Entanglement verification with realistic measurement devices via squashing operations

TL;DR

This paper introduces a method using squashing operations to verify entanglement in quantum systems with realistic measurement devices, ensuring the validity of entanglement claims despite device imperfections.

Contribution

It establishes a framework for entanglement verification with realistic measurements via positive linear maps called squashing operations, extending prior idealized models.

Findings

Positive entanglement verification is possible with squashing operations.

Lower bounds on entanglement can be derived using the method.

Applicable to polarization measurements with threshold detectors.

Abstract

Many protocols and experiments in quantum information science are described in terms of simple measurements on qubits. However, in a real implementation, the exact description is more difficult, and more complicated observables are used. The question arises whether a claim of entanglement in the simplified description still holds, if the difference between the realistic and simplified models is taken into account. We show that a positive entanglement statement remains valid if a certain positive linear map connecting the two descriptions--a so-called squashing operation--exists; then lower bounds on the amount of entanglement are also possible. We apply our results to polarization measurements of photons using only threshold detectors, and derive procedures under which multi-photon events can be neglected.