Fig. 2
From: Capacity estimation and verification of quantum channels with arbitrarily correlated errors
Comparison of the inference structures of the two protocols. a In the estimation protocol, all qubits are test qubits, and the goal is to estimate the capacity for the channel on all qubits. b In the verification protocol, one third of the qubits are data qubits that are left untouched. The remaining 2N qubits are test qubits, whose error rates allow to bound the capacity of the channel on the N data qubits
