1.

INTRODUCTION

Collective radiation effects such as sub-radiance and super-radiance arise in ordered structures of quantum emitters at sub wavelength distance. Such vaccuum-mediated dipole-dipole interactions in free space are nowadays attracting renewed interest. This is partially triggered by the fact that recently it has become possible to realize almost any spatial arrangements at will using individually trapped atoms in optical tweezers. Moreover, such sub-wavelength structures can also be implemented using superconducting qubits in the microwave waveguides or using structured growing of quantum dots. These systems can be regarded as novel quantum optics platforms that enable an enhanced atom-light coupling, which can outperform previously established bounds in quantum protocols including single photon storage, spectroscopy, or opto-mechanics. Moreover, it represents a new playground for exploring fundamental physics involving quantum many body states of light and matter.

An array of closely spaced, dipole coupled quantum emitters exhibits collective energy shifts as well as super-and sub-radiance with characteristic tailor-able spatial radiation patterns. Symmetric configurations as straight lines, 2D regular lattice structures or ring shaped regular polygons have particularly special properties.¹ As striking example we show a single photon antenna build from a ring of dipoles with central absorber. For the fully symmetric case a 9-ring exhibits optimal performance. The setup is depicted in Fig.1.^2–4 The corresponding absorption cross section as function of ring size and center loss rate is depicted in Fig.2. On clearly sees that a 9-ring has superior properties in particular for very small sample sizes.

Figure 1.

Exemplaric scheme of a single photon nano antenna build of a circular dipole array with central absorber

Figure 2.

(left) Absorption efficiency as function of ring atom number and energy extraction ratio and (right) as function of ring size and emitter number.