
- Jul 2026PaperExact chiral symmetry with quantum signal processingarXiv:2607.28524
- Feb 2026TalkNonperturbative Real-Time Simulations of Chiral Gauge Theories and BaryogenesisInstitute for Nuclear Theory, University of Washington, Seattle
Research Interests
Chiral Fermions & Chiral Gauge TheoriesBaryogenesisQubit RegularizationQuantum SimulationFew-Body Nuclear Physics
Selected Publications
H. Lamm, A. Roggero, H. Singh, L. Spagnoli
arXiv:2607.28524
We give a quantum signal processing (QSP) algorithm for the overlap fermion Hamiltonian which preserves the Ginsparg-Wilson relation up to a controllable error . Quantum simulations of Dirac fermions with exact chiral symmetry are thus nearly free: applying the overlap Hamiltonian costs only a factor logarithmic in more than the Wilson-Dirac Hamiltonian. Comparing to domain-wall fermions, a mild overhead is found in circuit complexity while reducing qubit costs. We show how QSP effectively constructs an extra dimension when simulating the overlap operator, illustrating that the scaling of quantum algorithms reflects the deeper physics of overlap fermions arising at the boundary of domain-wall fermions.
@article{Lamm:2026xqk,
author = "Lamm, Henry and Roggero, Alessandro and Singh, Hersh and Spagnoli, Luca",
title = "{Exact chiral symmetry with quantum signal processing}",
eprint = "2607.28524",
archivePrefix = "arXiv",
primaryClass = "hep-lat",
reportNumber = "FERMILAB-PUB-26-0223-T",
month = "7",
year = "2026"
}H. Singh
arXiv:2505.20419
We construct a family of Ginsparg-Wilson Hamiltonians with improved chiral properties, starting from a construction of Creutz-Horvath-Neuberger that provides a doubler-free Hamiltonian lattice regularization for Dirac fermions in even spacetime dimensions. We use a higher-order generalization of the Ginsparg-Wilson relation due to Fujikawa, which yields an order- Hamiltonian overlap operator for each integer , with an exactly conserved but nonquantized chiral charge that becomes quantized as . Our construction provides physical insight into how Fujikawa's higher-order Ginsparg-Wilson relation improves chiral symmetry while reproducing the anomaly, highlighting the trade-offs inherent in any Hamiltonian lattice realization of an anomalous chiral symmetry. This class of Hamiltonian lattice regularizations, with their tunable chiral symmetry properties, offers potential advantages for quantum and tensor-network simulations.
@article{Singh:2025sye,
author = "Singh, Hersh",
title = "{Ginsparg-Wilson Hamiltonians with Improved Chiral Symmetry}",
eprint = "2505.20419",
archivePrefix = "arXiv",
primaryClass = "hep-lat",
reportNumber = "FERMILAB-PUB-25-0330-T",
month = "5",
year = "2025"
}M. Carena, Y.-Y. Li, T. Ou, H. Singh
Phys. Rev. D · 2026 · arXiv:2412.10365
Motivated by the out-of-equilibrium dynamics during an early-universe first-order phase transition, we perform real-time simulations of fermion-bubble scattering in dimensions. This nonequilibrium process can generate a charge-conjugation asymmetry outside the bubble wall, induced by the complex fermion mass profile. The resulting asymmetry is the 1+1-dimensional analog of the asymmetry in 3+1 dimensions, a key ingredient in baryon asymmetry generation at the electroweak scale. Using tensor network methods, we track the real-time evolution of the asymmetry in the charge density as the fermion interacts with the bubble wall, a regime inaccessible to analytic calculations. We further introduce two observables to quantify the asymmetry in the asymptotic region where reflected particles are well separated from the scattering point: one based on the net charge outside the bubble wall, and the other on the spatial displacement between the reflected particle and antiparticle wavepackets. Our study represents a first step toward nonperturbative, real-time computations of asymmetry in 3+1 dimensions for electroweak baryogenesis.
@article{Carena:2024peb,
author = "Carena, Marcela and Li, Ying-Ying and Ou, Tong and Singh, Hersh",
title = "{Real-time simulation of asymmetry generation in fermion-bubble collisions}",
eprint = "2412.10365",
archivePrefix = "arXiv",
primaryClass = "hep-ph",
reportNumber = "FERMILAB-PUB-24-0931-T",
doi = "10.1103/nphy-2y8q",
journal = "Phys. Rev. D",
volume = "113",
number = "1",
pages = "014502",
year = "2026"
}M. Clancy, D. B. Kaplan, H. Singh
Phys. Rev. D · 2024 · arXiv:2309.08542
We give a general derivation of Ginsparg-Wilson relations for both Dirac and Majorana fermions in any dimension. These relations encode continuous and discrete chiral, parity and time reversal anomalies and will apply to the various classes of free fermion topological insulators and superconductors (in the framework of a relativistic quantum field theory in Euclidean spacetime). We show how to formulate the exact symmetries of the lattice action and the relevant index theorems for the anomalies.
@article{Clancy:2023ino,
author = "Clancy, Michael and Kaplan, David B. and Singh, Hersh",
title = "{Generalized Ginsparg-Wilson relations}",
eprint = "2309.08542",
archivePrefix = "arXiv",
primaryClass = "hep-lat",
reportNumber = "INT-PUB-23-024, IQuS@UW-21-064, FERMILAB-PUB-23-541-T",
doi = "10.1103/PhysRevD.109.014502",
journal = "Phys. Rev. D",
volume = "109",
number = "1",
pages = "014502",
year = "2024"
}T. Bhattacharya, A. J. Buser, S. Chandrasekharan, R. Gupta, H. Singh
Phys. Rev. Lett. · 2021 · arXiv:2012.02153
We provide strong evidence that the asymptotically free (1+1)-dimensional non-linear O(3) sigma model can be regularized using a quantum lattice Hamiltonian, referred to as the "Heisenberg-comb", that acts on a Hilbert space with only two qubits per spatial lattice site. The Heisenberg-comb consists of a spin-half anti-ferromagnetic Heisenberg-chain coupled anti-ferromagnetically to a second local spin-half particle at every lattice site. Using a world-line Monte Carlo method we show that the model reproduces the universal step-scaling function of the traditional model up to correlation lengths of 200,000 in lattice units and argue how the continuum limit could emerge. We provide a quantum circuit description of time-evolution of the model and argue that near-term quantum computers may suffice to demonstrate asymptotic freedom.
@article{Bhattacharya:2020gpm,
author = "Bhattacharya, Tanmoy and Buser, Alexander J. and Chandrasekharan, Shailesh and Gupta, Rajan and Singh, Hersh",
title = "{Qubit regularization of asymptotic freedom}",
eprint = "2012.02153",
archivePrefix = "arXiv",
primaryClass = "hep-lat",
reportNumber = "LA-UR-20-29558",
doi = "10.1103/PhysRevLett.126.172001",
journal = "Phys. Rev. Lett.",
volume = "126",
number = "17",
pages = "172001",
year = "2021"
}Education
PhD in Physics (2014-2020)
B.Tech. and M.Tech. in Electrical Engineering (2009-2014)
Experience
Postdoctoral Researcher (2023 – present)
Fermilab Quantum Theory Fellow
Fermilab
Postdoctoral Researcher (2020 – 2023)
IQuS-Fermilab Quantized Fellow
InQubator for Quantum Simulation
Institute for Nuclear Theory
University of Washington, Seattle