Effects of multiple pairs on visibility measurements of entangled photons generated by spontaneous parametric processes

Abstract

Entangled photon-pair sources based on spontaneous parametric processes are widely used in photonic quantum information experiments. In this paper, we clarify the relationship between average photon-pair number and the visibility of two-photon interference (TPI) using those entanglement sources. We consider sources that generate distinguishable and indistinguishable entangled photon pairs, assuming coincidence measurements that use threshold detectors. We present formulas for the TPI visibility of a polarization entanglement that take account of all the high-order multi-pair emission events. Moreover, we show that the formulas can be approximated with simple functions of the average pair number when the photon collection efficiency is small. As a result, we reveal that an indistinguishable entangled pair provides better visibility than a distinguishable one.

Integrated Source of Spectrally Filtered Correlated Photons for Large-Scale Quantum Photonic Systems

“…Finally, in Fig. 4(g), we show the coincidence-toaccidental ratio [19,80,82] as a function of the pump power in chip A. A value of 50 AE 6-far above the classical limit of 2 and allowing for high-fidelity preparation of entangled-photon pairs or heralded single photons-is achieved under 0.3-mW pump power.…”

“…The sum of the intensities in the first five signal peaks (respectively, in the first five idler peaks) is a factor of 8 (respectively, 10) larger than the residual laser. Remaining pump photons follow Poissonian statistics and are not correlated in time; therefore, this level of suppression is already sufficient for many quantum optical experiments [80] like heralding of single photons or entanglement generation.…”

Random number generation from spontaneous Raman scattering

“…In our case, on average one photon is generated every 10 ns (corresponding to a 100 MHz in-fiber generation rate). Assuming a Poisson distribution for the photon generation 30 the probability of generating two photons within 100 fs is $5:0 Â 10 À5 , confirming the device is operating below the stimulated Raman threshold in the single-photon regime. Increasing the in-fiber generation rate to 1 GHz, this two photon probability remains low at $5:0 Â 10 À3 .…”

On-chip generation of photon-triplet states

“…It is known that parametric down-conversion processes, which are not pumped by single-photons, produce not only single, but also higher-order photon pairs [30]. Thus, we must expect to generate a statistical mixture of genuine photon triplets, |ψ triplet = |1 1 1 , and states including higher-order photon contributions in our process.…”