Experimental hierarchy of two-qubit quantum correlations without state tomography

TL;DR

This paper demonstrates an efficient experimental method to reveal the hierarchy of quantum correlations in two-qubit states using only six measurements, avoiding full state tomography.

Contribution

It introduces a measurement scheme that identifies quantum entanglement, steering, and Bell nonlocality with fewer parameters than traditional tomography methods.

Findings

Successfully demonstrated hierarchy detection with six correlation matrix elements

Applicable to generalized Werner states affected by white noise

Reduces measurement complexity compared to full state tomography

Abstract

A Werner state, which is the singlet Bell state affected by white noise, is a prototype example of states, which can reveal a hierarchy of quantum entanglement, steering, and Bell nonlocality by controlling the amount of noise. However, experimental demonstrations of this hierarchy in a sufficient and necessary way (i.e., by applying measures or universal witnesses of these quantum correlations) have been mainly based on full quantum state tomography, corresponding to measuring at least 15 real parameters of two-qubit states. Here we report an experimental demonstration of this hierarchy by measuring only six elements of a correlation matrix depending on linear combinations of two-qubit Stokes parameters. We show that our experimental setup can also reveal the hierarchy of these quantum correlations of generalized Werner states, which are any two-qubit pure states affected by white noise.