# How to observe and quantify quantum-discorded states

## TL;DR

This paper introduces a practical electronic protocol for detecting and quantifying quantum discord in unentangled bipartite systems, enabling experimental exploration of quantum correlations beyond entanglement.

## Contribution

It presents a simple, measurement-based protocol to observe quantum discord without requiring entanglement or full state tomography.

## Key findings

- Protocol successfully detects quantum discord via current correlation measurements.
- Enables experimental study of discord in many-body condensed matter systems.
- Provides a practical method for quantifying quantum correlations in unentangled states.

## Abstract

Quantum correlations between parts of a composite system most clearly reveal themselves through entanglement. Designing, maintaining, and controlling entangled systems is very demanding, which raises the stakes for understanding the efficacy of entanglement-free, yet quantum, correlations, exemplified by quantum discord. Discord is defined via conditional mutual entropies of parts of a composite system, and its direct measurement is hardly possible even via full tomographic characterization of the system state. Here we design a simple protocol to detect quantum discord and characterize a discorded state in an unentangled bipartite system. Our protocol is based on an electronic setup and relies on a characteristic of discord that can be extracted from repeated direct measurements of current correlations between subsystems. The proposed protocol opens a way of extending experimental studies of discord to many-body condensed matter systems.