First-Order Phase Transition of the Schwinger Model with a Quantum Computer
arxiv(2023)
摘要
We explore the first-order phase transition in the lattice Schwinger model in
the presence of a topological θ-term by means of the variational quantum
eigensolver (VQE). Using two different fermion discretizations, Wilson and
staggered fermions, we develop parametric ansatz circuits suitable for both
discretizations, and compare their performance by simulating classically an
ideal VQE optimization in the absence of noise. The states obtained by the
classical simulation are then prepared on the IBM's superconducting quantum
hardware. Applying state-of-the art error-mitigation methods, we show that the
electric field density and particle number, observables which reveal the phase
structure of the model, can be reliably obtained from the quantum hardware. To
investigate the minimum system sizes required for a continuum extrapolation, we
study the continuum limit using matrix product states, and compare our results
to continuum mass perturbation theory. We demonstrate that taking the additive
mass renormalization into account is vital for enhancing the precision that can
be obtained with smaller system sizes. Furthermore, for the observables we
investigate we observe universality, and both fermion discretizations produce
the same continuum limit.
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