Time-Bin QKD with Wavelength-Division Multiplexing

Humberg, Niklas; Sánchez-Postigo, Alejandro; Schuck, Carsten

Abstract

When doing Quantum Key Distribution, there are several different approaches to increase the secret key rate of a quantum channel. One possibility is Wavelength-Division Multiplexing (WDM), where photons of several different wavelengths are sent simultaneously in parallel over the same channel. These time-bin encoded qubits are generated by a narrow-band laser with adjustable wavelength in combination with electro-optic modulators for pulse generation. After transmission through a quantum channel with up to 90 km length, the qubits are demultiplexed and analyzed in the time domain using an 8-channel silicon nitride-on-insulator photonic integrated circuit. We use Mach-Zehnder interferometers with a 200 ps on-chip delay line to measure in complementary bases and enable a maximal key generation rate of up to 2.5 Gbit/s employing NbTiN superconducting nanowire single-photon detectors (SNSPDs) with high timing accuracy. We present simulation results, the QKD setup, and first measurements.