The Largest-Ever Quantum Calculation Uses 84 Qubits and Takes Just 270 Milliseconds

The answer was 8

Vancouver-based quantum computer maker D-Wave Systems is the kind of company that often gets mixed reviews–either kudos for working on the very edge of a new and potentially groundbreaking technology, or dismissal for not exactly delivering the kind of Earth-shattering technology that people were perhaps expecting. Regardless, today D-Wave is marking one in the win column after announcing that it has achieved the world’s largest quantum computation using 84 qubits.

A quick quantum computing primer: qubits, or quantum bits, are the basic units of quantum information, comparable to (but quite different from) a classical bit. The main benefit of qubits is that they can exploit the laws of quantum mechanics to exist in two states simultaneously. In comparison to classical computing, that means a single superconducting qubit can exist as both a “one” and a “zero” at the same time, whereas a classical bit can only be one or the other.

This vastly improves speed and computing power. It also has proven pretty difficult to execute. A decade ago quantum computers were using a handful of qubits to factorize numbers and do other grade-school level computations. And in recent years, they haven’t come much further forward, even as D-Wave released a $10 million 128-qubit quantum computer for sale.

To prove that quantum computing really is pushing forward, Zhengbing Bian at D-Wave used one of the company’s machines to tackle a very difficult calculation known as a “two-color Ramsey number.” This is somewhat explained by the “theorum on friends and strangers,” which you can feel free to read up on but will not be explained in detail here for reasons including, but not limited to, the fact that I can’t begin to adequately/coherently explain it. But the math isn’t the point here. The point is that the math is mind-numbingly difficult, and the quantum computer solved it in just 270 milliseconds.

The system required just 28 qubits to actually solve the Ramsey problem, using the other 56 for error correction. And, because this was a Ramsey problem that has already been solved by conventional means, Bian and company know that their D-Wave computer came up with the correct solution (it was 8).

Whether or not this glowing achievement is going to boost confidence in D-Wave’s technology and approach is yet to be seen, but the company already has some support in industry. A certain Mountain View-based Internet search company has taken an active interest in D-Wave’s computing technology, and last year Lockheed Martin bought one of D-Wave’s quantum computers for itself.

Technology Review