Experimental entanglement redistribution under decoherence channels

TL;DR

This paper investigates how entanglement redistributes among qubits and their environments under decoherence, combining theoretical analysis with optical experiments to observe entanglement transitions and genuine multipartite entanglement.

Contribution

It provides both theoretical and experimental insights into entanglement dynamics, including the observation of genuine four-qubit entanglement during decoherence.

Findings

Transition from bipartite to multipartite entanglement observed.

Genuine four-qubit entanglement detected at certain evolution points.

Entanglement sudden death and birth phenomena demonstrated.

Abstract

When an initially entangled pair of qubits undergoes local decoherence processes, there are a number of ways in which the original entanglement can spread throughout the multipartite system consisting of the two qubits and their environments. Here we report theoretical and experimental results regarding the dynamics of the distribution of entanglement in this system. The experiment employs an all optical set-up in which the qubits are encoded in the polarization degrees of freedom of two photons, and each local decoherence channel is implemented with an interferometer that couples the polarization to the path of each photon, which acts as an environment. We monitor the dynamics and distribution of entanglement and observe the transition from bipartite to multipartite entanglement and back, and show how these transitions are intimately related to the sudden death and sudden birth of entanglement. The multipartite entanglement is further analyzed in terms of 3- and 4- partite entanglement contributions, and genuine four-qubit entanglement is observed at some points of the evolution.