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Towards global quantum key distribution

Nature Reviews Electrical Engineering volume 2, pages 806–818 (2025)Cite this article

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Abstract

Quantum key distribution (QKD) is a cryptographic technology that supports the negotiation and sharing of private keys with unconditional security between authorized parties. As QKD scales to a global level, it must address performance limitations, high costs and practical security concerns. In this Review, we outline the key technical challenges, applications and prospective developments towards a global QKD network. Advances such as satellite-based QKD and newly developed protocols offer promising solutions for extending QKD over long distances. Field trials have progressively expanded from intercity links to larger-scale networks. Nevertheless, balancing cost–performance and security considerations will continue to challenge advanced research efforts. On the basis of the strategies addressing these obstacles, we highlight future directions that can support the efficient realization of global QKD infrastructures.

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Fig. 1: Schematic of quantum key distribution systems using discrete-variable and continuous-variable encoding.
Fig. 2: Fundamental limitations of quantum key distribution schemes.
Fig. 3: Advanced technologies in quantum key distribution developed to address practical challenges.
Fig. 4: Timeline of long-haul quantum key distribution developments.
Fig. 5: Main existing quantum key distribution networks worldwide.
Fig. 6: An envisioned layout for a global quantum key distribution network.

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References

  1. Devetak, I. The private classical capacity and quantum capacity of a quantum channel. IEEE Trans. Inf. Theory 51, 44–55 (2005).

    Article  MathSciNet  Google Scholar 

  2. Bennett, C. H. & Brassard, G. Quantum cryptography: public key distribution and coin tossing. Theor. Comput. Sci. 560, 7–11 (2014). Introduces the first quantum key distribution protocol, laying the foundation for modern quantum cryptography.

    Article  MathSciNet  Google Scholar 

  3. Renner, R., Gisin, N. & Kraus, B. Information-theoretic security proof for quantum-key-distribution protocols. Phys. Rev. A 72, 012332 (2005).

    Article  Google Scholar 

  4. Bernstein, D. J. & Lange, T. Post-quantum cryptography. Nature 549, 188–194 (2017).

    Article  Google Scholar 

  5. Shor, P. W. Polynomial-time algorithms for prime factorization and discrete logarithms on a quantum computer. SIAM Rev. 41, 303–332 (1999). Demonstrates that quantum algorithms efficiently solve integer factorization and discrete logarithm problems, posing a threat to the security of classical cryptosystems.

    Article  MathSciNet  Google Scholar 

  6. Mehic, M. et al. Quantum key distribution: a networking perspective. ACM Comput. Surv. 53, 1–41 (2020).

    Article  Google Scholar 

  7. Awschalom, D. D. et al. A Roadmap for Quantum Interconnects report number ANL-22/83, 179439 (US Department of Energy, 2022).

  8. Wehner, S., Elkouss, D. & Hanson, R. Quantum internet: a vision for the road ahead. Science 362, eaam9288 (2018). Presents a comprehensive vision for the quantum internet, situating quantum key distribution in the context of global quantum networks.

    Article  MathSciNet  Google Scholar 

  9. Pittaluga, M. et al. Long-distance coherent quantum communications in deployed telecom networks. Nature 640, 911–917 (2025).

    Article  Google Scholar 

  10. Li, Y. et al. Microsatellite-based real-time quantum key distribution. Nature 640, 47–54 (2025).

    Article  Google Scholar 

  11. Bennett, C. H. Quantum cryptography using any two nonorthogonal states. Phys. Rev. Lett. 68, 3121 (1992).

    Article  MathSciNet  Google Scholar 

  12. Vallone, G. et al. Free-space quantum key distribution by rotation-invariant twisted photons. Phys. Rev. Lett. 113, 060503 (2014).

    Article  Google Scholar 

  13. Inoue, K., Waks, E. & Yamamoto, Y. Differential phase shift quantum key distribution. Phys. Rev. Lett. 89, 037902 (2002).

    Article  Google Scholar 

  14. Stucki, D., Brunner, N., Gisin, N., Scarani, V. & Zbinden, H. Fast and simple one-way quantum key distribution. Appl. Phys. Lett. 87, 194108 (2005).

    Article  Google Scholar 

  15. Sasaki, T., Yamamoto, Y. & Koashi, M. Practical quantum key distribution protocol without monitoring signal disturbance. Nature 509, 475–478 (2014).

    Article  Google Scholar 

  16. Moroder, T. et al. Security of distributed-phase-reference quantum key distribution. Phys. Rev. Lett. 109, 260501 (2012).

    Article  Google Scholar 

  17. Sandfuchs, M., Haberland, M., Vilasini, V. & Wolf, R. Security of differential phase shift QKD from relativistic principles. Quantum 9, 1611 (2025).

