Quantum Feedback Controller 2D — Lyapunov Bloch-Disk Stabilizer

A qubit's Bloch vector is under constant attack from T1 relaxation and T2 dephasing, which relentlessly pull it toward the ground state and wash out its phase. This 2D simulator renders that fight on a rotatable flattened projection of the Bloch sphere: a Lyapunov-based feedback controller measures the gap between the current state and a target you choose, computes a corrective microwave drive field, and rotates the state back on course every frame. Drag the disk to orbit the view, tune the feedback gain against the decoherence rate to find the line between sluggish drift and unstable overshoot, switch the controller off to see the raw uncontrolled decay, and watch fidelity, control effort and the live per-axis component traces the whole time.