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arXiv:2503.14920 · Journal of Physics D Applied Physics

A heralded single-photon source implemented with second-order nonlinear photonic crystals

Hiroo Azuma

Published Jul 11, 2025• 0 citations
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Abstract

Abstract We study implementing a heralded single-photon source with second-order nonlinear photonic crystals. Injecting pump and signal light beams into a one-dimensional photonic crystal composed of a material with a large second-order nonlinear optical susceptibility χ ( 2 ) , we can transform the coherent incident signal light into squeezed light. Preparing two squeezed light beams by this method and input them into two ports of a 50-50 beam splitter independently, we can transform them into a two-mode squeezed state. Because those two modes of photons share entanglement, a single photon of the one mode is emitted with a high probability on the condition of the single-photon detection of the other mode as a heralding signal. We evaluate the efficiency and the second-order intensity correlation function g ( 2 ) ( 0 ) for this heralded single-photon source. Moreover, we examine changes in the efficiency and g ( 2 ) ( 0 ) when we assume that the single-photon detector for the heralding signal is imperfect. For a specific concrete example, we consider a case where the nonlinear medium is lithium niobate LiNbO 3 and the frequency of the incident signal light is on the order of 1014 Hz.

DOI
10.1088/1361-6463/adeea0

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Abstract We study implementing a heralded single-photon source with second-order nonlinear photonic crystals. Injecting pump and signal light beams into a one-dimensional photonic crystal composed of a material with a large second-order nonlinear optical susceptibility χ ( 2 ) , we can transform the coherent incident signal light into squeezed light. Preparing two squeezed light beams by this method and input them into two ports of a 50-50 beam splitter independently, we can transform them into a two-mode squeezed state. Because those two modes of photons share entanglement, a single photon of the one mode is emitted with a high probability on the condition of the single-photon detection of the other mode as a heralding signal. We evaluate the efficiency and the second-order intensity correlation function g ( 2 ) ( 0 ) for this heralded single-photon source. Moreover, we examine changes in the efficiency and g ( 2 ) ( 0 ) when we assume that the single-photon detector for the heralding signal is imperfect. For a specific concrete example, we consider a case where the nonlinear medium is lithium niobate LiNbO 3 and the frequency of the incident signal light is on the order of 1014 Hz.
Abstract We discuss the generation of entangled photons using a nonlinear photonic crystal and beam splitter. In our method, the photonic crystal is assumed to be composed of a material with a large second-order nonlinear optical susceptibility χ ( 2 ) . Our proposal relies on two facts: (1) A nonlinear photonic crystal changes coherent incident light into squeezed light. (2) A beam splitter transforms the squeezed light into entangled light beams flying in two different directions. We estimate the yield efficiency of pairs of entangled photons per pulse of the very weak coherent light for our method at 0.0783 for a specific concrete example. Our method is more effective because the conversion efficiency (entangled biphotons per incident pump photons) in the spontaneous parametric downconversion is of the order of 4 × 10 − 6 . The only drawback is that it requires very fine tuning of the frequency of signal photons fed into the photonic crystal; for example, an adjustment is given by Δ ν = 3.11 × 10 8 Hz for the signal light of ν = 3.23 × 10 14 Hz. We investigate the application of entangled photons produced by our method to the BB84 quantum key distribution protocol, and we explore how to detect an eavesdropper. We suggest that our method is promising for decoy-state quantum key distribution using weak coherent light.
We propose a heralded single-photon source based on injecting a superposition of oppositely squeezed states onto a beam splitter. Our superposition of squeezed states is composed of only even photon number states (the number of photons is equal to 2,6,10,...2,6,10,...2,6,10,...) meaning the probability for an emitted single photon given as a heralded single-photon event is higher than what one can achieve from the usual two-mode squeezed state. This enables one to realize an enhanced heralded single-photon source. We discuss how to create this superposition of squeezed states utilizing a single-mode squeezed state and the cross-Kerr nonlinearity. Our proposed method significantly improves the probability of emitting the heralded single photon compared to spontaneous parametric down-conversion.
Abstract In this paper, we investigate how to generate coherent squeezed-like light using a nonlinear photonic crystal. Because the photonic crystal reduces the group velocity of the incident light, if it is composed of a material with a second-order nonlinear optical susceptibility χ ( 2 ) , the interaction between the nonlinear material and the light passing through it strengthens and the quantum state of the emitted light is largely squeezed. Thus, we can generate a coherent squeezed-like light with a resonating cavity in which the nonlinear photonic crystal is placed. This coherent squeezed-like state is defined with the Lie–Trotter product formula and its mathematical expression is different from those of conventional coherent squeezed states. We show that we can obtain this coherent squeezed-like state with a squeezing level 15.9 dB practically by adjusting the physical parameters for our proposed method. Feeding the squeezed light whose average number of photons is given by one or two into a beam splitter and splitting the flow of the squeezed light into a pair of entangled light beams, we estimate their entanglement quantitatively. This paper is a sequel to Azuma (2022 J. Phys. D: Appl. Phys. 55 315106).
In this paper we present a scheme of a heralded single photon source based on active two-dimensional photonic crystal (PC) over LiNbO3 excited by continuous pump laser source. The use of 2D photonic crystal could improve the conversion light efficiency and obtain height density of mode (DOM) at 1310nm and 1550nm, which will increase the probability of obtaining single photon. The scheme is based on two photonic crystals arranged in serial configuration. The first one acts as extractor of the two wavelengths, and the second as a demultiplexer and can be considered as a time-delay coupler. Also constraints related to manufacturing process are reported in order to show performances of the CP on the heralded single photon source model.
Abstract Four-wave mixing (FWM) of ultrashort laser pulses in a highly nonlinear photonic-crystal fiber is shown to provide a multimodal source of broadband quantum states of light. In the regime of low pump powers, generation of two-photon states and heralded single photons with a bandwidth up to ≈6 THz is demonstrated within an FWM-sideband tunability range of ≈55 THz. In the modality of heralded single-photon generation, three-detector measurements of the conditional second-order correlation function reveal a strong antibunching in the signal-photon channel, with more than 99.2% of the signal counts identified as truly single-photon states. At high pump powers, two-detector signal-idler correlation function measurements indicate broadband bright squeezed vacuum generation.
Quantum states of light, such as single photons, pairs of entangled photons, and squeezed light are a key resource for photonic quantum technologies. All these states can be obtained via the nonlinear optical effect of spontaneous parametric down-conversion (SPDC). In SPDC, a higher-energy photon of a coherent beam (pump) splits in two lower-energy daughter photons, called signal and idler. The photons of such a pair can be entangled in polarization, time/frequency, and position/momentum. Efficient generation of photon pairs requires a high second-order susceptibilityχ(2)\chi^{(2)}χ(2)of the material where it occurs, and the phase matching between the pump and the down-converted photons.