This study aims at extending the concept of QKD to the optical free-space quantum communications domain. Moreover, the feasibility of a global satellite based quantum key distribution, in the low earth orbit (LEO) is investigated. Inline with this, three different link scenarios, including ground-to-ground, ground-to-satellite and satellite-to-satellite are considered. Moreover, system performance is analysed to show the sensitivity of the link to effect such as atmospheric attenuation, turbulence and detector noise. Generally, these factors are assumed to impair system performance by causing an overall increase in the systems quantum bit error rate (QBER), let alone limiting the communication bit rate and transmission distance of the link. The obtained results reveal the feasibility of satellite-based quantum key distribution in the LEO platform, a concept which could be potentially extended to geostationary earth orbit (GEO).
This study aims at extending the concept of QKD to the optical free-space quantum communications domain. Moreover, the feasibility of a global satellite based quantum key distribution, in the low earth orbit (LEO) is investigated. Inline with this, three different link scenarios, including ground-to-ground, ground-to-satellite and satellite-to-satellite are considered. Moreover, system performance is analysed to show the sensitivity of the link to effect such as atmospheric attenuation, turbulence and detector noise. Generally, these factors are assumed to impair system performance by causing an overall increase in the systems quantum bit error rate (QBER), let alone limiting the communication bit rate and transmission distance of the link. The obtained results reveal the feasibility of satellite-based quantum key distribution in the LEO platform, a concept which could be potentially extended to geostationary earth orbit (GEO).
Satellite-based free-space quantum key distribution (QKD) provides a practical framework for achieving secure global communication beyond the limitations of optical fibers. In this work, the quantum bit error rate (QBER) and secure key rate of four representative protocols-BB84, B92, BBM92, and E91 are investigated over low earth orbit (LEO) links in both uplink and downlink configurations. The optical link is modeled using a Gaussian beam formalism, incorporating the effects of diffraction, pointing errors, atmospheric turbulence, and background noise contributions. The protocols are examined under day and night-time operating conditions, and their dependence on the zenith angle is analyzed. The findings show that downlink links generally exhibit lower QBER and higher secure key rates than uplinks, and among prepare-and-measure schemes, BB84 consistently outperforms B92, while in entanglement-based approaches, BBM92 achieves higher key rates than E91.
Optical quantum communication utilizing satellite platforms has the potential to extend the reach of quantum key distribution (QKD) from terrestrial limits of ∼200 km to global scales. We have developed a thorough numerical simulation using realistic simulated orbits and incorporating the effects of pointing error, diffraction, atmosphere and telescope design, to obtain estimates of the loss and background noise which a satellite-based system would experience. Combining with quantum optics simulations of sources and detection, we determine the length of secure key for QKD, as well as entanglement visibility and achievable distances for fundamental experiments. We analyse the performance of a low Earth orbit satellite for downlink and uplink scenarios of the quantum optical signals. We argue that the advantages of locating the quantum source on the ground justify a greater scientific interest in an uplink as compared to a downlink. An uplink with a ground transmitter of at least 25 cm diameter and a 30 cm receiver telescope on the satellite could be used to successfully perform QKD multiple times per week with either an entangled photon source or with a weak coherent pulse source, as well as perform long-distance Bell tests and quantum teleportation. Our model helps to resolve important design considerations such as operating wavelength, type and specifications of sources and detectors, telescope designs, specific orbits and ground station locations, in view of anticipated overall system performance.
In this paper we analyze the feasibility of performing Quantum Key Distribution (QKD), in Earth-satellite up and downlinks and in intersatellite links, with two quantum cryptography protocols: BB84 and SARG04, and with two implementation options: with and without decoy states. As real measurements in these scenarios are not possible yet, the objective is to obtain results as realistic as possible to support the design of future satellite missions performing QKD. Therefore, we use realistic values for the optical hardware and take into account usual atmospheric conditions. In the same line, we assume specific types of attacks, namely the photon number splitting and the intercept-resend with unambiguous discrimination attacks, which could likely be the main threat to the first satellite-based QKD applications. A lower bound on the key generation rate of SARG04 with two decoy states is presented. The optimum signal- and decoy-states mean photon numbers for each protocol and each distance are also computed. The resulting values for the signal-state are larger than those often employed. We show that it may be possible to establish QKD with LEO (Low Earth Orbit) and, under certain circumstances, with MEO (Medium Earth Orbit) satellites, but not with GEO (Geostationary) ones. Furthermore, we obtain that the optimum signal-state mean photon number for SARG04 with two decoy states is almost independent of the link distance, which greatly facilitates its use in a real scenario.
