Tailored First-order and Interior-point methods and a new semidefinite programming hierarchy for entanglement detection

TL;DR

This paper introduces a new semidefinite programming hierarchy called PST for entanglement detection, along with scalable algorithms that improve detection accuracy and efficiency in high-dimensional quantum systems.

Contribution

It develops a novel SDP hierarchy and tailored algorithms that enable scalable, stable, and more accurate entanglement detection compared to existing methods.

Findings

PST hierarchy offers tighter approximation than EXT and lower computational cost than DPS.

The proposed algorithms can detect entanglement near the boundary of separability.

Numerical experiments show improved detection capabilities in benchmark quantum states.

Abstract

Quantum entanglement lies at the heart of quantum information science, yet its reliable detection in high-dimensional or noisy systems remains a fundamental computational challenge. Semidefinite programming (SDP) hierarchies, such as the Doherty-Parrilo-Spedalieri (DPS) and Extension (EXT) hierarchies, offer complete methods for entanglement detection, but their practical use is limited by exponential growth in problem size. In this paper, we introduce a new SDP hierarchy, PST, that is sandwiched between EXT and DPS--offering a tighter approximation to the set of separable states than EXT, while incurring lower computational overhead than DPS. We develop compact, polynomially-scalable descriptions of EXT and PST using partition mappings and operators. These descriptions in turn yield formulations that satisfy desirable properties such as the Slater condition and are well-suited to both first-order methods (FOMs) and interior-point methods (IPMs). We design a suite of entanglement detection algorithms: three FOMs (Frank-Wolfe, projected gradient, and fast projected gradient) based on a least-squares formulation, and a custom primal-dual IPM based on a conic programming formulation. These methods are numerically stable and capable of producing entanglement witnesses or proximity measures, even in cases where states lie near the boundary of separability. Numerical experiments on benchmark quantum states demonstrate that our algorithms improve the ability to solve deeper levels of the SDP hierarchy. In particular, the PST hierarchy combined with FOMs enables scalable and effective entanglement detection in relatively easy instances, while our IPM approach offers robustness and early witness recovery for the more difficult ones. Our results highlight the benefits of tailoring algorithmic formulations to hierarchy structure to advance entanglement detection at scale.