I’ve played chess all my life. I’m a pretty average strength club level player and like many experienced players I’ve always enjoyed chess variants. This quantum variant is an interesting idea (each non-king piece has a dual identity in pseudo-quantum superposition, changing state on black squares - see the Wired UK article on it) but I’m not really sure about a couple of the implementation details. My feeling, after one game, is that too many of the normal chess rules have been abandoned.

Firstly, the board is oriented differently to normal chess, with a white square in the lower left hand corner and the white king on the left hand side. That may have been a deliberate design decision but setting the board up that way is also a typical beginner’s mistake and it is not the decision I would have made. I’ve not come across another 8x8 board chess variant that does this; it doesn’t inspire confidence.

I played and won a game before having read over all the rules and was quite enjoying it until I had a piece captured by the king while it was protected by a quantum knight on a white square in the knight state. To win the game I had to actually capture the king. This astonished and disappointed me.

Finally reading the rules page I found that major rule changes have been made in addition to the quantum piece variance rule: moving into check is allowed, there is no requirement to move out of check, and checkmate does not exist; capturing the king is the win condition. There is no mention of the non-standard board orientation. Additionally, en passant and castling have been removed.

I can’t see why any of these extra changes have been made. Castling could easily be retained, substituting ‘piece that starts in corner’ for ‘rook’. En passant could easily be retained, perhaps with the proviso that it only applies if both quantum pawns remain in the pawn state. Simply abandoning these rules comes across as lazy more than anything else, but they are not game-changers, so to speak.

Changing the rules about check and checkmate, however, is a very big deal. Checkmate is the object of the game of chess; the rules around check play an enormous part in all aspects of standard (and variant) chess strategy. Remove check and checkmate and, to me at least, it is just not chess any more.

I can see that there is a hard question which arises when devising quantum chess rules: what do you do when a piece in a quantum state may or may not be giving check? Surely the game would work just as well if a straight answer either way was arbitrarily given to this question as a further rule. Given that a single move can consist of touching a piece and putting it in a quantum state that gives check, it would make sense that the rule be ‘a piece in an indeterminate state cannot give check.’ After that, normal rules of check and checkmate can apply. You would then have an actual chess variant.

In sum Quantum Chess is a fun idea but the thing that makes other chess variants such as exchange, mini-chess etc work, for chessplayers, is that as much as possible of original chess is retained - the variant rules add spice but the game itself remains intact. This game may use a chessboard and chess pieces but without check and checkmate it just doesn’t feel like chess any more, and I am left feeling slightly cheated.

It’s a shame because right now I’d really like to play a version of quantum chess using these piece changing rules that actually also retains the rules of chess. A further variant might be to have the pieces change state on every move, not just on black squares. Why not?.

(An earlier draft of this appears, without formatting as one of the comments on the Wired UK article.)