Classical computers push bits around with and, or, not. Quantum computers add two more moves: superposition and entanglement.
A quantum bit (qubit) can sit between 0 and 1. The Hadamard gate H parks it exactly in the middle, so a measurement comes out 0 half the time and 1 the other half. Try it on the Bloch sphere below. What happens if you press the H button?
That is superposition, and you already know it. It is a coin flip. Measuring collapses the qubit to a plain 0 or 1, so a single run tells you almost nothing. You run the same circuit hundreds of times and read the statistics instead. Those runs are called shots.
Entanglement is the part coin flips do not prepare you for. Two qubits can be wired so their results always agree: both heads, or both tails. Neither outcome is decided in advance, and the two simply match. Each individual result is still random, while the set of results that can occur has shrunk from four to two.
Neither idea is exotic: both computing traditions grew out of the same nineteenth-century algebra.
Every quantum milestone lands roughly fifty years after its classical twin. Qubits are tiny and unstable, and that costs time. Closing the gap takes specialists from every profession, not only physicists. You, right now, working through the tutorial. From the Kipu team, a big ♥-thank you.
Ready for the hands-on part? Start the hands-on tutorial.