Every two decades or so, a new technology upends national security. In the 1940s and 1950s, the atomic and hydrogen bombs established nuclear deterrence. In the 1970s and 1980s, microelectronics led to the creation of stealth and precision weapons and early digital networks. In the 1990s, the Internet and the deployment of the Global Positioning System (GPS) remade communications. Now, of course, artificial intelligence is powering autonomous weapons and supercharging cyber-capabilities, but soon, it will be quantum technologies that transform myriad areas from exposing national security secrets to projecting military power.

Quantum technologies work by leveraging the strange behavior of extremely small particles. They can therefore do things that conventional technologies can’t, such as precisely measuring location while entirely offline and, in theory, cracking encryptions that are widely used today. A classical supercomputer would need roughly 300 trillion years and “brute force” to break a common encryption, known as a 2048-bit RSA key. A quantum computer, by contrast, could theoretically decrypt that same key, which is used to protect medical records, financial transactions, and state secrets, in under eight hours. Innovations in the field of quantum sensing will soon enable armies to operate in “GPS denied” environments, where satellite signals are blocked, disrupted, or unavailable.

Although this future seems far off, it is not. According to reports from U.S. intelligence agencies, the United States’ adversaries are already harvesting encrypted U.S. data in the hopes that once they acquire quantum capabilities—be it in five or ten years—they can read it. China especially is investing in quantum communications and encryption tools. Washington and its allies need to do everything in their power to win the quantum race while also preparing for a world in which Beijing or Moscow builds a quantum computer first. Most urgently, this means encrypting today’s secrets with more advanced cryptography that can’t be cracked in the future.

Because quantum computing has the potential to crack the encryption most broadly used by governments and individuals alike, the threat that it poses to national security is difficult to overstate. The cryptography that secures much of the Internet today relies on the difficulty that conventional computers have solving certain math problems, such as factoring very large numbers. Quantum computers, however, are expected to perform some of these computations far more efficiently, enabling attackers to break the codes and seize sensitive data.

No such machines exist yet, and it is difficult to predict when they might come online. But recent advances suggest that a quantum computer could break at least some forms of commonly used cryptography within the next few years. More important, rivals of the United States are not waiting around for a quantum computer to materialize. China and Russia have already collected encrypted U.S. secrets, betting that some of the information will still be relevant once they have the tools to decrypt it.

The implications of quantum technologies for national security extend beyond cryptography. Quantum sensors can measure time and differences in........

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