The short version
- Physicists in Erlangen got light and sound waves in an optical fibre to exchange energy faster than either was lost.
- Until now that kind of strong coupling needed a cavity where light circles up to a million times, while here the light passed through once.
- Sound moves far slower than light, so the result could one day let fibres store and convert quantum signals.
When light travels down a glass fibre, it shakes the glass very slightly, and those vibrations are sound. They in turn scatter the light, an effect called Brillouin scattering. A team led by Birgit Stiller at the Max Planck Institute for the Science of Light in Erlangen, with Leibniz University Hannover, reports in Nature Physics that it has pushed this exchange into “strong coupling.” Light and sound trade energy back and forth faster than either one dies away. They did it in a fibre cooled to about 4 K, in a single pass, with no mirrors or resonator.
Strong coupling has been seen before, but only in cavities where light circles, the release says, up to a million times. The tell-tale sign is a gap that opens in the system’s response as light and sound merge into hybrid waves. First author Laura Blázquez Martínez says a new measurement method let them see “the clearest sign of strong coupling.” The release gives no coupling or loss figures, and the journal page would not open here. The work first appeared as a preprint in July 2025.
Sound moves far more slowly than light, which is why physicists want it as a buffer that holds signals and converts them between optical and microwave frequencies, the kind a quantum computer uses. It is a cousin of the single quanta of sound Stanford physicists watched vanish last month.
