Correlations in atomic systems: Diagnosing coherent superpositions

While investigating quantum correlations in atomic systems, we note that single measurements contain information about these correlations. Using a simple model of measurement-analogous to the one used in quantum optics-we show how to extract higher-order correlation functions from individual "photographs" of the atomic sample. As a possible application, we apply the method to detect a subtle phase coherence in mesoscopic superpositions.