Correlation between Events in Photon Detectors

Teodora Murariu, Larisa-Milena Pioraş-Ţimbolmaş, Cristian Tudoran +4 more

We used a microcontroller-based setup for the data acquisition in a down-conversion experiment to detect single photon events. This type of setup allows us to compare the effect of the detector's dead time as well as the delay in the data acquisition on the measured data. By using various time windows for the single-photon data acquisition, we estimate the magnitude of the errors in the measuring process as a function of the correlation between the electronics delay and the detector's dead time. Our conclusions are validated by analyzing the particle number, detection rates, and statistical distributions, as well as the correlations between signal and idler photons.

A. Widom, Yogendra Narain Srivastava, E. Sassaroli

Carl A. Kocher

Fabio Severini, Francesca Madonini, Federica Villa

The ability to generate and handle quantum correlations in twin-beam states is the foundation to overcome the imaging limitations imposed by classical light [1], relying on efficient detectors able to select temporal correlations among photons with maximized signal-to-noise ratio. Indeed, quantum information is contained in the interaction with the sample of just two photons, thus losing even one of them or mixing them up with background can completely compromise the experiment. To this end, assessing and evaluating the expected probability of measurement errors is of utmost importance to optimize the detector design. A typical experimental setup of a quantum imaging system based on Spontaneous Parametric Down Conversion (SPDC), the most effective way of producing temporally and spatially correlated entangled photons [2], involves a pump laser hitting a non-linear birefringent crystal producing a down-converted signal, some passive optical components to generate polarization-entangled photons and a pixelated photon detector that eventually reveals the position of coincident entangled photons. The overall detection efficiency of the measurement setup (i.e. heralding efficiency ηH) gathers all its possible losses and non-idealities of the mentioned setup components, namely the crystal conversion efficiency, the optical losses, the detector Photon Detection Efficiency (PDE) and fill-factor. In this study, we consider a detection based on a Single Photon Avalanche Diode (SPAD) array, able to detect coincidences on-chip and with event-driven architecture, which provides fast readout, low power consumption and optimized data throughput. However, related to every on-chip coincidence detection and event-driven based architecture, some operations require a certain amount of time to be performed that, combined with the generation of undesired single photons (both due to limited heralding efficiency and SPAD Dark Count Rate, DCR), yield to three measurement errors, here described with their related probabilities. Firstly, due to the finite duration of the coincidence window ∆tCOINC, there exist a probability Pfalseof wrongly detecting as coincident photons two single photons, and can be expressed as:\begin{equation*}{P_{false}} = \frac{{\left[ {2{\mu _{SOURCE{\text{ }}}}{\eta _H}\left( {1 - {\eta _H}} \right) + {\text{DCR}}} \right]\left( {1 - {e^{ - \left[ {2{\mu _{SOURCE}}{\eta _H}\left( {1 - {\eta _H}} \right) + {\text{DCR}}} \right]\Delta {t_{COINC}}}}} \right)}}{{{\mu _{SOURCE}}\eta _H^2 + \left[ {2{\mu _{SOURCE}}{\eta _H}\left( {1 - {\eta _H}} \right) + DCR} \right]\left( {1 - {e^{ - \left[ {2{\mu _{SOURCE}}{\eta _H}\left( {1 - {\eta _H}} \right) + {\text{DCR}}} \right]\Delta {t_{COINC}}}}} \right)}}\tag{1}\end{equation*}where µSOURCEis the number of photon pairs generated by an ideal non-linear crystal. Secondly, in the time needed for the array to "freeze" the pixels state after a coincidence event (∆tFREEZE) so that they can be readout, there is the probability Pspuriousof detecting a third spurious event after a coincidence has been detected, which is expressed as:\begin{equation*}{P_{spurious}} = 1 - {e^{ - \left[ {2{\mu _{SOURCE\eta }}_H\left( {1 - {\eta _H}} \right) + DCR} \right]\Delta {t_{FREEZE}}}}\tag{2}\end{equation*}

R. v. Baltz

D. S. Tasca, M. Edgar, Frauke Izdebski +2 more

Intensity correlation measurements form the basis of many experiments based on spontaneous parametric down-conversion. In the most common situation, two single-photon avalanche diodes and coincidence electronics are used in the detection of the photon pairs, and the coincidence count distributions are measured by making use of some scanning procedure. Here we analyze the measurement of intensity correlations using multielement detector arrays. By considering the detector parameters such as the detection and noise probabilities, we found that the mean number of detected photons that maximizes the visibility of the two-photon correlations is approximately equal to the mean number of noise events in the detector array. We provide expressions predicting the strength of the measured intensity correlations as a function of the detector parameters and on the mean number of detected photons. We experimentally test our predictions by measuring far-field intensity correlations of spontaneous parametric down-conversion with an electron multiplying charge-coupled device camera, finding excellent agreement with the theoretical analysis.