Quantum Key Distribution Research Articles

A Study on Security in Mode-Pairing and Sending-or-Not-Sending Quantum Key Distribution Protocols

In recent years, quantum key distribution (QKD) protocols have undergone rapid evolution, thus significantly advancing the field of quantum communications. The exploitation of quantum properties enables quantum communication to achieve superior security, yet many traditional protocols still face challenges in terms of stability and practicality. Since 2019, two new QKD protocols have emerged: mode-pairing QKD and sending-or-not-sending TF-QKD. In this paper, through an in-depth analysis of the existing literature, a simple mathematical derivation of the quantum uncertainty relation is provided, along with a systematic summary of the process for proving the security of these two new protocols. The results demonstrate that sending-or-not-sending TF-QKD can still effectively ensure the security of information in the presence of large bit error rates, showing its potential application in quantum communication. In addition, the paper explores future research directions, including experimental validation in diverse real-world environments, performance optimization, and the development of robust error correction techniques. These studies provide a critical foundation for the practicalization of QKD and promote the further development of quantum communication technology.

A Gray Image Quantum Encryption using GNEQR Representation

In the digital era, characterized by extensive online data exchange, information security has become a priority. While traditional encryption methods have proven effective in protecting data transfers, the advent of advanced quantum computing has increased susceptibility to security breaches. Quantum encryption provides a revolutionary solution to this problem by using quantum mechanics principles to establish algorithms that are impermeable to decryption. Using these quantum properties, cryptographic protocols are developed to provide superior security, unlike traditional encryption methods. The image plays an important role in transmitting information in all areas. Therefore, quantum image encryption methods are specifically designed to counter the potential risks posed by quantum computers, which can compromise conventional encryption protocols. This ensures the preservation of data security despite advances in quantum computing technology. In addition, quantum image encryption improves data transmission efficiency by establishing secure communication channels using quantum stats, thereby reducing the need for bandwidth and improving transmission speed. This paper proposes a new method of quantum encryption based on GNEQR representation and the modification of pixel values and positions in an image. After converting the image into a quantum form, we applied an algorithm to modify the values and positions of the pixels using a succession of quantum gates. We concluded this study with a statistical analysis showing the robustness of our quantum image encryption method.

Demonstration of a three-node wavelength division multiplexed hybrid quantum-classical network through multicore fiber

This paper presents the practical development of a hybrid quantum-classical network through multiple links of four- and seven-core industrial jacketed multicore fiber. The network utilizes dense wavelength division multiplexing to propagate the C-band quantum and classical information in the same core, making full use of the unidirectional nature of quantum key distribution. Total network transmission of 1.16 Tbps is achieved with a total network secret key rate of approximately 7.4 kbps through a combination of 1 and 2 km links of multicore fiber. The deployment configurations presented are independent of the classical modulation format, and the maximal transmission rate for an operational hybrid network is found to be dependent only on classical optical power occupying the quantum channel wavelength. A model was developed to estimate the impact classical optical channels will have on coexisting quantum channels, which may allow engineers to quickly validate hybrid network designs.

Security of hybrid BB84 with heterodyne detection

Abstract Quantum key distribution (QKD) promises everlasting security based on the laws of physics. Most common protocols are grouped into two distinct categories based on the degrees of freedom used to carry information, which can be either discrete or continuous, each presenting unique advantages in either performance, feasibility for near-term implementation, and compatibility with existing telecommunications architectures. Recently, hybrid QKD protocols have been introduced to leverage advantages from both categories. In this work we provide a rigorous security proof for a protocol introduced by Qi in 2021, where information is encoded in discrete variables as in the widespread Bennett Brassard 1984 (BB84) protocol but decoded continuously via heterodyne detection. Security proofs for hybrid protocols inherit the same challenges associated with continuous-variable protocols due to unbounded dimensions. Here we successfully address these challenges by exploiting symmetry. Our approach enables truncation of the Hilbert space with precise control of the approximation errors and lead to a tight, semi-analytical expression for the asymptotic key rate under collective attacks. As concrete examples, we apply our theory to compute the key rates under passive attacks, linear loss, and Gaussian noise.

