The Quantum Locker Puzzle
This looks pretty cool. One of the neatest parts is that they consider the case of a cheating referee! The parallelism here is reminiscent of that in Quantum Tic-Tac-Toe though there is not necessarily any entanglement as there is in the latter case (superpositions do not necessarily imply entanglement!). Actually it’s a pretty straightforward application of Grover’s algorithm but has a pretty wild conclusion in the optimized case.