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Perfect single-photon sources. S. Khalid and F. P. Laussy in Sci. Rep. 14:2684 (2024). Pdf-48px.png  What the paper says!?
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In this paper, with Sana Khalid, I show that if a light source has a compact support of exactly zero auto-correlations—thereby implementing a perfect single-photon source resilient to detectors time uncertainty—then it develops oscillations as a result of the high ordering of the photons in a stream of successive heralders.

We provide a closed-form expression for the Glauber g^{(2)} that ensues (Eq. (4)): g^{(2)}(\tau) = (1+\gamma t_\mathrm{G})e^{-\gamma(|\tau|-t_\mathrm{G})}\sum^{\infty}_{n = 0} \frac{\big[\gamma\big(|\tau| - (n+1)t_\mathrm{G}\big)e^{\gamma t_\mathrm{G}}\big] ^{n}}{n!}\mathbb{1}_{[(n+1)t_\mathrm{G}, \infty [} (|\tau|)\,.

Copy-paste the following in a Mathematica notebook to plot it:

Ind[t1_, t2_, t_] := If[t1 <= t <= t2, 1, 0] (* Indicator function *)

imax = 20; (* number of peaks - increase until converged *)
max\[Tau] = 75; (* max autocorrelation time *)
\[Gamma] = 
 1/5; tG = 10; (* source radiative lifetime and temporal gap *)

Plot[(\[Gamma] tG + 1) Exp[-\[Gamma] (Abs[t] - tG)] \!\(
\*SubsuperscriptBox[\(\[Sum]\), \(n = 0\), \(imax\)]\(
\*FractionBox[\(
\*SuperscriptBox[\((\[Gamma]\ \((Abs[t] - 
          n\ tG)\) Exp[\[Gamma]\ tG])\), \(n - 
       1\)]\(\ \)\), \(\((n - 1)\)!\)] Ind[n*tG, \[Infinity], 
     Abs[t]]\)\), {t, 0, max\[Tau]},
 PlotStyle -> {{Red, Thick, Opacity[.75]}}, PlotPoints -> 1000, 
 PlotRange -> {-.1, 2}, Filling -> Axis]

This paper was the first in a series studying such types of quantum light.[1][2] It is discussed in this Springer Nature blog post as well as in several Blog posts on this web, namely on the pair correlation function and on a mechanism for implementing such a perfect single-photon source. It is also discussed in various threads on 𝕏:

References

  1. Photon liquefaction in time. E. Zubizarreta Casalengua, E. del Valle and F. P. Laussy in APL Quant. 1:026117 (2024). Pdf-48px.png
  2. Correlations in circular quantum cascades. M. A. Palomo Marcos, E. Zubizarreta Casalengua, E. del Valle and F. P. Laussy in Phys. Rev. A 111:023704 (2025).