Feasibility of phase stabilization for satellite-mediated twin-field quantum key distribution

Quantum key distribution (QKD) is critical for future proofed secure communication. Satellites will be necessary to mediate QKD on a global scale. The limitations of the existing quantum memory and repeater technology mean that twin-field QKD (TF-QKD) provides the most feasible near-term solution to perform QKD with an untrusted satellite. However, the TF-QKD requires links between ground stations and satellites to be phase stable. We show that phase stabilization of the links to LEO and MEO satellites is feasible in spite of phase noise due to atmospheric turbulence, laser instability, and path length asymmetry while only incurring a quantum bit error rate (QBER) penalty of less than 1.5%. These results are also applicable to future untrusted satellite networks employing precisely synchronized quantum memories or quantum repeaters.

Continuous-variable quantum key distribution with noisy squeezed states

Abstract We address the crucial role of noisy squeezing in security and performance of
continuous-variable (CV) quantum key distribution (QKD) protocols. Squeezing has
long been recognized for its numerous advantages in CV QKD, such as enhanced
robustness against channel noise and loss, and improved secret key rates. However, the
excess noise of the squeezed states, that unavoidably originates already from optical
loss as well as other imperfections in the source, raises concerns about its potential
exploitation by an eavesdropper. For the widely adopted trust assumption on the excess
noise in the signal states, we confirm the stability of the protocol against the noisy
squeezing in both purely attenuating as well as noisy channels in the asymptotic limit,
which implies perfect parameter estimation. In the finite-size regime we show that
this stability largely holds at up to 107 data points using optimal biased homodyne
detection for key distribution and parameter estimation. Untrusted assumption on
the noisy squeezing, on the other hand, introduces additional security bounds on the
squeezing excess noise already in the asymptotic regime, which is further enforced
by the finite-size effects. Additionally, we show the critical negative role of noisy
squeezing in the case of atmospheric free-space channels, already in the trusted-noise
and asymptotic assumptions, which emphasizes the importance of squeezing purity
in the free-space quantum channels. Our results pave the way towards practical
realization of squeezed-state CV QKD protocols in both fibre and free-space channels.

A Novel 5G Fronthaul Architecture Based on Quantum Security Protection

In the digital age, 5G technology has significantly enhanced global communication capabilities, providing strong support for various industries. However, 5G falls short of achieving comprehensive intelligence within the Internet of Things (IoT), propelling the development of 6G technology. 6G is expected to further enhance network performance by integrating advanced technologies such as AI and quantum communication, while expanding application scenarios to include communication in extreme environments for comprehensive global connectivity. This paper proposes an innovative fronthaul architecture that applies Quantum Key Distribution (QKD) technology to the 5G fronthaul, leveraging its unconditionally secure key generation and distribution mechanism. In this design, costlier Alice devices are placed on the AAU side, while less expensive Bob devices are positioned on the DU side, optimizing deployment to reduce engineering costs and lower deployment barriers. The feasibility of this architecture is demonstrated by calculating the secure key rate. Comparative analysis with existing research is performed to clarify future research directions. These innovations not only enhance 5G network security but also offer new solutions for the security requirements of 6G networks, such as data security, network resilience, and algorithm transparency. Our research offers strategic value for future network security, laying the groundwork for reliable networks.

An Analysis of Temperature-Dependent Timing Jitter Factors in the Structural Design of Complementary Metal-Oxide-Semiconductor Single-Photon Avalanche Detectors

Single-Photon Avalanche Photodiodes (SPADs) are increasingly utilized in high-temperature-operated, high-performance Light Detection and Ranging (LiDAR) systems as well as in ultra-low-temperature-operated quantum science applications due to their high photon sensitivity and timing resolution. Consequently, the jitter value of SPADs at different temperatures plays a crucial role in LiDAR systems and Quantum Key Distribution (QKD) applications. However, limited studies have been conducted on this topic. In this study, we analyze the jitter characteristics of SPAD devices, focusing on the influence of device structures in two SPAD designs fabricated using the TSMC 18HV and TSMC 13HV processes. Using picosecond lasers with wavelengths ranging from ultraviolet (405 nm) to near-infrared (905 nm), we investigate the impact of different diffusion carrier types on jitter values and their temperature dependence across a range of 0 °C to 60 °C. Our results show that the jitter value of SPAD devices with low electric field regions varies significantly with temperature. This variation can be attributed to the higher temperature-dependent diffusion constant, as demonstrated by fitting the jitter diffusion tail with two diffusion time constants. In contrast, SPADs designed with modified electric field distributions exhibit smaller diffusion time constants and weaker temperature dependence, resulting in a much smaller temperature-dependent jitter value.

