This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A research team at the Institute of Applied Physics at TU Darmstadt has shown for the first time that atoms that are completely disordered and in constant motion can nevertheless emit jointly directed light preferentially in one direction—even though neither the atoms nor their environment exhibit a direction—and that the strength of this asymmetry can be specifically adjusted. The paper is published in the journal Physical Review Letters.
Atoms normally emit light uniformly and independently in all directions. To make atoms emit light in a specific direction, they must either be placed in an environment that determines the direction of light emission or be able to communicate with one another. The latter can be achieved, for example, by bringing the atoms very close together or coupling them through optical elements such as mirrors or optical fibers.
Despite the directional emission of light, however, it still occurs in opposite directions. Until now, generating directional light in only one direction required atoms to be fixed in specially arranged structures that distinguished the two directions from the outset. In contrast, the atoms in the researchers' experiment move freely and are disordered—yet still emit concentrated, directional light.
This is made possible by a hollow fiber that connects all the atoms: Through this shared channel, the atoms coordinate and build short, intense pulses of light that preferentially propagate along the fiber. Until now, these pulses traveled with equal strength in both directions of the fiber. The team shows—confirmed by experiments and simulations at RPTU Kaiserslautern-Landau—that this balance can be deliberately shifted by matching the speed of atomic motion to the duration of the emission pulse.
As a result, more light is emitted in the desired direction. The work shows that precise, engineered structures and arrangements of atoms are not necessary for directional light emission: disordered moving atoms can also jointly emit light in only one direction. The findings open a new path for building directional light sources and optical components.
Yoan Spahn et al, Motion-Induced Directionality of Collective Emission in a Nonchiral Waveguide, Physical Review Letters (2026). DOI: 10.1103/9dhz-dxc8 Journal information: Physical Review Letters Provided by Technische Universitat Darmstadt MA in English, copy editor since 2021 with experience in higher education and health content. Dedicated to trustworthy science news.
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