Complete temporal characterization of a single photon
  Precise information about the temporal mode of optical states is crucial for optimizing their interaction efficiency between themselves and/or with matter in various quantum communication devices. Here we propose and experimentally demonstrate a method of determining both the real and imaginary components of a single photon's temporal density matrix by measuring the autocorrelation function of the photocurrent from a balanced homodyne detector at multiple local oscillator frequencies. We test our method on single photons heralded from biphotons generated via four-wave mixing in an atomic vapor and obtain excellent agreement with theoretical predictions for several settings. 
Zhongzhong Qin, Adarsh S. Prasad, Travis Brannan, Andrew MacRae, A.   Lezama, A. I. Lvovsky
quant-ph