Figure 4: Triggered generation of photon twins.
From: A bright triggered twin-photon source in the solid state
(a) Measured photon auto-correlation histogram 
of photon twins under pulsed above-band excitation at low excitation power (P=87 nW). A bunching of 
=A0/A=5.1 is observed, where A0 and A correspond to the zero-delay peak and the peaks at finite τ. (b) HOM TPI experiment using photon twins under pulsed p-shell excitation. Measured histograms of 
for co-polarized (solid line) and cross-polarized (dashed line) configuration using a symmetric Mach–Zehnder interferometer (data in cross-polarization shifted by +2 ns for clarity). (c) Direct detection of photon twins using a PNR detection system based on a TES. The histogram shows the pulse-area-distribution of photon detection events from the twin-photon cascade, where the labeled peaks correspond to the detection of one (‘1’), two (‘2’) or three (‘3’) photons. (d) Reconstructed photon number distribution of the twin-photon source (TPS), deduced from the PNR measurement in c by taking into account the total losses of the experimental setup. Results obtained for a quantum dot single-photon source (SPS) are displayed for comparison. The error bars result from the uncertainties of the setup efficiency and the photon extraction efficiency of the microlens.
