FIGURE 3. Inference of the concurrence C^z_i (a) and density matrix (b) at the three locations z_i indicated in Fig. 1b.

At each location, two pairs of results are given corresponding to the measurement-induced state created from detection at D_1a and D_1b, taking into account the efficiency of the detectors and propagation losses. a, Concurrence C, for two different detection windows t_d at D_2a,2b,2c. Filled symbols are for t_d = 190 ns, enough to acquire the whole temporal wavepacket of field 2. Open symbols are for t_d = 120 ns. We see then that the degree of entanglement can be further enhanced, similar to the increase of nonclassical correlations between fields 1 and 2 reported in ref. 23 for specific detection windows for these fields. All values shown in this figure, including the ones for z₀, are already corrected for the efficiencies of the detectors. Error bars reflect 1 standard deviation, taking into account the finite number of counts and the uncertainties in the efficiency and propagation loss. b, Density matrix given in the basis |n_2L|m_2R corresponding to equation (3) with {n, m} = {0, 1} for t_d = 190 ns.