This is an important development:

Shor’s algorithm was first demonstrated in a computing system based on nuclear magnetic resonance — manipulating molecules in a solution with strong magnetic fields. It was later demonstrated with quantum optical methods but with the use of bulk components like mirrors and beam splitters that take up an unwieldy area of several square meters.

Last year, the Bristol researchers showed they could miniaturize this optical setup, building a quantum photonic circuit on a silicon chip mere millimeters square. They replaced mirrors and beam splitters with waveguides that weave their way around the chip and interact to split, reflect, and transmit light through the circuit. They then injected photons into the waveguides to act as their qubits.

Now they’ve put their circuit to work: Using four photons that pass through a sequence of quantum logic gates, the optical circuit helped find the prime factors of the number 15. While the researchers showed that it was possible to solve for the factors, the chip itself didn’t just spit out 5 and 3. Instead, it came up with an answer to the “order-finding routine,” the “computationally hard” part of Shor’s algorithm that requires a quantum calculation to solve the problem in a reasonable amount of time, according to Jeremy O’Brien, a professor of physics and electrical engineering at the University of Bristol. The researchers then finished the computation using an ordinary computer to finally come up with the correct factors.