    Article  Google Scholar 

  18. Ralph, T. C. Continuous variable quantum cryptography. Phys. Rev. A 61, 010303 (1999).

    Article  MathSciNet  Google Scholar 

  19. Weedbrook, C. et al. Quantum cryptography without switching. Phys. Rev. Lett. 93, 170504 (2004).

    Article  Google Scholar 

  20. Grosshans, F. et al. Quantum key distribution using Gaussian-modulated coherent states. Nature 421, 238–241 (2003).

    Article  Google Scholar 

  21. Hillery, M. Quantum cryptography with squeezed states. Phys. Rev. A 61, 022309 (2000).

    Article  Google Scholar 

  22. Weedbrook, C., Pirandola, S., Lloyd, S. & Ralph, T. C. Quantum cryptography approaching the classical limit. Phys. Rev. Lett. 105, 110501 (2010).

    Article  Google Scholar 

  23. Silberhorn, C., Ralph, T. C., Lütkenhaus, N. & Leuchs, G. Continuous variable quantum cryptography: beating the 3 dB loss limit. Phys. Rev. Lett. 89, 167901 (2002).

    Article  Google Scholar 

  24. Usenko, V. C. & Grosshans, F. Unidimensional continuous-variable quantum key distribution. Phys. Rev. A 92, 062337 (2015).

    Article  MathSciNet  Google Scholar 

  25. Lo, H.-K., Ma, X. & Chen, K. Decoy state quantum key distribution. Phys. Rev. Lett. 94, 230504 (2005). Introduces the decoy-state method, enabling feasible long-distance quantum key distribution.

    Article  Google Scholar 

  26. Wang, X.-B. Beating the photon-number-splitting attack in practical quantum cryptography. Phys. Rev. Lett. 94, 230503 (2005).

    Article  Google Scholar 

  27. Albota, M. A. & Wong, F. N. Efficient single-photon counting at 1.55 µm by means of frequency upconversion. Opt. Lett. 29, 1449–1451 (2004).

    Article  Google Scholar 

  28. Gol’Tsman, G. et al. Picosecond superconducting single-photon optical detector. Appl. Phys. Lett. 79, 705–707 (2001).

    Article  Google Scholar 

  29. Zhang, H. et al. Noise-reducing quantum key distribution. Rep. Prog. Phys. 88, 016001 (2025).

    Article  Google Scholar 

  30. Itzler, M. A. et al. Advances in InGaAsP-based avalanche diode single photon detectors. J. Mod. Opt. 58, 174–200 (2011).

    Article  Google Scholar 

  31. Ceccarelli, F. et al. Recent advances and future perspectives of single-photon avalanche diodes for quantum photonics applications. Adv. Quantum Technol. 4, 2000102 (2021).

    Article  Google Scholar 

  32. Zappa, F., Lotito, A., Giudice, A. C., Cova, S. & Ghioni, M. Monolithic active-quenching and active-reset circuit for single-photon avalanche detectors. IEEE J. Solid-State Circuits 38, 1298–1301 (2003).

    Article  Google Scholar 

  33. Acerbi, F., Anti, M., Tosi, A. & Zappa, F. Design criteria for InGaAs/InP single-photon avalanche diode. IEEE Photon. J. 5, 6800209 (2013).

    Article  Google Scholar 

  34. Chang, J. et al. Detecting telecom single photons with 99.5−2.07+0.5% system detection efficiency and high time resolution. APL Photon. 6, 036114 (2021).

    Article  Google Scholar 

  35. Caloz, M. et al. High-detection efficiency and low-timing jitter with amorphous superconducting nanowire single-photon detectors. Appl. Phys. Lett. 112, 061103 (2018).

    Article  Google Scholar 

  36. Hu, P. et al. Detecting single infrared photons toward optimal system detection efficiency. Opt. Express 28, 36884–36891 (2020).

    Article  Google Scholar 

  37. Chiles, J. et al. New constraints on dark photon dark matter with superconducting nanowire detectors in an optical haloscope. Phys. Rev. Lett. 128, 231802 (2022).

    Article  Google Scholar 

  38. You, L. Superconducting nanowire single-photon detectors for quantum information. Nanophotonics 9, 2673–2692 (2020).

    Article  Google Scholar 

  39. Renema, J. et al. Experimental test of theories of the detection mechanism in a nanowire superconducting single photon detector. Phys. Rev. Lett. 112, 117604 (2014).

    Article  Google Scholar 

  40. Qi, R., Zhang, H., Gao, J., Yin, L. & Long, G.-L. Loophole-free plug-and-play quantum key distribution. N. J. Phys. 23, 063058 (2021).

