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.

Evolution of Nanowire Transmon Qubits and Their Coherence in a Magnetic Field

“…The Josephson junction (JJ), usually implemented as a superconductor-insulatorsuperconductor (SIS) tunnel barrier, allows the realization of anharmonic oscillators that can be operated in the quantum regime and used as qubits [4]. Circuit QED has found applications in many areas, including scalable quantum computation [5], quantum optics [6], quantum foundations [7], and quantum measurement and control [8]. So far, CQED has been limited by standard SIS JJs based on aluminum and its oxide to fields <10 mT, the critical field of bulk aluminum [9].…”

The Negativity‐to‐Violation Map between Wigner Function and Quantum Contextuality Inequality for a Single Qudit

“…In Appendix A we will further expand equivalence in our method between this contextuality inequality and value assignment analogous to Equation (2). [21][22][23][24] Furthermore for testing the relation between state-dependent contextuality and the discrete Wigner function multiple qudits are involved in the most methods, [13,14,16,17] even for the test on a single qudit [13] the second auxiliary qudit is needed. The currently known testing methods on a single qutrit with the minimum numbers of measurements consist of five measurements for a state-dependent test [2] and 13 measurements for a state-independent test.…”

“…By using Equation (19), Equation (20), and Equation (21), it is easy to find that projectors P t are orthogonal to [u,v] 1 , [u,v] 2 , and [u,v] 3 . By using Equation (19), Equation (20), and Equation (21), it is easy to find that projectors P t are orthogonal to [u,v] 1 , [u,v] 2 , and [u,v] 3 .…”

Memory cost for simulating all quantum correlations from the Peres–Mermin scenario

“…Alternatively, the outcomes can be obtained by measuring the observables in a context sequentially. This approach has been preferred in recent experiments on quantum contextuality [15][16][17][18][19][20]. When an observable X from the Peres-Mermin square is measured, then the quantum state ρ changes according to…”