Satellite-based quantum key distribution (QKD) has lately received considerable attention due to its potential to establish a secure global network. Associated with its application is a turbulent atmosphere that sets a notable restriction to the transmission efficiency, which is especially challenging for ground-to-satellite uplink scenarios. Here, we propose a novel noiseless attenuation (NA) scheme involving a zero-photon catalysis operation for source preparation to improve the performance of continuous-variable (CV) QKD over uplink. Numerical analysis shows that the NA-based CV-QKD, under attenuation optimization, outperforms the traditional CV-QKD, which is embodied in extending the allowable zenith angle while improving the effective communication time. Attributing to characteristics of the attenuation optimization, we find that the NA-involved source preparation improves the security bound by relatively reducing the amount of information available to eavesdroppers. Taking the finite-size effect into account, we achieve a tighter bond of security, which is more practical compared with the asymptotic limit.
Satellite-based quantum key distribution (QKD) has lately received considerable attention due to its potential to establish a secure global network. Associated with its application is a turbulent atmosphere that sets a notable restriction to the transmission efficiency, which is especially challenging for ground-to-satellite uplink scenarios. Here, we propose a novel noiseless attenuation (NA) scheme involving a zero-photon catalysis operation for source preparation to improve the performance of continuous-variable (CV) QKD over uplink. Numerical analysis shows that the NA-based CV-QKD, under attenuation optimization, outperforms the traditional CV-QKD, which is embodied in extending the allowable zenith angle while improving the effective communication time. Attributing to characteristics of the attenuation optimization, we find that the NA-involved source preparation improves the security bound by relatively reducing the amount of information available to eavesdroppers. Taking the finite-size effect into account, we achieve a tighter bond of security, which is more practical compared with the asymptotic limit.
Abstract Quantum key distribution (QKD) has reached a global scale by utilizing the powerful scheme in free space scenes with a more flexible transmission. Unfortunately, the practical applicability of free-space QKD is usually curtailed by the fact that the atmospheric turbulence unavoidably destructs the quality of the quantum signal, which limits its maximum transmission distance. Here we propose an attenuation scheme for the Gaussian modulated coherent state QKD, in which a quantum catalysis operation acts as a noiseless attenuation process to regulate the potentially deteriorated quantum signal, enabling the improvement of maximal transmission distance. Compared with the original protocol, the QC-assisted attenuation presents a promotion of maximum transmission distance. In particular, we find that the zero-photon catalysis-based protocol performs better than the QC-based one. Numerical analysis shows that the QC-assisted attenuation can reduce the amount of information obtained by eavesdroppers, whereas it has a relatively light impact on mutual information. It provides a promising solution towards tackling the atmospheric turbulence in practice.
Abstract Driven by the necessitates of wide-area quantum secure communication networks, ground-to-satellite quantum key distribution (QKD) has been highlighted in the field of quantum information. Continuous variable QKD (CV-QKD) shows the advantages of a high secure key rate generation and compatibility in the fiber channel, but the communication range is limited by low attenuation tolerance. In this study, the feasibility of the uplink CV-QKD for Very Low Earth Orbit satellite is studied, and the influence of practical factors such as atmospheric turbulence and beam pointing errors under dynamic time-varying satellite orbital parameters is analyzed to model realistic transmission channels. A parameter optimization scheme for orbital parameters, spot size, receiving telescope aperture, and modulation variance has been proposed to enhance the performance of the actual uplink CV-QKD, providing a reference for parameter selection in CV-QKD experiments.
Satellite-based continuous-variable quantum key distribution (CV-QKD) is fundamentally constrained by finite communication windows, channel attenuation, and statistical fluctuations arising from a limited number of exchanged quantum states. This work develops a finite-size CV-QKD framework for satellite quantum communication under a hybrid noise model that jointly incorporates satellite geometry, atmospheric and propagation losses, quantum Poissonian noise coexisting with classical additive white Gaussian noise, detector imperfections, and composable finite-key security under collective attacks. A single canonical finite-size secret key rate (SKR) expression is derived in which the finite-size correction is stated in a strictly decreasing form in the block size, removing the ambiguity between the segmented and the block-level formulations used in earlier treatments. The finite-size accounting is further extended to the quantum bit error ratio (QBER) through an explicit parameter estimation penalty, so that the feasibility constraint inherits the same block-size dependence as the key rate. The framework quantifies the influence of reconciliation efficiency, transmission efficiency, detection efficiency, receiver aperture, beam waist, zenith angle, wavelength, and effective communication time. Numerical results reveal a significant performance gap between finite-size and asymptotic operation, indicating that asymptotic analysis can overestimate the feasible satellite altitude by a factor of several, and that the achievable range is governed by the number of signals actually exchanged rather than by any single physical channel parameter. These results establish block size as a first-class design variable for satellite CV-QKD mission dimensioning.
In this work we study the use of noiseless attenuation and noiseless amplification, in terms of multi-mode Continuous-Variable (CV) Quantum Key Distribution (QKD) over satellite-to-ground channels. We propose an improved multi-mode CV-QKD protocol where noiseless attenuation and noiseless amplification operations are applied at the transmitter and the receiver, respectively. Our results show that consistent with single-mode CV-QKD, the noiseless amplification operation, when applied at the receiver, can increase the transmission distance and the channel noise tolerance of multi-mode CV-QKD. Different from single-mode CV-QKD, in multi-mode CV-QKD the key rate improvement offered by noiseless amplification can be further enhanced by adding noiseless attenuation at the transmitter.
The satellite-mediated continuous-variable quantum key distribution (CV-QKD) protocol, which relies on off-the-shelf telecommunication components, has the potential for a global quantum communication network with all-day operation. However, the transmittance fluctuation of satellite-mediated links leads to the arriving quantum state showing non-Gaussian property, introducing extra fading noise in security analysis and limiting the secret key rate of the protocol. Here, we consider the clusterization method for data post-processing to suppress the fading noise in both downlink and uplink scenarios, where the measurement data are divided into several clusters, and we perform security analysis separately. In particular, we set the optimal upper and lower bounds of each cluster in terms of the probability distribution of transmittance (PDT), while finding an optimal cluster number for the trade-off between fading noise and the composable finite-size effect. Numerical analysis shows that the proposed method can improve the composable finite-size rate when the fading noise is large enough, even with only two clusters. Moreover, a high-speed CV-QKD system with a higher frequency of signal preparation and detection can extend the proposed method to work in the case of lower fading noise.
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.