FPB probe. The $I_R = 0, P_E = 0$ point in this figure corresponds to Eve’s operating her CNOT gate with $|T_{\rm in}\rangle = |+\rangle$ for its target qubit input. It is well known that such an input is unaffected by and does not affect the control qubit. Thus Bob suffers no errors but Eve gets no Rényi information. The $I_R = 1, P_E = 1/3$ point in this figure corresponds to Eve’s operating her CNOT gate with $|T_{\rm in}\rangle = \sqrt{1/3}|+\rangle + \sqrt{2/3}|-\rangle$, which leads to $|T_\pm\rangle \propto |d_\pm\rangle$. In this case Eve’s Fig. 3 receiver makes no errors, so she obtains the maximum (1 bit) Rényi information about each of Bob’s error-free bits. The $I_R = 0, P_E = 1/2$ point in this figure corresponds to Eve’s operating her CNOT gate with $|T_{\rm in}\rangle = |-\rangle$, which gives $|T_+\rangle = |T_-\rangle = |T_E\rangle = \sqrt{1/2}|-\rangle$. Here it is clear that Eve gains no information about Bob’s error-free bits, but his error probability is 1/2 because of the action of the $|-\rangle$ target qubit on the control qubit.

Physical Simulation in SPTQ Logic
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In single-photon two-qubit quantum logic, each photon encodes two independently controllable qubits [@SPTQ1]. One of 