Admittedly, one of the most common uses of computers is to play computer games, and in no small part did games influence the historic development of computer hardware. For example, the primary purpose of today’s high-end graphics cards is to compute the complex graphics effects of 3D games. Almost as an afterthought, it has been made possible to harness this brute computational power for productive purposes: Using frameworks such as OpenCL or CUDA, graphics cards can provide huge computational speedups in specific areas such as cryptography, molecular dynamics, fluid dynamics and distributed computing.

As far as quantum computers are concerned, some guys at the National Institute of Informatics (NII) in Tokyo believe that we can go in the opposite direction: By playing a computer game, we aid the development of error-correcting codes used for performing fault-tolerant quantum computations. The NII group is developing a mobile game whose goal is to compactify the surface codes used in topological quantum computation. To give an example, the quantum circuit on the left can be implemented by the surface code shown in the middle. The white and black "loops" in the surface code correspond to logical qubits, and quantum operations such as the CNOT-gate correspond to the braiding of the loops. For the finer details of how such codes correspond to the physical system, I refer to arXiv:1209.1441 and arXiv:1209.0510 (from which the three figures below were taken).

The code on the right shows a much compressed variant of the same underlying circuit, obtained from the code in the middle by a series of circuit-preserving transformations. One example of circuit-preserving transformations are transformations that preserve the topology of the loops and braids in the surface code, but there also exist non-trivial transformations, and the aim of the game is to minimize the volume of surface codes by performing such transformations. You can get an idea of how this will look like by viewing the trailer on the official homepage or at YouTube:

Reducing the code size of important circuits, such as the ones performing purifications, has a huge potential to reduce the amount of resources (both in space and time) needed for the fault-tolerant implementation of quantum algorithms. However, little is known about the best strategies to compress surface codes, and this is where both fellow scientists and casual gamers step in: Their progress will be tracked online, thus enabling fancy stuff like score leaderboards and alerting the project managers when new compactification strategies have been discovered. Finding such strategies would be helpful for the development of compilers that automatically translate quantum algorithms into efficient surface codes with minimal overhead. Best of all, the discovery of particularly strong compactifications might earn you joint authorship in a scientific publication!

During a talk given by Simon Devitt, one of the project leaders, at CQT, I was able to try out a pre-release version of the game. The game is based on touch input, and will be available for Android- and Apple-powered phones and tablets. The 3D engine was fully working, and manipulations of the code were already possible. The roadmap is as follows: A closed beta version aimed towards the scientific community is scheduled to be released later this month. The feedback and "peer-review" from fellow researchers ensures that possible glitches (e.g. in the implementation of valid code transformations) can be spotted and fixed. Later this spring, the game will be released to the public, featuring a much refined user interface.