Fig. 1
From: Demonstration of Einstein–Podolsky–Rosen steering with enhanced subchannel discrimination
The process of subchannel discrimination (SD). a The collection of subchannels {Λ h } h composing a quantum channel Λ. b The protocol for realizing the Kraus operators K ij using the entanglement-breaking channel (EBC) scenario. The state ρ is measured along the z direction with output result i after passing through the intermediate subchannel A j . A new state is prepared based on the value of i. c The single-qubit protocol for SD in the case of two measurement settings. The unitary operation U related to the intermediate subchannels A0 and A1 is demonstrated with the qubit state ρ and an auxiliary qubit \(\left| 0 \right\rangle\) which is finally measured along z with output result j. After the EBC, the measurement along a direction \(\vec n\) is performed on the signal qubit, and the result b is obtained. d The two-qubit protocol for SD with multiple measurement settings. One of the two qubits, in a state ρ AB , is sent to Bob, and the other is sent to Alice. On Bob’s side, the qubit passes through one of the unitary gates g m with probability 1/m before the evolution K ij . Alice chooses one of the measurement directions \(\vec n_i\) based on the result b|g m from Bob and obtains the result a
