Leggett-Garg inequality with a kicked quantum pump

TL;DR

This paper introduces a kicked quantum nondemolition measurement method using a pumped current to weakly measure a qubit, demonstrating a violation of a generalized Leggett-Garg inequality linked to detector backaction.

Contribution

It presents a novel measurement scheme combining weak measurement with unitary operations and applies it to test Leggett-Garg inequality violations in a quantum point contact system.

Findings

Violation of generalized Leggett-Garg inequality observed

Measurement backaction linked to entanglement with detector excitations

Method applicable to double quantum dot systems

Abstract

A kicked quantum nondemolition measurement is introduced, where a qubit is weakly measured by pumping current. Measurement statistics are derived for weak measurements combined with single qubit unitary operations. These results are applied to violate a generalization of Leggett and Garg's inequality. The violation is related to the failure of the noninvasive detector assumption, and may be interpreted as either intrinsic detector backaction, or the qubit entangling the microscopic detector excitations. The results are discussed in terms of a quantum point contact kicked by a pulse generator, measuring a double quantum dot.