Single-photon quantum communications (QC) offers the attractive feature of 'future proof', forward security rooted in the laws of quantum physics. Ground based quantum key distribution (QKD) experiments in optical fiber have attained transmission ranges in excess of 200km, but for larger distances we proposed a methodology for satellite-based QC. Over the past decade we have devised solutions to the technical challenges to satellite-to-ground QC, and we now have a clear concept for how space-based QC could be performed and potentially utilized within a trusted QKD network architecture. Functioning as a trusted QKD node, a QC satellite ('QC-sat') could deliver secret keys to the key stores of ground-based trusted QKD network nodes, to each of which multiple users are connected by optical fiber or free-space QC. A QC-sat could thereby extend quantum-secured connectivity to geographically disjoint domains, separated by continental or inter-continental distances. In this paper we describe our system concept that makes QC feasible with low-earth orbit (LEO) QC-sats (200-km-2,000-km altitude orbits), and the results of link modeling of expected performance. Using the architecture that we have developed, LEO satellite-to-ground QKD will be feasible with secret bit yields of several hundred 256-bit AES keys per contact. With multiple ground sites separated by {approx} 100km, mitigation of cloudiness over any single ground site would be possible, potentially allowing multiple contact opportunities each day. The essential next step is an experimental QC-sat. A number of LEO-platforms would be suitable, ranging from a dedicated, three-axis stabilized small satellite, to a secondary experiment on an imaging satellite. to the ISS. With one or more QC-sats, low-latency quantum-secured communications could then be provided to ground-based users on a global scale. Air-to-ground QC would also be possible.
As Quantum Key Distribution (QKD) seems to turn towards satellite communication infrastructure to interconnect distant nodes aiming to a global quantum secured network, the number of assisting satellites is expected to increase. In this work, a feasibility analysis of a large-scale Low Earth Orbit (LEO) satellite constellation supporting LEO to ground QKD links is presented. A software tool to simulate the physical properties of a large-scale satellite constellation and a link budget calculator tailored for LEO satellite to ground QKD links have been developed. A large-scale LEO satellite constellation with 100 satellites orbiting at 550km altitude with 53deg inclination angle in ten different orbital planes (10 satellites per orbital plane) has been simulated and subsatellite points for 1 year have been obtained. Assuming, an optical ground station network consisting of nine different optical ground stations located in observatories across Europe, the performance of this large-scale constellation is evaluated in terms of availability and Secure Key Rate (SKR) employing the prepare and measure Decoy-State BB84 QKD protocol, during nighttime, under different atmospheric conditions including cloud coverage and turbulence effects among others, while two different wavelengths (i.e., 800nm and 1550nm) are examined. For each Optical Ground Station (OGS) location, Gbits of distilled keys per year per ground station and key rates up to Kbps are reported.
Security is a major concern of digital society, and quantum key distribution (QKD) can contribute with an un-conditional secure mechanism for symmetric key distribution. Satellites have the opportunity to overcome the range limit of quantum communications based on fiber networks. This paper presents a method for performance evaluation of QKD based on satellites, exemplified with a case study that considers small satellites (CubeSats) in low Earth orbits (LEO), to illustrate a flexible configuration of the quantum range extender use case. To the best of the authors’ knowledge, this is the first time that a system evaluation derived from orbital propagation data is conducted while also considering QKD with a finite key statistics approach. This evaluation aims to match with the shortness and variability of visibility intervals typical of LEO orbits. The results confirm the feasibility of proposed case study and show the impact of relevant systems and orbital parameters in the key generation performance, such as system characteristics, uplink or downlink configuration, satellite altitude and orbital inclination. The estimated performance is then scaled to a year along with some sensitivity scenarios. The presented results may guide the design of future QKD satellite mission proposals.