Integrated sources of entangled photons at telecom wavelength in femtosecond-laser-written circuits

TL;DR

This paper demonstrates an integrated, femtosecond-laser-written photonic circuit that generates high-visibility entangled photon pairs at telecom wavelengths, advancing quantum photonic technologies.

Contribution

It introduces a novel hybrid integrated source of entangled photons using femtosecond laser inscription, capable of producing various entangled states with high fidelity.

Findings

Achieved high-visibility (>0.92) entanglement in integrated circuits.

Enabled switching between path and polarization entanglement.

Demonstrated stable, efficient entangled photon generation at telecom wavelengths.

Abstract

Photon entanglement is an important state of light that is at the basis of many protocols in photonic quantum technologies, from quantum computing, to simulation and sensing. The capability to generate entangled photons in integrated waveguide sources is particularly advantageous due to the enhanced stability and more efficient light-crystal interaction. Here we realize an integrated optical source of entangled degenerate photons at telecom wavelength, based on the hybrid interfacing of photonic circuits in different materials, all inscribed by femtosecond laser pulses. We show that our source, based on spontaneous parametric down-conversion, gives access to different classes of output states, allowing to switch from path-entangled to polarization-entangled states with net visibilities above 0.92 for all selected combinations of integrated devices.