Quadratic Quantum Measurements

TL;DR

This paper develops a theory of quadratic quantum measurements by mesoscopic detectors, revealing their unique quantum information properties and potential for entangling non-interacting qubits, with analysis of detector output spectra.

Contribution

It introduces a theoretical framework for quadratic quantum measurements and demonstrates their ability to entangle qubits and analyze detector spectra.

Findings

Quadratic measurements can entangle non-interacting qubits.

The output spectrum of detectors reveals coherent qubit oscillations.

Quadratic measurements have non-trivial quantum information properties.

Abstract

We develop a theory of quadratic quantum measurements by a mesoscopic detector. It is shown that quadratic measurements should have non-trivial quantum information properties, providing, for instance, a simple way of entangling two non-interacting qubits. We also calculate output spectrum of a quantum detector with both linear and quadratic response continuously monitoring coherent oscillations in two qubits.