Testing time order and Leggett-Garg inequalities with noninvasive measurements on public quantum computers

2025/07/10 by Rybotycki, Tomasz, Białecki, Tomasz, Batle, Josep +4 · 1 citation
#FOS: Physical sciences #Quantum Physics (quant-ph)

paper · doi:10.48550/arxiv.2507.07904

Abstract

We present two protocols, with one and two two-qubit gates, to noninvasively measure two incompatible observables on a qubit. Both protocols are completed with a projective measurement. By gathering sufficiently large statistics, we have been able to violate Leggett-Garg inequality and time-order invariance. The detailed analysis of the data on 10 qubit sets from 5 devices available on IBM Quantum and one on IonQ reveals violations beyond 5 standard deviations in almost all cases. We implemented our protocols using fractional gates, newly available on the IBM Heron devices, allowing us to benchmark them in application to weak measurements. The noninvasiveness is supported by a qualitative and quantitative agreement with the model of weak disturbance. These results show another characteristic feature of quantum measurements.

Citations

• Testing precision and accuracy of weak value measurements in an IBM quantum system
• Preserving entanglement during weak measurement demonstrated with a violation of the Bell-Leggett-Garg inequality
• "No Information Without Disturbance": Quantum Limitations of Measurement
• Quantum mechanical interaction-free measurements
• Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?
• Quantum Theory: Concepts and Methods

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