    Article  MathSciNet  Google Scholar 

  41. Zhang, X. et al. Polarization-encoded quantum key distribution with a room-temperature telecom single-photon emitter. Natl Sci. Rev. 12, nwaf147 (2025).

    Article  Google Scholar 

  42. Zhang, H. et al. Metropolitan quantum key distribution using a GaN-based room-temperature telecommunication single-photon source. Phys. Rev. Appl. 23, 054022 (2025).

    Article  Google Scholar 

  43. Chen, J.-P. et al. Twin-field quantum key distribution over a 511 km optical fibre linking two distant metropolitan areas. Nat. Photon. 15, 570–575 (2021).

    Article  Google Scholar 

  44. Lu, C.-Y., Cao, Y., Peng, C.-Z. & Pan, J.-W. Micius quantum experiments in space. Rev. Mod. Phys. 94, 035001 (2022).

    Article  Google Scholar 

  45. Avesani, M. et al. Full daylight quantum-key-distribution at 1550 nm enabled by integrated silicon photonics. npj Quantum Inf. 7, 93 (2021).

    Article  Google Scholar 

  46. Scriminich, A. et al. Optimal design and performance evaluation of free-space quantum key distribution systems. Quantum Sci. Technol. 7, 045029 (2022).

    Article  Google Scholar 

  47. Tian, X.-H. et al. Experimental demonstration of drone-based quantum key distribution. Phys. Rev. Lett. 133, 200801 (2024).

    Article  Google Scholar 

  48. Liao, S.-K. et al. Satellite-to-ground quantum key distribution. Nature 549, 43–47 (2017). Demonstrates the first successful satellite-to-ground quantum key distribution, paving the way for global-scale quantum network.

    Article  Google Scholar 

  49. Liao, S.-K. et al. Long-distance free-space quantum key distribution in daylight towards inter-satellite communication. Nat. Photon. 11, 509–513 (2017).

    Article  Google Scholar 

  50. Kundu, N. K., Dash, S. P., McKay, M. R. & Mallik, R. K. Channel estimation and secret key rate analysis of MIMO terahertz quantum key distribution. IEEE Trans. Commun. 70, 3350–3363 (2022).

    Article  Google Scholar 

  51. Chen, J.-P. et al. Quantum key distribution over 658 km fiber with distributed vibration sensing. Phys. Rev. Lett. 128, 180502 (2022).

    Article  Google Scholar 

  52. Zhang, H. et al. Realization of quantum secure direct communication over 100 km fiber with time-bin and phase quantum states. Light Sci. Appl. 11, 83 (2022).

    Article  Google Scholar 

  53. Takeoka, M., Guha, S. & Wilde, M. M. Fundamental rate-loss tradeoff for optical quantum key distribution. Nat. Commun. 5, 5235 (2014).

    Article  Google Scholar 

  54. Pirandola, S., Laurenza, R., Ottaviani, C. & Banchi, L. Fundamental limits of repeaterless quantum communications. Nat. Commun. 8, 15043 (2017). Defines the tight fundamental rate-loss bound for repeaterless point-to-point QKD, now a benchmark for emerging protocols.

    Article  Google Scholar 

  55. Mizutani, A. & Tsurumaru, T. Tight scaling of key rate for differential-phase-shift quantum key distribution. Phys. Rev. Res. 6, 043300 (2024).

    Article  Google Scholar 

  56. Lucamarini, M., Yuan, Z. L., Dynes, J. F. & Shields, A. J. Overcoming the rate–distance limit of quantum key distribution without quantum repeaters. Nature 557, 400–403 (2018). Proposes the twin-field quantum key distribution protocol, first to surpass the fundamental rate-loss bound, revolutionizing long-distance quantum key distribution research.

    Article  Google Scholar 

  57. Numkam Fokoua, E., Abokhamis Mousavi, S., Jasion, G. T., Richardson, D. J. & Poletti, F. Loss in hollow-core optical fibers: mechanisms, scaling rules, and limits. Adv. Opt. Photon. 15, 1–85 (2023).

    Article  Google Scholar 

  58. Takesue, H. et al. Quantum key distribution over a 40-dB channel loss using superconducting single-photon detectors. Nat. Photon. 1, 343–348 (2007).

    Article  Google Scholar 

  59. Rey-Domínguez, J., Navarrete, Á., van Loock, P. & Curty, M. Hacking coherent-one-way quantum key distribution with present-day technology. Quantum Sci. Technol. 9, 035044 (2024).

    Article  Google Scholar 

  60. González-Payo, J., Trényi, R., Wang, W. & Curty, M. Upper security bounds for coherent-one-way quantum key distribution. Phys. Rev. Lett. 125, 260510 (2020).

