Optimal Scaling Quantum Interior Point Method for Linear Optimization

TL;DR

This paper introduces a hybrid quantum-classical interior point method for large-scale linear optimization that leverages quantum computing to achieve optimal scaling and improved efficiency over classical methods.

Contribution

It presents a novel quantum interior point method that constructs and solves Newton systems on a quantum computer, reducing complexity for dense large-scale problems.

Findings

Achieves an optimal $ ilde{O}(n^2)$ worst-case scaling for dense LO problems.

Provides a quantum complexity of $ ilde{O}(n^{1.5} \, \kappa_A \log(1/\epsilon))$ queries to QRAM.

Outperforms prior classical and quantum IPMs in scalability and efficiency.

Abstract

The emergence of huge-scale, data-intensive linear optimization (LO) problems in applications such as machine learning has driven the need for more computationally efficient interior point methods (IPMs). While conventional IPMs are polynomial-time algorithms with rapid convergence, their per-iteration cost can be prohibitively high for dense large-scale LO problems. Quantum linear system solvers have shown potential in accelerating the solution of linear systems arising in IPMs. In this work, we introduce a novel almost-exact quantum IPM, where the Newton system is constructed and solved on a quantum computer, while solution updates occur on a classical machine. Additionally, all matrix-vector products are performed on the quantum hardware. This hybrid quantum-classical framework achieves an optimal worst-case scaling of $\mathcal{O}(n^2)$ for fully dense LO problems. To ensure high precision, despite the limited accuracy of quantum operations, we incorporate iterative refinement techniques both within and outside the proposed IPM iterations. The proposed algorithm has a quantum complexity of $\mathcal{O}(n^{1.5} \kappa_A \log(\frac{1}{\epsilon}))$ queries to QRAM and $\mathcal{O}(n^2 \log(\frac{1}{\epsilon}))$ classical arithmetic operations. Our method outperforms the worst-case complexity of prior classical and quantum IPMs, offering a significant improvement in scalability and computational efficiency.