A single photon is like a perfectly smooth brick from which quantum technologies can be built. But to build a house, you need thousands of identical bricks. Rubidium atoms are natural emitters: each atom emits photons of exactly one wavelength, like a tuning fork that always produces a single note. The challenge is how to gather many atoms in one place and make them work in concert.

Scientists used optical tweezers — laser beams that hold atoms in place like fingers holding peas. Fifty rubidium atoms were arranged in a row with a spacing of 5 micrometers (10 times thinner than a human hair). Then each atom was connected to its own waveguide — a hair-thin glass thread through which a photon travels to a detector. But directly connecting atoms and fibers is not possible: the spacing between atoms is too small, while standard fiber connectors require a pitch of 127 micrometers. The solution was a glass chip with a fan of waveguides — channels that gradually widen, like the bell of a horn, converting the narrow pitch to a wide one.

Tests showed that the photons are indeed single, not in bunches. Neighboring channels barely interfere with each other — only 0.4% of light ends up in the wrong detector. If an atom is lost, it can be replaced from a reservoir of spare atoms floating nearby. In one second, 118 atoms can be restored, keeping the array 93% full. And a chip with 784 channels has already been fabricated, like a blueprint for a future skyscraper with nearly 800 windows instead of 50.

This platform is a first step toward a factory of single photons. Someday, thousands of such sources could be linked into a quantum internet, where information is transmitted not by electrical pulses but by single particles of light.