Simulation of IBM's kicked Ising experiment with Projected Entangled Pair Operator

TL;DR

This paper introduces a classical simulation method using projected entangled pair operators (PEPO) for the 127-qubit kicked Ising model, demonstrating superior efficiency and accuracy over existing techniques in simulating quantum circuits.

Contribution

The paper presents the first application of PEPO in simulating quantum circuit time evolution, outperforming traditional tensor network methods in efficiency and accuracy.

Findings

PEPO with bond dimension 2 matches CPT with bond dimension 10.

PEPO with bond dimension 184 yields exact results in 3 seconds.

Results show convergence with increasing bond dimension and agreement with quantum hardware.

Abstract

We perform classical simulations of the 127-qubit kicked Ising model, which was recently emulated using a quantum circuit with error mitigation [Nature 618, 500 (2023)]. Our approach is based on the projected entangled pair operator (PEPO) in the Heisenberg picture. Its main feature is the ability to automatically identify the underlying low-rank and low-entanglement structures in the quantum circuit involving Clifford and near-Clifford gates. We assess our approach using the quantum circuit with 5+1 trotter steps which was previously considered beyond classical verification. We develop a Clifford expansion theory to compute exact expectation values and use them to evaluate algorithms. The results indicate that PEPO significantly outperforms existing methods, including the tensor network with belief propagation, the matrix product operator, and the Clifford perturbation theory, in both efficiency and accuracy. In particular, PEPO with bond dimension $\chi=2$ already gives similar accuracy to the CPT with $K=10$ and MPO with bond dimension $\chi=1024$. And PEPO with $\chi=184$ provides exact results in $3$ seconds using a single CPU. Furthermore, we apply our method to the circuit with 20 Trotter steps. We observe the monotonic and consistent convergence of the results with $\chi$, allowing us to estimate the outcome with $\chi\to\infty$ through extrapolations. We then compare the extrapolated results to those achieved in quantum hardware and with existing tensor network methods. Additionally, we discuss the potential usefulness of our approach in simulating quantum circuits, especially in scenarios involving near-Clifford circuits and quantum approximate optimization algorithms. Our approach is the first use of PEPO in solving the time evolution problem, and our results suggest it could be a powerful tool for exploring the dynamical properties of quantum many-body systems.