    Article  Google Scholar 

  61. Grünenfelder, F., Boaron, A., Rusca, D., Martin, A. & Zbinden, H. Performance and security of 5 GHz repetition rate polarization-based quantum key distribution. Appl. Phys. Lett. 117, 144003 (2020).

    Article  Google Scholar 

  62. Boaron, A. et al. Secure quantum key distribution over 421 km of optical fiber. Phys. Rev. Lett. 121, 190502 (2018).

    Article  Google Scholar 

  63. Korzh, B. et al. Demonstration of sub-3 ps temporal resolution with a superconducting nanowire single-photon detector. Nat. Photon. 14, 250–255 (2020).

    Article  Google Scholar 

  64. Bouchard, F., England, D., Bustard, P. J., Heshami, K. & Sussman, B. Quantum communication with ultrafast time-bin qubits. PRX Quantum 3, 010332 (2022).

    Article  Google Scholar 

  65. Wang, W. et al. Fully passive quantum key distribution. Phys. Rev. Lett. 130, 220801 (2023).

    Article  Google Scholar 

  66. Zapatero, V., Navarrete, Á., Tamaki, K. & Curty, M. Security of quantum key distribution with intensity correlations. Quantum 5, 602 (2021).

    Article  Google Scholar 

  67. Yuan, Z. et al. 10-Mb/s quantum key distribution. J. Light Technol. 36, 3427–3433 (2018).

    Article  Google Scholar 

  68. Zhang, W. et al. A 16-pixel interleaved superconducting nanowire single-photon detector array with a maximum count rate exceeding 1.5 GHz. IEEE Trans. Appl. Supercond. 29, 1–4 (2019).

    Article  Google Scholar 

  69. Grünenfelder, F. et al. Fast single-photon detectors and real-time key distillation enable high secret-key-rate quantum key distribution systems. Nat. Photon. 17, 422–426 (2023).

    Article  Google Scholar 

  70. Li, W. et al. High-rate quantum key distribution exceeding 110 Mb s–1. Nat. Photon. 17, 416–421 (2023).

    Article  Google Scholar 

  71. Kržič, A. et al. Towards metropolitan free-space quantum networks. npj Quantum Inf. 9, 95 (2023).

    Article  Google Scholar 

  72. Cavaliere, F., Prati, E., Poti, L., Muhammad, I. & Catuogno, T. Secure quantum communication technologies and systems: from labs to markets. Quantum Rep. 2, 80–106 (2020).

    Article  Google Scholar 

  73. Dynes, J. et al. Cambridge quantum network. npj Quantum Inf. 5, 101 (2019).

    Article  Google Scholar 

  74. Dou, T. et al. Coexistence of 11 Tbps (110 × 100 Gbps) classical optical communication and quantum key distribution based on single-mode fiber. Opt. Express 32, 28356–28369 (2024).

    Article  MathSciNet  Google Scholar 

  75. Kumar, R., Qin, H. & Alléaume, R. Coexistence of continuous variable QKD with intense DWDM classical channels. N. J. Phys. 17, 043027 (2015).

    Article  Google Scholar 

  76. Mao, Y. et al. Integrating quantum key distribution with classical communications in backbone fiber network. Opt. Express 26, 6010–6020 (2018).

    Article  Google Scholar 

  77. Wang, B.-X. et al. Long-distance transmission of quantum key distribution coexisting with classical optical communication over a weakly-coupled few-mode fiber. Opt. Express 28, 12558–12565 (2020).

    Article  Google Scholar 

  78. Simmons, J. M. Optical Network Design and Planning (Springer International Publishing, 2014).

  79. Cao, Y. et al. The evolution of quantum key distribution networks: on the road to the qinternet. IEEE Commun. Surv. Tutor. 24, 839–894 (2022).

    Article  MathSciNet  Google Scholar 

  80. Bunandar, D. et al. Metropolitan quantum key distribution with silicon photonics. Phys. Rev. X 8, 021009 (2018).

    Google Scholar 

  81. Luo, W. et al. Recent progress in quantum photonic chips for quantum communication and internet. Light Sci. Appl. 12, 175 (2023).

    Article  Google Scholar 

  82. Zhang, G.-W. et al. Polarization-insensitive interferometer based on a hybrid integrated planar light-wave circuit. Photon. Res. 9, 2176–2181 (2021).

    Article  Google Scholar 

  83. Renaud, D. et al. Sub-1 volt and high-bandwidth visible to near-infrared electro-optic modulators. Nat. Commun. 14, 1496 (2023).

