Optimal Wavelength Allocation in Hybrid Quantum-Classical Networks

An efficient algorithm for optimal allocation of wavelengths in a hybrid dense-wavelength-division-multiplexing system, carrying both quantum and classical data, is proposed. The transmission of quantum bits alongside intense classical signals on the same fiber faces major challenges arising from the background noise generated by classical channels. Raman scattering, in particular, is shown to have detrimental effects on the performance of quantum key distribution systems. Here, by using an optimal wavelength allocation technique, we minimize the Raman induced background noise on quantum channels, hence maximize the achievable secret key generation rate for quantum channels. It turns out the conventional solution that the optimal arrangement would involve splitting the spectrum into only two bands, one for quantum and one for classical channels, is only a suboptimal one. We show that, in the optimal arrangement, we might need several quantum and classical bands interspersed among each other

Field-Trial of Machine Learning-Assisted Quantum Key Distribution (QKD) Networking with SDN

We demonstrated, for the first time, a machine-learning method to assist the coexistence between quantum and classical communication channels. Software-defined networking was used to successfully enable the key generation and transmission over a city and campus network

Crosstalk Reduction in Hybrid Quantum-Classical Networks

In this paper, we propose and investigate several crosstalk reduction techniques for hybrid quantum-classical dense-wavelength-division-multiplexing systems. The transmission of intense classical signals alongside weak quantum ones on the same fiber introduces some crosstalk noise, mainly due to Raman scattering and nonideal channel isolation, that may severely affect the performance of quantum key distribution systems. We examine the conventional methods of suppressing this crosstalk noise, and enhance them by proposing an appropriate channel allocation method that reduces the background crosstalk effectively. Another approach proposed in this paper is the usage of orthogonal frequency division multiplexing, which offers efficient spectral and temporal filtering features

Wavelength Assignment in Hybrid Quantum-Classical Networks

Optimal wavelength assignment in dense-wavelength-division-multiplexing (DWDM) systems that integrate both quantum and classical channels is studied. In such systems, weak quantum key distribution (QKD) signals travel alongside intense classical signals on the same fiber, where the former can be masked by the background noise induced by the latter. Here, we investigate how optimal wavelength assignment can mitigate this problem. We consider different DWDM structures and various sources of crosstalk and propose several near-optimal wavelength assignment methods that maximize the total secret key rate of the QKD channels. Our numerical results show that the optimum wavelength assignment pattern is commonly consisted of several interspersed quantum and classical bands. Using our proposed techniques, the total secret key rate of quantum channels can substantially be improved, as compared to conventional assignment methods, in the noise dominated regimes. Alternatively, we can maximize the number of QKD users supported under certain key rate constraints

Quantum and classical communications on shared infrastructure

Future communications networks not only should enable massive exchange of classical bits, but also the transmission of quantum bits on which many quantum applications rely. This will be the key to offering quantum technologies in a cost-efficient way, and it should encompass the integration of quantum and classical networks at the core of existing optical communications networks, as well as at the access end of such networks. In this work, we cover a range of proposals that enable such an integration for one of the imminent applications of quantum technologies, i.e., quantum key distribution (QKD), by which users can securely exchange a secret key for their cryptographic needs. This will include using wavelength division multiplexing techniques to send quantum and classical data on the same fiber as well as wireless access for QKD users to passive optical networks. In each case, we explore optimal arrangements to find the best way forward for an amicable coexistence

Architectural Considerations in Hybrid Quantum-Classical Networks

Three network architectures, compatible with passive optical networks, for future hybrid quantum-classical networks are proposed and compared. These setups rely on three different schemes for quantum key distribution (QKD): BB84, entanglement-based QKD, and measurement-device-independent QKD (MDI-QKD). It turns out that, while for small-to-moderatesize networks BB84 supports the highest secret key generation rate, it may fail to support large numbers of users. Its cost implications are also expected to be higher than other setups. For large networks, MDI-QKD offers the highest key rate if fast single-photon detectors are employed. Entanglement-based networks offer the longest security distance among the three setups. MDI-QKD is, however, the only architecture resilient to detection loopholes and possibly the most favorable with its less demanding end-user technology. Entanglement-based and MDI-QKD setups can both be combined with quantum repeater systems to allow for long-distance QKD with no trust constraints on the service provider

Modeling and Minimizing Spontaneous Raman Scattering for QKD Secured DWDM Networks

Quantum key distribution (QKD) provides\ua0information-theoretic security based on quantum mechanics. Integrating QKD with classical data traffic by using wavelength division multiplexing (WDM) techniques in a single fibre is a cost-efficient way to improve security in legacy infrastructure. In such a system, the main noise source to the quantum channel is spontaneous Raman scattering (SRS) caused by the classical channels. In this letter we introduce a channel allocation strategy for both quantum and classical signals to minimize the SRS noise. A use case that quantum and classical channels co-exist in a dense WDM system is investigated. The results show >26% increase of achievable transmission distance for the QKD system when implementing the introduced channel allocation strategy. Moreover, a network updating plan is proposed, which provides a guideline to light the new wavelengths for classical communications while minimizing the SRS noise to quantum channels