Save the Kets

Save the Kets is a hands-on course in quantum computing with a lab attached. Build a circuit, watch every gate act on the state, then break it on purpose and see error correction heal it, or fail. THREE ROOMS, ONE WORKSPACE • Error Correction: 11 chapters in four modules, from the principles of correction to surface codes, fault tolerance, qLDPC and bosonic codes. Every chapter has a working experiment, rendered formulas, references, side quests and room for your own notes. • Quantum Information: 12 lessons, from states and measurement through entanglement, channels and CHSH to BB84, teleportation, Grover search and phase estimation. Each lesson starts with a prediction. • Circuit Lab: up to six qubits. Step through every gate of nine editable algorithms or your own circuit, choose measurement branches, add noise and move a Pauli fault through the gates. 17 guided investigations set the lab up for you. The home screen is a study map: it picks up where you left off and shows how the topics connect. Each investigation keeps its circuit, noise settings and samples, even after you close the app. EXPERIMENTS YOU CAN RUN • Check the Knill–Laflamme conditions exactly for four codes and see which errors each one can correct. • Tap X, Y or Z faults onto a stabilizer code, read the syndrome and compare the minimum-weight recovery with the error you placed. • Seed noise on a surface code with periodic edges, distance 2 to 5, and step through the decoder's recovery paths, including the one that wraps around the torus and flips the encoded qubit. • Run a seeded Monte Carlo at distances 2 to 4 with 95% confidence intervals and an exact repetition-code baseline. • Measure a logical ZZ parity and follow both outcome branches. • Edit Tanner graphs and build hypergraph-product codes; the app computes their distance or gives honest bounds. • Drag a GKP displacement and see which correction its syndrome picks; compare even and odd cat states. • Erase qubits of the five-qubit code and check which regions can still recover the logical state. HONEST NUMBERS Values the app recognizes appear in exact form, such as 1/√2. Values it can't identify reliably stay decimal. Every experiment states where its model stops, and the hardware chapter is a dated snapshot of published results, not a live leaderboard. TAKE IT FURTHER Every lesson and guided investigation can export its worksheet as a file. Circuits can be shared as OpenQASM 3 for other quantum tools. Each chapter suggests further courses and open-source tools, with what each expects you to know. No link is sponsored. PRIVATE AND OFFLINE No account, no cloud simulator, no analytics. Notes, progress and experiments stay on your device, and formulas render without a connection. For iPhone, iPad and Mac.