    Article  Google Scholar 

  84. Paraïso, T. K. et al. A modulator-free quantum key distribution transmitter chip. npj Quantum Inf. 5, 42 (2019).

    Article  Google Scholar 

  85. Sibson, P. et al. Chip-based quantum key distribution. Nat. Commun. 8, 13984 (2017).

    Article  Google Scholar 

  86. Najafi, F. et al. On-chip detection of non-classical light by scalable integration of single-photon detectors. Nat. Commun. 6, 5873 (2015).

    Article  Google Scholar 

  87. Martinez, N. J. et al. Single photon detection in a waveguide-coupled Ge-on-Si lateral avalanche photodiode. Opt. Express 25, 16130–16139 (2017).

    Article  Google Scholar 

  88. Zhang, G. et al. An integrated silicon photonic chip platform for continuous-variable quantum key distribution. Nat. Photon. 13, 839–842 (2019).

    Article  Google Scholar 

  89. Bruynsteen, C., Vanhoecke, M., Bauwelinck, J. & Yin, X. Integrated balanced homodyne photonic–electronic detector for beyond 20 GHz shot-noise-limited measurements. Optica 8, 1146–1152 (2021).

    Article  Google Scholar 

  90. Dolphin, J. A. et al. A hybrid integrated quantum key distribution transceiver chip. npj Quantum Inf. 9, 84 (2023).

    Article  Google Scholar 

  91. Ma, R. et al. Disorder enhanced relative intrinsic detection efficiency in NbTiN superconducting nanowire single photon detectors at high temperature. Appl. Phys. Lett. 124, 072601 (2024).

    Article  Google Scholar 

  92. Gemmell, N. R. et al. A miniaturized 4 K platform for superconducting infrared photon counting detectors. Supercond. Sci. Technol. 30, 11LT01 (2017).

    Article  Google Scholar 

  93. Charaev, I. et al. Single-photon detection using large-scale high-temperature MgB2 sensors at 20 K. Nat. Commun. 15, 3973 (2024).

    Article  Google Scholar 

  94. Na, N. et al. Room temperature operation of germanium–silicon single-photon avalanche diode. Nature 627, 295–300 (2024).

    Article  Google Scholar 

  95. Marquardt, C. et al. Implementation Attacks Against QKD Systems (Federal Office for Information Security, 2023).

  96. Lucamarini, M. et al. Practical security bounds against the Trojan-horse attack in quantum key distribution. Phys. Rev. X 5, 031030 (2015).

    Google Scholar 

  97. Lo, H.-K., Curty, M. & Qi, B. Measurement-device-independent quantum key distribution. Phys. Rev. Lett. 108, 130503 (2012).

    Article  Google Scholar 

  98. Braunstein, S. L. & Pirandola, S. Side-channel-free quantum key distribution. Phys. Rev. Lett. 108, 130502 (2012).

    Article  Google Scholar 

  99. Wang, W., Xu, F. & Lo, H.-K. Asymmetric protocols for scalable high-rate measurement-device-independent quantum key distribution networks. Phys. Rev. X 9, 041012 (2019).

    Google Scholar 

  100. Zapatero, V. et al. Advances in device-independent quantum key distribution. npj Quantum Inf. 9, 10 (2023).

    Article  Google Scholar 

  101. Arnon-Friedman, R., Dupuis, F., Fawzi, O., Renner, R. & Vidick, T. Practical device-independent quantum cryptography via entropy accumulation. Nat. Commun. 9, 459 (2018).

    Article  Google Scholar 

  102. Hensen, B. et al. Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres. Nature 526, 682–686 (2015).

    Article  Google Scholar 

  103. Liu, W.-Z. et al. Toward a photonic demonstration of device-independent quantum key distribution. Phys. Rev. Lett. 129, 050502 (2022).

    Article  Google Scholar 

  104. Tan, E. Y.-Z. & Wolf, R. Entropy bounds for device-independent quantum key distribution with local Bell test. Phys. Rev. Lett. 133, 120803 (2024).

    Article  MathSciNet  Google Scholar 

  105. Gisin, N., Pironio, S. & Sangouard, N. Proposal for implementing device-independent quantum key distribution based on a heralded qubit amplifier. Phys. Rev. Lett. 105, 070501 (2010).

    Article  Google Scholar 

  106. Zhang, W. et al. A device-independent quantum key distribution system for distant users. Nature 607, 687–691 (2022).

    Article  Google Scholar 

  107. Nadlinger, D. P. et al. Experimental quantum key distribution certified by Bell’s theorem. Nature 607, 682–686 (2022). Together with Zhang et al. (2022), this study demonstrates device-independent quantum key distribution with entangled trapped ions, first to close untrusted-device loopholes and resist general attacks.

