In October 2019, researchers at Google announced to great fanfare that their embryonic quantum computer had solved a problem that would overwhelm the best supercomputers. Some said the milestone, known as quantum supremacy, marked the dawn of the age of quantum computing. However, Greg Kuperberg, a mathematician at the University of California, Davis, who specializes in quantum computing, wasn’t so impressed. He had expected Google to aim for a goal that is less flashy but, he says, far more important.


Whether it’s calculating your taxes or making Mario jump a canyon, your computer works its magic by manipulating long strings of bits that can be set to 0 or 1. In contrast, a quantum computer employs quantum bits, or qubits, that can be both 0 and 1 at the same time, the equivalent of you sitting at both ends of your couch at once. Embodied in ions, photons, or tiny superconducting circuits, such two-way states give a quantum computer its power. But they’re also fragile, and the slightest interaction with their surroundings can distort them. So scientists must learn to correct such errors, and Kuperberg had expected Google to take a key step toward that goal. “I consider it a more relevant benchmark,” he says.


If some experts question the significance of Google’s quantum supremacy experiment, all stress the importance of quantum error correction. “It is really the difference between a $100 million, 10,000-qubit quantum computer being a random noise generator or the most powerful computer in the world,” says Chad Rigetti, a physicist and co-founder of Rigetti Computing. And all agree with Kuperberg on the first step: spreading the information ordinarily encoded in a single jittery qubit among many of them in a way that maintains the information even as noise rattles the underlying qubits. “You’re trying to build a ship that remains the same ship, even as every plank in it rots and has to be replaced,” explains Scott Aaronson, a computer scientist at the University of Texas, Austin.

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