Abstract
Satellite-based, long-distance free-space quantum key distribution has the potential to realise global quantum secure communication networks. Detecting faint quantum optical pulses sent from space requires highly accurate and robust classical timing systems to pick out signals from the noise and allow for reconciliation of sent and received key bits. For such high-loss applications, a fault-tolerant synchronisation signal coding and decoding scheme based on de Bruijn sequences is proposed. A representative synchronisation timing system was tested in laboratory conditions and it demonstrated high fault tolerance for the error-correction algorithm even under high loss. The performance limitations of this solution are also discussed, and the maximum error tolerance of the scheme and the estimated computational overhead are analysed, allowing for the possibility of implementation on a real-time system-on-chip. This solution not only can be used for synchronisation of high-loss channels such as channels between satellites and ground stations but can also be extended to applications with low loss, high bit error rate, but require reliable synchronisation such as quantum and non-quantum communications over terrestrial free space or fibre optic channels.
Highlights
Quantum Key Distribution (QKD) is able to secure communication links making them immune to quantum computer‐based attacks that threaten the existing deployed public key cryptosystems such as the Rivest–Shamir–Adelman (RSA) algorithm and Elliptic Curve Cryptography (ECC) [1]
We have developed a laboratory demonstration of an optical timing and synchronisation (T&S) link designed for pulse gating and numbering of quantum signals in satellite QKD (Figure 1)
We propose a synchronisation method based on de Bruijn sequences which is suitable for timing and synchronisation over high‐loss communication channels
Summary
Quantum Key Distribution (QKD) is able to secure communication links making them immune to quantum computer‐based attacks that threaten the existing deployed public key cryptosystems such as the Rivest–Shamir–Adelman (RSA) algorithm and Elliptic Curve Cryptography (ECC) [1]. Transmitting faint quantum optical pulses between a satellite and the Earth is challenging due to high channel losses and rapid relative motion between the transmitter and receiver. There has been a general move towards space systems' miniaturisation with the rapid take‐up of small satellite systems such as CubeSats (1–10 kg) [6, 7]. This facilitates the deployment of QKD satellite constellations to provide widespread and low latency global coverage that would be difficult and/or expensive to achieve with conventionally sized satellites (Micius is ∼650kg). The cost and complexity of the ground segment, that is, optical ground station (OGS), so they may be deployed in large numbers, some of which may be mobile or transportable [9]
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