Bloch-sphere sensor dynamics
A qubit sensor is a rotating state vector whose direction encodes the signal.
$$U(\theta)=e^{-i\theta\mathbf n\cdot\boldsymbol\sigma/2}$$
Physical intuition
A qubit sensor is a rotating state vector whose direction encodes the signal.
Deep dive: physical mechanism
Hamiltonian evolution rotates the Bloch vector; pulse axes determine whether the final population is sensitive to the desired parameter.
What is measured experimentally?
Measure expectation values of sigma-x, sigma-y and sigma-z.
Assumptions, noise and limitations
A Bloch sphere describes a single qubit, not general mixed multiqubit correlations.
Research and simulation exercise
Numerically propagate a qubit under a weak longitudinal field.
Connect the ideas
Explore the chapter overview, learning path, and references.