Bad Qubits — Learn Quantum by Doing

Multiple choice

In the quantum metrology pipeline, the unknown parameter

\theta

is imprinted on the probe during the 'encoding' stage through which kind of operation?

A classical post-processing step applied after readout
Initialization of the probe in a fixed reference state $|0\rangle$
A unitary $U(\theta) = \exp(-i \theta G)$ , where $G$ is the generator coupling the probe to the parameter
A projective measurement that immediately collapses the probe