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Slovak-Czech-Polish Optical Conference on Wave and Quantum Aspects of Contemporary Optics

Simulating co-propagation of quantum key distribution and white rabbit protocols

Elisabeth Andriantsarazo, Jaroslav Roztočil, Josef Vojtěch

Published Feb 17, 2025• 0 citations
Publisher

Abstract

Quantum Key Distribution (QKD) protocols offer top-tier secure communication but face challenges with noise, particularly when quantum and classical channels coexist. In fiber-optic systems, strong classical signals for data and synchronization create noise through scattering, with inelastic scattering being the main contributor. This broad-spectrum noise can overlap with quantum communication wavelengths, leading to errors and deterioration of the quantum signal. Our study examines the theoretical coexistence limit for a 1500 nm classical synchronization signal from a White Rabbit switch and a 1320 nm quantum signal from an S-Fifteen Instruments source, identifying the maximum fiber length where the quantum signal remains clear of noise. We chose the BB84 protocol for our QKD implementation, which we plan to first test in a laboratory setting without an intermediate node. In the future, adding a node (often referred to as Charlie) would improve scalability and help manage synchronization delays.

DOI
10.1117/12.3056734

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Quantum Key Distribution (QKD) protocols offer top-tier secure communication but face challenges with noise, particularly when quantum and classical channels coexist. In fiber-optic systems, strong classical signals for data and synchronization create noise through scattering, with inelastic scattering being the main contributor. This broad-spectrum noise can overlap with quantum communication wavelengths, leading to errors and deterioration of the quantum signal. Our study examines the theoretical coexistence limit for a 1500 nm classical synchronization signal from a White Rabbit switch and a 1320 nm quantum signal from an S-Fifteen Instruments source, identifying the maximum fiber length where the quantum signal remains clear of noise. We chose the BB84 protocol for our QKD implementation, which we plan to first test in a laboratory setting without an intermediate node. In the future, adding a node (often referred to as Charlie) would improve scalability and help manage synchronization delays.
We investigate the coexistence of clock synchronization protocols with quantum signals in a common single-mode optical fiber. By measuring optical noise between 1500 nm to 1620 nm we demonstrate a potential for up to 100 quantum, 100 GHz wide channels coexisting with the classical synchronization signals. Both "White Rabbit" and pulsed laser-based synchronization protocols were characterized and compared. We establish a theoretical limit of the fiber link length for coexisting quantum and classical channels. The maximal fiber length is below approximately 100 km for off-the-shelf optical transceivers and can be significantly improved by taking advantage of quantum receivers.
Abstract As quantum computing continues to demonstrate its potential to break through existing cryptographic systems, quantum key distribution (QKD) provides a novel approach to protect communications in the post-quantum era, but presents complex challenges in terms of research and widespread adoption. Although the resource-intensive nature of QKD setups limits experimental studies to specialized laboratories, we present an end-to-end simulation that models photon generation, transmission, and detection, thereby lowering the barrier to testing hypotheses regarding experimental setups under realistic conditions. In this study, a fiber optic-based simulation was utilized along with a quantum circuit and a detailed noise model within the BB84 protocol to recreate an experimental setup. Our BB84 simulation retained ≈50% of transmitted bits after sifting, matching the experimental expectations, and produced quantum bit error rate (QBER) values that rose with increasing channel length. Our model incorporates customizable noise, such as multi-photon emissions and channel disturbances, directly into the key exchange process, yielding QBER values of ≈4.5% at 20 km and ≈11% at 120 km, consistent with physical systems under the same conditions. Our findings support the development of QKD as a scalable solution for securing the quantum internet and future communication networks.
Abstract Integrating quantum key distribution (QKD) into optical networks is a crucial step toward the adoption of quantum technologies in existing telecommunication fiber infrastructures. However, state-of-the-art solutions face significant challenges, including sensitivity to classical noise, particularly spontaneous Raman scattering, limited transmission distances, and varying network conditions. In this work, we present a novel discrete-variable QKD system running a time-bin BB84 protocol operating in the O-band (1295.56 nm), where the impact of dominant noise sources is effectively reduced. Combined with passive narrow-spectral filtering at the receiver, our system demonstrates robustness across diverse dense wavelength-division multiplexing scenarios, making it practical for real-world deployments. We validate its performance through extensive testing, showing stable key generation coexisting with different classical traffic conditions up to 17 dBm of total launch power. These results represent a significant advancement toward the integration of QKD into existing fiber networks, paving the way for secure quantum communication on a large scale.
Quantum Key Distribution (QKD) provides a novel alternative to Classical Key Distribution in protecting secure communications, but poses challenges in terms of research and widespread adoption. While the resource-intensive nature of QKD setups limit experimental studies to specialized laboratories, we present an end-to-end simulation that models photon generation, transmission, and detection, thereby lowering the barrier to testing hypotheses regarding experimental setups under realistic conditions. In this study, a fiber optic-based simulation is utilized along with a quantum circuit and a detailed noise model within the BB84 protocol to recreate an experimental setup. Our BB84 simulation retained ≈50% of transmitted bits after sifting, matching the experimental expectations. Our model incorporates customizable noise, such as multi-photon emissions and channel disturbances, directly into the key exchange process, allowing for an approach that utilizes simulated fiber optics and theoretical noise models to replicate physical conditions. Our findings support the development of QKD as a scalable solution for securing the quantum internet and future communication networks.
We investigate the coexistence of clock synchronization protocols with quantum signals propagating in a common optical single-mode fiber channel. By measuring optical forward and backward scattering noise in a range from 1510 nm to 1620 nm we demonstrate a potential for up to 100 quantum channels each with 100 GHz bandwidth coexisting with the classical synchronization signals using off-the-shelf optical components. Both “White Rabbit'' and a pulsed laser-based synchronization were characterized and compared.
We theoretically study the issues for long-distance transmission of quantum key distribution (QKD) coexisting with classical signals. The recently proposed phase-matching QKD protocol can drastically improve the transmission distance of QKD. However, in the coexistence system, the noise generated by classical signals, especially spontaneous Raman scattering noise, is a big challenge. Moreover, the classical optical amplifier, which is necessary for the realistic long-distance classical communication, makes the noise more serious. In view of this, we establish the unified Raman noise model for three discrete-variable QKD protocols (BB84, measurement-device-independent and phase-matching QKD protocols) in the presence of classical optical amplifiers, which can be applied to both single-core single-mode fiber and multicore fiber. Then, we derive the key rate of the three QKD protocols coexisting with classical signals using the proposed unified Raman noise model. Finally, simulation results show that multicore fiber is promising for simultaneous long-distance transmission of QKD and the dense wavelength division multiplexing system.