Quantum Algorithms for Open Lattice Field Theory

TL;DR

This paper develops quantum algorithms to simulate non-Hermitian lattice field theories, enabling the study of complex phenomena like phase transitions and Lee-Yang singularities on quantum hardware.

Contribution

It introduces non-Hermitian quantum circuits for lattice field theories and demonstrates their application to the quantum Ising model with complex fields.

Findings

Quantum circuits can simulate non-Hermitian dynamics effectively.

Observables probe Lee-Yang edge singularity in the Ising model.

Attractors emerge past critical points, useful for noisy hardware.

Abstract

Certain aspects of some unitary quantum systems are well-described by evolution via a non-Hermitian effective Hamiltonian, as in the Wigner-Weisskopf theory for spontaneous decay. Conversely, any non-Hermitian Hamiltonian evolution can be accommodated in a corresponding unitary system + environment model via a generalization of Wigner-Weisskopf theory. This demonstrates the physical relevance of novel features such as exceptional points in quantum dynamics, and opens up avenues for studying many body systems in the complex plane of coupling constants. In the case of lattice field theory, sparsity lends these channels the promise of efficient simulation on standardized quantum hardware. We thus consider quantum operations that correspond to Suzuki-Lee-Trotter approximation of lattice field theories undergoing non-Hermitian time evolution, with potential applicability to studies of spin or gauge models at finite chemical potential, with topological terms, to quantum phase transitions - a range of models with sign problems. We develop non-Hermitian quantum circuits and explore their promise on a benchmark, the quantum one-dimensional Ising model with complex longitudinal magnetic field, showing that observables can probe the Lee-Yang edge singularity. The development of attractors past critical points in the space of complex couplings indicates a potential for study on near-term noisy hardware.