Stationary entanglement in N-atom subradiant degenerate cascade systems

TL;DR

This paper demonstrates the existence of stationary entangled states in ultracold N-atom degenerate cascade systems, highlighting quantum features of subradiance and analyzing entanglement properties for small atom numbers.

Contribution

It provides the first quantum analysis of stationary subradiant states in small N-atom systems, including explicit entanglement evaluation and limitations of continuous variable descriptions.

Findings

Stationary subradiant states exist in quantum regimes for small atom numbers.

Full inseparability of entanglement in three-atom configurations.

Continuous variable methods are inadequate for detecting entanglement in these states.

Abstract

We address ultracold $N$-atom degenerate cascade systems and show that stationary subradiant states, already observed in the semiclassical regime, also exist in a fully quantum regime and for a small number of atoms. We explicitly evaluate the amount of stationary entanglement for the two-atom configuration and show full inseparability for the three-atom case. We also show that a continuous variable description of the systems is not suitable to detect entanglement due to the nonGaussianity of subradiant states.