We present the transmission of continuous variable quantum key distribution (CV-QKD) qubits, ultra-high capacity of multi-tera bits over atmospheric and inter-satellite channels via the C-band. With the aid of advanced modulation formats and modern photonic technologies, we argue that multi-satellite jumps are both feasible and realizable. Photonic transceivers utilizing photonic integrated circuits in Silicon and InP technology of electro-absorption modulation lasers are presented. It is shown that optical amplification techniques, booster power amplifiers, and highly sensitive optical preamplifiers can compensate for exceedingly high attenuation of links between optical ground stations and satellites with all optical routing and link distances of 12,000 to 45,000 km. The digital signal processing algorithms in coherent receivers for ultra-high capacity and ultra-low power quantum bit systems are demonstrated to play a critical role in system performance. We specifically provide a Nyquist-equivalent sampling theorem that studies the quantum bit error rate based on both the Nyquist sampling theorem and the Heisenberg uncertainty principle. Furthermore, the Nyquist pulse shaping method and constellation probability shaping are used to maximize tera-bit transmission over spatial channels.
We present the transmission of continuous variable quantum key distribution (CV-QKD) qubits, ultra-high capacity of multi-tera bits over atmospheric and inter-satellite channels via the C-band. With the aid of advanced modulation formats and modern photonic technologies, we argue that multi-satellite jumps are both feasible and realizable. Photonic transceivers utilizing photonic integrated circuits in Silicon and InP technology of electro-absorption modulation lasers are presented. It is shown that optical amplification techniques, booster power amplifiers, and highly sensitive optical preamplifiers can compensate for exceedingly high attenuation of links between optical ground stations and satellites with all optical routing and link distances of 12,000 to 45,000 km. The digital signal processing algorithms in coherent receivers for ultra-high capacity and ultra-low power quantum bit systems are demonstrated to play a critical role in system performance. We specifically provide a Nyquist-equivalent sampling theorem that studies the quantum bit error rate based on both the Nyquist sampling theorem and the Heisenberg uncertainty principle. Furthermore, the Nyquist pulse shaping method and constellation probability shaping are used to maximize tera-bit transmission over spatial channels.
Optical transmission over space links between satellites in intra-orbital constellations or inter-orbital constellations and optical ground stations are currently attracting a lot of attention, both for their ultra-high capacities reaching multi-tera-bits/sec and for their use in quantum key distribution for coding to transmitting over public channels.This paper outlines the followings: (i) Multi-dimensional considerations to reach Tera-bits/sec that include multiplexing of polarized modes, high-order modulation formats, high speed integrated photonic complex modulations, digital signal processing techniques etc.; (ii) Continuous variable quantum key distribution (CV-QKD) achieved through constant amplitude zero auto-correlation (CAZAC) sequence for quantum level signaling with phase-coded BB84protocol, decorrelation , high order sampling rate and digital signal processing for quantum key recovery.(iii) Discussion of advantages and disadvantages of both coherent and self-coherent reception techniques for space transmission channels for multi-photons to subphoton energy reception and transmission; (iv) Presentation of initial transmission results and Terabits/s optical transmission systems; (vi) Analytical considerations of CV-QKD space self-homodyne and homodyne reception system employing CAZAC and crosscorrelation decoding as a photonic-pre-processor.
Satellite based quantum key distribution (QKD) enables the delivery of keys for quantum secure communications over long distances. Maturity of the technology as well as industrial interest keep increasing. So does the technology readiness of satellite free-space optical communications. A satellite QKD system comprises a quantum communication subsystem and a classical communication subsystem (public channel). Both are implemented with free-space optics. Thus, in satellite QKD system design, there are strong synergies that should be exploited as much as possible and lead to an all-optical satellite QKD system. In this paper, we present a system like this locating all optical channels in ITU DWDM C-band. We focus on the overall conceptual design and the setup of the optical channels for quantum and classical signal transmission. The system description addresses the breadboards of a transmitter laser terminal (Alice terminal), a receiver laser terminal, (Bob terminal), the public channel implementation, the interfaced QKD system and the deployed encryption system. The design basis for the Alice terminal is the laser terminal development OSIRISv3. The design basis for the Bob terminal is the ground station development THRUST. The later contains an adaptive optics correction to enable single mode fiber coupling. This enables the interfacing to almost arbitrary quantum receivers such as the Bob modules used in the described experiment. The public channel is composed of a bi-directional 1 Gbps IM/DD system and a MODEM that implements a proprietary waveform optimized for free-space channels. The system was experimentally analyzed in a field test in the framework of the German initiative QuNET which addresses the use case of quantum secure communication for authorities. The results of the experiment are used to model a feasible LEO satellite-ground link. Performance indicators such as quantum bit error rate and secure key rate of a potential mission are estimated analytically.
