Various optical quantum key distribution protocols have been proposed and examined to implement a global quantum communication system both in fiber-based network and in free-space systems. Employing a satellite as a quantum relay is a possible solution to increase the secure covered distance, which is available for sharing secure keys between two remote ground stations. In this paper, combining with the idea of measurement device independent quantum key distribution, a modified free-space quantum communication protocol is proposed to build a QKD network with untrusted nodes, where the parties on the ground send quantum signals to the untrusted satellite relay that perform a joint measurement on the incoming signals. Our results demonstrate that though the modified protocol suffers higher link attentuation than the entanglement-based quantum communication protocol owing to higher effects of atmospheric turbulence for uplink, our modified protocol provides secure quantum communications with untrusted relays. Furthermore, the complex and non-space-qualified sources remain on the ground in our scheme , which makes our scheme more practical for bridging a seamless connection form ground to space.
Various optical quantum key distribution protocols have been proposed and examined to implement a global quantum communication system both in fiber-based network and in free-space systems. Employing a satellite as a quantum relay is a possible solution to increase the secure covered distance, which is available for sharing secure keys between two remote ground stations. In this paper, combining with the idea of measurement device independent quantum key distribution, a modified free-space quantum communication protocol is proposed to build a QKD network with untrusted nodes, where the parties on the ground send quantum signals to the untrusted satellite relay that perform a joint measurement on the incoming signals. Our results demonstrate that though the modified protocol suffers higher link attentuation than the entanglement-based quantum communication protocol owing to higher effects of atmospheric turbulence for uplink, our modified protocol provides secure quantum communications with untrusted relays. Furthermore, the complex and non-space-qualified sources remain on the ground in our scheme , which makes our scheme more practical for bridging a seamless connection form ground to space.
Quantum key distribution (QKD), the technology to generate distant secure keys for later usage in secure communication, has become a mature topic since the 1980s. While terrestrial QKD over fiber networks is suitable for short-distance urban networks, QKD via satellites promises to gap the distance requirement on a global scale that limits terrestrial QKD. Satellite QKD requires the exchange of quantum states between a satellite and multiple ground stations. The goal is then to facilitate shared secret keys between the ground stations, which can then be relayed to users near the ground stations. The satellite usually carries the quantum sources as its payload and sends them to the ground station via a downlink. The QKD protocol is heavily influenced by the choice of the quantum source, with typically one of two types: approximate single photon source (such as a weak laser) or an entangled source. Similarly, the ground station must be equipped to receive, measure and process the quantum signals sent by the satellite. Although there are also reverse schemes, where the satellite acts as the receiver and the ground station as the sender, these schemes are less explored due to higher noise in the uplink and less engineering experience. As with any system containing a high heterogeneity, many different implementation schemes lead to a variety of optimized use cases based on different criteria. Satellite QKD carries the further complication that it must be adapted to international standards. In this paper we present different satellite and ground station architectures that lean on the developments in the projects EAGLE-1, QUBE, QuNET, RoGloQuaN, addressing different protocols, sources, satellite sizes and telescope sizes. We also discuss the need for agility and configuration of components in a heterogeneous environment.
Measurement-device-independent quantum key distribution (MDI-QKD), based on two-photon interference, is immune to all attacks against the detection system and allows a QKD network with untrusted relays. Since the MDI-QKD protocol was proposed, fiber-based implementations aimed at longer distance, higher key rates, and network verification have been rapidly developed. However, owing to the effect of atmospheric turbulence, MDI-QKD over a free-space channel remains experimentally challenging. Herein, by developing a robust adaptive optics system, high-precision time synchronization and frequency locking between independent photon sources located far apart, we realized the first free-space MDI-QKD over a 19.2-km urban atmospheric channel, which well exceeds the effective atmospheric thickness. Our experiment takes the first step toward satellite-based MDI-QKD. Moreover, the technology developed herein opens the way to quantum experiments in free space involving long-distance interference of independent single photons.
In recent years, fiber-based quantum key distribution systems have emerged in a growing number of sectors. However, fiber optic links limit the distance that can be covered in point-to-point connections, so developments in free-space quantum communications are important. These can be used to establish free-space QKD links between buildings or to connect remote ground stations using satellite systems. In our research, we are developing an entanglement-based free-space QKD system based and we are simulating quantum communication satellite systems based on entanglement.
In this work we analyze a measurement-device-independent (MDI) protocol to establish continuous-variable (CV) quantum key distribution (QKD) between two ground stations. We assume communication occurs between the ground stations via satellite over two independent atmospheric-fading channels influenced by turbulence-induced beam wandering. In this MDI protocol the measurement device is the satellite itself, and the security of the protocol is analyzed through an equivalent entanglement-based swapping scheme. We quantify the positive impact the fading channels can have on the final quantum key rates, demonstrating how the protocol is able to generate a positive key rate even over high-loss atmospheric channels provided that the maximum transmission coefficient of the channel is sufficiently large. This is somewhat counter-intuitive given that the same outcome is only possible in the low-loss regime for a measurement device centrally positioned in a fiber-optic channel. Our results show that useful space-based quantum key generation rates between two ground stations are possible even when the relay satellite is held by an adversary. The cost in key rate incurred by altering the status of the satellite from trustworthy to untrustworthy is presented.
Satellite-based optical communication enables quantum key distribution (QKD) on global scales, with realistic near-term architectures usually considering prepare-and-measure protocols that employ satellites in Low Earth Orbit (LEO) acting as trusted nodes. One major challenge is constituted by the high loss in the free-space link from the satellite to the optical ground station (OGS) due to the large distances involved. If the quantum signal is directly forwarded from the OGS to an end-user via a ground-based fiber connection, the additional losses limit the key generation to the vicinity of a few kilometers. For longer-distance links, instead, the OGS would have to act as another trusted node to relay the key, introducing a severe bottleneck in the practical security. Here we consider an alternative solution based on the use of Mode-Pairing (MP) QKD, employing the OGS as an untrusted intermediate node. Due to its improved scaling of the key rate with the channel transmission, MP QKD allows end-users up to hundreds of kilometers around the OGS to establish a secure key with the satellite, without having to trust the OGS provider. We discuss the effect of Doppler shifts on the performance of MP QKD and propose a possible implementation to mitigate its impact with sufficient precision.
Quantum key distribution (QKD) has attracted much attention on secure communications across global networks. QKD over satellite networks can overcome the limitations of terrestrial optical networks, such as large attenuation over long distance fiber channel and difficulty of intercontinental domain communications. Different QKD networks (around the world) can intercommunicate through quantum satellites, leading to a global quantum network in near future. This raises a new resource allocation and management problem of QKD involving multiple satellite layers and distributed ground stations. Using existing schemes, a single satellite cannot perform QKD for ground stations for the whole day. Moreover, the research problem is more challenging due to limitations of satellite coverage: limited cover time of low earth orbit (LEO) satellite, high channel losses of geostationary earth orbit (GEO) satellite, etc. To overcome these limitations, our study proposes a double-layer quantum satellite network (QSN) implemented quantum key pool (QKP) to relay keys for ground stations. We propose a new architecture of trusted-repeater-based double-layer quantum satellite networks, comprising GEO and LEO satellites. We also address the routing and key allocation (RKA) problem for key-relay services over QSNs. We propose a novel joint GEO-LEO routing and key allocation (JGL-RKA) algorithm to solve the RKA problem. Simulative results show that the proposed scheme can increase success probability of key-relay services significantly. We also present the impact of different route selections mechanisms, number of satellite links, satellite node capability, and service granularity on network performance.