Quantum Bit Decoding Using Optical Path Delays
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Solution Overview
Problem
The high cost and complexity of optical receiver devices, particularly single photon avalanche photodetectors, limit the adoption and scalability of Quantum Key Distribution (QKD) systems, especially when encoding multiple qubits per photon, as the number of required detectors increases exponentially with the number of qubits.
Innovation Solution
A quantum bit decoding apparatus and system that employs optical modulators and routers to introduce time delays between optical paths, allowing a single detection apparatus to determine qubit values based on time delays, reducing the need for multiple photodetectors and simplifying the decoder architecture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple single photon avalanche photodetectors are used to decode multiple qubits per photon, then the decoding accuracy and reliability are improved, but the device complexity and cost increase exponentially
Solution Approach 1:
The patent merges multiple detection functions into a single photodetector by using temporal multiplexing. Different qubit values are encoded with different time delays, allowing the single detector to distinguish between multiple qubit states through time-resolved detection rather than requiring multiple simultaneous detectors
Solution Approach 2:
The patent transitions from spatial decoding (using multiple detectors in parallel) to temporal decoding (using time delays). By introducing the time dimension as the distinguishing feature between different qubit values, the system reduces the number of spatial components (photodetectors) needed while maintaining the ability to decode multiple qubits
2Reliability
If standalone spatial decoders are used for each qubit, then the decoding reliability is maintained, but the system cost and scalability are compromised
Solution Approach 1:
The single photodetector is designed to perform multiple detection functions simultaneously by resolving signals in the time domain. The same detector handles multiple qubit values that have been encoded with different time delays, making the detector universal rather than specialized for a single qubit state
Solution Approach 2:
The patent changes the distinguishing parameter from spatial position (which requires multiple detectors) to time delay (which can be handled by a single detector with time resolution). By modifying the temporal parameter of the photon encoding, the system achieves multi-qubit decoding with reduced hardware
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the complexity and cost of qubit decoding, enabling a lower-cost, scalable solution for decoding multiple qubits by replacing standalone spatial decoders with temporal decoders, significantly reducing the number of optical receivers required.
Implementation Method 1
The second optical path has a different optical path length to the first optical path to introduce a time delay between the first and second optical paths
Implementation Method 2
The detection apparatus is configured to detect a photon received from the optical combiner. The detection apparatus is operable to determine whether a detected photon is delayed relative to a reference time and to determine the qubit according to the determined time delay
Data Source
Figure 1(a)~1(b)
Figure 2~3
Figure 4~5
AI summary
Quantum bit decoding apparatus (200), configured to receive a photon having a qubit encoded in a property of the photon, comprising demodulation apparatus (210). The demodulation apparatus (210) comprises an optical modulator (212) configurable to randomly apply one of a plurality of modulation values for decoding the qubit to the property of the photon and an optical router (214, 414) to route the photon according to the qubit. The quantum bit decoding apparatus (200) also comprises optical delay apparatus (220) having an optical combiner (222), a first optical path (224), from the optical router to the optical combiner and a second optical path (226), from the optical router to the optical combiner. The second optical path (226) has a different optical path length to the first optical path to introduce a time delay between the paths. The quantum bit decoding apparatus (200) further comprises detection apparatus (230) configured to detect a photon and operable to determine whether a detected photon is delayed relative to a reference time and to determine the qubit according to the determined time delay.