The world’s first quantum chess tournament took place during the virtual Q2B conference, and a player from Amazon beat out representatives of five other companies involved in quantum computing to claim the title.
Quantum chess, developed by Chris Cantwell at Quantum Realm Games in California, is a strange version of the familiar game of chess. The rules incorporate several ideas from quantum mechanics. Pieces can be placed into a superposition of two locations, meaning that a piece can occupy more than one square simultaneously in a play called a “split”.
They can also be entangled with one another, so that measuring the location of one quantum chess piece – determining where the split piece actually resides – also determines the location of the piece making the measurement, generally the chess piece trying to capture it. There is no such thing check or checkmate, the game-ending move in ordinary chess, because the king can always make a quantum move so it is in more than one place at once. Therefore, to win the game, one must actually capture the opponent’s king while making a robust quantum measurement of its location.
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If a piece is split, capturing one of the split pieces could still leave another, so you could have half a king standing. This makes playing the game extremely complicated.
“It’s like you’re playing in a multiverse but the different boards [in different universes] are connected to each other,” said Spiros Michalakis at the California Institute of Technology during a of the tournament on 9 December. “It makes 4D chess from Star Trek look silly.”
He and the other hosts of the tournament discussed the possibility of an “infinite king run”, wherein a losing player postpones the end of the game indefinitely by continuing to split their king into more and more quantum superpositions. However, Cantwell said, eventually the probability of the king being on any particular square would be so low that the computer would have to round down and all the split kings would disappear.
In practice, though, the games in the tournament were timed – Amazon’s player, Aleksander Kubica, beat Doug Strain from Google in the final round because Strain ran out of time.
The ultimate goal of quantum chess, which is available to the public on Steam, is to teach the basic tenets of quantum mechanics through a familiar lens, Cantwell said.
“We know a board game called chess, and you apply the quantum concepts on top of a known game,” said International Grandmaster chess player Anna Rudolf during the livestream. Quantum chess is much more complex than the normal version, but the same basic concepts remain, she said.
“This idea of bridging quantum with something that’s a more understandable, practical game that people still invest a lot of thought into is, I thought that was really incredible,” said Alex Winter of Bill & Ted fame during a surprise visit to the livestream.
