The race is on to build the world’s first meaningful quantum computer—one that can deliver the technology’s long-promised ability to help scientists do things like develop miraculous new materials, encrypt data with near-perfect security and accurately predict how Earth’s climate will change. Such a machine is likely more than a decade away, but IBM, Microsoft, Google, Intel and other tech heavyweights breathlessly tout each tiny, incremental step along the way. Most of these milestones involve packing ever more quantum bits, or qubits—the basic unit of information in a quantum computer—onto a processor chip. But the path to quantum computing involves far more than wrangling subatomic particles.
A qubit can represent a 0 and a 1 at the same time, a uniquely quantum phenomenon known in physics as a superposition. This lets qubits conduct vast numbers of calculations at once, massively increasing computing speed and capacity. But there are different types of qubits, and not all are created equal. In a programmable silicon quantum chip, for example, whether a bit is a 1 or a 0 depends on the direction its electron is spinning. Yet all qubits are notoriously fragile, with some requiring temperatures of about 20 millikelvins—250 times colder than deep space—to remain stable.
Of course, a quantum computer is more than just its processor. These next-generation systems will also need new algorithms, software, interconnects and a number of other yet-to-be-invented technologies specifically designed to take advantage of system’s tremendous processing power—as well as allow the computer’s results to be shared or stored. “If it wasn’t complicated, we’d have one of these already,” says Jim Clarke, director of quantum hardware at Intel Labs (pdf). At the U.S. Consumer Electronics Show earlier this year, Intel introduced a 49-qubit processor code-named “Tangle Lake.” A few years ago the company created a virtual-testing environment for quantum-computing software; it leverages the powerful “Stampede” supercomputer (at The University of Texas at Austin) to simulate up to a 42-qubit processor. To really understand how to write software for quantum computers, however, they will need to be able to simulate hundreds or even thousands of qubits, Clarke adds.
Scientific American spoke with Clarke about the different approaches to building a quantum computer, why they are so fragile—and why this is all taking so long.
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