What’s the difference between quantum annealing and universal gate quantum computers?

Originally published at www.amarchenkova.com on February 28, 2016.

Just as a GPU processes instructions related to graphics exponentially faster than a CPU, certain problems can be solved quadratically or polynomially faster with quantum algorithms, by exploiting the quantum effects of superposition and entanglement. That’s why the race to build the first universal gate quantum computer is on, with Google and IBM leading the charge.

D-Wave, the most famous quantum annealer, and universal gate quantum computing are not competitors. While they rely on the same concepts, they are useful for different tasks and different sorts of problems, while also suffering from different challenges in design and manufacturing.

Quantum Annealing

The D-Wave machine is a quantum annealer running adiabatic quantum computing algorithms. This is great for optimizing solutions to problems by quickly searching over a space and finding a minimum (or “solution”). The latest announcement from Google states that the D-Wave machine is more than 10⁸ times faster than simulated annealing running on a single core. However, Selby’s algorithm still performs better than the D-Wave quantum computer, so there’s a long way to go for D-Wave.

But quantum annealing works best on problems where there are a lot of potential solutions and finding a “good enough” or “local minima” solution, making…