We discuss achievable limits for high-speed quantum key distribution (QKD) over optical fibers serving as an optical quantum channel and the ways to achieve high rates in secure QKD over non-regenerative optical fiber links. The multicarrier transmission is a viable option to increase the secure rate and it can be combined by the employment of the orbital angular momentum of the photons in order to further increase the total secure rate. Our numerical results indicate that it is possible to achieve QKD transmission rate that exceeds 100 Mb/s over non-regenerative optical fiber links, which could scale above 50 km of deployed fibers. The higher speed QKD with enhanced security could be achieved in a similar manner by employing the total angular momentum and a modified BB84 protocol.
We discuss achievable limits for high-speed quantum key distribution (QKD) over optical fibers serving as an optical quantum channel and the ways to achieve high rates in secure QKD over non-regenerative optical fiber links. The multicarrier transmission is a viable option to increase the secure rate and it can be combined by the employment of the orbital angular momentum of the photons in order to further increase the total secure rate. Our numerical results indicate that it is possible to achieve QKD transmission rate that exceeds 100 Mb/s over non-regenerative optical fiber links, which could scale above 50 km of deployed fibers. The higher speed QKD with enhanced security could be achieved in a similar manner by employing the total angular momentum and a modified BB84 protocol.
It has been widely recognized that the underlying principles of quantum mechanics could be used to enable secure communications, without any additional conventional cryptographic systems, while utilizing the properties of the photons. Considerable research efforts have been invested to develop an efficient quantum key distribution (QKD) scheme over either free-space optical or fiber-optics channels. Most of these research efforts have been focused on a two-dimensional QKD, commonly realized by the use of the polarization state of photons. However, the data rates for the quantum key exchange in two-dimensional QKD are still low, while transmission distance is limited. On the other hand, it is well known that photons can carry both the spin angular momentum (SAM) and the orbital angular momentum (OAM), associated with the polarization and azimuthal phase of the complex electric field, respectively. Accordingly, we can define the combined-OAM-SAM state of a photon as |l, σ〉, where l and σ correspond to OAM and SAM indexes, respectively. Since the OAM eigenstates are orthogonal, an arbitrary number of bits per single photon can be transmitted, which could considerably increase the total secure bit rate. To improve secure data rates, we propose two types of protocols, namely, nonentangled-based (such as weak coherent state) and entanglement-assisted protocols, both employing the photon combined-OAM-SAM state, which can be used for secure key distribution over free-space optical and few-mode fiber channels. Two types of entanglement-assisted protocols are described, namely, two-basis and (D + 1)-basis protocols ( D is dimensionality of corresponding Hilbert space). We further describe how to implement the qudit gates required for implementation of these protocols. Finally, we discuss the security issues of the proposed protocols and determine both infinite and finite secret key fraction rates.
Quantum key distribution (QKD) uniquely allows the distribution of cryptographic keys with security verified by quantum mechanical limits.Both protocol execution and subsequent applications require the assistance of classical data communication channels.While using separate fibers is one option, it is economically more viable if data and quantum signals are simultaneously transmitted through a single fiber.However, noise-photon contamination arising from the intense data signal has severely restricted both the QKD distances and secure key rates.Here, we exploit a novel temporal-filtering effect for noisephoton rejection.This allows high-bit-rate QKD over fibers up to 90 km in length and populated with error-free bidirectional Gb=s data communications.With a high-bit rate and range sufficient for important information infrastructures, such as smart cities and 10-Gbit Ethernet, QKD is a significant step closer toward wide-scale deployment in fiber networks.
Abstract Entanglement-based quantum key distribution (QKD) is an essential ingredient in quantum communication, owing to the property of source-independent security and the potential on constructing large-scale quantum communication networks. However, implementation of entanglement-based QKD over long-distance optical fiber links is still challenging, especially over deployed fibers. In this work, we report an experimental QKD using energy-time entangled photon pairs that transmit over optical fibers of 242 km (including a section of 19 km deployed fibers). The QKD is realized through the protocol of dispersive-optics QKD (DO-QKD) with high-dimensional encoding to utilize coincidence counts more efficiently. A reliable, high-accuracy time synchronization technology for long-distance entanglement-based QKD is developed based on the distribution of optical pulses in quantum channels. Our system operates continuously for more than 7 d without active polarization or phase calibration. We ultimately generate secure keys with secure key rates of 0.22 bps and 0.06 bps in the asymptotic and finite-size regimes, respectively. It shows that entanglement-based DO-QKD is reliable for long-distance realization in the field if its high requirement on time synchronization is satisfied.
Background: Quantum Key Distribution (QKD( is a promising technology for secure communication, leveraging the principles of quantum mechanics to provide theoretically unbreakable encryption. With the exponential growth in data traffic and the increasing need for secure communication in backbone fiber networks, integrating high-bit-rate multiplexing techniques into QKD systems can enhance their efficiency and scalability. Problem: Traditional QKD systems face limitations in terms of data rate and network scalability, particularly in high-capacity optical communication networks. As data demands increase, there is a critical need for methods that can support high-bit-rate multiplexing while maintaining the security and performance of QKD. Method: This study proposes a novel QKD approach using high-bit-rate multiplexing in backbone fiber networks. The method involves encoding quantum keys using multiple optical channels simultaneously to increase the data throughput of the QKD system. We employ a combination of time-division multiplexing (TDM( and wavelength-division multiplexing (WDM( to optimize the use of fiber resources and enhance key distribution rates. Results: Simulation results demonstrate that the proposed method achieves a key distribution rate of 10 Mbps over a 200 km fiber link with a quantum bit error rate (QBER( of 1.5%. This represents a 50% improvement in key rate compared to conventional QKD systems without multiplexing. Additionally, the method shows enhanced scalability and network utilization, supporting up to 16 multiplexed channels with minimal impact on security.
Quantum communication (QC) concerns the faithful transmission of quantum states between separated parties, and represents a key enabler for many quantum applications, ranging from quantum key distribution (QKD) to distributed quantum computing. However, low information rates and short propagation distances, due to high channel losses and perturbations of the quantum states, limit the development of this field and its practical applications. High-dimensional (Hi-D) quantum communication can address these challenges by adding more information per photon, directly enhancing the information rate and the system's error tolerance. We transmit Hi-D quantum states using photons prepared in four orbital angular momentum (OAM) modes in a 1.2 km long OAM-carrying fiber. This is the first experimental demonstration of Hi-D quantum states transmission using the OAM basis over an optical fiber. Furthermore, we successfully implement a real-time decoy-state Hi-D QKD protocol, and demonstrate the highest secret key rate and longest transmission distance of OAM-QKD presented to date.
The method and the scheme of multichannel quantum system of secure communication for transfer of confidential data on optical fiber are developed. The considered scheme combines quantum key distribution with quantum secure data transmission. Such approach does not give possibility to the eavesdropper to decipher that part of information, which he can receive before the detection. The suggested scheme provides higher security level of transferred confidential information, than known, which use traditional pro-tocols of symmetric enciphering in a combination to quantum key distribution. It is found out that for the transmission protected in such a way on optical fiber the choice of wavelengths of 850 and 1625 nanometers is optimum. It is found out that when using in such systems of the avalanche photo diode FD-115L it is possible to provide a speed of information transfer up to 0,8 Mbps in one channel. For increase in speed of transfer, it is proposed to use two and more channels of transfer.