The Quantum Tortoise and the Classical Hare: When Will Quantum Computers Outpace Classical Ones and When Will They Be Left Behind?

In the children’s story of the Tortoise and the Hare, the speedier Hare is outpaced by a Tortoise with other advantages (diligence). An analogous contest is happening in computing, between a Quantum Tortoise and a Classical Hare. Here, the Classical Hare’s speed advantage is literal—classical computers run faster than quantum ones. Like his namesake, the Quantum Tortoise is slower, but also has an advantage—in this case, the ability to run algorithms that are unavailable to classical computers. When this algorithmic advantage is substantial enough, the Quantum Tortoise can beat the Classical Hare and solve a problem faster. This article analyzes when the Quantum Tortoise will beat the Classical Hare—and when it will not.