Light in a gravitational-wave detector races through multi-kilometer tunnels, bouncing off mirrors. A perfectly uniform beam resembles a smooth sheet held by its corners. But if one mirror tilts by the width of an atom, the sheet develops wrinkles: 'parasitic' patterns, more complex light spots, awaken in the beam.
Previously, such wrinkles were dismissed as noise. It seemed that light in them dropped out of the game, reducing sensitivity. The authors built a model where these patterns don't vanish but flow into one another. It turns out that mirror misalignment acts like a translator: it doesn't destroy the message but rewrites it in another language — the language of higher-order modes, i.e., more intricate light patterns.
The big surprise is quantum entanglement. When mirrors are misaligned, the simple smooth mode and the complex patterns become linked by an invisible thread: the state of one instantly responds to the state of the other. The authors verified this with a rigorous mathematical criterion — positive partial transpose. Such entangled light need not be discarded; it can be used to extract signals from noise more cleverly than before.
Misalignment of optics in a gravitational-wave detector is not a malfunction but a rearrangement of the light orchestra. The conductor-laser waves its baton, and the instrument-modes begin to play not in unison but in complex polyphony. And in this polyphony, one can hear what was previously drowned out.
LIGO's mirrors weigh 40 kilograms each and are suspended on glass fibers as thin as a human hair to isolate them from the slightest tremors of the Earth.
In Carl Sagan's novel 'Contact', an alien signal is captured using a network of radio telescopes, but quantum amplification technology could pick up the whisper of the stars themselves.