Quantum computing: Photonic processor lights up the route to quantum computing

A quantum photonic processor that takes just 36 microseconds to perform a task that would take a supercomputer more than 9,000 years to complete is reported in Nature this week. The system has improvements relative to previously demonstrated photonic devices and may represent an important step towards creating quantum computers.

A key goal for quantum devices is for them to outperform classical systems, establishing a ‘quantum advantage’, but only a small number of experiments have reported this achievement to date. One approach to demonstrating the advantage of quantum systems over classical computers is comparing the speed with which devices sample from an unknown probability distribution that characterizes the propagation of photons through a network, a task known as Gaussian boson sampling. Calculations can be made about how long it would take classical computers to perform the same task. There is a threshold number of photons, above which classical computers are not capable of handling the computation in a reasonable time.

Previously reported experiments realizing Gaussian boson sampling have used up to 113 photons propagating through a network of fixed mirrors and lenses. Jonathan Lavoie and colleagues report experiments carried out on a single programmable photonic processor, called Borealis, that detects up to 219 photons (125 on average). They propose that this is the largest quantum-advantage photonic experiment reported to date. The improvement in performance, relative to other photonic processors, is attributed to the simplification of the photon-detecting experiment, the introduction of reprogrammability and reduced vulnerability to ‘spoofing’ (in which the quantum results could be replicated by classical algorithms). The experiment is notable because programmable photonic processors are much closer to the form that a quantum commercial device might take than are previous proof-of-principle experiments.

The work by Lavoie and colleagues “solves technological challenges that might put us ahead in the longer race towards viable quantum computers”, writes Daniel Jost Brod in an accompanying News & Views article.