- Open Access
Bootstrapping the Quantum Hall Problem
Phys. Rev. X 15, 031034 – Published 31 July, 2025
DOI: https://doi.org/10.1103/csnn-vjhn
Abstract
The bootstrap method aims to solve problems by imposing constraints on the space of physical observables, which often follow from physical assumptions such as positivity and symmetry. Here, we employ a bootstrap approach to study interacting electrons in the lowest Landau level by minimizing the energy as a function of the static structure factor subject to a set of constraints, bypassing the need to construct the full many-body wave function. This approach rigorously lower bounds the ground state energy, making it complementary to conventional variational upper bounds. We show that the lower bound we obtain is relatively tight, within at most a few percent from the ground state energy computed with exact diagonalization at small system sizes, and generally gets tighter as we include more constraints. We also show that, by combining the bootstrap lower bounds with variational Monte Carlo calculations for various quantum Hall states, we can obtain two-sided bounds on the ground state energy that rigorously bounds the error to below a few percentage for large system sizes where exact diagonalization is not accessible. Beyond the energetics, our results reproduce the correct power law dependence of the pair correlation function at short distances and the existence of a large entanglement gap in the two-particle entanglement spectra for the Laughlin states at . We further identify signatures of the composite Fermi liquid state close to half filling. This shows that the bootstrap approach is capable, in principle, of describing nontrivial gapped topologically ordered, as well as gapless, phases. We further study the evolution of the ground state energy and correlation functions as we interpolate between the lowest and first Landau levels at half filling and find indications of a phase transition from a composite Fermi liquid to a non-Abelian state. We also discuss more generally how the geometry of the allowed set of structure factors can be used to diagnose phase transitions. At the end, we discuss possible extensions and current limitations of this approach and how they can be overcome in future studies. Our work establishes numerical bootstrap as a promising method to study many-body phases in topological bands, paving the way to its application in moiré platforms where the energetic competition between fractional quantum anomalous Hall, symmetry broken, and gapless states remains poorly understood.
Physics Subject Headings (PhySH)
Popular Summary
The quantum Hall effect is a remarkable phenomenon: When a 2D electron system is placed in a strong magnetic field at low temperatures, its electrical resistance becomes precisely quantized. This effect has rich theoretical and experimental implications, but understanding the behavior of electrons in these systems—where interactions are strong and quantum effects dominate—presents significant challenges. Traditional methods for studying these systems often require constructing complex many-body wave functions, which become unmanageable for large systems. Here, we introduce a new method that avoids this difficulty and offers a powerful alternative.
In our approach, we apply bootstrap methods traditionally used in high-energy physics and conformal field theory to strongly interacting electron systems in condensed matter physics. By leveraging mathematical constraints on physical properties, such as the structure factor, we can bypass the need for full wave-function construction. This allows us to rigorously estimate ground state energies and explore the rich physics of both gapped and gapless phases, including those found in fractional quantum Hall states and composite Fermi liquids.
Our results demonstrate the power and generality of the bootstrap approach, providing new insights into the behavior of strongly correlated electrons. This work not only advances our understanding of the quantum Hall effect but also opens the door to applying bootstrap techniques to other complex many-body systems in condensed matter physics.
Article Text
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