Active Sagnac Loop for Polarization Entangled Photon Pairs
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Solution Overview
Problem
Existing Quantum Key Distribution (QKD) systems based on entangled photon pairs lack flexibility and control over the state of generated photon pairs, limiting their ability to generate keys securely and efficiently, as they can only produce entangled photon pairs in a single fixed state.
Innovation Solution
A source system comprising a laser, circulator, fiber-based Sagnac loop, and wavelength division multiplexing (WDM) means, with control mechanisms to adjust the state of polarization entangled photon pairs, allowing generation of photon pairs in multiple states and enabling secure key generation by controlling the state of each pair.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a Sagnac loop configuration with free space or fiber components is used to generate polarization entangled photon pairs, then the source can generate entangled photon pairs, but the state of the generated photon pairs is fixed and cannot be adjusted after generation
Solution Approach 1:
The patent applies the dynamics principle by making the source state adjustable and changeable during operation. The source can switch between different states (e.g., horizontal and vertical polarization states) dynamically, allowing adaptation to different QKD protocols and security requirements without requiring a completely different source design for each state.
Solution Approach 2:
The patent implements parameter changes by enabling adjustment of the source state through controllable elements in the Sagnac loop. The state of the generated photon pairs can be changed by modifying parameters such as polarization orientation, allowing the same physical source to operate in different states as needed.
2Adaptability or versatility
If the source state is adjusted before photon pair generation, then the source can be optimized for a specific state, but the source loses flexibility to generate photon pairs in multiple states
Solution Approach 1:
The source is designed to be dynamically adjustable, allowing it to switch between different states during operation. This dynamic capability enables the source to generate photon pairs in multiple states (e.g., different polarization orientations) while maintaining stability in each individual state through controlled adjustment mechanisms.
3Reliability
If known QKD systems use a separate untrusted source for entangled photon pairs, then the source can be optimized for photon pair generation, but the receivers cannot control or verify the source state
Solution Approach 1:
The patent incorporates feedback mechanisms that allow the receivers to verify and control the source state. The system includes means for the receivers to obtain information about the source state and provide feedback to ensure proper state generation, enabling both security verification and operational control.
Solution Approach 2:
The source is designed with multi-functionality to serve both as a photon pair generation device and as a controllable element for the receivers. The same source that generates the entangled photon pairs also provides controllable state adjustment capabilities that the receivers can utilize for verification and key generation.
4Productivity
If the source generates entangled photon pairs in a single fixed state, then the system is simple to implement, but the key generation efficiency and security are limited
Solution Approach 1:
The source incorporates dynamic state adjustment capabilities that allow it to switch between different states during operation. This enables the source to generate photon pairs in multiple states, increasing key generation efficiency and security by providing more measurement bases for QKD protocols without requiring multiple separate sources.
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 solution provides a flexible and secure method for generating polarization entangled photon pairs, allowing for the generation of keys in various states, enhancing the security and efficiency of QKD by enabling precise control over the entangled photon pairs, thus meeting the needs of both economic and security requirements.
Implementation Method 1
a Second-Harmonic-Generation (SHG) means, and a down conversion (DC) means, whereby the Second-Harmonic-Generation (SHG) means is pumped by the laser beam and generated pump photons
Implementation Method 2
the down conversion (DC) means is pumped by the pump photons and generates photon pairs
Implementation Method 3
the polarizing beam splitter (PBS), the polarization maintaining fiber, the Second-Harmonic-Generation (SHG) means, and the down conversion (DC) means are arranged in a Sagnac configuration
Implementation Method 4
the polarizing beam splitter (PBS), the polarization maintaining fiber, the Second-Harmonic-Generation (SHG) means, and the down conversion (DC) means are arranged in a Sagnac configuration
Data Source
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AI summary
It is claimed a source of polarization entangled photon pairs for Quantum Key Distribution (QKD), comprising a laser, a circulator, a fiber based Sagnac loop and a wavelength division multiplexing (WDM) means, whereby the fiber based Sagnac loop comprises a polarizing beam splitter (PBS) and a polarization maintaining fiber, a Second-Harmonic-Generation (SHG) means, and a down conversion (DC) means, and whereby the polarizing beam splitter (PBS), the polarization maintaining fiber, the Second-Harmonic-Generation (SHG) means, and the down conversion (DC) means are arranged in a Sagnac configuration in order to generate polarization entangled photon pairs, and whereby the wavelength division multiplexing (WDM) means comprises two or more WDM-output ports. According to the intention the source comprises a first control means arranged in the fiber based Sagnac loop and a second control means arranged behind one or more WDM-output ports, and the first and/or second control means control the state of the polarization entangled photon pairs.