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Cited by 1,821Quantum Information and CryptographyWireless Communication Security TechniquesOptical Wireless Communication Technologies

Satellite-to-ground quantum key distribution

Open access
Liao, Sheng-Kai, Cai, Wen-Qi, Liu, Wei-Yue, Zhang, Liang, Li, Yang, Ren, Ji-Gang, Yin, Juan, Shen, Qi +26 more·2017·Nature
DOI 10.1038/nature23655
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Abstract

Quantum key distribution (QKD) uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties. However, the distance over which QKD is achievable has been limited to a few hundred kilometres, owing to the channel loss that occurs when using optical fibres or terrestrial free space that exponentially reduces the photon transmission rate. Satellite-based QKD has the potential to help to establish a global-scale quantum network, owing to the negligible photon loss and decoherence experienced in empty space. Here we report the development and launch of a low-Earth-orbit satellite for implementing decoy-state QKD-a form of QKD that uses weak coherent pulses at high channel loss and is secure because photon-number-splitting eavesdropping can be detected. We achieve a kilohertz key rate from the satellite to the ground over a distance of up to 1,200 kilometres. This key rate is around 20 orders of magnitudes greater than that expected using an optical fibre of the same length. The establishment of a reliable and efficient space-to-ground link for quantum-state transmission paves the way to global-scale quantum networks.

AI snapshot

Written from the paper’s full text.

TL;DR

The paper reports satellite-to-ground quantum key distribution using the low-Earth-orbit Micius satellite and a ground station at Xinglong, achieving decoy-state BB84 QKD over distances up to 1200 km. It demonstrates kHz-rate key generation and an estimated link-efficiency advantage of up to ~20 orders of magnitude over a 0.2 dB/km optical fiber at 1200 km.

Key findings

  • For the 19 December 2016 orbit, with satellite-to-station separation from 645 km to 1200 km, the ground station collected 3,551,136 detection events and 1,671,072 sifted-key bits over 273 s; sifted key rate decreased from ~12 kbit/s at 645 km to ~1 kbit/s at 1200 km, with average QBER 1.1%.
  • After error correction and privacy amplification, the secure final key was 300,939 bits at a statistical failure probability of 10^-9, corresponding to ~1.1 kbit/s.
  • Across 23 different days, the sifted key had a peak rate of 40.2 kbits/s at 530 km and decreased to 1.2 kbits/s at 1034.7 km, with QBERs in the 1%–3% range.
  • At 1200 km, satellite-based QKD within the 273 s coverage time showed a channel efficiency ~20 orders of magnitude higher than direct transmission through 0.2 dB/km telecommunication fiber.

Methods

  • The experiment used a satellite-to-ground downlink decoy-state BB84 protocol with polarization encoding: a space-qualified transmitter on Micius at ~500 km altitude sent 848.6 nm pulses at 100 MHz and 0.2 ns, using signal/decoy mean photon numbers μ_s=0.8, μ_1=0.1, μ_2=0, sent with probabilities 50%, 25%, and 25%.
  • The receiver was the Xinglong ground station, using a 1 m aperture telescope, a BB84 decoder, and four single-photon detectors (efficiency 50%, dark counts <25 Hz, timing jitter 350 ps); overall optical efficiency including receiving telescope and fiber coupling was ~16%.
  • Data came from routine QKD since September 2016, including a detailed 19 December 2016 orbit and a summary of 23 different days; analysis included sifting, Hamming error correction, privacy amplification, and secure-key calculation accounting for <5% intensity fluctuation and a 10^-9 statistical failure probability.

Limitations

  • The paper states that the key analysis does not consider information leakage due to possible side channels such as imperfect spatial, temporal, and spectral overlap of the quantum light sources.
  • The experiment was limited to night-time operation to avoid sunlight, required reasonably good weather, and had short coverage time (273 s per day in the detailed orbit).
  • The paper states that the low-Earth-orbit satellite has shortcomings of limited coverage area and limited time spent at each ground station; future plans include higher orbits, satellite constellations, larger telescopes, better APT, adaptive optics, and daytime QKD.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1038/nature23655

Cites

36 of 36 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 10 cited sources checked · 0 supported · 0 flagged

  • Findingreasoning
    § Experimental challenges and solutions · p. 5

    The diffraction loss at 1200 km is estimated to be 22 dB.

