High-performance quantum entanglement generation via cascaded second-order nonlinear processes

Zichang Zhang,Heqing Wang,You Wang,Guangwei Deng,Si Shen,Haizhi Song,Qiang Zhou,Hao Li,Guangcan Guo,Lixing You,Ruiming Zhang,Hao Yu,Zhiming Wang,Chenzhi Yuan,Zhen Wang

doi:10.1038/s41534-021-00462-7

Abstract

In this paper, we demonstrate the generation of high-performance entangled photon-pairs in different degrees of freedom from a single piece of fiber pigtailed periodically poled LiNbO3 (PPLN) waveguide. We utilize cascaded second-order nonlinear optical processes, i.e., second-harmonic generation (SHG) and spontaneous parametric downconversion (SPDC), to generate photon-pairs. Previously, the performance of the photon-pairs is contaminated by Raman noise photons. Here by fiber-integrating the PPLN waveguide with noise-rejecting filters, we obtain a coincidence-to-accidental ratio (CAR) higher than 52,600 with photon-pair generation and detection rate of 52.36 kHz and 3.51 kHz, respectively. Energy-time, frequency-bin, and time-bin entanglement is prepared by coherently superposing correlated two-photon states in these degrees of freedom, respectively. The energy-time entangled two-photon states achieve the maximum value of CHSH-Bell inequality of S = 2.71 ± 0.02 with two-photon interference visibility of 95.74 ± 0.86%. The frequency-bin entangled two-photon states achieve fidelity of 97.56 ± 1.79% with a spatial quantum beating visibility of 96.85 ± 2.46%. The time-bin entangled two-photon states achieve the maximum value of CHSH-Bell inequality of S = 2.60 ± 0.04 and quantum tomographic fidelity of 89.07 ± 4.35%. Our results provide a potential candidate for the quantum light source in quantum photonics.

Highlights

Quantum correlated/entangled photon-pairs are serving as essential resources in quantum photonics, such as quantum key distribution (QKD)[1,2,3,4], quantum teleportation[5,6,7], quantumenhanced metrology[8,9], and linear optical quantum information processing (LOQC)[10,11]
The generation of 1.5 μm bright photon-pairs has been demonstrated via spontaneous parametric down conversion (SPDC) process in βBaB2O4 (BBO)[29,30], periodically poled KTiOPO4 (PPKTP)[31,32,33], periodically poled LiNbO3 (PPLN)[18,26,27,28,34,35,36,37,38], and other secondorder nonlinear optical materials[39,40], or spontaneous four-wave mixing (SFWM) process in silica fiber[14,41,42,43,44,45], silicon[15,16,25,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60], silicon nitride[61,62], chalcogenide glass[63], and other third-order nonlinear optical materials[64,65,66]
The cascaded second-harmonic generation (SHG) and type-0 SPDC process could take place in the PPLN waveguide with a pump light to generate the correlated/ entangled photon-pairs

Summary

Introduction

Quantum correlated/entangled photon-pairs are serving as essential resources in quantum photonics, such as quantum key distribution (QKD)[1,2,3,4], quantum teleportation[5,6,7], quantumenhanced metrology[8,9], and linear optical quantum information processing (LOQC)[10,11] Approaches, such as cascaded emissions in single-emitters[12,13] and spontaneous parametric processes[14,15,16,17,18,19,20,21,22], are developed to generate correlated/entangled photon-pairs. Our results show that a high-performance quantum light source with cascaded second-order nonlinear processes on a photonics chip should be feasible

Methods

Results

Conclusion