Epsilon Security Optimisation Advances Quantum Key Distribution Performance and Key Rates

Quantum key distribution promises unconditionally secure communication, but realising its full potential requires careful optimisation of security parameters. Alexander G. Mountogiannakis and Stefano Pirandola, both from the University of York, investigate how to maximise the achievable secure key rate within established security bounds. Their work focuses on optimising ‘epsilon’ parameters, which define acceptable levels of risk in two prominent quantum key distribution protocols, one utilising continuous variables and the other the well-known BB84 protocol. The team employs a continuous genetic algorithm to fine-tune these parameters, revealing significant improvements in key rates, particularly at high security levels where communication typically becomes impossible, and opening up entirely new possibilities for secure communication.

Optimizing QKD Security Parameters with Genetic Algorithms

The study pioneers a novel approach to quantum key distribution (QKD) by optimizing epsilon-security parameters to maximize achievable key rates, particularly at high security levels where performance typically diminishes. Researchers employed a continuous genetic algorithm (CGA) to fine-tune epsilon parameters within both the homodyne protocol, a continuous-variable (CV) QKD system, and the BB84 protocol, a discrete-variable (DV) QKD system. This optimization directly addresses fundamental rate limitations in QKD and seeks to unlock previously inaccessible positive-rate regimes. The methodology centers on a detailed analysis of composable security, a framework ensuring security even when protocols are combined or integrated into larger applications., The team decomposed the overall epsilon security into its constituent parameters, each representing a potential imperfection within the protocol.

For CV-QKD, the total epsilon security was defined as a function of parameter estimation errors, a correctness parameter, and a combined smoothing and hashing error. The BB84 protocol’s epsilon security was similarly defined. This precise decomposition enabled targeted optimization using the CGA. To determine the composable key rate, the study began with the asymptotic key rate, representing the theoretical maximum achievable rate with infinite data transmission. Researchers then incorporated finite-size limitations and parameter estimation errors, modifying the rate calculation to account for the estimated transmissivity and excess noise of the quantum channel.,.

Optimized Key Rates for Secure QKD Systems

Scientists have achieved substantial improvements in secure key generation rates for quantum key distribution (QKD) through optimization of security parameters, demonstrating a breakthrough in practical QKD system performance. The research focused on enhancing the achievable key rate while maintaining a fixed level of overall security, employing a continuous genetic algorithm (CGA) to fine-tune epsilon-security components within both continuous-variable (CV) and discrete-variable (DV) protocols, specifically the homodyne protocol and the BB84 protocol. Results demonstrate significant key rate improvements at high security levels, where key rates typically diminish to zero, and reveal positive-rate regimes previously inaccessible without optimization., For CV-QKD, the total epsilon security is calculated as 3εPE + εcor + εsec, while for single-photon BB84, it is defined as εPE + εcor + εsec. Experiments revealed that by optimizing these epsilon parameters, the team unlocked higher key rates, particularly in scenarios demanding stringent security. The analysis considers factors such as parameter estimation error, correctness, smoothing error, and hashing error, all contributing to the overall epsilon security. Specifically, the research shows that the composable key rate for CV-QKD is influenced by the channel transmissivity and excess noise, while the BB84 protocol’s rate is affected by the efficiency of single-photon detection.,.

Genetic Optimisation Boosts Quantum Key Rates

Researchers have demonstrated a significant advancement in quantum key distribution (QKD) by employing a continuous genetic algorithm (CGA) to optimise security parameters within both continuous-variable and discrete-variable protocols. This work addresses a critical challenge in QKD, namely maximising the secure key rate, particularly at high security levels where key rates typically diminish. By systematically exploring the parameter space, the team identified configurations that substantially improve key rates, even achieving positive rates in regimes previously inaccessible with standard or randomised parameter choices., The optimisation process focuses on epsilon-security parameters related to parameter estimation error, correctness, and secrecy, adjusting them to maximise the secret key rate. Results indicate that optimised values for parameter estimation and secrecy tend to be nearly identical, while the parameter relating to correctness remains notably smaller.

This approach unlocks improved performance, especially at lower security levels, where the gains are most pronounced, and demonstrates the potential to overcome limitations inherent in conventional QKD implementations. Future work could investigate extending this optimisation technique to more complex QKD scenarios, including those involving quantum repeaters or more realistic device imperfections. This research provides a valuable tool for enhancing the practical implementation of QKD systems and strengthening the security of quantum communication networks.