Entanglement detection from interference fringes in atom-photon systems

TL;DR

This paper explores how interference fringes in atom-photon systems can be used to detect and quantify entanglement among atomic qubits, revealing new methods for state tomography and entanglement measurement.

Contribution

It demonstrates a novel approach linking interference patterns to entanglement measures, including state tomography for closely spaced qubits and relations among entanglement metrics for three qubits.

Findings

Interference visibility equals concurrence for two qubits at large separation.

State tomography is feasible when qubits are within a wavelength of each other.

Interference visibility correlates with maximal bipartite negativity in three-qubit systems.

Abstract

A measurement scheme of atomic qubits pinned at given positions is studied by analyzing the interference pattern obtained when they emit photons spontaneously. In the case of two qubits, a well-known relation is revisited, in which the interference visibility is equal to the concurrence of the state in the infinite spatial separation limit of the qubits. By taking into account the super-radiant and sub-radiant effects, it is shown that a state tomography is possible when the qubit spatial separation is comparable to the wavelength of the atomic transition. In the case of three qubits, the relations between various entanglement measures and the interference visibility are studied, where the visibility is defined from the two-qubit case. A qualitative correspondence among these entanglement relations is discussed. In particular, it is shown that the interference visibility is directly related to the maximal bipartite negativity.