Quantum Lights Out
The Lights Out puzzle — press a tile, it toggles itself and its neighbours, and you have to turn every light off — solved by Grover's search running on a quantum simulator, with each step of the solution played out on the LED panel.
Needs: the LED panel · Start it with: rq_demo_run.sh quantum-lights-out
Run it
Double-click the Quantum Lights Out icon on the desktop; the puzzle and its solution appear on the LED panel.
It is also under Applications → RasQberry → Quantum Lights Out, or in
sudo raspi-config → 0 RasQberry → Quantum Computing Demos. There is a
console variant in the menu that plays in the terminal instead.
What you'll see
A 3×3 grid of lit tiles appears in the middle of the panel. After a short pause while the circuit runs, each press of the solution is shown in turn, until the grid goes dark.
How it works
Lights Out is a search problem: of all the combinations of presses, which one turns everything off? That is what Grover's algorithm is for.
The circuit holds the board, a set of "flip" qubits standing for the presses you might make, and an oracle — a piece of circuit that recognises a winning combination without being told what it is. Grover then alternates the oracle with a diffusion step, and each round nudges probability towards the answers. After enough rounds, measuring the flip qubits gives you a solution.
That is the interesting part: the oracle only checks a combination, yet Grover finds the one that works in noticeably fewer tries than testing them one by one.
The quantum code comes from the IBM Quantum Challenge 2020, and runs on the local Aer simulator — no IBM Quantum account, no network.
Credits and links
Built by Luka Dojcinovic — Luka-D/Quantum-Lights-Out, with the quantum algorithm from the IBM Quantum Challenge 2020.
See the Demo List for everything else on the image.