Last month, physicists Toronto-based startup Xanadu has published a unique experiment on NATURE where they generate seemingly random numbers. During the pandemic, they built a tabletop machine called the Borealis, which consisted of lasers, mirrors, and more than a mile of optical fiber. Inside the Borealis, 216 rays of infrared light bounce around through a complex network of prisms. Then, a series of detectors counts the number of photons in each beam after they cross the prisms. Finally, the machine generated 216 numbers at a time — a number equal to the number of photons in each individual beam.
The Borealis is a quantum computer, and according to Xanadu researchers, this laser-powered dice roll is beyond the capabilities of classical, or non-quantum, computing. It takes Borealis 36 microseconds to generate a set of 216 numbers from a complex statistical distribution. They estimated that Fugaku, the most powerful supercomputer at the time of the experiment, would take an average of 9,000 years to produce a set of numbers from the same distribution.
The experiment is the latest in a series of demonstrations of the so-called quantum advantage, in which a quantum computer defeats a state-of-the-art supercomputer in a specific task. The experiment “pushes the boundaries of the machines we can make,” says physicist Nicolas Quesada, a member of the Xanadu team who now works at Polytechnique Montréal.
“It’s a great technological breakthrough,” said Laura García-Álvarez of Chalmers University of Technology in Sweden, who was not involved in the experiment. “This device makes a calculation that is considered difficult for classical computers. But it doesn’t mean commercial quantum computing is useful.”
So what, exactly, does Xanadu’s claim to quantum advantage mean? Caltech physicist John Preskill coined the concept in 2011 as “quantum supremacy,” which he described as “the point at which quantum computers can do things that classical computers cannot, even if they are worthwhile work. ” (Since then, many researchers in the field have moved to call this “quantum advantage,” to avoid the echoes of “white supremacy.” Useful work — without it.)
Preskill’s words suggest that achieving quantum advantage could be a turning point, marking the beginning of a new technological era in which physicists will begin to create useful tasks for quantum computers. . In fact, people expected it to be so significant that the first acquisition of a quantum computer — more than a classic computer — by Google researchers in 2019 — was leaked.
But while many researchers claim a value advantage for their machines, the definition of success has become even greater. For one thing, quantum advantage does not mark the end of a race between quantum and classical computers. This is the beginning.
Each claim of quantum advantage has caused other researchers to develop faster classical algorithms to challenge that claim. In the case of Google, its researchers conducted a random-number-generating experiment similar to Xanadu’s. They wrote that it would take a state-of-the-art supercomputer 10,000 years to create a collection of numbers, while it would take their quantum computer only 200 seconds. A month ago, IBM researchers argued that Google used the wrong classical algorithm for comparison, and that a supercomputer should only last 2.5 days. In 2021, a team using China’s Sunway TaihuLight supercomputer showed they could complete the task in 304 seconds — just a hair slower than Google’s quantum computer. The larger supercomputer can perform the algorithm in seconds, says physicist Pan Zhang of the Chinese Academy of Sciences. That will put the classical computer on top again.