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| Deployment strategies | Terrestrial QKD via optical fibers | Free-space QKD on ground | Free-space QKD ground-to-air | Satellite QKD (trusted relay) | Satellite QKD (untrusted relay) |
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| Attenuation | Fiber absorption | Diffraction
Turbulence
Weather
Absorption | Same as ground-based QKD plus
Misalignment
Vibration | Diffraction
Turbulence
Weather | Diffraction
Turbulence
Weather |
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| Interferences from classical channels | Spontaneous Raman scattering noise | No | No | No | No |
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| Channel loss | High, scale exponentially with fiber length | High, scale exponentially with distance | Low
Scale quadratically with distance |
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| Distance | ~100 km in fields without relay
Unlimited distance with trusted relay
MDI-QKD:
404 km in the lab [40]
200 km in fields [35]
TF-QKD:
>500 km in lab [45, 46, 48]
428 km in fields [47] | 144 km in experiments [82]
<10 km in real fields | 96 km in experiments [84] | Satellite to the ground distance over 1200 km [90]
Unlimited distance between ground stations | 1200 km between ground stations for a 500-km altitude LEO satellite
Longer for MEO/GEO |
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| Compatibility to P2MP topology | P2MP | P2MP | P2P at a time | P2P at a time | Satellite to two ground stations |
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| Line of sight | No | Yes | Yes | Yes | Simultaneous LoS with both ground stations |
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| Time window | Whole day | Only night
Need special care for daytime operation | Short window in the clear night |
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| Deployment | Low cost
Dedicated fiber or reuse existing ones | Low cost
Simple and fast installation
No fiber trenching | Expensive and slow
Synergy with satellite laser communication in space |
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| Application scenarios | Metro, access | Last few miles of access networks | Long haul |
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