On-Chip Generation of Copolarized and Spectrally Separable Photon Pairs

Area of Science:

• Quantum Optics
• Nanophotonics
• Quantum Information Science

Background:

• Scalable photonic quantum technologies require on-chip generation of high-purity single photons.
• Spontaneous parametric down-conversion (SPDC) is a common method, but spectral correlations limit photon purity.
• Current methods to reduce correlations involve lossy filtering or complex polarization schemes.

Purpose of the Study:

• To develop a novel method for generating spectrally separable photon pairs on-chip.
• To overcome limitations of existing SPDC techniques for high-purity single-photon sources.
• To enable flexible spectral and temporal engineering of quantum light sources.

Main Methods:

• Exploiting higher-order spatial modes in thin-film lithium niobate nanophotonic circuits.
• Engineering group-velocity matching using higher-order transverse-electric modes.
• Utilizing a Gaussian-apodized poling profile to suppress residual spectral correlations.
• Employing on-chip mode conversion (>95% efficiency) to route photons.

Main Results:

• Achieved spectrally separable photon-pair generation in the same polarization.
• Heralded photons demonstrated spectral purities up to 94% (joint-spectral intensity) and 89% (g^{(2)} measurement).
• Successfully mapped higher-order modes to the fundamental mode for distinct output channels.

Conclusions:

• The higher-order spatial mode approach effectively suppresses spectral correlations in SPDC.
• This technique provides a pathway for high-purity, on-chip single-photon generation.
• Enables advanced quantum light sources crucial for quantum computing and networking.