At the Max Planck Institute of Quantum Optics (MPQ), physicists have designed the lightest ever optical mirror. The new metamaterial is composed of a single-structured layer that includes just a few hundred identical atoms.
The atoms are organized in the two dimensional (2D) array of an optical lattice created by interfering laser beams. The results of the study are the first-ever experimental observations of their kind in a newly emerging field of subwavelength quantum optics that involves using ordered atoms. The mirror is the only one of its kind developed to date. The study outcomes were recently reported in the Nature journal.
In general, specially coated optical glasses or highly polished metal surfaces are used for mirrors to optimize for the performance in smaller weights. However, for the first time, physicists at MPQ demonstrated that an optical mirror can be formed even using a single structured layer of a few hundred atoms, making it the lightest one conceivable.
The thickness of the newly developed mirror is just several tens of nanometers—a thousand times less than the width of a strand of human hair. But the reflection is so strong that it could even be observed with the naked eye.
The Mechanism Behind the Mirror
The mirror works based on the arrangement of identical atoms in a 2D array. They are arranged in a regular pattern with spacing less than the atom’s optical transition wavelength, which are essential and required characteristics of metamaterials.
Metamaterials are artificially developed structures that have highly unique characteristics that are rare in nature. Their properties do not emerge from the materials they are composed of but from the unique structures they are developed with.
The characteristics—the subwavelength spacing and the regular pattern—and their interplay are the two significant causes behind this innovative type of optical mirror. Firstly, the subwavelength spacing and the regular pattern of atoms inhibit a diffuse scattering of light, thus clustering the reflection into a steady, one-directional light beam.
Secondly, due to the relatively close, discrete distance between the atoms, an incoming photon is able to bounce back and forth between the atoms multiple times before it is reflected.
Both the bouncing of the photons and the suppressed scattering of light result in an “enhanced cooperative response to the external field,” which denotes a very strong reflection in this case.
Advancements on the Way to More Efficient Quantum Devices
The mirror has a diameter of about 7 μm, which is so small that it cannot be visually recognized easily. But the apparatus in which the device is developed is huge. Completely analogous in style with other similar quantum optical experiments, it counts more than a thousand single optical components and has a weight of about two tons.
Thus, the novel material would not have much effect on the commodity mirrors used by people every day. On the other side, the scientific impact may be wide-ranging.
The results are very exciting for us. As in typical dilute bulk ensembles, photon-mediated correlations between atoms, which play a vital role in our system, are typically neglected in traditional quantum optics theories.
Jun Rui, Study First Author and Postdoc Researcher, Max Planck Institute of Quantum Optics
Rui added, “On the other hand, ordered arrays of atoms made by loading ultracold atoms into optical lattices were mainly exploited to study quantum simulations of condensed matter models. But it now turns out to be a powerful platform to study the new quantum optical phenomena as well.”
Future studies in this area could offer in-depth insights into the fundamental understanding of the quantum theories of light-matter interaction, many-body physics including optical photons, and facilitate the designing of quantum devices with a higher efficiency.
Many new exciting opportunities have been opened, such as an intriguing approach to study quantum optomechanics, which is a growing field of studying the quantum nature of light with mechanical devices. Or, our work could also help to create better quantum memories or even to build a quantum switchable optical mirror. Both of which are interesting advancements for quantum information processing.
David Wei, Study Second Author and Doctoral Researcher, Max Planck Institute of Quantum Optics
Rui, J., et al. (2020) A subradiant optical mirror formed by a single structured atomic layer. Nature. doi.org/10.1038/s41586-020-2463-x.