As some of the most promising quantum applications such as high resolution quantum optical coherence tomography (QOCT) [1] with dispersion cancellation as well as quantum key distribution require frequency entanglement. Therefore, frequency entanglement light sources are an essential importance for implement of many quantum optical applications. So Far, the most prominent method used for the entangled photon pair generation is spontaneous parametric down-conversion (SPDC) in nonlinear crystals. Recently, with adopting chirp quasi-phase matching (QPM) PPSLT (periodically poled stoichiometric lithium tantalate) has been used as source of entangled photons with large bandwidth [2]. However, improving the overall system efficiency is still remain challenging.
We present a theoretical analysis of the process of spontaneous parametric down conversion (SPDC) in a nonlinear crystal characterized by a linearly-chirped χ(2) grating along the direction of propagation. Our analysis leads to an expression for the joint spectral amplitude, based on which we can derive various spectral–temporal properties of the photon pairs and of the heralded single photons obtained from the photon pairs, including: The single-photon spectrum (SPS), the chronocyclic Wigner function (CWF) and the Schmidt number. The simulations that we present are for the specific case of a collinear SPDC source based on a PPLN crystal with the signal and idler photons emitted close to the telecom window. We discuss the mechanism for spectral broadening due to the presence of a linearly chirped χ(2) grating, showing that not only the width but also to some extent the shape of the SPDC spectrum may be controlled. Also, we discuss how the fact that the different spectral components are emitted on different planes in the crystal leads to single-photon chirp.
Spontaneous parametric down-conversion is an essential tool for a quantum light source in the infrared region ranging 2-5 µm for the purpose of material identification, chemical analysis, and gas sensing. So far, photon pairs from the process in a nonlinear crystal have low tunability and a narrow spectral range because of the phase-matching condition. Here, we propose a novel type of spontaneous parametric down-conversion processes that overcomes these challenges, where two photon pairs are simultaneously produced in the visible and infrared regions in periodically poled stoichiometric lithium tantalite. It allows broadband and tunable generation of infrared photon pairs that can be employed as an alternative light source for quantum infrared spectroscopy.
Chip-integrated photon-pair sources based on spontaneous parametric down-conversion (SPDC) have emerged as a promising solution for scalable quantum light generation. Thin-film lithium tantalate (TFLT) is a compelling
χ(2) platform, combining strong nonlinearity with a high optical-damage threshold, weak photorefractive response, and ferroelectricity that enables quasi-phase matching. However, SPDC-based photon-pair generation on TFLT has not yet been demonstrated. Here, we combine high-quality periodic poling with low-loss nanophotonic waveguides to realize photon-pair sources on TFLT in both traveling-wave and resonant configurations. In periodically poled straight waveguides, we achieve broadband photon-pair generation with high efficiency (
2.1 GHz mW−1) and coincidence-to-accidental ratio (up to
3.8×105). We further confirm high-purity single-photon operation via heralded second-order correlation (
gH(2)(0)=0.0018±0.0002) and high-fidelity time-energy entanglement through Franson interference (visibility of
98.9±0.5%). In periodically poled racetrack resonators, we map out a broad quantum frequency comb spanning the telecom C- and L-bands. By isolating individual frequency-correlated pairs, we measure a high spectral brightness of
11 GHz mW−1 GHz−1. These results are competitive with the state of the art across
χ(2) integrated platforms, positioning TFLT as a strong contender for integrated quantum light sources, with applications in wavelength-multiplexed quantum communications and photonic quantum information processing.
Abstract Chip-integrated photon-pair sources based on spontaneous parametric down-conversion (SPDC) have emerged as a promising solution for scalable quantum light generation. Thin-film lithium tantalate (TFLT) is a compelling
χ(2) platform, combining strong nonlinearity with a high optical-damage threshold, weak photorefractive response, and ferroelectricity that enables quasi-phase matching. However, SPDC-based photon-pair generation on TFLT has not yet been demonstrated. Here, we combine high-quality periodic poling with low-loss nanophotonic waveguides to realize photon-pair sources on TFLT in both traveling-wave and resonant configurations. In periodically poled straight waveguides, we achieve broadband photon-pair generation with high efficiency (2.1~GHz~mW
−1) and coincidence-to-accidental ratio (up to
3.8×105). We further confirm high-purity single-photon operation via heralded second-order correlation (
gH(2)(0)=0.0018±0.0002) and high-fidelity time-energy entanglement through Franson interference (visibility of
98.9±0.5%). In periodically poled racetrack resonators, we map out a broad quantum frequency comb spanning the telecom C- and L-bands. By isolating individual frequency-correlated pairs, we measure a high spectral brightness of 11~GHz~mW
−1~GHz
−1. These results are competitive with the state of the art across
χ(2) integrated platforms, positioning TFLT as a strong contender for integrated quantum light sources, with applications in wavelength-multiplexed quantum communications and photonic quantum information processing.