title: Contextuality without nonlocality in a superconducting quantum system.
abstract: Classical realism demands that system properties exist independently of whether they are measured, while noncontextuality demands that the results of measurements do not depend on what other measurements are performed in conjunction with them. The Bell-Kochen-Specker theorem states that noncontextual realism cannot reproduce the measurement statistics of a single three-level quantum system (qutrit). Noncontextual realistic models may thus be tested using a single qutrit without relying on the notion of quantum entanglement in contrast to Bell inequality tests. It is challenging to refute such models experimentally, since imperfections may introduce loopholes that enable a realist interpretation. Here we use a superconducting qutrit with deterministic, binary-outcome readouts to violate a noncontextuality inequality while addressing the detection, individual-existence and compatibility loopholes. This evidence of state-dependent contextuality also demonstrates the fitness of superconducting quantum circuits for fault-tolerant quantum computation in surface-code architectures, currently the most promising route to scalable quantum computing.
authors.affiliation: ARC Centre of Excellence for Engineered Quantum Systems, The University of Queensland, St Lucia, Queensland 4072, Australia.
authors.forename: Markus
authors.initials: M
authors.lastname: Jerger
authors.affiliation: School of Mathematics and Physics, The University of Queensland, St Lucia, Queensland 4072, Australia.
authors.forename: Yarema
authors.initials: Y
authors.lastname: Reshitnyk
authors.affiliation: Department of Physics, ETH Zurich, CH-8093 Zurich, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Oppliger
authors.affiliation: Department of Physics, ETH Zurich, CH-8093 Zurich, Switzerland.
authors.forename: Anton
authors.initials: A
authors.lastname: Potočnik
authors.affiliation: Department of Physics, ETH Zurich, CH-8093 Zurich, Switzerland.
authors.forename: Mintu
authors.initials: M
authors.lastname: Mondal
authors.affiliation: Department of Physics, ETH Zurich, CH-8093 Zurich, Switzerland.
authors.forename: Andreas
authors.identifier: 0000-0002-3476-4485
authors.initials: A
authors.lastname: Wallraff
authors.affiliation: QuTech, Delft University of Technology, Lorentzweg 1, 2611 CJ Delft, The Netherlands.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Goodenough
authors.affiliation: QuTech, Delft University of Technology, Lorentzweg 1, 2611 CJ Delft, The Netherlands.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Wehner
authors.affiliation: Quantronics group, SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, Gif-sur-Yvette 91191, France.
authors.forename: Kristinn
authors.initials: K
authors.lastname: Juliusson
authors.affiliation: QuTech, Delft University of Technology, Lorentzweg 1, 2611 CJ Delft, The Netherlands.|Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands.
authors.forename: Nathan K
authors.initials: NK
authors.lastname: Langford
authors.affiliation: ARC Centre of Excellence for Engineered Quantum Systems, The University of Queensland, St Lucia, Queensland 4072, Australia.|School of Mathematics and Physics, The University of Queensland, St Lucia, Queensland 4072, Australia.
authors.forename: Arkady
authors.initials: A
authors.lastname: Fedorov