Bell inequality violation in gate-defined quantum dots
Quantum computers leverage entanglement to achieve superior computational power. However, verifying that the entangled state does not follow the principle of local causality has proven difficult for spin qubits in gate-defined quantum dots, as it requires simultaneously high concurrence values and readout fidelities to break the classical bound imposed by Bell's inequality. While low error rates for state preparation, control, and measurement have been independently demonstrated, a simultaneous demonstration remained challenging. We employ advanced protocols like heralded initialization and calibration via gate set tomography (GST), to push fidelities of the full 2-qubit gate set above 99%, including state preparation and measurement (SPAM). We demonstrate a 97.17% Bell state fidelity without correcting for readout errors and violate Bell's inequality using direct parity readout with a Bell signal of S = 2.731. Our measurements exceed the classical limit even at 1.1 K or entanglement lifetimes of 100 μs. Violating Bell's inequality in a silicon quantum dot qubit system is a key milestone, as it proves quantum entanglement, fundamental to achieving quantum advantage.
Authors
- Kohei M. Itoh (ORCID: https://orcid.org/0000-0002-8153-4893)
- Arne Laucht (ORCID: https://orcid.org/0000-0001-7892-7963)
- Chih Hwan Yang (ORCID: https://orcid.org/0000-0002-8713-150X)
- Andrew S. Dzurak (ORCID: https://orcid.org/0000-0003-1389-5096)
- Wee Han Lim (ORCID: https://orcid.org/0000-0002-8821-2758)
- MengKe Feng (ORCID: https://orcid.org/0000-0002-8894-7383)
- Fay E. Hudson (ORCID: https://orcid.org/0000-0003-0134-3657)
- Ensar Vahapoglu (ORCID: https://orcid.org/0000-0002-3047-8414)
- Andrea Morello (ORCID: https://orcid.org/0000-0001-7445-699X)
- Jonathan Huang (ORCID: https://orcid.org/0000-0002-5901-8403)
- Tuomo Tanttu (ORCID: https://orcid.org/0000-0002-2832-3237)
- Christopher C. Escott (ORCID: https://orcid.org/0000-0003-1458-2980)
- Nard Dumoulin Stuyck (ORCID: https://orcid.org/0000-0003-0731-7679)
- André Saraiva (ORCID: https://orcid.org/0000-0002-7209-9180)
- Cameron Jones (ORCID: https://orcid.org/0000-0002-8765-5178)
- Paul Steinacker (ORCID: https://orcid.org/0009-0000-6515-2513)
- Santiago Serrano (ORCID: https://orcid.org/0000-0002-3950-1174)
- Rocky Y. Su
Institutions
- Keio University (JP)
- UNSW Sydney (AU)
- Water Research Australia (AU)
Publication Details
- Journal
- Nature Communications
- Published
- 2025-04-22
- DOI
- https://doi.org/10.1038/s41467-025-57987-0
- Citations
- 5
- Primary Topic
- Quantum Information and Cryptography
- Type
- article
- Field-Weighted Citation Impact
- 12.40
Funders
- Australian National Fabrication Facility
- University of New South Wales
- Centre of Excellence for Electromaterials Science, Australian Research Council
- U.S. Air Force
- Army Research Office