2: Quantum correlations
The Erlangen group has measured the correlations between the different wavelengths in the soliton. Wavelength is measured with respect to the central soliton wavelength. Purple corresponds to strong positive correlations, seen most clearly in the long-wavelength part of the spectrum, while pale blue corresponds to negative correlations (see colour bar). The squares along the diagonal give the photon-number variance (noise level) of each wavelength. The correlations between the low-intensity parts of the spectrum had large error bars and have been left blank. (From Spälter et al.)