Set up as in traditional chess
Pawns and Kings can only move classically. Other pieces have the option to move quantumly.
A quantum move is one of the following:
- split a classical piece into two quantum pieces (a superstate) and move each to a different location. These pieces are negatively entangled
- move a pair of quantum pieces to different locations
When moved, a quantum piece can also be "observed", collapsing it into one of the two positions and collapsing any other entangled pieces. From here, you must make either a quantum or classical move with the newly-collapsed piece.
If a pawn moves diagonally onto a quantum piece, that piece is collapsed to that location and captured. This is because the piece had to be there for the pawn to move diagonally.
If a pawn moves forward onto a quantum piece, that piece is collapsed to the other location.
Pawns only promote classically.
If a classical piece crosses through the path of a quantum piece, that piece is collapsed to the other location.
If a classical piece captures a quantum piece, it is only considered captured if the other location is somehow collapsed to empty.
Quantum pieces can only put the enemy king into check if both quantum moves put it into check.
Kings are allowed to move into spaces that are only threatened by quantum pieces and collapse those pieces to the other location. This is allowed as long as it is possible for said pieces to collapse non-threateningly. (This may be impossible under certain cases of entanglement)
If a quantum piece crosses the path of another quantum piece, it becomes entangled with that piece.
Under no circumstances can a piece pass through two negatively entangled pieces. The second along the path must be captured or the piece must stop before it.
Moving one of your own classical pieces onto one of your own quantum pieces will cause the quantum piece to collapse to the other position
When an entangled piece is collapsed, the piece it is entangled with collapses to the opposite state.