Preserving entanglement during weak measurement demonstrated with a violation of the Bell-Leggett-Garg inequality

TL;DR

This paper demonstrates that weak measurements can preserve entanglement in a Bell state, evidenced by a significant violation of the Hybrid Bell-Leggett-Garg inequality in a four-qubit transmon system.

Contribution

It experimentally shows the preservation of entanglement during weak measurement using the BLGI on a multi-qubit system, extending prior single-qubit results.

Findings

Achieved a 27 standard deviation violation of the BLGI.

Demonstrated correlation between weak ancilla measurements and projective readout.

Confirmed entanglement preservation during weak measurement process.

Abstract

Weak measurement has provided new insight into the nature of quantum measurement, by demonstrating the ability to extract average state information without fully projecting the system. For single qubit measurements, this partial projection has been demonstrated with violations of the Leggett-Garg inequality. Here we investigate the effects of weak measurement on a maximally entangled Bell state through application of the Hybrid Bell-Leggett-Garg inequality (BLGI) on a linear chain of four transmon qubits. By correlating the results of weak ancilla measurements with subsequent projective readout, we achieve a violation of the BLGI with 27 standard deviations of certainty.