Aaron Hutchins in Maclean's:
When Prime Minister Justin Trudeau visited the Perimeter Institute for Theoretical Physics in Waterloo, Ont. last week and offered his explanation for how a quantum computer works, it sparked intense media coverage from around the world. It also led to a backlash over whether Trudeau really knew anything about the cutting-edge technology, or was just pretending.
But what happens when experts in quantum computing themselves are asked to explain the technology to a lay audience in 35 seconds, the time Trudeau took to give his explanation? “This is something that cannot be explained well in 35 seconds,” says Aephraim Steinberg, a professor of physics at the University of Toronto and member of the Centre for Quantum Information and Quantum Control. But Steinberg—and a half-dozen other experts from across North America—were willing to step up to our challenge and give it a try.
A quantum computer is a proposed device that exploits quantum mechanics to solve certain specific problems like factoring huge numbers much faster than we know how to solve them with any existing computer. Quantum mechanics has been the basic framework of physics since the 1920s. It’s a generalization of the rules of probability themselves. From day to day life, you’d never talk about a minus-20 per cent chance of something happening, but quantum mechanics is based on numbers called amplitudes, which can be positive or negative or even complex numbers. The goal in quantum computing is to choreograph things so that some paths leading to a wrong answer have positive amplitudes and others have negative amplitudes, so on the whole they cancel out and the wrong answer is not observed.