Experimental entanglement activation from discord in a programmable quantum measurement

TL;DR

This paper experimentally demonstrates that local quantum measurements can activate quantum discord into entanglement between a measurement apparatus and a bipartite system, revealing fundamental insights into quantum observation and correlations.

Contribution

It introduces an experimental protocol showing how quantum discord can be converted into entanglement through local measurements using a programmable two-photon setup.

Findings

Quantum discord can be activated into entanglement via local measurements.

The experiment confirms the fundamental role of measurement in quantum correlation dynamics.

A flexible two-photon system effectively demonstrates the activation process.

Abstract

In quantum mechanics, observing is not a passive act. Consider a system of two quantum particles A and B: if a measurement apparatus M is used to make an observation on B, the overall state of the system AB will typically be altered. When this happens no matter which local measurement is performed, the two objects A and B are revealed to possess peculiar correlations known as quantum discord. Here we demonstrate experimentally that the very act of local observation gives rise to an activation protocol which converts discord into distillable entanglement, a stronger and more useful form of quantum correlations, between the apparatus M and the composite system AB. We adopt a flexible two-photon setup to realize a three-qubit system (A,B,M) with programmable degrees of initial correlations, measurement interaction, and characterization processes. Our experiment demonstrates the fundamental mechanism underpinning the ubiquitous act of observing the quantum world, and establishes the potential of discord in entanglement generation.