Fig. 2
From: Nondestructive detector for exchange symmetry of photonic qubits
Data for the non-demolition measurement of purity using the NDES with error bars corresponding to one standard deviation. x-axis always shows purity of a single input state Pa,off as measured by complete tomography with the NDES off. Dashed lines correspond to ideal theoretical predictions while the points represent the experimental data. a Direct non-demolition measurement of purity using NDES. b Mutual information estimated from the tomographic reconstruction of the qubits a and b. Black circles are for NDES on, gray squares are for NDES off, the nearly overlapping solid lines are predictions based on the actual estimated process matrix. c On-off-fidelities obtained from tomographic data. Red triangles pointing up relate to qubit a, blue triangles pointing down relate to qubit b, and black circles are for the joint state of a and b. d Purity and e fidelity for conditional purification of two copies of input qubit producing qubit a as the output. The circles mark the quantities for the single purified qubit while the squares show them when NDES is off
