Parton Distributions on a Quantum Computer

TL;DR

This paper demonstrates the first quantum computation of a parton distribution function (PDF) using a real quantum device, specifically calculating the lightcone correlator of positronium in the Schwinger model, highlighting quantum advantages over classical methods.

Contribution

It presents the first quantum computation of a PDF on a real quantum device, showcasing the feasibility and potential advantages of quantum computing for high-energy physics calculations.

Findings

Quantum computation of PDF shows good agreement with classical results in central values.

Reducing two-qubit gate depth to around 500 is crucial for obtaining meaningful results.

Quantum methods can access a broader range of parton momentum fractions than classical approaches.

Abstract

We perform the first quantum computation of parton distribution function (PDF) with a real quantum device by calculating the PDF of the lightest positronium in the Schwinger model with IBM quantum computers. The calculation uses 10 qubits for staggered fermions at five spatial sites and one ancillary qubit. The most critical and challenging step is to reduce the number of two-qubit gate depths to around 500 so that sensible results start to emerge. The resulting lightcone correlators have excellent agreement with the classical simulator result in central values, although the error is still large. Compared with classical approaches, quantum computation has the advantage of not being limited in the accessible range of parton momentum fraction $x$ due to renormalon ambiguity, and the difficulty of accessing non-valence partons. A PDF calculation with 3+1 dimensional QCD near $x=0$ or $x=1$ will be a clear demonstration of the quantum advantage on a problem with great scientific impact.