Validating the calibrated creation of heralded single photons

TL;DR

This work tackles calibrated creation of heralded single photons by leveraging loss-tolerant state characterization via coincidence-count discrimination. It implements a PDC source in a PP-KTP waveguide and uses CAR and Klyshko efficiencies to extract the heralded state's mean photon number and photon-number parity from simple photon-correlation measurements, avoiding complex loss-inversion techniques. The results show that high CAR values suppress multi-photon contributions, yielding near-ideal single-photon characteristics (e.g., ⟨n⟩ ≈ 1.016, ⟨Π⟩ ≈ −0.973 at CAR ≈ 97, with g_h^(2) ≈ 0.028). The approach provides a practical, loss-tolerant calibration tool for heralded photon sources, enabling rapid benchmarking and comparison of quantum-light devices.

Abstract

Coincidence-count discrimination have turned utterly practical in the characterization of photon-pair processes and heralded single photons. Here, we implement a heralded single photon source based on parametric down-conversion (PDC) in a PP-KTP waveguide in the telecom wavelength range involving a low number of optical modes. We extend the toolbox for the loss-tolerant state characterization by combining conventional figures-of-merit in order to access the heralded state's mean photon number and its photon-number parity. Our experiment demonstrates that an accurate determination of these characteristics is possible just through simple photon-correlation measurements. We believe that our results can find usage in the calibrated creation of heralded single photons and in determining the expectation values of observables that are crucial for denoting a single quantum.

Figures (5)

• Figure 1: Experimental setup for the generation and characterization of heralded single photons. For details and abbreviations see the main text.
• Figure 2: Conventional photon-pair characteristics in terms of pump power. (a) The measured values of the CAR are computed via Eq. (\ref{['eq:CAR_Pump']}). The red solid line illustrates a theoretical fit being inversely proportional to the pump power. (b) The overall detection efficiencies in the idler (light green dots) and signal (light blue dots) beams are power dependent, whereas the corrected ones given by Eq. (\ref{['eq:klyshko']}) for idler (green dots) and signal (blue dots) deliver a constant values. The red solid lines represents the mean values extracted with Eq. (\ref{['eq:klyshko']}).
• Figure 3: The extracted $\mathcal{K}$-number for signal (blue symbols) and idler (green symbols) versus the CAR. The inset shows the measured values of the unconditional $g^{(2)}$ in terms of the pump power.
• Figure 4: Heralded second-order correlation function in terms of CAR. The red(green)-shaded area corresponds to values with different heralding efficiency for a single(multi)-mode twin-beam PDC emission.
• Figure 5: Expectation values for the studied observables in terms of CAR in cases (i) and (ii). When CAR increases, both (a) the mean photon number and (b) the photon-number parity approach the desired values of 1 and -1, respectively. The theoretical prediction (red line) agrees well with the second-order approximation investigated in case (ii).