Executive Summary
In a world heading towards quantum supremacy, traditional encryption methods are becoming vulnerable. Quantum Key Distribution (QKD) promises unbreakable encryption by using the principles of quantum mechanics. When combined with Multi-Core Fibre (MCF) — an optical fiber technology that contains multiple cores within a single fiber — we unlock high-capacity, scalable, and ultra-secure communication networks.
Key Learnings (2025 Edition)
| Learning | Insights |
|---|---|
 Scalability |
MCF allows parallel QKD channels, multiplying secure key rates without new physical infrastructure. |
 Deployment Feasibility |
MCF-QKD trials show >90% compatibility with existing metro & backbone optical networks. |
 Enhanced Security |
Isolating individual cores can significantly minimize crosstalk and potential quantum hacking risks. |
 Cost Efficiency |
MCF reduces fibre leasing and trenching costs by ~45% when compared to single-core quantum deployments. |
 Global Momentum |
Governments & telecoms in Japan  , China  , Europe  , and the US  are investing heavily in QKD over MCF pilots and standards. |
Global Deployment Status of QKD over MCF (as of April 2025)
| Country | Key Projects | Notes |
|---|---|---|
| Japan |
NICT (National Institute of Information and Communications Technology) — Tokyo-Osaka 300km MCF QKD trial | World’s first MCF-QKD field trial across live urban network, achieving 2.1 Gbps secure key rate. |
| China |
Beijing-Shanghai Quantum Backbone Project — Phase 2 | Testing MCF for urban dense QKD nodes; China Mobile and Huawei leading trials. |
 UK |
Quantum Communications Hub — Quantum City pilot | Partnered with BT and Toshiba Europe to implement MCF-QKD in Cambridge smart city project. |
| USA |
DARPA Quantum Network Expansion | MCF evaluated for critical infrastructure protection across Defense networks. |
| EU |
OpenQKD Project | Integrating MCF-QKD into Vienna-Paris secure link. Horizon Europe funds €15M towards scaling trials. |
Key Data Points
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Secure Key Rate Record (2025):
→ 2.1 Gbps achieved between Tokyo and Osaka over 300km using 7-core fibre (NICT, Japan). -
Projected Global Market for QKD (incl. MCF) by 2030:
→ $5.4 billion (source: MarketsandMarkets, 2025 update). -
MCF-based Quantum Networks Operational:
→ 12 major cities globally (Tokyo, Beijing, Shanghai, London, Vienna, Boston, Paris, Berlin, Hong Kong, Singapore, Seoul, San Francisco). -
Crosstalk Reduction:
→ 0.04 dB/km — record low for MCF deployed in quantum networks (Toshiba Europe 2025 report). -
Cost Savings:
→ Up to 45% reduction vs traditional single-core QKD network expansions (ITU-T QKD Task Force 2025 findings).
How Does QKD over MCF Work?
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Quantum States (photons) are encoded inside different cores of the MCF.
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Each core carries independent QKD channels.
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At the receiver end, multi-core decoders extract and verify quantum keys.
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Classical communication channels run in parallel without interference.
Advantage:
→ Multiply secure channels without the need for multiple fibers.
→ Drastically improve density, speed, and reach.
Real-World Example
Tokyo–Osaka MCF-QKD Field Trial (2024–2025)
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Fibre Used: 7-core fibre from Sumitomo Electric
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Distance: 300 km
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Key Results:
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Average secure key rate: 2.1 Gbps
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Stability: Maintained <1% QBER (Quantum Bit Error Rate) over 6 months
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Operational Success: Survived real-world urban network disturbances
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Partners: NICT Japan, NEC Corporation, Sumitomo Electric, Toshiba.
This project set the benchmark for future commercial quantum network deployments over MCF.
Policy and Standards Updates (2025)
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ITU-T released Recommendation Y.3808 for “QKD Network Over MCF Systems” (March 2025).
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ETSI launched the QKD Interoperability Framework for MCF, a collaboration between Europe and Japan.
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NIST in the USA emphasized hybrid cryptography that includes QKD-over-MCF integration for critical infrastructure.
Challenges Ahead
| Challenge | Current Progress |
|---|---|
 Inter-core crosstalk |
Advanced fibre manufacturing bringing crosstalk down to 0.04 dB/km. |
 High power classical channels interference |
Hybrid modulation and quantum-classical coexistence experiments succeeding. |
 Infrastructure retrofitting |
MCF-compatible amplifiers, switches, and splitters being commercialized (2025). |
The Future: Quantum Internet Backbone
MCF-QKD is seen as a cornerstone for developing the Quantum Internet, where quantum computers, sensors, and networks will need massive, secure, parallelized data channels.
By 2030, experts forecast that 40% of all new quantum communication links will utilize MCF infrastructure.
Final Takeaway
QKD over Multi-Core Fibre is no longer experimental — it’s the future of secure, scalable global communication.
Governments, telecoms, and enterprises must start planning now to integrate MCF-QKD systems if they want to future-proof their data infrastructure against the quantum threat.
“The countries that lead in QKD over MCF will lead the future of cybersecurity.”
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