Scattering Processes from Quantum Simulation Algorithms for Scalar Field Theories

TL;DR

This paper develops practical quantum simulation methods for scalar field theories, optimizing asymptotic costs and providing concrete gate and qubit estimates, making such simulations feasible on near-term quantum hardware.

Contribution

It introduces optimized algorithms for simulating scalar field theories on quantum computers, including finite volume approaches and fault-tolerant algorithms with detailed resource estimates.

Findings

Simulations can be performed with approximately 4 million physical qubits.

Estimated resource costs are around 10^12 T-gates for a day-long simulation.

The methods bring scalar field theory simulation within reach of current quantum technology.

Abstract

We provide practical simulation methods for scalar field theories on a quantum computer that yield improved asymptotics as well as concrete gate estimates for the simulation and physical qubit estimates using the surface code. We achieve these improvements through two optimizations. First, we consider a finite volume approach for estimating the elements of the S-matrix. This approach is appropriate in general for 1+1D and for certain low-energy elastic collisions in higher dimensions. Second, we implement our approach using a series of different fault-tolerant simulation algorithms for Hamiltonians formulated both in the field occupation basis and field amplitude basis. Our algorithms are based on either second-order Trotterization or qubitization. The cost of Trotterization in occupation basis scales as $O(\lambda N^7 |\Omega|^3/(M^{5/2} \epsilon^{3/2}))$ where $\lambda$ is the coupling strength, $N$ is the occupation cutoff, $|\Omega|$ is the volume of the spatial lattice, $M$ is the mass of the particles and $\epsilon$ is the uncertainty in the energy calculation used for the $S$-matrix determination. Qubitization in the field basis scales as $O(|\Omega|^2 (k^2 \Lambda +kM^2)/\epsilon)$ where $k$ is the cutoff in the field and $\Lambda$ is a scaled coupling constant. We find in both cases that the bounds suggest physically meaningful simulations can be performed using on the order of $4\times 10^6$ physical qubits and $10^{12}$ $T$-gates which corresponds to roughly one day on a superconducting quantum computer with surface code and a cycle time of 100 ns. This places the simulation of scalar field theory within striking distance of the gate counts for the best available chemistry simulation results.