Time-bin encoded quantum key distribution over 120 km with a telecom quantum dot source (2506.15520v1)

Abstract: Quantum key distribution (QKD) with deterministic single photon sources has been demonstrated over intercity fiber and free-space channels. The previous implementations relied mainly on polarization encoding schemes, which are susceptible to birefringence, polarization-mode dispersion and polarization-dependent loss in practical fiber networks. In contrast, time-bin encoding offers inherent robustness and has been widely adopted in mature QKD systems using weak coherent laser pulses. However, its feasibility in conjunction with a deterministic single-photon source has not yet been experimentally demonstrated. In this work, we construct a time-bin encoded QKD system employing a high-brightness quantum dot (QD) single-photon source operating at telecom wavelength. Our proof-of-concept experiment successfully demonstrates the possibility of secure key distribution over fiber link of 120 km, while maintaining extraordinary long-term stability over 6 hours of continuous operation. This work provides the first experimental validation of integrating a quantum dot single-photon source with time-bin encoding in a telecom-band QKD system. In addition, it demonstrates the highest secure key rate among the time-bin QKDs based on single-photon sources. This development signifies a substantial advancement in the establishment of a robust and scalable QKD network based on solid-state single-photon technology

• The paper introduces a time-bin encoded QKD system that uses deterministic telecom quantum dots to overcome polarization vulnerabilities in fiber networks.
• The paper achieved long-distance secure key distribution over 120 km with a stable secure key rate of 2×10⁻⁷ per pulse over six hours.
• The paper employs a Sagnac interferometer with active phase stabilization to maintain a low QBER, highlighting a practical path for scalable quantum networks.

Analysis of Time-Bin Encoded Quantum Key Distribution with a Telecom Quantum Dot Source

The paper presents a significant advancement in the domain of Quantum Key Distribution (QKD) via the experimental realization of a time-bin encoded QKD system which utilizes deterministic single-photon sources. Traditional QKD implementations have predominantly relied on polarization encoding, which is vulnerable to polarization mode dispersion and birefringence, inherent issues in practical fiber networks. Time-bin encoding, however, offers inherent robustness against these challenges, establishing a more stable channel for QKD systems. This paper provides the first experimental validation of integrating high-brightness quantum dot (QD) single-photon sources with time-bin encoding in a telecom-band QKD system.

Key Experimental Achievements

• The system was demonstrated over a 120 km optical fiber, maintaining consistent performance with a secure key rate per pulse of $2 \times 10^{-7}$ over six hours. This reflects an encouraging level of long-term operational stability, a crucial factor for practical deployment.
• The time-bin encoded system achieved the highest secure key rate amongst similar QKD systems based on single-photon sources, underlining the potential advantages of using deterministic quantum dot sources for secure communication over extensive networks.
• The paper presented significant experimental findings, including a lower quantum bit error rate (QBER) sustained over a long fiber channel, achieved through strategic use of a Sagnac interferometer configuration, alongside active feedback control for phase stabilization.

Theoretical and Practical Implications

From a theoretical standpoint, integrating deterministic QD-based sources in QKD systems pushes the boundaries of what can be achieved with solid-state quantum emitters. The feasibility of combining quantum dot technologies with time-bin encoded photons suggests a pathway towards more resilient and scalable quantum communication networks. This has implications for the development of robust, long-distance secure communication that can handle quantum features and imperfections in real-world implementations.

Practically, this research reduces system complexity while highlighting the robustness of time-bin encoding, leveraging inherent temporal stability without requiring polarization control. Furthermore, it prescribes a methodology for future QKD systems to sustain low QBERs through symmetric use of phase modulation. It outlines how to balance mean photon number and error rates to optimize secure key generation over realistic transmission distances.

Speculation on Future AI Developments

Looking ahead, a combination of AI and QKD could play a transformative role in optimizing key distribution protocols, analyzing quantum signals, and predicting environmental impacts on QD systems. AI could be instrumental in dynamically stabilizing quantum channels and improving the adaptive modulation schemes necessary for maintaining stable communication links amid variable conditions.

In conclusion, the presented work successfully demonstrates the practical implementation and advantages of using time-bin encoded QKD with deterministic quantum dots as a promising alternative to conventional systems. Its comprehensive experimentation offers a blueprint for future research aiming to utilize QD-based technologies within scalable quantum communication infrastructures. By ensuring secure key distribution over considerable distances with minimal errors, this paper contributes substantially towards making quantum communication networks an operational reality.