Entanglement and purity of single- and two-photon states

TL;DR

This paper investigates how the entanglement of single- and two-photon states is affected when these states are mixed rather than pure, revealing that entanglement in single-photon states depends on their purity.

Contribution

It provides a detailed analysis of entanglement degradation in mixed photon states and clarifies the relationship between purity and entanglement in single-photon states.

Findings

Entanglement of a delocalized single-photon state is determined by its purity.

Mixed two-photon states exhibit reduced entanglement.

Vacuum components influence the entanglement properties of photon states.

Abstract

Whereas single- and two-photon wave packets are usually treated as pure states, in practice they will be mixed. We study how entanglement created with mixed photon wave packets is degraded. We find in particular that the entanglement of a delocalized single-photon state of the electro-magnetic field is determined simply by its purity. We also discuss entanglement for two-photon mixed states, as well as the influence of a vacuum component.