Fig. 4: Frequency-resolved quantum-state tomography.
From: Entangling entanglement: coupling frequency and polarization of biphotons on demand
a The concurrence is dependent on the signal/idler photon frequencies (wavelengths) when the polarization and frequency DoFs are coupled. The error bars represent the standard deviation obtained from the Monte Carlo simulations fed by the actual coincidence measurement data. The polarization state density matrix reconstructed from the polarization quantum-state tomography with high concurrence \({{{{\mathcal{C}}}}}^{{{{\rm{Pol}}}}}=0.95(3)\) and fidelity F = 97.4% (b), and low concurrence \({{{{\mathcal{C}}}}}^{{{{\rm{Pol}}}}}=0.11(4)\) and fidelity F = 51.0% (c).