    “The diffraction loss is estimated to be 22 dB at 1200 km.”
    Quote in the paperSubstantial claim
  • Findingnone given
    § Experimental challenges and solutions · p. 5

    At 1200 km, the loss due to atmospheric absorption and turbulence is in the range of 3 dB to 8 dB.

    “We estimate that at 1200 km the loss due to atmospheric absorption and turbulence is in the range of 3 dB to 8 dB”
    Quote in the paperNot a substantial claim
  • Findingreasoning
    § Experimental procedure and results · p. 8

    The sifted key rate decreased from ~12 kbit/s at 645 km to ~1 kbit/s at 1200 km.

    “The sifted key rate decrease from ~12 kbit/s at 645 km to ~1 kbit/s at 1200 km, because of the increase of both the physically separated distance and the effective thickness of the atmosphere near the earth at smaller elevation angles.”
    Quote in the paperNot a substantial claim
  • Findingown data
    § Abstract: · p. 2

    The satellite implemented decoy-state QKD with over kHz key rate from the satellite to the ground over a distance up to 1200 km.

    “Here, we develop and launch a low-Earth-orbit satellite to implement decoy-state QKD with over kHz key rate from the satellite to ground over a distance up to 1200 km”
    • Also stated in: § Introduction · p. 4 · plain
      “we establish the decoy-state QKD with polarization encoding from the satellite to the ground with ~kHz rate over a distance up to 1200 km.”
    Quote in the paperSubstantial claim
  • Findingnone given
    § Experimental challenges and solutions · p. 5

    At 1200 km, the loss due to pointing error is less than 3 dB.

    “and the loss due to pointing error is less than 3 dB.”
    Quote in the paperNot a substantial claim
  • Classified as probably not a substantial claim. 10
  • May combine two claims. 12

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Findingnone given
    § Experimental procedure and results · p. 7

    The lasers are synchronized to be within <10 ps, much smaller than their pulse duration of ~200 ps.

    “The lasers are synchronized to be within <10 ps, much smaller than their pulse duration of ~200 ps.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data
    § Experimental procedure and results · p. 8

    The observed QBER had an average of 1.1%, consistent with the expected error rate due to background noise and polarization visibility.

    “Figure 3c shows the observed quantum bit error rate (QBER) with an average of 1.1%, consistent with the expected error rate due to background noise and polarization visibility.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Experimental challenges and solutions · p. 5

    The transmitter achieves a tracking accuracy of ~1.2 μrad, much smaller than the beam divergence.

    “Using a feedback closed-loop, the transmitter achieves a tracking accuracy of ~1.2 μ rad (see Fig. 2b), much smaller than the beam divergence.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Experimental procedure and results · p. 8

    Within a duration of 273 s for QKD data collection, the ground station collected 3,551,136 detection events, of which 1,671,072 bits were sifted keys.

    “Within a duration of 273 s for the QKD data collection, the ground station collected 3,551,136 detection events, and thereof 1,671,072 bits of sifted keys (see Fig. 3b).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data
    § Experimental procedure and results · p. 7

    The average photon numbers in the output of the telescope are μs=0.8, μ1=0.1, μ2=0.

    “Independent electric control of the eight lasers and adjustment of the attenuation allow us to accurately obtain the average photon number in the output of the telescope: μ s=0.8, μ 1=0.1, μ 2=0.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Experimental procedure and results · p. 8

    For the orbit on 19th December 2016, the minimal (maximal) separation was 645 km (1200 km).

    “Figure 3a shows the data for the orbit on 19th December 2016 with the minimal (maximal) separation of 645 km (1200 km).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingnone given
    § Experimental procedure and results · p. 7

    The overall optical efficiency including the receiving telescope and the fiber coupling on the ground station is ~16%.

