Loophole-free Bell inequality violation with superconducting circuits

• Published in: Nature (London) 2023-05, Vol.617 (7960), p.265-270
• Main Authors: Storz, Simon, Schär, Josua, Kulikov, Anatoly, Magnard, Paul, Kurpiers, Philipp, Lütolf, Janis, Walter, Theo, Copetudo, Adrian, Reuer, Kevin, Akin, Abdulkadir, Besse, Jean-Claude, Gabureac, Mihai, Norris, Graham J., Rosario, Andrés, Martin, Ferran, Martinez, José, Amaya, Waldimar, Mitchell, Morgan W., Abellan, Carlos, Bancal, Jean-Daniel, Sangouard, Nicolas, Royer, Baptiste, Blais, Alexandre, Wallraff, Andreas
• Format: Article
• Language: English
• Subjects: 142/126; 639/766/1130/1064; 639/766/483/1139; 639/766/483/2802; 639/766/483/3925; Bell's inequality; Circuits; Experiments; Humanities and Social Sciences; Information technology; Loopholes; multidisciplinary; Physics; Quantum computing; Quantum entanglement; Quantum phenomena; Quantum Physics; Quantum theory; Qubits (quantum computing); Science; Science (multidisciplinary); Superconductivity
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-023-05885-0

Superposition, entanglement and non-locality constitute fundamental features of quantum physics. The fact that quantum physics does not follow the principle of local causality 1 – 3 can be experimentally demonstrated in Bell tests 4 performed on pairs of spatially separated, entangled quantum systems. Although Bell tests, which are widely regarded as a litmus test of quantum physics, have been explored using a broad range of quantum systems over the past 50 years, only relatively recently have experiments free of so-called loopholes 5 succeeded. Such experiments have been performed with spins in nitrogen–vacancy centres 6 , optical photons 7 – 9 and neutral atoms 10 . Here we demonstrate a loophole-free violation of Bell’s inequality with superconducting circuits, which are a prime contender for realizing quantum computing technology 11 . To evaluate a Clauser–Horne–Shimony–Holt-type Bell inequality 4 , we deterministically entangle a pair of qubits 12 and perform fast and high-fidelity measurements 13 along randomly chosen bases on the qubits connected through a cryogenic link 14 spanning a distance of 30 metres. Evaluating more than 1 million experimental trials, we find an average S value of 2.0747 ± 0.0033, violating Bell’s inequality with a P value smaller than 10 −108 . Our work demonstrates that non-locality is a viable new resource in quantum information technology realized with superconducting circuits with potential applications in quantum communication, quantum computing and fundamental physics 15 . A loophole-free violation of Bell’s inequality with superconducting circuits shows that non-locality is a viable new resource in quantum information technology realized with superconducting circuits, promising many potential applications.