In 2019, Google announced that it had reached “quantum supremacy.” Researchers had built a quantum computer, one using the peculiar properties of the subatomic world. Chilled to a temperature colder than the coldest parts of outer space, Google’s machine used an understanding of quantum mechanics to complete a calculation in seconds that would, it said, have taken a conventional computer ten thousand years. It had just fifty-three “qubits,” or quantum bits, the core units of quantum computing. To store equivalent information on a classical computer, you would need seventy-two billion gigabytes
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