The shift in the Communication paradigm from the bit to the qubit is increasingly exploited in terrestrial long range links and networks, with strong potentials in secure communications, quantum computing and metrology. The space-to-ground quantum key distribution was also considered as feasible. A new different scenario for the quantum communications is that of the intersatellite link. In this study we focus on the extension of intersatellite communications into the quantum domain. The long distances involved and the fast relative motion are severe constraints, partially compensated by the absence of beam degradation due to the propagation in the atmosphere as well as the relatively low background noise level. We address the conception of the optical terminal and the predicted performances in the case of constellations of LEO and MEO satellite including the quantum communications and quantum teleportation.
The shift in the Communication paradigm from the bit to the qubit is increasingly exploited in terrestrial long range links and networks, with strong potentials in secure communications, quantum computing and metrology. The space-to-ground quantum key distribution was also considered as feasible. A new different scenario for the quantum communications is that of the intersatellite link. In this study we focus on the extension of intersatellite communications into the quantum domain. The long distances involved and the fast relative motion are severe constraints, partially compensated by the absence of beam degradation due to the propagation in the atmosphere as well as the relatively low background noise level. We address the conception of the optical terminal and the predicted performances in the case of constellations of LEO and MEO satellite including the quantum communications and quantum teleportation.
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).
The aim of my thesis is to demonstrate the feasibility of Quantum Communication in free space and space, pointing out how ESA Galileo constellation could be strengthens into an Optical Quantum Communication Network (OQCN), by the employment of a compact and low cost prototype (SaNe-QKD OPT). Considering table 2 according the guidelines of [70] (2012) for the European Quantum Information Processing and Quantum Communication, three crucial long term goals are fulfilled, (Satellite Quantum Communication, besides 1000 kilometers of spatial Quantum Cryptography, multi-node Quantum Network), with reference to Galileo constellation: the new devised OQCN will perform Quantum Communication between approaching satellites of the constellation in multi-node mode, and Quantum Key Distribution scheme will be employed over large distances, definitely above 1000 kilometers. My thesis summarizes three years of researches at the Luxor Laboratories in Padova. It is dedicated to two core topics, which are twofold aspects of the same issue: beam propagation in Quantum Communication over ground and over space, with the final realization of a Quantum Communication Network in which concretized the acquired knowledges in Quantum field. And Inter-island Canary links have been chosen as representing a worse case scenario for Quantum Communication experiments, an ideal test bed to investigate beam propagation in view of the space applications, where crucial aspects are the huge distances that Communication beams have to cover. The thesis is divided in two complementary parts: Ground beam propagation Beam propagation in free space along horizontal links in Canary Islands, performing long distances (143 kilometers) and aiming to exploit beam propagation through a turbulent medium. The results pointed out optical configurations and specifics in order to obtain an effective and stable communication link. These researches are within of the strategic project Quantum Future of the University of Padova, "the shift in the Quantum paradigm" Space beam propagation. The second part is dedicated to space beam propagation, regarding design and arrangement of the Quantum prototype SaNe-QKD to fuse with the Optical Communication prototype OPT (by Thales Alenia Space). The resulting system, SaNe-QKD OPT, will be positioned on board of Galileo satellites for performing Quantum Optical Inter-satellite links. Simulations about inter-satellite links, network topology features and key length evaluation, have allowed to obtain results and specifications about operative wavelengths and telescope apertures to use for inter-satellite communications. Then, the prototype SaNe-QKD have been arranged and is here shown in each part. This researches are part of the project "Application of Optical Quantum Communication Links for GNSS" by the European space Agency (ESA). My thesis is divided in four chapters, as follows Ground beam propagation Chapter 1 introduces an overview of main concepts of photonics, atmospheric models and turbulence parameters, optics and fiber-optics and telescopes, used throughout the treatment. The Newtonian telescope is investigated in order to analyze the optical path arriving at the prototype SaNe-QKD for space purpose and the Canary Telescope in order to realize an optical system implementing the centroid spot following system. Zemax simulations are presented for both to check aberrations and for collimation issues. For Newtonian off-axis field, coma and field curvature are revealed. For Canary Telescope chromatic aberration is revealed and the arrangement scheme of the experiment of beam propagation in free space in Canary Islands with co-propagating beams control is described. Kolmogorov atmospheric turbulence models with Hughnagel Valley model is then briefly reported too. It will be used in Canary experiments over 143 kilometers and in chapter 3 for up/downlink quantum communication simulations between a ground base transceiver and a satellite. Chapter 2. It is known that an unconfined optical mode propagating in a turbulent medium suffers of distortions. In Quantum Communication the information is encoded and transmitted as a train of single photons with mean average of about one photon for pulse; it follows that the link losses of a beam propagating in atmosphere increase with the distance; in contrast they cannot be reduced by increasing the signal power as in optical communication. Consequently, it is crucial to exploit beam propagation over long ranges, in order to analyze photon statistics, the transformations on the beam due to the ground in order to prevent the unleashing of the beam between transmitter and receiver. The turbulence introduces two contributes according the eddies size [51] [52]respect to the optical beam: • Beam wandering, which occurs when a laser beam is refracted by eddies with size larger than the beam diameter, causing a displacement of the beam center (centroid). • Beam spreading, which is due to the laser beam being refracted by eddies smaller than the beam diameter. The short-term beam spread is an additional spread with respect to the standard spread due to the free space laser beam propagation (without turbulence effects). These effects appears in relation to the exposition time: on short time scales the beam wandering is the dominant effect, while on long time scales the beam spread-ing is the dominant effect. Using turbulence as a resource, the research of beam propagation in free-space communication links opens to test a new equipment, the custom Canary telescope (Chapter1). The