Intensity correlations, quantum interference

The visibility of the interference pattern of the intensity correlations provides a means of testing for quantum correlations between two light fields. Mandel et al. [18] have measured the visibility in the interference of signal and idler modes simultaneously generated in the process of degenerate parametric downconver-sion, and observed a visibility of about 75%, that is a clear violation of the upper bound of 50% allowed by classical correlations. Richter [19] has extended the analysis of the visibility into the third-order correlation function and also found significant differences in the visibility of the interference pattern of the classical and quantum fields. 

The possibility of measurement of Mg2+ concentration in a matrix complicated by alkali and alkaline earth metal ions has been explored by titration of 68 (5 x 10-5 M) in 1 1 MeOH/H20 solution (pH 7.2) containing Na+ (5 x 10 3 M), K+ (1 X 10-3 M), Ba2+ (1 x 10 3 M), Sr2 (1 x 1(T3 M), and Ca2+ (1 x 10-4 M). The titration was monitored via fluorescence.125 The fluorescence intensity reached a maximum at 1 equiv of Mg2+, indicating that fluorescent intensity could be directly correlated to Mg2+ concentration. The lack of interference from the other metal ions present can be a result of their lower binding constants with 68 and lower quantum yields of the charged complexes of 68 with Na+, K+, Ca2+, Sr2+, and Ba2+ at this pH. Thus, ligand 68 possesses characteristics of an efficient fluorescent chemosensor for Mg2+ and may find use in determining Mg2+ in biological samples and, if immobilized on a solid support, may be incorporated into sensory devices for measurement of Mg2+ concentrations in aqueous solutions. 

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