Figure 1

Entangled photons are generated by two bismuth borate (BiBO) nonlinear crystals in two spatial modes (1 and 2). The down-converted photons are frequency filtered (F) and then analyzed in polarization (A${}_1$ and A${}_2$) before detection and correlation. The physical design employs collinear down conversion and a 50:50 beam splitter to separate the two photons.Reuse & Permissions

Figure 2

Parametric plot of the mutual information sum $M_J$ and concurrence for the examples given in the text. Note that, for a given concurrence, $M_J$ for ${\rho }_M$ and $\rho \left(\beta \right)$ (they fall on the same curve) is uniformly higher than for the other three states. The points shown for the two-parameter state $\rho (a,b)$ are evaluated for a random, uniform sample of $a$ and $b$.Reuse & Permissions

Figure 3

Mutual information $M_{J_C}$ recorded for the maximally correlated mixed state (hollow circles) and the singlet state (solid circles). Points are data composed of 36 min of integration (over 12 separate measurements) for the singlet state and 48 s of integration for the maximally correlated mixed state. The solid and dotted-dashed lines correspond to theoretical predictions of $M_{J_C}$ based upon the tomographic reconstruction [26] of the singlet state and the maximally correlated mixed state, respectively. The error bars, which are smaller than the points for the maximally correlated mixed state, are calculated assuming shot noise limited detection. The dashed line indicates the classical bound of $M_{J_C}$.Reuse & Permissions