team performed two free-space propagation links with the telescope: the former, a ‘short’ local range (about 20 km) test link between Asiago and Monte Grappa (Italy) in order to examine the Canary Tele-scope and check the communication equipment at the transmitting part; the latter, a ‘long’ range (143 km long) link between La Palma and Tenerife (Canary Islands) for free-space propagation experiments with severe turbulence conditions. Developments and data analysis are presented, pointing out methodologies for turbulence characterization in Ground Quantum Optical Links. The results of the propagation of single, double beams along 143 kilometers have demonstrated that it is possible to optimize an optical system in order to reconstruct the beam long-term diameter and by techniques of beam co-propagating technique, the loss link could be reduced. This is promising as link losses are crucial aspect in Quantum Communication, when in a noisy channel the quantum signal (the in-formation encoded in single photons) cannot be improved by increasing the signal power. Besides we observed that the statistic of arrival of single photons over a free-space 143 km optical link confirms that there is a transformation from Poissonian to log-normal distribution: There is still the evidence of consecutive subintervals of low losses allowing us to envisage the exploitation of turbulence as an SNR improvement technique. Space beam propagation Chapter 3 according the requests of the ESA project, a feasibility study for Quantum Communication applications to Galileo constellation is shown. The chapter starts with an overview of the merits of Optical Communication (data rate exchanging, lightness, compactness, low power consumption..) Pointing out that the intrinsically secure is the added value that only the Quantum counterpart could supply. A brief part recalling orbital motion in space in order to check satellite orbital motion. Then we open to up/downlink simulations overview: recalling the simulations in literature of ground to space or space to ground beam propagation through the atmosphere, the feasibility study shows that unfortunately Galileo constellation can realize only inter-satellite communication links, as the atmosphere and the altitude of the satellite constellation prevents any effective and real single photon transmission with the current technologies. However, simulation results of inter-satellite beam propagation show us that the huge distances can be overwhelmed (derived requirements are telescope diameters >20 cm and operating wavelength <532nm), and time interval within perform Quantum Communication can be calculated: respect to a reference satellite of different orbital plane, the time interval in which the intra-satellite distances are within 15000 kilometers are • For satellite called three of about 176 minutes • For satellite called two of about 168 minutes Then exploiting the relative motion of satellites lying in different orbital planes, we show that it is possible to target communication between satellites that are closer in turns, and to achieve appreciable transmission rates: the distance intervals in which we calculated the raw key rate values are 6000, 10000 and 19000 kilometers, and the best values in raw key rates (18M bits/s at 6600 kilometers, related to lower attenuation values) are obtained for a telescope diameter of 50 cm and wavelength of 50nm, while the worse values in raw key rates (2.2 Kbits/s at 6600 kilometers, related to higher attenuation values) are for a telescope diameter of 20 cm and wavelength of 800nm. Finally, today information-based society security is of paramount importance: Galileo Optical Quantum Network will guarantee intrinsically secure key exchanging, free of PSN attack, within a satellite distance signed by decoy scheme approach. After a brief review of a model for a Quantum Communication System, simulations about key rate are shown in the final section, showing that for same wavelengths and within same beam propagation distances, larger apertures present higher values of key rate[bit/s]. At the same time we have observed that shorter operating wave- lengths presents higher values of key rate, assuring that in merit to Galileo OQCN decoy schemes could be applied in order to beat PNS attack over well defined communication links in relation to the link distance covered, the operative
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.
Space-based quantum key distribution (QKD) has emerged as the leading approach for establishing information-theoretically secure communication links beyond the reach of terrestrial fiber networks. Over the past decade, missions ranging from the 635 kg Micius satellite to 3U CubeSats such as SpooQy-1 have demonstrated satellite-to-ground QKD, entanglement distribution, and quantum teleportation across distances exceeding 1,200 km. However, existing reviews of these missions focus primarily on quantum protocols and link layer physics, leaving the system level engineering trade offs particularly those governing platform selection, SWaP budgets, and subsystem integration largely unexamined. This paper presents a systems engineering review of space based quantum communication missions developed between 2016 and 2025. Each mission is analyzed through a unified framework encompassing link budget decomposition, payload miniaturization trends, and Acquisition, Tracking, and Pointing (ATP) architectures. A comparative SWaP analysis reveals that payload mass has decreased by approximately one order of magnitude from ~230 kg (Micius) to ~23 kg (Jinan-1) while reported quantum bit error rates have remained below 5%. The analysis identifies three critical gaps: (i) the absence of formal Multidisciplinary Design Optimization (MDO) frameworks in quantum satellite design, (ii) the lack of standardized performance metrics for cross mission comparison, and (iii) the disconnect between constellation level network studies and subsystem level hardware constraints. Based on these findings, system-level design strategies and a technology roadmap are proposed to support the transition from single-link demonstrations to scalable, constellation-ready quantum communication infrastructures.
Quantum key distribution (QKD) has gained a lot of attention over the past few years, but the implementation of quantum security applications is still challenging to accomplish with the current technology. Towards a global-scale quantum-secured network, satellite communications seem to be a promising candidate to successfully support the quantum communication infrastructure (QCI) by delivering quantum keys to optical ground terminals. In this research, we examined the feasibility of satellite-to-ground QKD under daylight and nighttime conditions using the decoy-state BB84 QKD protocol. We evaluated its performance on a hypothetical constellation with 10 satellites in sun-synchronous Low Earth Orbit (LEO) that are assumed to communicate over a period of one year with three optical ground stations (OGSs) located in Greece. By taking into account the atmospheric effects of turbulence as well as the background solar radiance, we showed that positive normalized secure key rates (SKRs) up to 3.9×10−4 (bps/pulse) can be obtained, which implies that satellite-to-ground QKD can be feasible for various conditions, under realistic assumptions in an existing infrastructure.
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.