Quantum Key Distribution Optimality Is Determined for Systems Utilizing Infinite Quantum Systems

Quantum key distribution promises secure communication, but achieving peak performance demands efficient use of both quantum signals and classical data. Georgi Bebrov from the Technical University of Varna, and colleagues, now present a method for determining whether a quantum key distribution system operates at its theoretical limit.

The team introduces a new quantity, termed ‘optimality’, which represents the maximum possible efficiency a system can achieve under any conditions, and demonstrates how to attain this ideal performance through a combination of advanced quantum channels and highly compressed classical communication. This work introduces optimal versions of established protocols, including BB84 and twin-field, and establishes a benchmark for evaluating and improving future quantum communication systems. The research focuses on the total efficiency of Quantum Key Distribution (QKD) under all circumstances, considering any values of QKD parameters. Optimality is defined for the asymptotic operation of a QKD system, specifically when infinitely many quantum systems are transferred in a quantum key distribution protocol, or a QKD system is used infinitely many times. A method for attaining this optimality is considered, and the implementation of a completely efficient QKD system, combining a capacity-reaching quantum channel with a completely compressed classical channel, is presented. Optimal versions of both BB84-QKD and twin-field QKD are introduced.

Biased Bases Optimise Quantum Key Distribution Scientists have established a new approach to evaluating and improving Quantum Key Distribution (QKD) systems, introducing a metric called “optimality” to quantify performance. This optimality measures the maximum possible efficiency a QKD system can achieve when used repeatedly or with a very large number of quantum signals. The research demonstrates that achieving this peak efficiency requires both a highly effective quantum channel for transmitting information and a classical channel that is almost entirely compressed, minimizing data transfer. Surprisingly, the team found that using extremely biased choices of preparation and measurement bases, favouring one basis almost exclusively, can actually increase optimality. This challenges conventional wisdom, as it reduces the randomness typically associated with QKD. The key lies in combining this biased approach with a highly compressed classical channel, effectively removing it as a limiting factor in the communication process.

The team utilizes Huffman coding as an example of a compression algorithm, assigning shorter codes to more frequent measurement basis choices and longer codes to less frequent ones. The scientists developed optimal versions of both the BB84 and Lucamarini 2018 QKD protocols, demonstrating improved efficiency compared to standard implementations. These optimized protocols leverage the principles of extreme bias and classical channel compression. The analysis, supported by computational results, shows a clear distinction between optimal and standard BB84-QKD, confirming the potential for increased efficiency under specific conditions. This work provides a theoretical framework for understanding how to achieve optimal QKD and paves the way for maximizing the security and efficiency of future quantum communication systems.

Quantum Key Distribution Optimality Fully Characterized Scientists have developed a method to determine if a quantum key distribution (QKD) system is operating at peak efficiency, introducing a new quantity called “optimality” to measure performance. This optimality is defined for systems operating with a very large number of quantum systems or repeated uses, allowing researchers to assess the maximum possible efficiency under any conditions. The work demonstrates that achieving optimality requires a combination of highly efficient quantum channels and completely compressed classical channels.

The team introduced optimal versions of both the BB84 and twin-field QKD protocols, evaluating their performance with specific parameters. Results show a clear distinction between optimal and standard BB84-QKD, with computations demonstrating the efficiency limit for the scenario considered. To further enhance QKD efficiency, researchers proposed a classical channel compression technique called “channel squeezing. ” This process aims to minimize the amount of data transmitted over the public classical channel, effectively reducing it to almost nothing. The compression is characterized by a parameter ‘k’, representing the degree of compression, and is achieved through a process of assigning shorter codewords to more probable messages. Evaluations demonstrate that the compression coefficient approaches 100% as k increases, indicating complete compression of the classical channel.

The team rigorously proved that asymptotically, a QKD protocol can approach optimal performance when biased preparation and measurement bases are used in conjunction with this compression technique, provided an infinite number of qubits are transferred. This breakthrough delivers a pathway to maximizing the efficiency and security of future quantum communication systems.

Optimality Defines Quantum Key Distribution Limits This research introduces a new method for evaluating the performance of quantum key distribution (QKD) protocols, defined through a quantity called ‘optimality’.

The team demonstrates that optimality represents the maximum possible efficiency a QKD system can achieve under any circumstances, specifically when a large number of quantum systems are used or the system operates over an extended period. Crucially, the researchers identify that achieving optimality requires a combination of a quantum channel operating at its maximum capacity and a classical channel with complete compression. By applying this new framework, the scientists developed optimal versions of both BB84 and twin-field QKD, highlighting potential improvements in key generation efficiency. The work establishes a benchmark against which existing and future QKD systems can be measured, offering a pathway towards maximizing the secure transmission of information. The authors acknowledge that the analysis operates within an asymptotic regime, assuming a large number of quantum systems are used, and that practical implementations may encounter limitations. Future research directions could focus on exploring the feasibility of achieving the required channel compression in real-world scenarios and investigating the performance of other QKD protocols under this new optimality framework. This work provides a fundamental understanding of the limits of QKD performance and guides the development of more efficient and secure quantum communication systems. 👉 More information 🗞 On the Optimality of a Quantum Key Distribution 🧠 ArXiv: https://arxiv.org/abs/2512.10351 Tags: