This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Imagine shuffling a deck of cards where some of the cards are fading just because of the way they interact with the external environment as you shuffle them. Your job is to figure out the interplay between the shuffling, or "imposed randomness," due to the way you shuffle your cards and how that relates to the fading as cards are exposed to the external environment.
That's a rough analogy for what Matthew Duschenes and his Ph.D. advisers were doing in a paper that received an Editors' Suggestion in the journal Physical Review A. Duschenes is currently a postdoctoral researcher at the University of Guelph, and he earned his Ph.D. at Perimeter Institute and the University of Waterloo with the late Ray Laflamme, a Perimeter founding faculty member and founding director of the Institute for Quantum Computing, who died in 2025. The paper bears the names of Laflamme and other advisers—Juan Carrasquilla, a Perimeter visiting fellow who is currently at ETH Zurich in Switzerland, and Roger Melko, a Perimeter associate faculty member who is also at the University of Waterloo.
The research, which was started more than two years ago, is likely one of the last scientific papers to bear Laflamme's name. "I feel very honored to have been Raymond's second-to-last Ph.D. student," Duschenes says. We all know about randomness in our everyday world, such as the spin of a roulette wheel or the throw of the dice.
But in the quantum world, randomness is much more intrinsic. There is an inherent probabilistic nature in systems described by quantum mechanics, meaning any properties of these systems are characterized not by specific measurement outcomes, but by probabilities of observing these outcomes. But beyond that, as Duschenes explains, there can also be an "imposed randomness" in quantum computing systems.
"Our systems of study involve imposing that the systems evolve randomly, due to random protocols that are applied." A quantum computation model runs on a huge number of possible circuits, representing sequences of quantum gates, measurements and qubit initializations. Instead of studying just one circuit, researchers need to pick many at random to describe a complex quantum process. To extend the card-shuffling analogy: It's a bit like learning about card games by studying many well-shuffled decks instead of one hand.
But also, there is "noise" caused by the quantum systems interacting with their environment. One can imagine ensembles of quantum bits—qubits—being like soap bubbles, each holding delicate information in its shape and color. But any touch from the outside will disturb them, causing some of them to disappear.
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