What’s the difference between quantum annealing and universal gate quantum computers?
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. But what is quantum annealing, and how does it differ from a universal gate quantum computer?
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.
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 will never be able to 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 also be able to run on a universal quantum computer.
This means that a universal quantum computer can be used for many more problems than a quantum annealer, but comes with its own challenges and a different design than a quantum annealer. The quantum annealer, like D-Wave, is becoming a great standard for proof of concept, but design of universal quantum computing chips for various applications and making sure that qubits are properly manufactured will be the tipping point for the quantum computing industry.
It all comes down to designing the chips. For universal gate quantum computing, the problem is being able to R&D chips and test them in an efficient manner to improve coherence (length of time the information is stored and can be manipulated) and qubit reliability.
The all Silicon chip breakthroughs mean that standard microfabrication facilities can be used to create quantum processor units, which leads towards cheaper and less specialized facilities for qubit manufacturing. Anyone* will be able to design a universal gate quantum computing chip, specialized for their purposes.