Quantum State Filter

A quantum filter is a projective measurement: it lets a qubit through with a probability set by the angle between the qubit's state and the filter's own axis on the Bloch sphere, and — unlike a classical filter — it collapses whatever passes onto that axis. This simulator streams qubits through one or two such filters in real time so you can tune the input state and each filter's orientation, watch individual qubits pass or get blocked, and compare the exact Born-rule prediction cos²(Δ/2) against the fraction actually measured. Load the built-in 3-filter paradox preset to see how inserting a middle filter between two perpendicular ones counter-intuitively lets more particles through than either filter alone.