Nonsymmetrized Correlations in Quantum Noninvasive Measurements

TL;DR

This paper explores the distinction between symmetrized and nonsymmetrized current noise correlations in quantum measurements, demonstrating how both can be understood within quantum weak-measurement theory and linking negativity in quasiprobabilities to electron squeezing.

Contribution

It introduces a unified framework for understanding symmetrized and nonsymmetrized noise correlations using quantum weak-measurement theory with memory effects.

Findings

Both noise order schemes can be embedded in weak-measurement theory.

Negativity in quasiprobabilities indicates quantum features like squeezing.

Experimental tests can detect negativity through second-order correlations.

Abstract

A long-standing problem in quantum mesoscopic physics is which operator order corresponds to noise expressions like <I(-\omega)I(\omega)>, where I(\omega) is the measured current at frequency \omega. Symmetrized order describes a classical measurement while nonsymmetrized order corresponds to a quantum detector, e.g., one sensitive to either emission or absorption of photons. We show that both order schemes can be embedded in quantum weak-measurement theory taking into account measurements with memory, characterized by a memory function which is independent of a particular experimental detection scheme. We discuss the resulting quasiprobabilities for different detector temperatures and how their negativity can be tested on the level of second-order correlation functions already. Experimentally, this negativity can be related to the squeezing of the many-body state of the transported electrons in an ac-driven tunnel junction.