For Valeria Saggio to boot up the computer in her former Vienna lab, she needed a special crystal, only as big as her fingernail. Saggio would place it gently into a small copper box, a tiny electric oven, which would heat the crystal to 77 degrees Fahrenheit. Then she would switch on a laser to bombard the crystal with a beam of photons.
This crystal, at this precise temperature, would split some of those photons into two photons. One of these would go straight to a light detector, its journey finished; the other would travel into a tiny silicon chip — a quantum computing processor. Miniature instruments on the chip could drive the photon down different paths, but ultimately there were only two outcomes: the right way, and the many wrong ways. Based on the result, her processor could choose another path and try again.
The sequence feels more Rube Goldberg than Windows, but the goal was to have a quantum computer teach itself a task: Find the right way out. For Saggio, a quantum physicist who moved to the Massachusetts Institute of Technology a few weeks ago, the project was akin to sticking a robot in a maze. The computer must learn the right path without any prior knowledge of where to turn along the way. It’s not too hard a chore — a normal classical computer could brute-force its way through dead ends and lucky guesses. But Saggio wondered, “Can quantum mechanics help?” She and her collaborators showed last year that it can.
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