Figure 1
APS/Alan Stonebraker

Figure 1: (Top) Experimental setup for single-photon generation and tomographic characterization. A “write” laser pulse stores an excitation in a quantum memory made of a cloud of cold rubidium atoms. A “read” pulse converts this excitation into an emitted single photon that is characterized by interferometric measurements. (Bottom) Tomographic reconstruction reveals that the Wigner function of the single photon dips to negative values (blue), proving that the quantum state of light is nonclassical.