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).
Losses and attenuation are the main limitations to implementing secure quantum networks based on fiber or free-space optical links over long distances. A hybrid satellite–ground approach offers an effective solution to overcome these constraints and achieve higher key transmission rates. This article presents a systematic review of publications on satellite quantum communication, providing an overview of quantum key distribution with satellites, the use of satellite networks with emphasis on commonly adopted orbits, and the role of satellites in such architectures. Special attention is given to the implementation of continuous-variable QKD (CV-QKD) in satellite-based channels, highlighting its challenges and potential for integration into future satellite-based quantum networks.
We address the applicability of quantum key distribution (QKD) with continuous-variable (CV) coherent and squeezed signal states of light over long-distance satellite-based links, considering low Earth orbits in the advantageous downlink scenario and taking into account strong varying channel attenuation (referred to as fading), atmospheric turbulence and finite data ensemble size effects.The study is motivated by the possibility to use highly efficient homodyne detection for CV protocols, which can serve as filter of background radiation due to matching of the quantum signal to a narrowband intense local oscillator beam.Considering feasible Gaussian modulation, compatible with the most advanced security proofs, we obtain tight security bounds on the untrusted excess noise at the channel output, which suggest that the protocols are very sensitive to the channel noise at the respective loss levels.In this regime, either a set-up stabilization resulting in drastic decrease of noise or relaxation of security assumptions to individual or passive collective attacks is required for implementation over the low Earth orbit satellites.Relaxation of security assumptions can be particularly motivated by the possibility of line-of-sight control of the absence of equipment capable of active collective eavesdropping attacks using quantum memories.Furthermore, splitting the satellite pass into discrete segments and extracting the keys from each rather than from the overall single pass allows one to effectively improve robustness against the untrusted channel noise and establish a secure key even under active collective attacks.Such satellite pass segmentation provides another viable option to reduce channel fading thus improving the secure key rate and allowing to establish the secure link with satellites at higher altitudes.We show that the use of signal squeezing can make the protocols more applicable in the satellite links, allowing for higher attenuation and levels of noise at the given security assumptions, and it has to be optimized in the collective attacks scenario.On the other hand, in the case of trusted noise assumption and at high repetition rates, squeezed-state CV QKD can tolerate attenuation levels up to 42 dB, allowing for higher orbit altitudes or smaller receiving telescope apertures.The obtained results are promising for satellite-based QKD, potentially applicable in daylight conditions.
Continuous variable quantum key distribution (CV-QKD) has emerged as a promising candidate for quantum-secure communication due to its experimentally demonstrated high key rates in fiber-optic channels. However, the feasibility of discrete modulation CV-QKD in satellite-to-ground downlinks remains an open question due to practical challenges such as high transmission loss, limited communication windows, and atmospheric turbulence. In this work, a comprehensive framework is proposed to evaluate the feasibility of discrete modulation CV-QKD by integrating orbital dynamics and atmospheric channel models, and to comprehensively analyze the influence of the parameter space on free-space discrete modulation CV-QKD. To achieve this, a free-space CV-QKD simulation platform is employed, which calculates the elevation angle and transmission distance based on precise orbital models, thereby providing a more practical assessment of the key rate for discrete modulation CV-QKD. Simulation results verify the feasibility and practicality of discrete modulation CV-QKD in satellite-based quantum communication systems. Furthermore, the critical factors influencing the key rate performance are identified, and parameter optimization strategies are proposed, providing theoretical support for realizing the future satellite-to-ground discrete modulation CV-QKD.