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Recycled photons set fresh quantum computing record  Reusing old
computer parts sounds like a terrible way to boost processing
power, but it has enabled a quantum computer to set a new
algorithmic record.  Anthony Laing and colleagues at the
University of Bristol, UK, have used recycled quantum bits, or
qubits, to carry out a quantum calculation known as Shor's
algorithm on a larger number than ever before.  The algorithm
exploits quantum mechanics to simplify the factorisation of
numbers into their prime components  – a hard task for ordinary,
classical computers when the numbers get really large. However,
until now, the largest number factorised using Shor's algorithm
was 15.  "There have been four demonstrations of 15 in the last
10 years, that's as good as we've got," says Laing. Part of the
difficulty in reaching higher numbers is creating enough qubits
to do the job.  Shor's record  Laing and colleagues used a
photon as their qubit. They