Experimental investigation of the dynamics of entanglement: Sudden death, complementarity, and continuous monitoring of the environment

TL;DR

This experimental study explores how entanglement between qubits and their environments evolves, demonstrating phenomena like entanglement sudden death, the effects of continuous monitoring, and the transfer of entanglement to multipartite states.

Contribution

The paper provides the first experimental investigation of entanglement dynamics, including entanglement sudden death and transfer to GHZ states, using photonic qubits and continuous environmental monitoring.

Findings

Entanglement can vanish before coherence disappears.

Continuous monitoring can increase entanglement and enable entanglement distillation.

Entanglement can transfer from qubits to environments, forming GHZ states.

Abstract

We report on an experimental investigation of the dynamics of entanglement between a single qubit and its environment, as well as for pairs of qubits interacting independently with individual environments, using photons obtained from parametric down-conversion. The qubits are encoded in the polarizations of single photons, while the interaction with the environment is implemented by coupling the polarization of each photon with its momentum. A convenient Sagnac interferometer allows for the implementation of several decoherence channels and for the continuous monitoring of the environment. For an initially-entangled photon pair, one observes the vanishing of entanglement before coherence disappears. For a single qubit interacting with an environment, the dynamics of complementarity relations connecting single-qubit properties and its entanglement with the environment is experimentally determined. The evolution of a single qubit under continuous monitoring of the environment is investigated, demonstrating that a qubit may decay even when the environment is found in the unexcited state. This implies that entanglement can be increased by local continuous monitoring, which is equivalent to entanglement distillation. We also present a detailed analysis of the transfer of entanglement from the two-qubit system to the two corresponding environments, between which entanglement may suddenly appear, and show instances for which no entanglement is created between dephasing environments, nor between each of them and the corresponding qubit: the initial two-qubit entanglement gets transformed into legitimate multiqubit entanglement of the Greenberger-Horne-Zeilinger (GHZ) type.