Quantum Key Distribution Timing with Subframe Sync Signals
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Solution Overview
Problem
Existing quantum key distribution systems face challenges in accurately detecting data patterns with long lengths due to device jitter and errors in time measurement, leading to reduced key rates and increased uncertainty in bit detection.
Innovation Solution
A quantum key distribution system that divides frames into subframes, using subframe identification signals to measure elapsed times from these signals to photon detection, enabling precise detection of photons and generating secure keys even with long data patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the clock frequency is increased to increase the key rate, then the productivity is improved, but the measurement precision deteriorates due to inter-symbol interference from device jitter
Solution Approach 1:
The patent divides a frame into multiple subframes and introduces subframe identification signals. This segmentation allows the time measurement to be performed relative to the nearest subframe boundary rather than the frame boundary, effectively reducing the measurement interval and minimizing the impact of device jitter on measurement precision while maintaining high clock frequencies for improved key rate.
2Reliability
If the data pattern length is increased to generate secure keys, then the reliability is improved, but the measurement precision deteriorates due to accumulated error from the synchronization signal
Solution Approach 1:
By dividing the long data pattern into multiple subframes with intermediate identification signals, the patent reduces the maximum time distance between any detected photon and its reference signal. This segmentation prevents error accumulation over long distances while maintaining the required data pattern length for secure key generation.
Solution Approach 2:
The subframe identification signals act as intermediary reference points between the frame synchronization signal and the actual data photons. These intermediaries provide fresh reference points for time measurement, reducing the accumulated error that would otherwise occur over long distances from the frame synchronization signal.
3Reliability
If the measurement time is extended to cover the entire data pattern length, then the reliability is improved, but the device complexity increases due to the voltage value limitation of the ramp signal in TC-SPC
Solution Approach 1:
The patent divides the measurement period into multiple subframes, each with its own identification signal. This allows the use of shorter ramp signals for each subframe measurement rather than requiring a single long ramp signal, thereby reducing the voltage value requirements and simplifying the measurement system while ensuring complete coverage of the data pattern.
Data Source
AI summary
A transmission device (1) includes a modulation unit (14) that modulates photons with a predetermined data pattern, a synchronization signal generation unit (12) that generates a frame synchronization signal of a random number data pattern, an identification signal generation unit (13) that divides the frame into a plurality of subframes and generate a subframe identification signal indicating a subframe, and a transmission unit (17) that transmits the photons modulated by the modulation unit (14), the frame synchronization signal, and the subframe identification signal. A reception device (2) includes a reception unit (30) that receives the photons, the frame synchronization signal, and the subframe identification signal transmitted from the transmission unit (17), a decoding unit (21) that detects and decodes a data pattern from the photons, a time measurement unit (26) that measures an elapsed time from the subframe identification signal until a photon is detected in each subframe, and a detection time calculation unit (27) that calculates a photon detection time from the frame synchronization signal to photon detection in one frame, based on the elapsed time.