Photon-Pair Parasites: Menace or Nuisance?

Summary form only given. Sources of indistinguishable single photons are a key component of many optical quantum systems such as linear optical quantum computers [1] or quantum communication [2]. Spontaneous four-wave mixing is a promising method for in-fiber photon-pair generation with tailored spectral properties. However, a number of parasitic effects can negatively influence the quality of photons heralded from the pair. In this work, we investigate the impact on the quantum purity of heralded photons of arguably the three most important effects: nonlinear phase modulation (NPM), higher-order dispersion (HOD) and dispersion fluctuations (DF) along the fiber leading to variations in phase matching. For the first time, we directly compare two schemes under each of these effects. The first is the asymmetric scheme in which one of the quantum fields is group-velocity matched to the single pump field while the other walks off [3]. The second is the symmetric collision scheme, which uses two pump fields with different group velocities that pass through each other with each of the two quantum fields copropagating with one of the pumps [4]. In all calculations presented here, we use identical Gaussian pumps ∝ exp[-t
²
/(2T
²
₀
)] with T
₀
= 1 ps and a group-slowness difference of Δβ
₁
= 1 x 10
^-11
s/m between all non-copropagating fields. For both schemes we include the effect of NPM using analytical time-domain models [4,5] and choose a high generation probability of R= 0.2 to illustrate the impact. The effect of HOD is included with a novel analytical model for the asymmetric scheme and a numerical split-step method [5] for the collision scheme with all fields experiencing group-velocity dispersion of β
₂
= 50 x 10
^-26
5
²
/m. Lastly, the effect of DFs is investigated using a Brownian-motion model for the phase-matching frequency [6] with a standard deviation σ
_ω
= 0.5/T
₀
and a correlation length in fluctuations of 10 cm.