Quasiprobability distributions with weak measurements

TL;DR

This paper explores the role of quantum coherence in sequential weak measurements using photonic qubits, demonstrating how quasiprobability distributions can reveal nonclassical features and aid in quantum monitoring.

Contribution

It introduces an experimental protocol for sequential weak measurements with photonic qubits and analyzes quasiprobability distributions to identify quantum coherence effects.

Findings

Quasidistributions can exhibit negativity depending on measurement parameters.

Weak measurements preserve quantum coherence useful for quantum monitoring.

The approach distinguishes classical from quantum behavior via quasiprobability analysis.

Abstract

We discuss and experimentally demonstrate the role of quantum coherence in a sequence of two measurements collected at different times using weak measurements. For this purpose, we have realized a weak-sequential measurement protocol with photonic qubits, where the first measurement is carried out as a positive operator-valued measure, whereas the second one is a projective operation. We determine the quasiprobability distributions associated to this procedure using both the commensurate and the Margenau-Hill quasiprobabilities approaches. By tuning the weak measurements, we obtain a quasidistribution that may or may not exhibit negative parts, depending on the suitability of a contextual model for describing the experiment. Our results show how quasidistributions may find application in inspecting quantum monitoring, when part of the initial quantum coherence needs to be preserved.