    Article  Google Scholar 

  108. Townsend, P. D., Rarity, J. & Tapster, P. Single photon interference in 10 km long optical fibre interferometer. Electron. Lett. 7, 634–635 (1993).

    Article  Google Scholar 

  109. Stucki, D., Gisin, N., Guinnard, O., Ribordy, G. & Zbinden, H. Quantum key distribution over 67 km with a plug&play system. N. J. Phys. 4, 41 (2002).

    Article  Google Scholar 

  110. Peng, C.-Z. et al. Experimental long-distance decoy-state quantum key distribution based on polarization encoding. Phys. Rev. Lett. 98, 010505 (2007).

    Article  Google Scholar 

  111. Stucki, D. et al. High rate, long-distance quantum key distribution over 250 km of ultra low loss fibres. N. J. Phys. 11, 075003 (2009).

    Article  Google Scholar 

  112. Yin, H.-L. et al. Measurement-device-independent quantum key distribution over a 404 km optical fiber. Phys. Rev. Lett. 117, 190501 (2016).

    Article  Google Scholar 

  113. Liao, S.-K. et al. Satellite-relayed intercontinental quantum network. Phys. Rev. Lett. 120, 030501 (2018).

    Article  Google Scholar 

  114. Chen, J.-P. et al. Sending-or-not-sending with independent lasers: secure twin-field quantum key distribution over 509 km. Phys. Rev. Lett. 124, 070501 (2020).

    Article  Google Scholar 

  115. Wang, S. et al. Twin-field quantum key distribution over 830-km fibre. Nat. Photon. 16, 154–161 (2022).

    Article  Google Scholar 

  116. Zeng, P., Zhou, H., Wu, W. & Ma, X. Mode-pairing quantum key distribution. Nat. Commun. 13, 3903 (2022).

    Article  Google Scholar 

  117. Xie, Y.-M. et al. Breaking the rate-loss bound of quantum key distribution with asynchronous two-photon interference. PRX Quantum 3, 020315 (2022).

    Article  Google Scholar 

  118. Liu, Y. et al. Experimental twin-field quantum key distribution over 1000 km fiber distance. Phys. Rev. Lett. 130, 210801 (2023).

    Article  Google Scholar 

  119. Cao, Y. et al. From single-protocol to large-scale multi-protocol quantum networks. IEEE Netw. 36, 14–22 (2022).

    Article  Google Scholar 

  120. Azuma, K. et al. Quantum repeaters: from quantum networks to the quantum internet. Rev. Mod. Phys. 95, 045006 (2023).

    Article  MathSciNet  Google Scholar 

  121. Liu, J.-L. et al. Creation of memory–memory entanglement in a metropolitan quantum network. Nature 629, 579–585 (2024).

    Article  Google Scholar 

  122. Peev, M. et al. The SECOQC quantum key distribution network in Vienna. N. J. Phys. 11, 075001 (2009).

    Article  Google Scholar 

  123. Yang, C., Zhang, H. & Su, J. The QKD network: model and routing scheme. J. Mod. Opt. 64, 2350–2362 (2017).

    Article  Google Scholar 

  124. Cao, Y. et al. Hybrid trusted/untrusted relay-based quantum key distribution over optical backbone networks. IEEE J. Sel. Areas Commun. 39, 2701–2718 (2021).

    Article  Google Scholar 

  125. Long, G.-L. et al. An evolutionary pathway for the quantum internet relying on secure classical repeaters. IEEE Netw. 36, 82–88 (2022).

    Article  Google Scholar 

  126. Garms, L. et al. Experimental integration of quantum key distribution and post-quantum cryptography in a hybrid quantum-safe cryptosystem. Adv. Quantum Technol. 7, 2300304 (2024).

    Article  Google Scholar 

  127. Long, G.-L. & Liu, X.-S. Theoretically efficient high-capacity quantum-key-distribution scheme. Phys. Rev. A 65, 032302 (2002).

    Article  Google Scholar 

  128. Wu, J., Long, G.-L. & Hayashi, M. Quantum secure direct communication with private dense coding using a general preshared quantum state. Phys. Rev. Appl. 17, 064011 (2022).

    Article  Google Scholar 

  129. Wang, M. & Long, G.-L. Lattice-based access authentication scheme for quantum communication networks. Sci. China Inf. Sci. 67, 222501 (2024).

    Article  MathSciNet  Google Scholar 

  130. Zhu, H.-T. et al. Experimental mode-pairing measurement-device-independent quantum key distribution without global phase locking. Phys. Rev. Lett. 130, 030801 (2023).

    Article  Google Scholar 

  131. Zhang, L. et al. Experimental mode-pairing quantum key distribution surpassing the repeaterless bound. Phys. Rev. X 15, 021037 (2025).

