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 9 deep courses(101 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 just a bit with some randomness added. If you scramble a random bit again, it stays random. But send a qubit through two Hadamard gates in a row after: qubit-vs-bit · ~7 minWhat superposition actually isSuperposition means a qubit's state is two amplitudes, one for the answer 0 and one for the answer 1. An amplitude is a number that can be positive or negative after: superposition · ~7 minWhat measurement actually gives youOne measurement gives you one plain bit: a 0 or a 1. You never see an amplitude or a chance directly, and afterward the qubit is left in the state that matches after: superposition · measurement · ~9 minPhase: the part you can't measure directlyAn amplitude is not a chance. It carries a sign (more generally, a phase) that does not change what you see when you measure that state. The phase only shows up
Gates & entanglement4 lessons
The working vocabulary of circuits
after: measurement · ~8 minSingle-qubit gatesSingle-qubit gates are fixed, reversible steps that change one qubit's amplitudes. X swaps the 0 and 1 amplitudes. Z flips the sign of the 1 amplitude. H opens after: single-qubit-gates · ~8 minTwo-qubit gatesA two-qubit gate makes what happens to one qubit depend on another qubit. CX flips the target qubit exactly when the control qubit is 1. Because control and tarafter: two-qubit-gates · ~9 minEntanglementEntanglement is when two or more qubits share one joint state that can't be split into a separate state for each qubit. A Bell pair, made with one H and one CX,after: entanglement · ~7 minGHZ states and correlationsA GHZ state is a group of qubits in a superposition of "all zeros" and "all ones." Every measurement gives a string where all the bits agree, like 000 or 111, e
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 steps in a row it takes, once every gate that can run at the same time has been grouped together. On after: circuit-depth-and-width · ~10 minConnectivity costsOn most quantum chips, each qubit can only work directly with a few neighbors. So a two-qubit gate between far-apart qubits must be routed: the compiler adds SWafter: connectivity-costs · ~10 minNative gates and transpilationNo quantum chip runs H, CP, or SWAP directly. Each one offers a small, carefully tuned native set of gates, for example RZ, SX and X plus one two-qubit gate. Thafter: native-gates-and-transpilation · ~12 minReading hardware specsLook at five numbers, and the fine print behind each: two-qubit gate fidelity (is it the typical pair or the best pair?), the coherence times T1/T2, readout fid