QKD Service Channel Clock Embedding for Continuous Synchronization
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Solution Overview
Problem
Existing Quantum Key Distribution (QKD) systems require a dedicated synchronization channel, which increases costs and can lead to synchronization loss due to external parameter fluctuations, necessitating continuous reinitialization and reducing the secret key rate.
Innovation Solution
The method involves transmitting clock signals through the service channel, embedding them within information data signals, and using clock data recovery techniques to continuously synchronize the quantum communication channel without a dedicated synchronization channel, allowing for phase alignment and tracking of phase misalignments using an over-sampling method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated synchronization channel is used, then synchronization reliability is improved, but device complexity and implementation costs increase
Solution Approach 1:
The patent combines the synchronization function with the existing service channel by embedding clock signals within information data signals. This merging eliminates the need for a dedicated synchronization channel, reducing device complexity and implementation costs while maintaining synchronization functionality through the shared service channel infrastructure.
Solution Approach 2:
The service channel is designed to perform multiple functions: transmitting both information data and synchronization clock signals simultaneously. This multi-functionality allows the single service channel to replace what would traditionally require separate dedicated channels, reducing overall system complexity while maintaining reliable synchronization through the versatile service channel.
2Stability of the object's composition
If a dedicated synchronization channel is used, then synchronization stability is improved, but loss of time due to reinitialization increases
Solution Approach 1:
By embedding clock signals within the continuous information data stream on the service channel, the synchronization function operates continuously without interruption. This eliminates the periodic reinitialization required when using dedicated synchronization channels that may experience parameter fluctuations, thereby reducing time loss while maintaining synchronization stability through uninterrupted clock signal transmission.
3Device complexity
If clock signals are transmitted through the service channel, then device complexity is reduced, but measurement precision of phase alignment may worsen
Solution Approach 1:
The patent introduces an intermediary process of extracting clock signals from the embedded information data signals using clock data recovery techniques. This intermediary step allows the system to maintain low device complexity by using the service channel while achieving precise phase alignment through the specialized extraction and recovery processes that separate the synchronization function from the data transmission function.
4Quantity of substance
If clock signals are embedded within information data signals, then the number of channels is reduced, but difficulty of detecting and measuring clock signals increases
Solution Approach 1:
The patent replaces the mechanical/apparatus-based approach of separate physical channels with an information-processing approach where clock signals are embedded within and extracted from data signals using clock data recovery techniques. This substitution reduces the number of physical channels while managing the detection difficulty through specialized signal processing methods that automatically recover the embedded clock signals from the data stream.
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AI summary
System and methods for synchronizing and aligning Alice and Bob quantum channel for Quantum Key Distribution. The primary object of the invention is to allow a Quantum Key Distribution (QKD) apparatus to work continuously with only two communication channels, a quantum communication channel and a service channel. This is achieved by linking the clock frequencies of both channels and completed by an over-sampling method for phase synchronization tracking. Clock signal carry is done through data thanks to a clock data recovery encoding algorithm. Having a continuous operating QKD system is not possible without a tracking system that enables phase alignment. This synchronization and alignment system and method for QKD has multiple benefits as it allows real-time synchronization with continuous data flow and is not dedicated to a specific quantum protocol A data link usually used as the classical channel needed by QKD is used as a mean for clock carry allowing keeping same frequency on both sides at the emitter and receiver. The system and method disclosed enable QKD frequency synchronization and phase alignment with only two channels, whereas a dedicated channel for clock transmission and synchronization is usually needed. Additionally a tracking system based on over-sampling of the quantum link allowing maintaining the phase between sender and receiver thus allowing running continuously after calibration, without any need for resynchronization