Unidirectional absorption, storage, and emission of single photons in a collectively responding bilayer atomic array

TL;DR

This paper demonstrates how a bilayer atomic array can efficiently absorb, store, and emit single photons in a controlled, directional manner, enabling advanced quantum communication protocols.

Contribution

It introduces a bilayer lattice design that achieves directional single-photon absorption and emission, surpassing single-layer limitations.

Findings

Bilayer arrays can absorb photons from arbitrary directions.

Subradiant states enable long-lived photon storage.

Directional emission is controlled by symmetry analysis.

Abstract

Two-dimensional regular arrays of atoms are a promising platform for quantum networks, with collective subradiant states providing long-lived storage and collimated emission allowing for natural coherent links between arrays in free space. However, a single-layer lattice can only efficiently absorb or emit light symmetrically in the forward and backward directions. Here we show how a bilayer lattice can absorb a single photon either incident from a single direction or an arbitrary superposition of forward and backward propagating components. The excitation can be stored in a subradiant state, transferred coherently between different subradiant states, and released, again in an arbitrary combination of highly collimated forward and backward propagating components. We explain the directionality of single and bilayer arrays by a symmetry analysis based on the scattering parities of different multipole radiation components of collective excitations. The collective modes may exhibit the conventional half-wave loss of fields near the array interface or completely eliminate it. The proposed directional control of absorption and emission paves the way for effective one-dimensional quantum communication between multiple arrays, with single-photons propagating backward and forward between quantum information-processing and storage stages.