Photonic Quantum Computer Displays “Supremacy” Over Supercomputers

(SpectrumIEEE) A milestone Chinese demonstration with photonic quantum computing comes just a year after Google’s quantum advantage claim. When Google unveiled its unprecedented demonstration of quantum computational advantage over classical computing in late 2019, Chinese researchers reported progress toward their own milestone demonstration.
This new finding does more than just confirm that quantum computers can solve certain problems faster than conventional supercomputers. (That’s the “supremacy” part.) It also adds a surprising twist: It now appears possible to achieve phenomenal computational feats with lasers and nonlinear crystals. Photonic systems have sometimes been considered more of a bridge technology between quantum devices than the core of a quantum computer itself.
Chao-Yang Lu, a quantum physicist at the University of Science and Technology of China in Hefei and his colleagues engineered one of the most intricate versions of a light-based quantum computing experiment yet. It’s effectively a maze for identical photons to travel through depending on the photons’ quantum properties.
MIT theorists Scott Aaronson and Aleksandr Arkhipov first envisioned this kind of device in 2010. They called it a boson sampling machine.
This machine’s photon detectors could help figure out where the randomly distributed photons end up. Which is a very complex mathematical problem. And that is the kind of math problem that a classical computer bogs down over as the number of distributed photons increases.
In this case, then, quantum advantage or supremacy is achieved when even the fastest supercomputers take substantially longer to solve the photon distribution problem than the quantum system takes.
Scott Aaronson, who is currently at the University of Texas at Austin, wrote a blog post in which he described himself as “gratified” by the Chinese team’s work. Other researchers who previously worked on earlier and smaller versions of boson sampling machines also praised the experiment.
One of the challenges with this great demonstration is it’s not programmable,” says Christian Weedbrook, founder and CEO of the Toronto-based quantum computing startup Xanadu. “In terms of applications you do need to have a full programmability, and this has no programmability.”
Engineering hurdles remain on the path to commercializing large-scale photonic quantum computing, says Matthew Broome, a quantum physicist at the University of Warwick in the UK, despite the apparent success of the Chinese experiment.