Measuring the entanglement of photons produced by a nanosecond pulsed source

M´ONICA B. AG¨UERO,ALEJANDRO A. HNILO, AND MARCELO G. KOVALSKY

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS

OPTICAL SOC AMER

Lugar: Washington; Año: 2014 vol. 31 p. 3088 - 3098

0740-3224

A source of entangled photons based on well separated laser pump pulses with duration in the nanosecond range is of interest for many applications. Yet, such a source has intrinsic problems arising from the simultaneous arrival of the signal and noise photons to the detectors, what makes unsuitable the methods for dealing with accidental (or spurious) coincidences applied in the continuous-wave or mode-locked pump regimes. Those problems are analyzed, and practical methods to calculate the number of accidental coincidences are described and experimentally checked. These methods are useful not only to measure entanglement, but also in every situation where extracting the number of valid two-photon coincidences from noisy data generated by such a pulsed process is required. As an original example of the use of these methods, we present the time-resolved measurement of the Concurrence of the field produced by spontaneous parametric down conversion with pump pulses of duration in the ns-range at a repetition of kHz.