Polarized biphotons as “optical quarks”

Central-moment description of polarization for quantum states of light

“…Changing the mixing ratios somewhat, one finds that the mixed state 7 18 |3,0 3,0| + 1 3 |1,2 1,2| + 5 18 |0,3 0,3| also has no first-order polarization but second-and third-order structure. The second-order central moment is again "peanut shaped" with "half-axes lengths" (19,13,13)/3, and ˆ 3 n 3 is similar to that in Fig.…”

“…Stokes established an operational procedure to characterize not only the polarization properties of light but also to what extent a field is polarized [1]. The method is still the standard way of assessing polarization, although several generalizations, such as polarization of nonplane [2][3][4][5] and multimode [6][7][8] fields, have been developed. A limitation of Stokes' approach is that it only considers the average intensities (or photon numbers) and, hence, only assesses the first-order polarization moments.…”

Limit quantum efficiency for violation of Clauser-Horne inequality for qutrits

“…In order to better investigate this point, we have therefore considered as a second example the case where qutrit basis is realized by using degenerate biphotons [23,24] …”

“…In particular we have considered the case of entangled qutrits generated by means of a tritter scheme (as in Ref. [17]) and of qutrits based on biphotons (as suggested in [23,24]). …”

“…In order to give a first hint to the effect of using non-maximally entangled states, we will consider two examples: one is given by entangled systems built by multiport beam-splitters (interferometers), a second is given by an entangled state generated by using biphoton states [23]. Both these qutrits states have already been realized with photons [22,24] (for the first also entanglement has been obtained [22]) and, therefore, our results, showing a relevant improvement by using non-maximally entangled states, are of a large relevance for future experimental tests of LRT against QM and applications to quantum information.…”