Localizing genuine multiparty entanglement in noisy stabilizer states

TL;DR

This paper develops a method to quantify and analyze genuine multiparty entanglement in large, noisy stabilizer states, using graph-based techniques and exploring the effects of noise on entanglement localization.

Contribution

It introduces a polynomial-scaling graph-based approach to calculate lower bounds of localizable genuine multiparty entanglement in stabilizer states under noise, including large and complex systems.

Findings

Lower bounds of entanglement can be efficiently computed for large graph states.

Existence of a critical noise threshold beyond which entanglement becomes biseparable.

Application of the method to large stabilizer states like the toric code under noise.

Abstract

Characterizing large noisy multiparty quantum states using genuine multiparty entanglement is a challenging task. In this paper, we calculate lower bounds of genuine multiparty entanglement localized over a chosen multiparty subsystem of multi-qubit stabilizer states in the noiseless and noisy scenario. In the absence of noise, adopting a graph-based technique, we perform the calculation for arbitrary graph states as representatives of the stabilizer states, and show that the graph operations required for the calculation has a polynomial scaling with the system size. As demonstrations, we compute the localized genuine multiparty entanglement over subsystems of large graphs having linear, ladder, and square structures. We also extend the calculation for graph states subjected to single-qubit Markovian or non-Markovian Pauli noise on all qubits, and demonstrate, for a specific lower bound of the localizable genuine multiparty entanglement corresponding to a specific Pauli measurement setup, the existence of a critical noise strength beyond which all of the post measured states are biseparable. The calculation is also useful for arbitrary large stabilizer states under noise due to the local unitary connection between stabilizer states and graph states. We demonstrate this by considering a toric code defined on a square lattice, and computing a lower bound of localizable genuine multiparty entanglement over a non-trivial loop of the code. Similar to the graph states, we show the existence of the critical noise strength in this case also, and discuss its interesting features.