Hong-Ou-Mandel Interference with Imperfect Single Photon Sources

Quantifying n-photon indistinguishability with a cyclic integrated interferometer

“…We measure the indistinguishability via two-photon HOM interference in a path-unbalanced Mach-Zender interferometer. We extract the visibility of HOM interference, V HOM , and correct for the non-zero g (2) (0) to extract the indistinguishability of the single photon component, M s [14]. When the delay between the photons is 12.3 ns, corresponding to the pulse separation of the laser, the visibility (indistinguishability) is V HOM = (88.6 ± 0.1)% (M s = (92.3 ± 0.1)%).…”

“…2). Therefore, by observing the two-photon coincidences on outputs 2 and 3 we directly measure the HOM interference visibility (and the two-photon indistinguishability [14]) between photons A and B, V AB (M AB ). Similarly, the interference between photons B and C is measured at outputs 4 and 5, C and D at outputs 6 and 7, and D and A at outputs 1 and 8.…”

“…Within this model, we will neglect higher order noise terms. For quantum dot sources [14], the overlap of such noise photon with the principal one can be approximated to ∼ 0, that is, the noise photon ( 1) is distinguishable from the others (1) [14]. The complete input state after demultiplexing can be written as a density matrix:…”

“…In the case of two photons, the indistinguishability is readily measured by performing a Hong-Ou-Mandel (HOM) interference experiment [10,11]. For two-photon wavepackets, the visibility of the quantum interference fringe gives access to the indistinguishability parameter, provided that the sources of noise are well understood [12][13][14]. However, when more than two photons are involved, the genuine indistinguishability of the full set of photons is not completely characterized by the HOM interference of all possible pairs [11,15], while only methods capable to provide lower and upper bounds to this quantity have been defined [15,16].…”

“…This can be performed by considering that those parameters are strictly related to the two-photon overlaps M ij = x i x j , and can thus be retrieved from the measured visibilities V ij = (V AB , V BC , V CD , V DA ), by including the effect of g (2) (0) to find the instrinic indistinguishability M ij as discussed in Ref. [14], and by correcting for imperfect directional couplers.…”