Leggett-Garg test of superconducting qubit addressing the clumsiness loophole

TL;DR

This paper reports a Leggett-Garg inequality test on a superconducting qubit system, providing evidence against macrorealism and addressing concerns about invasive measurement loopholes in quantum experiments.

Contribution

The study adapts a Leggett-Garg test to IBM's superconducting qubits, specifically targeting the clumsiness loophole in macrorealism tests.

Findings

Qubit Q2 violates the Leggett-Garg inequality

Evidence against noninvasive macrorealism in superconducting qubits

Addresses measurement invasiveness concerns in quantum tests

Abstract

The Leggett-Garg inequality holds for any macrorealistic system that is being measured noninvasively. A violation of the inequality can signal that a system does not conform to our primal intuition about the physical world. Alternatively, a violation can simply indicate that "clumsy" experimental technique led to invasive measurements. Here, we consider a recent Leggett-Garg test designed to try to rule out the mundane second possibility. We tailor this Leggett-Garg test to the IBM 5Q Quantum Experience system and find compelling evidence that qubit $Q_2$ of the system cannot be described by noninvasive macrorealism.