In early July, Google announced that it will expand its commercially available cloud computing services to include quantum computing . A similar service has been available from IBM since May. These aren’t services most regular people will have a lot of reason to use yet. But making quantum computers more accessible will help government, academic, and corporate research groups around the world continue their study of the capabilities of quantum computing.

Understanding how these systems work requires exploring a different area of physics than most people are familiar with. From everyday experience we are familiar with what physicists call “classical mechanics,” which governs most of the world we can see with our own eyes, such as what happens when a car hits a building, what path a ball takes when it’s thrown, and why it’s hard to drag a cooler across a sandy beach.

Quantum models, however, describe the subatomic realm—the behavior of protons, electrons, and photons. The laws of quantum mechanics are very different from those of classical mechanics and can lead to some unexpected and counterintuitive results, such as the idea that an object can have negative mass.

Physicists around the world—in government, academic, and corporate research groups—continue to explore real-world deployments of technologies based on quantum mechanics. And computer scientists, including me, are looking to understand how these technologies can be used to advance computing and cryptography.

A Brief Introduction To Quantum Physics

In our regular lives, we are used to things existing in a well-defined state: A lightbulb is either on or off, for example. But in the quantum world, objects can exist in a what is called a superposition of states: A hypothetical atomic-level lightbulb could simultaneously be both on and off. This strange feature has important ramifications for computing.

The smallest unit of information in classical mechanics—and, therefore, classical computers—is the bit, which can hold a value of either 0 or 1, but never both at the same time. As a result, each bit can hold just one piece of information. Such bits, which can be represented as electrical impulses, changes in magnetic fields, or even a physical on-off switch, form the basis for all calculations, storage, and communication in today’s computers and information networks.

Qubits—quantum bits—are the quantum equivalent of classical bits. One fundamental difference is that, due to superposition, qubits can simultaneously hold values of both 0 and 1. Physical realizations of qubits must inherently be at an atomic scale: for example, in the spin of an electron or the polarization of a photon.