Subradiance and entanglement in atoms with several independent decay channels

TL;DR

This paper demonstrates that in multi-channel atomic systems, highly entangled states can be engineered to be completely decoupled from spontaneous emission, extending the concept of subradiance beyond two-atom systems.

Contribution

It introduces a method to construct highly entangled states that are immune to decay in atoms with multiple independent decay channels, generalizing subradiance phenomena.

Findings

Existence of a unique highly entangled dark state for any number of decay channels.

The subradiant property persists at finite atomic distances.

Construction of states that completely decouple from radiation field regardless of decay channels.

Abstract

Spontaneous emission of a two--level atom in free space is modified by other atoms in its vicinity leading to super- and sub-radiance. In particular, for atomic distances closer than the transition wavelength the maximally entangled antisymmetric superposition state of two individually excited atomic dipole moments possesses no total dipole moment and will not decay spontaneously at all. Such a two-atom dark state does not exist, if the atoms possess alternative decay channels towards other atomic lower energy states. However, we show here that for any atomic state with $N-1$ independent spontaneous decay channels one can always find a $N$-particle highly entangled state, which completely decouples from the free radiation field and does not decay. Moreover, we show that this state is the unique state orthogonal to the subspace spanned by the lower energy states with this property. Its sub-radiant property largely survives at finite atomic distances.