Optical computer does its first math

The first ever calculation has been performed by an optical computer. It wasn’t a really hard sum – finding the prime factors of 15 – but it’s a huge step towards the creation of a quantum computer.

The chip takes four photons that carry the input for the calculation, and then implements a quantum program called Shor’s algorithm to find and output the answer – 3 and 5, as any fule no.  Finding prime factors is the basis of modern encryption schemes, including those used for secure internet communication.

“This task could be done much faster by any school kid, but this is a really important proof-of-principle demonstration,” said PhD student Alberto Politi from the University of Bristol.

The team from the university’s newly established Centre for Nanoscience and Quantum Information have worked to develop devices where photons propagate in silica waveguides micro-fabricated on a silicon chip.

“This approach results in miniature, high-performance and scalable devices,” said Professor Jeremy O’Brien, Director of the Centre for Quantum Photonics, who led the research.

The team coupled four photons into and out of the chip using optical fibres. On the chip the photons traveled through silica waveguides that were brought together to form a sequence of quantum logic gates. The output was determined by which waveguides the photons exited the chip in. By detecting the photons at the output of the device they confirmed high-performance operation of the quantum algorithm.

“As well as quantum computing and quantum metrology, ‘on-chip’ photonic quantum circuits could have important applications in quantum communication, since they can be easily integrated with optical fibres to send photons between remote locations,” said Politi.

The full report appears in Science.