Light under Control: One-Way Photons Without Magnets express
Light loves symmetry: in an open channel, it flows equally both ways. To steer it one way, physicists often use magnets. A new approach does without, using rotation — just the speed of a vinyl record — and interference from two atoms. Rotation changes the “pitch” of light for different directions, just as a siren’s tone shifts when a car approaches or recedes. This frequency shift for photons is minuscule, but atoms near the spinning optical resonator (a light ring) act as amplifiers. Quantum interference transforms that microscopic difference into a stark contrast: single photons fly out one way, while bunched-up queues head the other. The difference hits 65 decibels — a whisper versus a jet engine’s roar. This trick, predicted by Leonard Mandel and Roy Glauber, has been realized in experiments by Nobel laureate Serge Haroche, opening the door to one-way quantum light sources.
Original abstract
as written by the authors arXiv:2605.27447
Quantum nonreciprocity at few-photon level typically requires strong symmetry breaking, posing significant experimental challenges. Here we demonstrate that phase-controlled quantum interference can amplify weak chirality into giant quantum nonreciprocity. We consider two phase-programmable atoms coupled to a spinning whispering-gallery-mode resonator, where interference dramatically amplifies the effect of weak Fizeau splitting. This mechanism generates pronounced directional asymmetry in photon statistics, featuring bright antibunched emission in one direction and strongly bunched emission in the opposite direction. Remarkably, both correlation and brightness isolations obey phase-controlled power-law scaling with Fizeau splitting, reaching up to 65~dB and 17.3~dB, respectively. Our results establish interference-enhanced weak chirality as a powerful route toward directional nonclassical light sources.
The Fizeau effect, key to this method, allowed measurement of light’s speed in moving water in 1851 — a crucial step toward relativity.
One-way mirrors and force fields that let light pass only one way are a staple of sci-fi. This new work turns that exotic fiction into lab reality.