The Making of Quantum Chess
By: Madeline Farina
Tags: Chess, Quantum Game, Game Development, Quantum Computing, Quantum Mechanics

The Making of Quantum Chess

Demo of Quantum Chess in Real Time

Just when you thought regular video games couldn’t get any more complex, scientists and software devs had to prove us wrong and show technology will always advance. Although quantum game development is still in its early stages much like any other field of quantum computing, it’s still very possible for any interested party — developer or otherwise — to get involved. In fact, as a (recently graduated!) computer science student, I just finished a quantum computing 2D platform game as my senior project. While the details and a demo of this game are to be saved for another time, my point is that it doesn’t take years of graduate study and/or programming expertise to get started.

This also applies for playing quantum games, like the world-renowned Quantum Chess. This game gained internet stardom in 2016 following its debut in the viral video “Anyone Can Quantum”. Featuring the late Dr. Stephen Hawking and famous actors like Paul Rudd and Keanu Reeves, this video (created by CalTech’s IQIM group) was to humorously show the public that anyone can learn quantum computing — a field growing in popularity and importance.

Earlier this year, I actually had the pleasure of attending a virtual colloquium hosted by Western Illinois University, with Chris Cantwell as its guest speaker. Cantwell is a quantum physicist, quantum game developer, and more notably, the creator of Quantum Chess. During this colloquium, he explained his creation process, his goals as a quantum game developer, and general tips for those interested in following in his footsteps.

What is Quantum Chess?

As its name would imply, Quantum Chess is a variation of chess which involves both the standard moves of the game and moves involving quantum concepts like superposition and entanglement. Technologically speaking, chess was one of the first games available on a classical computer, dating as far back as 1950 when the great Claude Shannon published “Programming a Computer for Playing Chess”, one of the first papers on the subjects.

Likewise, in 1951, Alan Turing published the first program (developed on paper) that was capable of playing a full game of chess. Fast forward a few decades to 1997, and we have history being made when IBM’s “Deep Blue” chess program beat Garry Kasparov (considered to be the best chess player in the world at the time). These events illustrate the long-standing relationship chess has with computers, and the introduction of quantum computers only magnifies the possibilities for the game.

Cantwell began developing his version of the game for a class project when he was a physics student at USC. He’d dabbled in quantum games before but always knew he wanted to make more. In 2019 he collaborated with Google to run Quantum Chess on their quantum computer, eventually leading to a successful live demonstration for Google’s 2020 Quantum Summer Symposium. This was followed by the Q2B 2020 Quantum Chess tournament (featuring Doug Strain vs. Aleksander Kubica in the final match) which had over 45,000 views on Twitch during its stream.

So, although it took several years of hard work and collaboration with CalTech and Google, he finally produced the game anyone can now play.

And how exactly does one play?



The rules are as follows:

All standard chess moves apply

Players may choose to perform a quantum move instead of a standard chess move

Pawns may not perform a quantum move, but they can exist in superposition

Capturing is not allowed during a quantum move

There is no check or checkmate since the King can exist in superposition

If you’ve ever played standard chess, you know it is a game of strategy and there are endless possibilities for moves to be made. So adding in quantum options only increases the complexity of the game, allowing for even more choices for a move and more outcomes from that move.

Developing a Quantum Game

When creating the game which he hoped to educate people about quantum concepts, Cantwell kept the following design goals in mind:

The movement in the game could be considered a “swapping” of empty positions with occupied ones, so the concept of superposition could be illustrated with a partial swap. In other words, a chess piece on the board could be in a superposition of states where each state is a different classical chess piece.

Moreover, touching a Quantum Chess piece to make a move is the act of making an observation/measurement which, according to the laws of quantum physics, causes a piece in superposition to lose its coherence and collapse into one of its states. This also ties into the concept of interference, which relates to wave functions.

(Side note: if you’re wondering what wave functions have to do with Quantum Chess, it’s because one of the most popular interpretations of quantum mechanics is the Copenhagen interpretation which expresses the idea that everything known about a particle can be summarized with a wave functions, and wave functions can be used to calculate the probabilities of all possible observations. But I digress)

Entanglement is shown in how the state of a chess piece is “bound” to the state of another piece, regardless of how far apart on the board they are. If one piece is affected, so is the other. The two entangled pieces can belong to the same player or one to each player, and multiple entanglements are allowed.

An interesting tidbit of note is that the quantum computer (or quantum simulator) only has to use as many qubits as there are pieces in superposition, as well as a few extra ancilla qubits, which improves efficiency and runtime.

Also, notice #5, which states that the game does not strictly teach quantum mechanics but instead gives the player an opportunity to interact with the concepts and develop an intuitive understanding. Although this does not necessarily have to be your goal when making a quantum game (it certainly wasn’t for me; my goal was to explicitly teach quantum mechanics), it’s an important idea to consider. And this brings us to our next subject…

Teaching Quantum Mechanics

As the great physicist Richard Feynman said: “I think I can safely say that nobody understands quantum mechanics.” It’s a well-used quote in the field because of how blatantly it expresses that even the experts who dedicate their lives to the study of this field still find themselves stumped upon occasion.

Unlike other branches of physics like kinematics or magnetism, we don’t experience quantum mechanics in a tangible way on a daily basis. Consequently, we have no intuitive understanding of it. Quantum games thereby allow people to interact with quantum phenomena to then develop an intuitive feel for QM.

Additionally, games are a promising tool for quantum education and inclusion because they have a lower barrier to entry than, say, a quantum mechanics course. There is a multitude of resources available both online and in libraries if you want to learn the subject, but in my opinion, it won’t be as entertaining and fun as a video game.

Opinions aside, you can read more about Cantwell’s development experience here, in a blog post written by Cantwell himself. In the colloquium, Cantwell mentioned that he is currently working on an AI which plays quantum chess against a player. This is exciting because it relates to Quantum Machine Learning, which as I covered, has a promising future in both research and industry.

And if you want more details about Quantum Chess itself before playing the game, you’re welcome to read more details in Selim G. Akl’s paper found here, published in 2016. The author goes much more in depth and explains the relevant quantum concepts more thoroughly.