What can quantum computers do

Uni­ver­si­ties and lab­o­ra­to­ries around the world, as well as the big tech com­pa­nies, Google, IBM, Intel and Microsoft, are study­ing and devel­op­ing A quan­tum com­put­er is not real­ly a ‘com­put­er’ as such, but rather a super-cal­cu­la­tor, capa­ble of run­ning spe­cif­ic pow­er­ful quan­tum algo­rithms much faster than an ordi­nary proces­sor. It does this using the prin­ci­ples of quan­tum mechan­ics, which are respon­si­ble for the behav­iour of ele­men­tary par­ti­cles such as pho­tons, elec­trons and atoms, but also of larg­er sys­tems such as super­con­duct­ing circuits. Such sys­tems allow for the imple­men­ta­tion of quan­tum bits (‘qubits’): two-state quan­tum sys­tems that rep­re­sent the fun­da­men­tal com­pu­ta­tion­al bricks of quan­tum information. Unlike con­ven­tion­al com­put­ers, which encode infor­ma­tion in bina­ry form, qubits are not lim­it­ed to ‘0’ and ‘1’ but can be in any com­bi­na­tion (or ‘super­po­si­tion’) of the two. This abil­i­ty, com­bined with the fact that N qubits can be com­bined or ‘entan­gled’ to rep­re­sent 2 Nstates simul­ta­ne­ous­ly, allows cal­cu­la­tions to be per­formed in par­al­lel on a mas­sive scale. A quan­tum com­put­er could there­fore, in prin­ci­ple, out­per­form a clas­si­cal com­put­er for some impor­tant tasks, such as sort­ing large unsort­ed lists or for ‘prime fac­tori­sa­tion’. The lat­ter forms the basis of most encryp­tion algo­rithms in use today – in par­tic­u­lar for bank­ing operations. Quan­tu...

In one quantum computer, scientists braided quantum objects called non-abelian anyons within an array of quantum bits (depicted as a grid). In this illustration, which depicts snapshots in time from left to right, the anyons keep a record of being moved around one another (red and green trails). Google Quantum AI Anyons, anyone? Scientists have created strange new particle-like objects called non-abelian anyons. These long-sought quasiparticles can be “braided,” meaning that they can be moved around one another and retain a memory of that swapping, similar to how a braided ponytail keeps a record of the order in which strands cross over each other. Two independent teams — one led by researchers at Google, the other by researchers at the quantum computing company Quantinuum — have reported creating and braiding versions of these anyons using quantum computers. The Google and Quantinuum results, respectively reported Nature and Non-abelian anyons defy common intuition about what happens to objects that swap locations. Picture the street game with cups and balls, where a performer swaps identical cups back and forth. If you weren’t watching closely, you’d never know if two cups had been moved around one another and back to their original positions. In the quantum world, that’s not always the case. “It’s predicted that there is this crazy particle where, if you swap them around each other while you have your eyes closed, you can actually tell after the fact,” says physicist Tr...

Computers built on the principles of quantum physics—as opposed to ‘classical’ physics—promise a revolution on the order of the invention of the microprocessor or the splitting of the atom. D-Wave, a small Canadian company backed by Jeff Bezos, NASA, and the CIA among others, is the first firm to sell a so-called quantum computer—at roughly $10 million a pop. The vast increase in power could revolutionize fields as disparate as medicine, space exploration, and artificial intelligence. In The company has plenty of critics, some of whom claim its machines aren’t quantum computers at all. And yet, the technology could herald radical changes for the following areas, to name a few: 1. Safer airplanes—Lockheed Martin plans to use its D-Wave to test jet software that is currently too complex for classical computers. 4. Boost GDP—Hyper-personalized advertising, based on quantum computation, will stimulate consumer spending. 5. Detect cancer earlier—Computational models will help determine how diseases develop. 6. Help automobiles drive themselves—Google is using a quantum computer to design software that can distinguish cars from landmarks. 7. Reduce weather-related deaths—Precision forecasting will give people more time to take cover. 8. Cut back on travel time—Sophisticated analysis of traffic patterns in the air and on the ground will forestall bottlenecks and snarls. 9. Develop more effective drugs—By mapping amino acids,for example, or analyzing DNA-sequencing data, doctors w...

One of the secrets to building the world’s most powerful computer is probably perched by your bathroom sink. At IBM’s Thomas J. Watson Research Center in New York State’s Westchester County, scientists always keep a box of dental floss—Reach is the preferred brand—close by in case they need to tinker with their oil-drum-size Inside the shimmering aluminum canister of IBM’s System One, which sits shielded by the same kind of protective glass as the Mona Lisa, are three cylinders of diminishing circumference, rather like a set of Russian dolls. Together, these encase a chandelier of looping silver wires that cascade through chunky gold plates to a quantum chip in the base. To work properly, this chip requires super-cooling to 0.015 kelvins—a smidgen above absolute zero and colder than outer space. Most materials contract or grow brittle and snap under such intense chill. But ordinary dental floss, it turns out, maintains its integrity remarkably well if you need to secure wayward wires. “But only the unwaxed, unflavored kind,” says Jay Gambetta, IBM’s vice president of quantum. “Otherwise, released vapors mess everything up.” Quantum’s earliest adopters are asset-management firms—for which incorporating quantum calculations involves few increased overhead costs—but commercial uses aren’t far behind. Spanish firm Multiverse Computing has run successful pilot projects with multinational clients like BASF and Bosch that show its quantum algorithms can double foreign-exchange tr...

Bavarian science minister Markus Blume views part of a quantum computer with Dieter Kranzlmüller (left) at the Leibniz Supercomputing Center. Credit: Sven Hoppe/dpa/Alamy Most researchers have never seen a quantum computer. Winfried Hensinger has five. “They’re all terrible,” he says. “They can’t do anything useful.” In fact, all quantum computers could be described as terrible. Decades of research have yet to yield a machine that can kick off the promised revolution in computing. But enthusiasts aren’t concerned —and development is proceeding better than expected, researchers say. “I’m not trying to take away from how much work there is to do, but we’re surprising ourselves about how much we’ve done,” says Jeannette Garcia, senior research manager for quantum applications and software at technology giant IBM in San Jose, California. Nature Spotlight: Quantum computing Hensinger, a physicist at the University of Sussex in Brighton, UK, published a proof of principle in February for a large-scale, modular quantum computer If you believe the hype, computers that exploit the strange behaviours of the atomic realm could accelerate drug discovery, crack encryption, speed up decision-making in financial transactions, improve machine learning, develop revolutionary materials and even address climate change. The surprise is that those claims are now starting to seem a lot more plausible — and perhaps even too conservative. According to computational mathematician Steve Brierley, w...