Broadband polarization-entangled source for C+L-band flex-grid quantum networks

TL;DR

This paper presents an ultrabroadband polarization-entangled photon source covering C+L bands, enabling advanced quantum network management and capacity expansion through spectral control and high-fidelity entanglement distribution.

Contribution

The work introduces a novel ultrabroadband entangled photon source with integrated wavelength switches for spectral routing in C+L bands, tailored for flex-grid quantum networks.

Findings

Achieved 0.98 average fidelity in polarization state tomography.

Demonstrated total distillable entanglement >181 kebits/s.

Covered 7.5 THz spectral range with spectral control.

Abstract

The rising demand for transmission capacity in optical networks has motivated steady interest in expansion beyond the standard C-band (1530-1565 nm) into the adjacent L-band (1565-1625 nm), for an approximate doubling of capacity in a single stroke. However, in the context of quantum networking, the ability to leverage the L-band will require advanced tools for characterization and management of entanglement resources which have so far been lagging. In this work, we demonstrate an ultrabroadband two-photon source integrating both C- and L-band wavelength-selective switches for complete control of spectral routing and allocation across 7.5 THz in a single setup. Polarization state tomography of all 150 pairs of 25 GHz-wide channels reveals an average fidelity of 0.98 and total distillable entanglement greater than 181 kebits/s. This source is explicitly designed for flex-grid optical networks and can facilitate optimal utilization of entanglement resources across the full C+L-band.