Lasers Hold a Few Hundred Atoms to Create the Smallest Optical Mirror

Physicists at the Max Planck Institute of Quantum Optics (MPQ) have made an optical mirror using only a few hundred identical atoms. They used a new metamaterial made of a single structured layer. few hundred identical atoms. Interfering laser beams hold two layers of atoms in arrays. This has come from an emerging new field of subwavelength quantum optics with ordered atoms. The mirror is the only one of its kind.

The new mirror is only several tens of nanometers thin but the reflection can be seen by the human eye. The mirror has a diameter of around seven microns.

The machinery has a thousand single optical components and weighs about two tons.

Nature – A subradiant optical mirror formed by a single structured atomic layer

Metamaterials properties are not from the materials they are made of but from the specific structures they are designed with. The characteristics – the regular pattern and the subwavelength spacing – and their interplay are the two crucial workings behind this novel kind of optical mirror.

1. the regular pattern and the subwavelength spacing of atoms both suppress a diffuse scattering of light, bundling the reflection into a one-directional and steady beam of light.

2. because of the comparatively close and discrete distance between the atoms, an incoming photon can bounce back and forth between the atoms more than once before it is being reflected. Both effects, the suppressed scattering of light and the bouncing of the photons, lead to an “enhanced cooperative response to the external field”, which means in this case: a very strong reflection.

Versatile interfaces with strong and tunable light–matter interactions are essential for quantum science1 because they enable mapping of quantum properties between light and matter. Recent studies have proposed a method of controlling light–matter interactions using the rich interplay of photon-mediated dipole–dipole interactions in structured subwavelength arrays of quantum emitters. However, a key aspect of this approach—the cooperative enhancement of the light–matter coupling strength and the directional mirror reflection of the incoming light using an array of quantum emitters—has not yet been experimentally demonstrated. Here we report the direct observation of the cooperative subradiant response of a two-dimensional square array of atoms in an optical lattice. We observe a spectral narrowing of the collective atomic response well below the quantum-limited decay of individual atoms into free space. Through spatially resolved spectroscopic measurements, we show that the array acts as an efficient mirror formed by a single monolayer of a few hundred atoms. By tuning the atom density in the array and changing the ordering of the particles, we are able to control the cooperative response of the array and elucidate the effect of the interplay of spatial order and dipolar interactions on the collective properties of the ensemble. Bloch oscillations of the atoms outside the array enable us to dynamically control the reflectivity of the atomic mirror. Our work demonstrates efficient optical metamaterial engineering based on structured ensembles of atoms and paves the way towards controlling many-body physics with light and light–matter interfaces at the single-quantum level.

SOURCES- Nature, Max Planck Institute of Quantum Optics
Written By Brian Wang,