(OFC 2024) Comparison of Distributed and Centralized Quantum Key Management Systems for Meshed QKD Networks

(OFC 2024) Comparison of Distributed and Centralized Quantum Key Management Systems for Meshed QKD Networks

One-decoy-state quantum key distribution with advantage distillation based on planar-lightwave-circuit-integration modules

One-decoy-state quantum key distribution with advantage distillation based on planar-lightwave-circuit-integration modules

Experimental demonstration of polarization-based decoy-state BB84 quantum key distribution utilizing a single laser and single detector

Experimental demonstration of polarization-based decoy-state BB84 quantum key distribution utilizing a single laser and single detector

Experimental verification of on-chip quantum key distribution based on advantage distillation

Quantum key distribution (QKD) has been extensively studied for practical applications. Advantage distillation (AD) represents a key technique to extract highly correlated bit pairs from weakly correlated ones, improving QKD protocol performance, particularly in large-error scenarios. However, its practical implementation remains underexplored. This study integrates AD into the three-intensity decoy-state BB84 protocol and demonstrates its performance on a high-speed phase-encoding platform. The experimental system employs asymmetric Mach-Zehnder interferometers (AMZI) fabricated on a silicon dioxide optical waveguide chip for phase encoding, benefiting from its low coupling loss and minimal waveguide transmission loss. Phase-randomized weak coherent pulses, generated by a distributed feedback laser at 625 MHz, are modulated into decoy states of varying intensities. The signals are encoded via an AMZI and attenuated to single-photon levels before transmission. At the receiver, another AMZI demodulates the signals, detected by avalanche photodiodes in gated mode. Experiments conducted at 50 km and 105 km demonstrated secure key rates of 104 kbps and 59 bps, respectively. Results at shorter distances closely matched theoretical predictions, while slight deviations at 105 km were attributed to signal attenuation and noise. Despite these challenges, the 105 km results highlight the effectiveness of AD in enhancing secure key rates at large-error scenario. This study confirms the potential of AD in extending secure communication range of QKD. By leveraging the high integration and scalability of silicon dioxide photonic chips, the proposed system provides a foundation for large-scale QKD deployment, paving the way for advanced protocols and real-world quantum networks.

Time and frequency dissemination and quantum key distribution on the Niedersachsen Quantum Link – A practical approach

Time and frequency dissemination and quantum key distribution on the Niedersachsen Quantum Link – A practical approach

Simple portable quantum key distribution for science outreach

Quantum key distribution (QKD) has become an essential technology in the realm of secure communication, with applications ranging from secure data transmission to quantum networks. This paper presents a simple, compact, and cost-effective setup for undergraduate tutorial demonstrations of QKD. It relies on using weak coherent pulses, which can be readily produced using an attenuated laser. The system employs the simplified three-state BB84 protocol in free space, with states encoded using linear polarization. Polarization encoding can be done passively or actively, depending on the budget available. Time multiplexing is implemented at the receiver to reduce the number of required detectors. Only two detectors are used to implement measurements on two bases, with a total of four outcomes. The result demonstrates the practicality of the system for free-space quantum communication, and its compact and portable nature makes it particularly suitable for pedagogical demonstrations. This work paves the way for engaging undergraduate students in the field of quantum communication through hands-on laboratory projects.

Laser damage attack on continuous variable measurement-device-independent quantum key distribution: Practical security and countermeasure

Laser damage attack on continuous variable measurement-device-independent quantum key distribution: Practical security and countermeasure

Optimizing two-photon quantum scissor with imperfect detectors for continuous variable quantum key distribution

Optimizing two-photon quantum scissor with imperfect detectors for continuous variable quantum key distribution

Rate-adaptive Reconciliation for Experimental Continuous-variable Quantum Key Distribution with Discrete Modulation over a Free-space Optical Link

Rate-adaptive Reconciliation for Experimental Continuous-variable Quantum Key Distribution with Discrete Modulation over a Free-space Optical Link

Quantum Key Distribution Spectral Allocation and Performance in Coexistence With Passive Optical Network Standards

Quantum Key Distribution Spectral Allocation and Performance in Coexistence With Passive Optical Network Standards

Enhanced Lightweight Quantum Key Distribution Protocol for Improved Efficiency and Security

Enhanced Lightweight Quantum Key Distribution Protocol for Improved Efficiency and Security

Entanglement-based intercity quantum key distribution: Metrology and implementation

Entanglement-based intercity quantum key distribution: Metrology and implementation