    “The overall optical efficiency including the receiving telescope and the fiber coupling on the ground station is ~16%.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data
    § Experimental procedure and results · p. 8

    The QBERs become slightly higher in the second half of the orbit when the ground telescope points to Beijing that brings more city stray light.

    “The QBERs become slightly higher in the second half of the orbit when the ground telescope points to Beijing that brings more city stray light.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

    Findingnone given
    § Experimental procedure and results · p. 7

    The output beams are coaligned to ensure that both concentricity and coaxiality are better than 95%.

    “The output beams are coaligned to ensure that both concentricity and coaxiality are better than 95%.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data
    § Experimental procedure and results · p. 9

    After error correction and privacy amplification, the secure final key was 300,939 bits when the statistical failure probability is set to 10^-9, corresponding to a key rate of ~1.1 kbit/s.

    “we calculate secure final key of 300,939 bits when the statistical failure probability is set to be 10 -9 , corresponding to a key rate of ~1.1 kbit/s.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data
    § Experimental procedure and results · p. 9

    The key rate fluctuation due to different weather conditions is observed.

    “From Extended Data Figure 9, we also observe the key rate fluctuation due to different weather conditions.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data
    § Experimental procedure and results · p. 9

    The QKD experiments were performed at 23 different days.

    “The QKD experiments performed at 23 different days is summarized in Extended Data Table 3 and Extended Data Figure 9”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data
    § Experimental procedure and results · p. 9

    The obtained sifted key has a peak rate of 40.2 kbits/s at 530 km and decreases at larger distances, for instance, to 1.2 kbits/s at 1034.7 km.

    “The obtained sifted key has a peak rate of 40.2 kbits/s at 530 km and decreases at larger distances, for instance, to 1.2 kbits/s at 1034.7 km.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation
    § Experimental procedure and results · p. 6

    The decoy-state BB84 protocol can detect photon-number-splitting eavesdropping and thus allow secure QKD using weak coherent pulses with significantly increased distance and rate.

    “we use the decoy-state 28,29 Bennett-Brassard 1984 (BB84) 1 protocol for the QKD, which can detect photon-number-splitting eavesdropping and thus allow secure QKD using weak coherent pulses with significantly increased distance and rate.”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [28] Wang, X.-B. Beating the photon-number-splitting attack in practical quantum cryptography. Phys. Rev. Lett. 94, 230503 (2005) source

      Not checked in the free run.

    • cites [29] Lo, H.-K., Ma, X. & Chen, K. Decoy state quantum key distribution. Phys. Rev. Lett. 94, 230504 (2005) source

      Not checked in the free run.

    • cites [1] Bennett, C. H. & Brassard, G. Quantum cryptography: public key distribution and coin tossing. In Proc. Int. Conf. on Computers, Systems and Signal Processing 175–179 (1984)

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation
    § Abstract: · p. 2

    QKD uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties.

    “Quantum key distribution (QKD) uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [1] Bennett, C. H. & Brassard, G. Quantum cryptography: public key distribution and coin tossing. In Proc. Int. Conf. on Computers, Systems and Signal Processing 175–179 (1984)

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning
    § Experimental challenges and solutions · p. 5

    The downlink protocol (satellite to ground) has reduced beam spreading compared to the uplink and thus has higher link efficiency.

    “Therefore, the downlink has reduced beam spreading compared to the uplink and thus has higher link efficiency.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning
    § Discussion and outlook · p. 10

    The satellite can be further exploited as a trustful relay to conveniently connect any two points on the earth for high-security key exchange.

    “Our satellite can be further exploited as a trustful relay to conveniently connect any two points on the earth for high-security key exchange.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The satellite can serve as a trusted relay (i.e., the satellite is trusted).

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Interpretationnone given
    § Discussion and outlook · p. 10

    The low-Earth-orbit satellite has shortcomings of limited coverage area and amount of time spent in each ground station.

    “Thus far, the low-Earth-orbit satellite has shortcomings of limited coverage area and amount of time spent in each ground station.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationcitation
    § Discussion and outlook · p. 10

    The satellite-based QKD can be linked to metropolitan quantum networks where fibers are sufficient and convenient to connect numerous users within a city at ~100 km scale.

