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

Anastasia Marchenkova
Quantum Bits
Published in
3 min readFeb 28, 2016

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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 something like faster flight possible. D-Wave could be able to speed up research on better aerospace materials which can shield from radiation or stand up to heat, or model the flow over the wing, which Airbus is counting on to speed R&D.

However, quantum annealing can’t efficiently run Shor’s algorithm, which breaks common forms of modern cryptography used to protect our bank information, logins, and all web communication.

Universal Gate Quantum Computing

Universal gate quantum computing is much broader. A universal gate quantum computing system relies on building reliable qubits where basic quantum circuit operations, similar to the classical operations we all know, can be put together to create any sequence, running increasingly complex algorithms. Algorithms like Shor’s (to break RSA cryptography) and Grover’s (faster search) as well as the approximately 50 other quantum algorithms will…

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