    Google Scholar 

  132. Wang, S. et al. Beating the fundamental rate-distance limit in a proof-of-principle quantum key distribution system. Phys. Rev. X 9, 021046 (2019).

    Google Scholar 

  133. Shao, S.-F. et al. High-rate measurement-device-independent quantum communication without optical reference light. Phys. Rev. X 15, 021066 (2025).

    Google Scholar 

  134. Liu, H. et al. Field test of twin-field quantum key distribution through sending-or-not-sending over 428 km. Phys. Rev. Lett. 126, 250502 (2021).

    Article  Google Scholar 

  135. Zhu, H.-T. et al. Field test of mode-pairing quantum key distribution. Optica 11, 883–888 (2024).

    Article  Google Scholar 

  136. Pirandola, S. End-to-end capacities of a quantum communication network. Commun. Phys. 2, 51 (2019).

    Article  Google Scholar 

  137. Zou, M. et al. Realization of an untrusted intermediate relay architecture using a quantum dot single-photon source. Nat. Phys. https://doi.org/10.1038/s41567-025-03005-5 (2025).

    Article  Google Scholar 

  138. Ribezzo, D. et al. Deploying an Inter-European Quantum Network. Adv. Quantum Technol. 6, 2200061 (2023).

    Article  Google Scholar 

  139. Lim, C. C.-W., Xu, F., Pan, J.-W. & Ekert, A. Security analysis of quantum key distribution with small block length and its application to quantum space communications. Phys. Rev. Lett. 126, 100501 (2021).

    Article  MathSciNet  Google Scholar 

  140. Villoresi, P. et al. Experimental verification of the feasibility of a quantum channel between space and Earth. N. J. Phys. 10, 033038 (2008).

    Article  Google Scholar 

  141. Nauerth, S. et al. Air-to-ground quantum communication. Nat. Photon. 7, 382–386 (2013).

    Article  Google Scholar 

  142. Wang, J.-Y. et al. Direct and full-scale experimental verifications towards ground–satellite quantum key distribution. Nat. Photon. 7, 387–393 (2013).

    Article  Google Scholar 

  143. Chen, Y.-A. et al. An integrated space-to-ground quantum communication network over 4,600 kilometres. Nature 589, 214–219 (2021). Reports the largest integrated space-to-ground QKD network, spanning 4,600 km.

    Article  Google Scholar 

  144. Cao, Y. et al. Long-distance free-space measurement-device-independent quantum key distribution. Phys. Rev. Lett. 125, 260503 (2020).

    Article  Google Scholar 

  145. Ji, L. et al. Towards quantum communications in free-space seawater. Opt. Express 25, 19795–19806 (2017).

    Article  Google Scholar 

  146. Chen, T.-Y. et al. Implementation of a 46-node quantum metropolitan area network. npj Quantum Inf. 7, 134 (2021).

    Article  Google Scholar 

  147. Zhong, X., Wang, W., Qian, L. & Lo, H.-K. Proof-of-principle experimental demonstration of twin-field quantum key distribution over optical channels with asymmetric losses. npj Quantum Inf. 7, 8 (2021).

    Article  Google Scholar 

  148. Chen, T.-Y. et al. Metropolitan all-pass and inter-city quantum communication network. Opt. Express 18, 27217–27225 (2010).

    Article  Google Scholar 

  149. Chen, J.-P. et al. Twin-field quantum key distribution with local frequency reference. Phys. Rev. Lett. 132, 260802 (2024).

    Article  Google Scholar 

  150. Lu, F.-Y. et al. Experimental demonstration of fully passive quantum key distribution. Phys. Rev. Lett. 131, 110802 (2023).

    Article  Google Scholar 

  151. Cerf, N. J., Bourennane, M., Karlsson, A. & Gisin, N. Security of quantum key distribution using d-level systems. Phys. Rev. Lett. 88, 127902 (2002).

    Article  Google Scholar 

  152. Zhou, X.-Y. et al. Enhancing the performance of mode-pairing quantum key distribution by wavelength division multiplexing. Opt. Express 32, 18366–18378 (2024).

    Article  Google Scholar 

  153. Kimble, H. J. The quantum internet. Nature 453, 1023–1030 (2008).

    Article  Google Scholar 

  154. Makarov, V. et al. Preparing a commercial quantum key distribution system for certification against implementation loopholes. Phys. Rev. Appl. 22, 044076 (2024).

    Article  Google Scholar 

  155. Länger, T. & Lenhart, G. Standardization of quantum key distribution and the ETSI standardization initiative ISG-QKD. N. J. Phys. 11, 055051 (2009).

