You and a quantum computer take turns flipping a coin — without looking at it. If it shows heads at the end, the quantum computer wins. Play a few rounds and you’ll notice something unsettling: you lose. Almost every time.

The trick is that the quantum computer doesn’t flip the coin, it puts it into superposition — a state that is neither heads nor tails. Whatever you do on your turn, its second move uses interference to steer the coin back to heads with certainty. The game is the friendliest possible introduction to the two effects that make quantum computers tick.

The notebook lets you play interactively, then lifts the curtain: you see the quantum circuit behind each move, run it on a simulator, and can modify the strategy to convince yourself there is no way to win.