Q Day

Illustration: Nicholas Law

Ah, viable quantum computing, the long sought after holy grail, is worth pursuing no matter the cost as said tech not only goes beyond computation in terms of crunching numbers but also has the ability to model reality due to the superposition of qubits connected by entanglement, the prime driver to an existence in which we all share. With this being said, there's always a cost to everything, in this instance, privacy as QCs are uniquely qualified to deal with the issue of primes as prime numbers are the building blocks of cryptography, the mathematical construct on which privacy depends.

The general definition of a qubit as the quantum state of a two-level quantum system.

To whit ...

Suppose you ask a classical computer to solve a simple math problem: Break the number 15 into its smallest prime factors. The computer would try all the options one by one and give you a near-instantaneous answer: 3 and 5. If you then ask the computer to factor a number with 1,000 digits, it would tackle the problem in exactly the same way—but the calculation would take millennia. This is the key to a lot of modern cryptography.

Take RSA encryption, developed in the late 1970s and still used for securing email, websites, and much more. In RSA, you (or your encrypted messaging app of choice) create a private key, which consists of two or more large prime numbers. Those numbers, multiplied together, form part of your public key. When someone wants to send you a message, they use your public key to encrypt it. You’re the only person who knows the original prime numbers, so you’re the only person who can decrypt it. Until, that is, someone else builds a quantum computer that can use its spooky powers of parallel computation to derive the private key from the public one—not in millennia but in minutes. Then the whole system collapses.

The algorithm to do this already exists. In 1994, decades before anyone had built a real quantum computer, an AT&T Bell Labs researcher named Peter Shor designed the killer Q-Day app. Shor’s algorithm takes advantage of the fact that quantum computers run not on bits but on qubits. Rather than being locked in a state of 0 or 1, they can exist as both simultaneously—in superposition. When you run an operation on a handful of qubits in a given quantum state, you’re actually running that same operation on those same qubits in all their potential quantum states. With qubits, you’re not confined to trial and error. A quantum computer can explore all potential solutions simultaneously. You’re calculating probability distributions, waves of quantum feedback that pile onto each other and peak at the correct answer. With Shor’s algorithm, carefully designed to amplify certain mathematical patterns, that’s exactly what happens: Large numbers go in one end, factors come out the other.

There are now hundreds of companies trying to build quantum computers using wildly different methods, all geared toward keeping qubits isolated from the environment and under control: superconducting circuits, trapped ions, molecular magnets, carbon nanospheres. While progress on hardware inches forward, computer scientists are refining quantum algorithms, trying to reduce the number of qubits required to run them. Each step brings Q-Day closer.

That bomb going off will only be the beginning. When Q-Day becomes public knowledge, either via grim governmental address or cheery big-tech press release, the world will enter the post-quantum age. It will be an era defined by mistrust and panic—the end of digital security as we know it. “And then the scramble begins,” says Demchak.

Illustration: Nicholas Law