Quantum Cryptography Moves Closer with Working BB84 and E91 Protocols

Researchers are increasingly focused on bolstering network communication security against evolving computational threats, and Quantum Key Distribution (QKD) offers a promising solution for establishing secure shared secrets. Abel C. H. Chen from Chunghwa Telecom Laboratories, along with colleagues, investigates the practical implementation of two prominent QKD protocols, BB84 and E91, in a real computing environment. Their work details the use of SX gate operations to create uniform superposition states, demonstrating how these principles of quantum mechanics can facilitate secure key exchange and prevent eavesdropping. This study is significant because it moves beyond theoretical models to evaluate the feasibility of QKD on actual hardware, assessing critical metrics such as entropy, IID characteristics, and error rates to provide valuable insights into real-world deployment challenges. Quantum key distribution realised on IBM superconducting hardware demonstrates a promising path toward secure communication Scientists have demonstrated the successful implementation of quantum key distribution (QKD) protocols, BB84 and E91, on the IBM Quantum Platform, marking a significant step towards practical quantum-safe communication. Secure communication networks are becoming increasingly critical in the modern era, and QKD offers a theoretically unbreakable method for establishing secure connections. This work confirms that QKD is not merely a theoretical concept but can be realised using currently available quantum computing technology. The research involved leveraging the unique properties of superposition and entanglement to enable communicating parties to generate and share a secret key. This key can then be used to encrypt and decrypt messages, ensuring confidentiality. The implementation utilised Python 3.11.14 and IBM Qiskit 2.2.3, running on IBM Quantum Platform hardware with 133 qubits and a connectivity of 156, utilising 128 shots per computation. The study rigorously validated the generated keys using established methods, including NIST SP 800-90B, to ensure their randomness and suitability for cryptographic applications. Specifically, the researchers employed both Hadamard gate and SX gate-based approaches for both the BB84 and E91 protocols. Validation involved assessing entropy, utilising p-values to confirm randomness, and performing independent tests such as the NIST SP 800-90B tests for independence, goodness of fit, and longest repeated substring analysis. Results, detailed in accompanying tables, demonstrate that the SX gate-based approach consistently yielded higher entropy values and improved performance in statistical tests. Furthermore, error rate analysis revealed that the SX gate implementation achieved zero error rates for the BB84 protocol and a low error rate of 0.094 for the E91 protocol, surpassing the performance of the Hadamard gate-based implementations. These findings suggest that the proposed SX gate method offers a promising pathway for enhancing the efficiency and reliability of QKD systems. The research aligns with industry standards, such as those defined by the European Telecommunications Standards Institute (ETSI), paving the way for the integration of QKD into future communication infrastructures. Implementation of BB84 and E91 protocols using superconducting transmon qubits represents a significant step towards practical quantum key distribution The IBM Quantum Platform served as the foundation for implementing and evaluating both the BB84 and E91 quantum key distribution (QKD) protocols. This work utilized superconducting transmon qubits within the platform’s hardware to demonstrate a practical realisation of quantum-safe communication. Specifically, the study leveraged SX gate operations to generate uniform superposition states, a methodological innovation designed to enhance the fidelity of qubit preparation. These superposition states are crucial for encoding quantum information and enabling secure key exchange. Experiments began by preparing qubits in these superposition states, then manipulating them according to the BB84 and E91 protocols. The BB84 protocol employs four polarisation states, while E91 relies on entangled photon pairs, both designed to detect any eavesdropping attempts. Control signals, designated as Alice’s and Bob’s, were meticulously applied to the qubits to enact the protocols and facilitate the exchange of quantum information. Bell state measurements were then performed to verify the entanglement generated in the E91 protocol and to analyse the correlations between the qubits. Evaluation of the generated keys involved several key metrics. Entropy calculations, alongside Independent and Identically Distributed (IID) bit string tests, were performed to assess the randomness and security of the shared secrets. The study reported a p-value of 0.000005 for both BB84 and E91 protocols when assessed using the NIST SP 800-90B standard, indicating a statistically significant level of security. Furthermore, error-rate verification confirmed the feasibility of generating shared secrets with minimal errors, with the SX gate-based E91 protocol achieving an error rate of 0.094. These results demonstrate the potential of QKD to provide theoretically unbreakable communication security using currently available quantum computing resources. Implementation and verification of BB84 and E91 protocols on IBM Quantum hardware represent a significant step towards quantum key distribution Researchers successfully implemented the BB84 and E91 quantum key distribution (QKD) protocols on the IBM Quantum Platform, demonstrating a practical pathway towards secure communication. The study leveraged SX gate operations to generate uniform superposition states, enabling secure secret key generation between communicating parties. Experiments were conducted to illustrate how parties can obtain a shared secret while preventing potential interception by adversaries. Evaluation of the protocols considered metrics including entropy, Independent and Identically Distributed (IID) bit strings, and error-rate verifications, confirming the feasibility of generating shared secrets. The BB84 protocol was implemented using both Hadamard gates and SX gates with inversed SX gates, exploring different methods for qubit manipulation. In one implementation of the BB84 protocol, Alice prepared qubits with a 50% probability of being in the |0⟩ state and a 50% probability of being in the |1⟩ state. Further analysis involved the selection of identical and differing control signals between Alice and Bob during protocol execution. When both parties selected the same control signals in the BB84 protocol, the resulting states were observed and compared. The E91 protocol was also explored, utilizing Bell states for qubit transmission and employing Hadamard and SX gates for state preparation. In the E91 protocol, Alice and Bob adopted Bell states for each pair of qubits, transmitting them to each other for subsequent measurement. The study demonstrated that with the adoption of Bell states, Alice and Bob could establish a shared secret through a series of control signal exchanges and measurements. Alice and Bob each selected control signals for their respective qubits, enabling the secure exchange of information. These results highlight the potential of QKD protocols for establishing secure communication channels using current quantum computing technology. Implementation and validation of BB84 and E91 protocols on IBM Quantum hardware demonstrate feasibility for quantum key distribution Recent advances in computing have driven the development of practical applications across numerous fields, including network communication security. This work successfully implements and tests the BB84 and E91 quantum key distribution (QKD) protocols on the IBM Quantum Platform, demonstrating a viable pathway towards quantum-safe communication. The study utilises SX gate operations to generate uniform superposition states, leveraging the principles of superposition and entanglement to enable secure shared secret generation between communicating parties and prevent potential eavesdropping. Evaluation of these protocols considered metrics such as entropy and the generation of Independent and Identically Distributed (IID) bit strings, confirming the feasibility of establishing shared secrets using current quantum computing technology. This implementation marks a move beyond theoretical QKD concepts, demonstrating its potential for real-world applications. While the study confirms the feasibility of these protocols, specific quantitative values for metrics like entropy and error rates were not detailed. Future research may focus on optimising these protocols for higher key generation rates and longer transmission distances, as well as exploring integration with existing communication infrastructure. These results represent a significant step towards establishing secure communication networks resilient to emerging quantum computing threats. 👉 More information 🗞 Implementation Challenges in Quantum Key Distribution 🧠 ArXiv: https://arxiv.org/abs/2602.01500 Tags: