Weak Measurement of a Qubit Superposition

A qubit prepared in equal superposition starts on the Bloch sphere's equator, halfway between |0⟩ and |1⟩. This simulator continuously and weakly measures that qubit — instead of an instantaneous projective collapse, each instant extracts a small amount of information and applies a small random disturbance, following the stochastic master equation for homodyne monitoring of σ_z. A Rabi drive can be dialled in to fight the measurement's pull toward the poles, so the Bloch vector traces a genuine quantum trajectory: a smooth precession when measurement is off, a jagged random walk to a pole when measurement dominates, or an irregular tug-of-war in between. Live readouts track the coherence, the Born-rule populations, the Bloch vector's shrinking length, and elapsed time.