CelestialScience writes "A recycling technique has enabled a quantum computer to carry out a quantum calculation known as Shor's algorithm on a larger number than ever before. The benchmark algorithm exploits quantum mechanics to simplify the factorization of numbers into their prime components — a hard task for classical computers when the numbers get large. Until now, the largest number factorized using Shor's algorithm was 15. Now Anthony Laing at the University of Bristol, UK and colleagues report in Nature Photonics that they used a recycled photon to factorize 21 — still far too small and trivial to spook cryptographers, who rely on the difficulty of factorizing large numbers for their widely-used techniques. But a record nonetheless."