Anomalous values, Fisher information, and contextuality, in generalized quantum measurements

TL;DR

This paper explores the connections between anomalous measurement values, Fisher information, and contextuality in generalized quantum measurements, focusing on qubits and the implications of postselection and weak measurements.

Contribution

It investigates the potential links between anomalous values, Fisher information, and contextuality within a unified framework for qubits, revealing complex relationships.

Findings

No one-to-one mapping between postselected measurements and anomalous values.

Postselection can lead to enhanced Fisher information.

Non-contextual models can explain outcomes in extremely weak measurements.

Abstract

Postselection following weak measurements has long been investigated for its peculiar manifestation of quantum signatures. In particular, the postselected events can give rise to anomalous values lying outside the spectrum of the measured quantity, and may provide enhanced Fisher information. Furthermore, the Pusey inequality highlights that, for extremely weak measurements, non-contextual models can account for the outcome probabilities. It is then interesting to investigate whether these are linked in a unified framework. Here we discuss on the existence of a possible connection in the case of qubits. We show that when performing generic postselected measurements there exist no one-to-one mapping between them, an instance that leads to drawing more involved considerations.