Explicit qubit Choi confidence region

Let $\{P_k{\}}_{k=1}^{15}$ be the nonidentity two-qubit Pauli basis, with $\mathrm{Tr}(P_k{P}_{\ell })=4{\delta }_{k\ell }$. Informationally complete local Pauli measurements can produce simultaneous calibrated intervals

Their statistical and calibration risks must be accounted for.

Define

This is a confidence region of CPTP Choi states, not a best-fit matrix. If empty, report incompatibility or an inconclusive result; do not silently enlarge error bars.