Google announced last month that it had achieved “quantum supremacy,” demonstrating the potential of a new kind of computer that can perform certain tasks many orders of magnitude faster than the most advanced supercomputers. It’s a crucial moment for America’s national security, which depends on winning the race to do what quantum computers will do best: decrypt the vast majority of existing public-key encryption systems.
Google reports that its quantum computer, dubbed Sycamore, solved a mathematical calculation in 200 seconds that would take a supercomputer 10,000 years. IBM, a quantum competitor, asserted that Google’s claim of supremacy is overblown, and that the world’s most powerful classical computer, the Summit OLCF-4 at Oak Ridge National Laboratory, could have done the same calculation in 2.5 days—roughly a thousandfold difference rather than 1.5 trillionfold. Still, quantum computers are no longer science fiction.
To process information, digital computers use bits, essentially switches that can be either off or on, corresponding with the binary digits, 0 and 1. Quantum computers employ “qubits,” which use the probabilistic nature of quantum physics to represent any combination of 0 and 1 simultaneously, enabling them to encode more complicated data.
Their computing power grows exponentially as the number of qubits expands. Sycamore’s 54-qubit chip allowed it to outcompute the best supercomputer. A 2,000- to 4,000-qubit quantum computer would render most public-key encryption architectures—used for applications from banking and credit cards to the power grid—obsolete. They rely on numbers too big for conventional computers to factorize, but which a quantum computer could.
Building quantum computers is a very heavy lift. They require hugely expensive infrastructure to stabilize the qubits at temperatures near absolute zero. They also generate high error rates, or “quantum noise,” for which researchers have to compensate. Developers are probably years away from the large-scale code-breaking quantum computer everyone worries about—although once scientists and engineers start using quantum computers to build the next generation of quantum computers (since modeling complex systems like themselves is one of their strengths) the timeline could quickly shorten.