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arXiv · 2512.20235

A resource-efficient and noise-robust entanglement witness based on the swap test

Sebastiano Guaraldo·Sonia Mazzucchi·Alessio Baldazzi·Stefano Azzini·Lorenzo Pavesi
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Abstract

Quantum entanglement is an essential resource for quantum technologies, and the controlled swap test provides a versatile tool for its detection and quantification. Here, we propose a SWAP-based entanglement witness that applies to arbitrary two-qubit states - both pure and mixed - and provides a lower bound on the concurrence. The method is resource-efficient, robust to noise, and platform-independent. As an example, we validate the approach on a room-temperature photonic chip, where the swap test is carried out using only linear and well-established integrated optical components. The robustness of the method against photonic-hardware noise is also analysed. Our results establish a simple and reliable tool for entanglement witnessing.

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Sebastiano Guaraldo, Sonia Mazzucchi, Alessio Baldazzi, Stefano Azzini, Lorenzo Pavesi. 2025-12-23. A resource-efficient and noise-robust entanglement witness based on the swap test. https://arxiv.org/abs/2512.20235

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