Noise Helps Catch Single Photons Faster ✛ ✦
Detecting a single molecule amid light noise is like spotting a candle flame in a brightly lit room. If its light overlaps with itself, interference reveals the source. This principle of wave superposition has been adopted by physicists in quantum optics.
In the experiment, faint light is mixed with a laser on a semi-transparent mirror, and two detectors look for simultaneous spikes. An algorithm based on quantum information theory analyzes the coincidences and gives an answer with 95.4% accuracy. The strangest part: the more noise and imperfections in the device, the faster it finds the target. For ordinary detectors, interference is the enemy — here it’s a helper. The effect uses correlations akin to quantum entanglement.
The method speeds up quantum measurements for photometry and quantum computers, allowing harmless observation of living cells under dim light. Unexpectedly, decoherence, normally the nemesis of quantum technologies, plays into our hands here. The work builds on the theories of Roy Glauber.
Although the Hong–Ou–Mandel effect usually requires two indistinguishable photons, here it works with a single photon and a laser beam — the idea was predicted back in 2012, but only now found practical use.
Signal enhancement through wave overlap recalls the “quantum vision” from Greg Egan’s novels, where characters see in pitch darkness using a special light.