    Article  Google Scholar 

  156. Mao, Y. et al. Hidden-Markov-model-based calibration-attack recognition for continuous-variable quantum key distribution. Phys. Rev. A 101, 062320 (2020).

    Article  MathSciNet  Google Scholar 

  157. Qin, H., Kumar, R. & Alléaume, R. Quantum hacking: saturation attack on practical continuous-variable quantum key distribution. Phys. Rev. A 94, 012325 (2016).

    Article  Google Scholar 

  158. Huang, J.-Z. et al. Quantum hacking of a continuous-variable quantum-key-distribution system using a wavelength attack. Phys. Rev. A 87, 062329 (2013).

    Article  Google Scholar 

  159. Huang, A. et al. Laser-seeding attack in quantum key distribution. Phys. Rev. Appl. 12, 064043 (2019).

    Article  Google Scholar 

  160. Tang, Y.-L. et al. Source attack of decoy-state quantum key distribution using phase information. Phys. Rev. A 88, 022308 (2013).

    Article  Google Scholar 

  161. Xu, F., Qi, B. & Lo, H.-K. Experimental demonstration of phase-remapping attack in a practical quantum key distribution system. N. J. Phys. 12, 113026 (2010).

    Article  Google Scholar 

  162. Qin, H., Kumar, R., Makarov, V. & Alléaume, R. Homodyne-detector-blinding attack in continuous-variable quantum key distribution. Phys. Rev. A 98, 012312 (2018).

    Article  Google Scholar 

  163. Yuan, Z., Dynes, J. F. & Shields, A. J. Avoiding the blinding attack in QKD. Nat. Photon. 4, 800–801 (2010).

    Article  Google Scholar 

  164. Ma, X.-C., Sun, S.-H., Jiang, M.-S. & Liang, L.-M. Local oscillator fluctuation opens a loophole for Eve in practical continuous-variable quantum-key-distribution systems. Phys. Rev. A 88, 022339 (2013).

    Article  Google Scholar 

  165. Peng, Q. et al. Practical security of twin-field quantum key distribution with optical phase-locked loop under wavelength-switching attack. npj Quantum Inf. 11, 7 (2025).

    Article  Google Scholar 

  166. Stucki, D. et al. Long-term performance of the SwissQuantum quantum key distribution network in a field environment. N. J. Phys. 13, 123001 (2011).

    Article  Google Scholar 

  167. Wang, S. et al. Field test of wavelength-saving quantum key distribution network. Opt. Lett. 35, 2454–2456 (2010).

    Article  Google Scholar 

  168. Sasaki, M. et al. Field test of quantum key distribution in the Tokyo QKD Network. Opt. Express 19, 10387–10409 (2011).

    Article  Google Scholar 

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Acknowledgements

This work is supported by ASTAR (M21K2c0116 and M24M8b0004), Singapore National Research Foundation (NRF-CRP22-2019-0004, NRF2023-ITC004-001, NRF-CRP30-2023-0003, NRF-CRP31-0001 and NRF-MSG-2023-0002) and Singapore Ministry of Education Tier 2 Grant (MOE-T2EP50222-0018). The authors acknowledge the support of Dieter Schwarz Stiftung gGmbH for the QUASAR project. L.H. acknowledges the financial support of the following Engineering and Physical Sciences Research Council (EPSRC) projects: Platform for Driving Ultimate Connectivity (TITAN) under Grant EP/X04047X/1; Robust and Reliable Quantum Computing (RoaRQ), EP/W032635/1; India-UK Intelligent Spectrum Innovation ICON UKRI-1859; PerCom, EP/X012301/1; EP/X01228X/1 and EP/Y037243/1.

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  1. These authors contributed equally: Haoran Zhang, Haotao Zhu.

Authors and Affiliations

  1. School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore

    Haoran Zhang, Haotao Zhu & Weibo Gao

  2. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore

    Haoran Zhang, Haotao Zhu, Ruihua He, Yan Zhang, Chao Ding & Weibo Gao

  3. School of Electronics and Computer Science, University of Southampton, Southampton, UK

    Lajos Hanzo

  4. Centre for Quantum Technologies, Nanyang Technological University, Singapore, Singapore

    Weibo Gao

  5. Quantum Science and Engineering Centre (QSec), College of Engineering, Nanyang Technological University, Singapore, Singapore

    Weibo Gao

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H. Zhang and H. Zhu researched data for the article. All authors contributed substantially to discussion of the content and wrote the article. H. Zhang, H. Zhu, L.H. and W.G. reviewed and edited the manuscript before submission.

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Zhang, H., Zhu, H., He, R. et al. Towards global quantum key distribution. Nat Rev Electr Eng 2, 806–818 (2025). https://doi.org/10.1038/s44287-025-00238-7

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