We provide the technical considerations for using an oscilloscope as a photon counter. The histogram of coincidences is extracted after a little signal processing.
HYPRES, Inc. has introduced to the commercial marketplace a Sampling Oscilloscope/Time Domain Reflectometer (TDR) based on Josephson junction technology. The unit offers measurement performance commensurate with the inherent high speed of the Josephson elements, e.g., bandwidths in excess of 70 GHz and rise times on the order of 5 ps. A Josephson {rigger recognizer and delay circuit allows triggering of the sampling oscilloscope from the signal itself, with full view of the trigger point. Input modules offering different sensitivities or TDR capability are quickly interchangeable, and operating temperature is achieved in less than one minute. The technical details of the cooling technique and the chip circuitry will be described in this paper .
This work presents a probability theory of coincidence detection to address the detection limit of time-correlated photon sources. We use Bayes’ theorem to model instruments as a noisy communication channel and apply statistical inference to identify the minimum detectable coincidence rate. Photon triplet generation is considered as a case study to illustrate the application of coincidence detection theory for time-correlated photon sources that are based on spontaneous parametric down-conversion. A triplet generation rate of 1–100 Hz is required for source characterization performed over 1–72 hours using superconducting nanowire single-photon detectors. We envision the connection between Bayes’ theorem and coincidence detection opens up a new avenue for applying signal processing techniques available in information theory to photon coincidence measurements.