Quantum Feedback Control — Measurement Backaction Loop

Continuous weak measurement of a qubit collapses its state stochastically (measurement backaction), while a feedback controller attempts to stabilize it near a target state. The competition between decoherence, measurement-induced diffusion, and feedback drives the qubit Bloch vector along complex stochastic trajectories on the Bloch sphere.

0.30
1.00
0.10
Bloch purity |r|
1.000
Fidelity to target
Measurement record