    “The satellite-based QKD can be linked to metropolitan quantum networks where fibers are sufficient and convenient to connect numerous users within a city at ~100 km scale 31 .”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [31] Chen, T.-Y. et al. Metropolitan all-pass and inter-city quantum communication network. Opt. Express 18, 27217–27225 (2010) source

      Not checked in the free run.

19 of 19

  • The paper relies on this without support.

    The effective thickness of the atmosphere is about 10 km, and most of the photon's propagation path is in empty space with negligible absorption and turbulence.

    “This is mainly because that the effective thickness of the atmosphere is ~10 km, and most of the photon's propagation path is in empty space with negligible absorption and turbulence.”

  • The paper relies on this without support.

    The satellite can serve as a trusted relay (i.e., the satellite is trusted).

    “Our satellite can be further exploited as a trustful relay to conveniently connect any two points on the earth for high-security key exchange.”
2 of 2

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • Ground-to-satellite key exchanges require sophisticated infrastructure for generation, transmission, and reception of quantum keys.

    “ground-to-satellite key exchanges require sophisticated infrastructure for generation, transmission, and reception of quantum keys36,37.”

    From Quantum-resistance in blockchain networks (2023) · cites this paper as [36]

    The figure caption (p. 13) and Experimental challenges and solutions (p. 5) describe sophisticated equipment for generating, transmitting, and receiving quantum signals, including lasers, telescopes, detectors, and tracking systems. But the experiment sends those signals from satellite to ground; the paper does not establish the same infrastructure requirements for the claimed ground-to-satellite direction. (LLM, conf=0.86)

    Experimental — accuracy not yet measured

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Nighttime pass is scheduled for 12:50 PM

    Minor

    12:50 PM is in the afternoon, contradicting the stated nighttime-only operation.

  • Ground beacon divergence differs between text and caption

    Minor

    The main text gives the ground station beacon a divergence of 0.9 mrad, while the Figure 2 caption gives the ground-sent red laser a divergence of 1.2 mrad.

2 of 2

Cites

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Related

Authors
Liao, S.-K., Cai, W.-Q., Liu, W.-Y., Zhang, L., Li, Y., Ren, J.-G., Yin, J., Shen, Q., Cao, Y., Li, Z.-P., Li, F.-Z., Chen, X.-W., Sun, L.-H., Jia, J.-J., Wu, J.-C., Jiang, X.-J., Wang, J.-F., Huang, Y.-M., Wang, Q., Zhou, Y.-L., Deng, L., Xi, T., Ma, L., Hu, T., Zhang, Q., Chen, Y.-A., Liu, N.-L., Wang, X.-B., Zhu, Z.-C., Lu, C.-Y., Shu, R., Peng, C.-Z., Wang, J.-Y., & Pan, J.-W.
Affiliations
  • University of Science and Technology of China (CN)
  • Chinese Academy of Sciences (CN)
Corresponding author
  • Peng, Cheng-Zhi
  • Pan, Jian-Wei
ORCID
Venue
Nature
Publisher
Springer Science and Business Media LLC
Published
2017-08-09
Volume
549
Issue
7670
Pages
43-47
ISSN
  • 0028-0836 (ISSN-L)
  • 1476-4687
DOI
10.1038/nature23655
OpenAlex
W2728092904
Cited by
1,821
References
36
Citations by year
2026: 199 · 2025: 278 · 2024: 209 · 2023: 226 · 2022: 196 · 2021: 213 · 2020: 189 · 2019: 199 · 2018: 96 · 2017: 15
FWCI
81.40
Type
journal article
Language
en
Open access
Licence
Locations
  • Nature (publishedVersion)
  • PubMed (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • RePEc: Research Papers in Economics (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Information and Cryptography
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Wireless Communication Security Techniques
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Optical Wireless Communication Technologies
Keywords
satellite quantum key distribution, decoy-state QKD, Micius satellite, low Earth orbit satellites, key rate, quantum teleportation, single-photon qubits, quantum networks

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