Physicists from the Max Planck Institute of Quantum Optics (MPQ) have engineered the lightest optical mirror imaginable. The unique metamaterial is composed of a single structured layer that consists only of a few hundred identical atoms. The atoms are organized in the two-dimensional array of an optical lattice created by conflicting laser beams. The newly developed mirror is only several tens of nanometers thin, which is a thousand times thinner than the width of a human hair. The reflection, however, is so strong it could even be observed with the human eye. Researchers believe further research could develop the fundamental understanding of the quantum theories of light-matter interaction, many-body physics with optical photons, and enable the engineering of more efficient quantum devices.