Lab — Learn by measuring
Learn quantum computing from scratch
Twelve lessons, basic to complex, every one runnable. You'll build the circuits yourself, measure them on an exact simulator in your browser, and finish able to read a real hardware spec sheet critically. Prerequisites are signposts, not locks — enter anywhere. When you want to go deeper, the eight deep courses(89 chapters) pick up where these twelve end — including a free from-zero math on-ramp.
Foundations4 lessons
What a qubit actually is — built from runs, not metaphors
no prerequisites · ~8 minWhy a qubit is not a probabilistic bitA qubit is not a bit with randomness attached. A random bit, re-scrambled, stays random — but a qubit sent through two Hadamard gates in a row returns 0 on everafter: qubit-vs-bit · ~7 minWhat superposition actually isSuperposition means a qubit's state is two amplitudes — signed (in general complex) numbers, one per outcome — not that the qubit is "both 0 and 1 at once". Meaafter: superposition · ~7 minWhat measurement actually gives youOne measurement gives one classical bit — you never observe an amplitude or a probability directly, and the qubit is left in the state matching the bit you readafter: superposition · measurement · ~9 minPhase: the part you can't measure directlyAmplitudes are not probabilities: they carry a sign — more generally a phase — that leaves the measurement statistics of that state completely unchanged. Phase
Gates & entanglement4 lessons
The working vocabulary of circuits
after: measurement · ~8 minSingle-qubit gatesSingle-qubit gates are fixed, reversible operations on one qubit's amplitudes: X swaps the 0 and 1 amplitudes, Z flips the sign of the 1-amplitude, H opens and after: single-qubit-gates · ~8 minTwo-qubit gatesA two-qubit gate makes the operation on one qubit conditional on another. CX applies an X to the target exactly when the control is 1 — and because control and after: two-qubit-gates · ~9 minEntanglementEntanglement is when qubits share one joint state that cannot be split into individual per-qubit states. A Bell pair — one H, one CX — measures as 00 or 11 at rafter: entanglement · ~7 minGHZ states and correlationsA GHZ state is n qubits in a superposition of all-zeros and all-ones: every measurement returns a string where all the bits agree, even though each qubit alone
Hardware reality4 lessons
What real processors do to your circuit — the QPU137 difference
after: two-qubit-gates · ~9 minCircuit depth and widthWidth is how many qubits a circuit uses; depth is how many sequential layers of operations remain after everything that can run in parallel has been packed togeafter: circuit-depth-and-width · ~10 minConnectivity costsOn most processors each qubit can interact with only a few neighbors, so a two-qubit gate between distant qubits must be routed: the compiler inserts SWAP gatesafter: connectivity-costs · ~10 minNative gates and transpilationNo processor executes H, CP, or SWAP directly. Each exposes a small calibrated native set — for example RZ, SX, X plus one entangler — and the compiler rewritesafter: native-gates-and-transpilation · ~12 minReading hardware specsFive numbers, and the fine print behind each: two-qubit gate fidelity (median or best pair?), coherence times T1/T2, readout fidelity, qubit count, and connecti