Spin chirality across quantum state copies detects hidden entanglement

TL;DR

This paper introduces a novel multi-copy entanglement detection method using spin chirality, achieving high accuracy in identifying bound entanglement, validated experimentally on IBM Quantum processors.

Contribution

It develops a physical structure-based multi-copy entanglement detection technique utilizing spin chirality and spectral classifiers, surpassing existing criteria in accuracy.

Findings

Achieved 99.9% recall in detecting bound entanglement.

Validated detection of pure, mixed, and bound entangled states experimentally.

Developed a spectral classifier combining realignment features with chirality corrections.

Abstract

Entanglement can hide in two fundamentally different ways. First, multi-copy correlations can carry information that no single-copy measurement on an unknown state is able to access. Second, bound entangled states possess a positive partial transpose, which makes them invisible to the Peres-Horodecki criterion and all moment inequalities that depend on it. Here we show that the moment difference between the partial transpose and purity decomposes exactly as a chirality-chirality correlator, where the relevant operator is the scalar spin chirality -- the same quantity that governs chiral spin liquids and the topological Hall effect. This decomposition identifies the specific physical structure that multi-copy entanglement detection probes. Using the same controlled-SWAP circuits, we develop a multi-channel spectral classifier for bound entanglement. The classifier combines realignment spectral features with chirality corrections and achieves 99.9% recall at zero false positives across all three known 3x3 bound entangled families, compared with ~40% for the CCNR criterion alone. We also introduce a marginal-noise construction that produces CCNR-invisible bound entangled states, which the classifier detects but which remain invisible to all single-parameter criteria. We validate our approach experimentally on three IBM Quantum processors and demonstrate negativity reconstruction with mean errors of 0.002-0.027, chirality detection for pure and mixed entangled states, and bound entanglement detection across two structurally distinct families (Horodecki and chessboard) on a single gate-based superconducting processor.