Guess the circuit from its truth table
Every input the hidden circuit is run on, and the exact state it outputs. Fill the board below so your circuit matches every row.
| Input | Output state |
|---|
Each puzzle shows the truth table of a hidden quantum circuit — computational-basis inputs mapped to the exact state each one outputs. Easy shows every row; Advanced shows only half of them, so you’ll have less to go on. You can reveal any hidden row on demand, but each one you reveal counts as a hint — your results screen shows how many you used. The board below has the same circuit with some gates already revealed and some left blank. Click a blank and pick a gate, then hit Check.
Two-qubit gates (CNOT, CZ) don’t reveal which qubits they connect. Drag either endpoint up or down on the board to set which wires it acts on — that’s part of the guess too. CNOT is directional, so its control and target are drawn differently (a filled dot vs. a crossed circle) and which one is which matters. CZ is symmetric — both endpoints look the same on purpose, because the gate works identically either way, so only the pair of wires you pick matters, not which one you dragged first.
Each blank you guess is colored: green if that exact gate (and, for two-qubit gates, those exact wires) belongs in that exact slot, yellow if it’s used somewhere else in the solution, and gray if it isn’t used at all. You get 6 attempts.
Once a round ends, “How this circuit works” walks the solved circuit gate by gate for whichever input you pick — the exact amplitudes at every step, not just the final row. Switch it to “Full matrix” to see the whole solved circuit as a single unitary instead, with every column showing one input’s output at once. Some days the circuit is built around a named construction (a Bell pair, a GHZ cascade); if so, it’s named there too, never before you’ve solved it.
Play any past day’s puzzles. Archive results are saved but don’t count toward your streak.