What is quantum computing?

Quantum computers are incredibly powerful machines that take a new approach to processing information. Built on the principles of quantum mechanics, they exploit complex and fascinating laws of nature that are always there, but usually remain hidden from view. By harnessing such natural behavior, quantum computing can run new types of algorithms to process information more holistically. They may one day lead to revolutionary breakthroughs in materials and drug discovery, the optimization of complex manmade systems, and artificial intelligence. We expect them to open doors that we once thought would remain locked indefinitely. Acquaint yourself with the strange and exciting world of quantum computing.

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Introduction to quantum information theory

How does quantum computing compare with conventional computing?

A common metaphor used to compare the two is a coin. In conventional computer processor a transistor is either up or down, heads or tails. But if I ask you whether that coin is heads or tails while it’s spinning, you might say the answer is both. That’s what a quantum computer builds on. Instead a conventional bit that’s either 0 or 1, you have a quantum bit that simultaneously represents 0 and 1, until that qubit stops spinning and comes to a resting state.

The state space—or the ability to sample a large number of possible combinations—is exponential with a quantum computer. Taking the coin metaphor further, imagine I have two coins in my hand and I toss them in the air at the same time. While they’re both spinning they would represent four possible states. If I tossed three coins in the air, they would represent eight possible states. If I had 50 coins and tossed them all up in the air and asked you how many states that represents, the answer would be more states than is possible with the largest supercomputer in the world today. Three hundred coins—still a relatively small number—would represent more states than there are atoms in the universe.