Feasibility of entanglement-based QKD protocols with SPDC and quantum-dot sources

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Experimental Physics

Background:

• Entanglement-based quantum key distribution (QKD) protocols are crucial for secure communication.
• Device-independent QKD (DI-QKD) and entanglement-based BB84 (EPR-BB84) offer enhanced security.
• Spontaneous parametric down-conversion (SPDC) and quantum-dot (QD) sources are leading candidates for entanglement generation.

Purpose of the Study:

• To theoretically analyze the feasibility of DI-QKD and EPR-BB84 using SPDC and QD sources.
• To evaluate the performance of these protocols under realistic experimental conditions, including detector imperfections.
• To compare the effectiveness of QD and SPDC sources for practical QKD implementation.

Main Methods:

• A unified photodetection-theory framework was employed.
• Key performance indicators analyzed include the Bell parameter, quantum bit error rate (QBER), and asymptotic Devetak-Winter secret key rate.
• Consideration was given to multiphoton emission in SPDC, fine-structure splitting (FSS) in QDs, and imperfect detection (finite efficiency, dark counts).

Main Results:

• Quantum-dot (QD) sources demonstrate sufficient Bell violation and positive secret key rates, even with the detrimental effect of fine-structure splitting (FSS).
• Spontaneous parametric down-conversion (SPDC) sources, under standard CHSH-based DI-QKD framework and detection strategies, do not yield a positive secret key rate.
• Loophole-free Bell tests are feasible with SPDC sources, but they do not translate to secure key generation in this context.

Conclusions:

• Semiconductor quantum-dot (QD) sources are a viable option for practical entanglement-based QKD, offering positive secret key rates under realistic conditions.
• Standard spontaneous parametric down-conversion (SPDC) sources face limitations in achieving secure key distribution for DI-QKD protocols, despite enabling Bell tests.
• The findings highlight the importance of source characteristics and detection strategies for the successful implementation of entanglement-based QKD systems.