Maintaining secure key distribution, and protected local node state, across an intermittent or disrupted long-distance link is the problem addressed here. A deep-space path is the extreme case. Dust, distance, and loss of the carrier do not by themselves preserve that state, distribute a key, or protect the ground system that holds the key register. The March 2025 communications file raised deep-space relays as a subject. A baryonic radio or laser terminal is not the regulator of the deposited layer partition. Frequency-bin entanglement supplies the key on a channel that can break and resume. The proposed ground architecture uses a haloscope mesh to intercept and dissipate an in-band microwave disturbance before it can couple into the key register or the clock. The node keeps its own state through the outage. The monitor may read telemetry and may not write protected state. Write-back remains W = 0, as an architectural constraint and not as a consequence of operator commutation. No new link, key protocol, or industry is claimed.
Maintaining secure key distribution, and protected local node state, across an intermittent or disrupted long-distance link is the problem addressed here. A deep-space path is the extreme case. Dust, distance, and loss of the carrier do not by themselves preserve that state, distribute a key, or protect the ground system that holds the key register. The March 2025 communications file raised deep-space relays as a subject. A baryonic radio or laser terminal is not the regulator of the deposited layer partition. Frequency-bin entanglement supplies the key on a channel that can break and resume. The proposed ground architecture uses a haloscope mesh to intercept and dissipate an in-band microwave disturbance before it can couple into the key register or the clock. The node keeps its own state through the outage. The monitor may read telemetry and may not write protected state. Write-back remains W = 0, as an architectural constraint and not as a consequence of operator commutation. No new link, key protocol, or industry is claimed.
The feasibility of trust-free long-haul quantum key distribution (QKD) is addressed. We combine measurement-device-independent QKD, as an access technology, with a quantum repeater setup, at the core of future quantum communication networks. This will provide a quantum link none of whose intermediary nodes need to be trusted, or, in our terminology, a trust-free QKD link. As the main figure of merit, we calculate the secret key generation rate when a particular probabilistic quantum repeater protocol is in use. We assume the users are equipped with imperfect single photon sources, which can possibly emit two single photons, or laser sources to implement decoy-state techniques. We consider apparatus imperfection, such as quantum efficiency and dark count of photodetectors, path loss of the channel, and writing and reading efficiencies of quantum memories. By optimizing different system parameters, we estimate the maximum distance over which users can share secret keys when a finite number of memories are employed in the repeater setup.
Entanglement-based quantum links are the backbone of future quantum internet networks, enabling secure communication between distant cities. Realizing such networks requires addressing multiple practical challenges in long-distance quantum key distribution : time synchronisation, interferometer stabilisation and automation. Here, we report several advances. First, we maintained an operational QKD link continuously for 325hours over 50km between two remotes locations, demonstrating the feasibility of long-duration key generation. We further extended secure key distribution up to a 100km operational link connecting the University of Nice to a ground-based optical station, a setup compatible with future quantum satellite connections. Finally, by employing wavelength demultiplexing to separate photons of entangled pairs, we performed QKD across multiple ITU channels, achieving secure key exchange via the BBM92 protocol and time-energy observables.
A Mathematical Framework for a Lunar-to-Mars Quantum Key Distribution Architecture (revised)A link-budget framework for a direct, single-hop entanglement-based (BBM92) QKD link at 1550 nm from a lunar terminal to a Martian receiver, using 10 m apertures on a 30–40 year technology horizon. The link gives about 6 bit/s of secure key at the mean distance and about 115 bit/s near opposition. Key generation stops when the Martian dust optical depth exceeds about 2.8, and the link is unavailable for roughly two to three months around each solar conjunction.This revision derives the QBER from a single noise model, models dust by optical depth, adds the solar-conjunction outage, and corrects the relativistic clock drift to include solar gravity (433 µs/day). Includes the verification script.
The feasibility of trust-free long-haul quantum key distribution (QKD) networks is addressed. We combine measurement-device-independent QKD (MDI-QKD), as an access technology, with a quantum repeater setup, at the core of future quantum communication networks. This will provide a quantum link none of whose intermediary nodes need to be trusted, or, in our terminology, a trust-free QKD link. As the main figure of merit, we calculate the secret key generation rate when a particular probabilistic quantum repeater protocol is in use. We assume the users are equipped with imperfect single photon sources, which can possibly emit two single photons, or laser sources to implement decoy-state techniques. We consider apparatus imperfection, such as quantum efficiency and dark count of photodetectors, path loss of the channel, and writing and reading efficiencies of quantum memories. By optimizing different system parameters, we estimate the maximum distance over which users can share secret keys when a finite number of memories are employed in the repeater setup.
Quantum Key Distribution (QKD) is currently the only known technique that is able to guarantee information-theoretic secure communications.While many countries have already started developing use-cases based mostly on terrestrial links, the high losses that afflict fiber-based channels make them unsuitable for very-long-distance communications.Taking the quantum networks to a national and global scale thus requires the use of satellite-based quantum communications, as the attenuation experienced by photons in space communications is order of magnitudes lower than the one that characterizes terrestrial networks.Thales Alenia Space in Italy (TAS-I) is positioning itself as a key actor in the development of the technology needed to perform space quantum communications.In this work, we present an overview of the initiatives that are currently being carried out by TAS-I, and define a roadmap whose steps are planned to take the current laboratory experimentation towards the development of a fully operational QKD constellation meant to provide secret keys on a global scale.We also describe a possible implementation of an Italian demonstrator mission based on a LEO satellite that acts as a trusted node to distribute shared keys among a certain number of ground stations; we study the effects of some major system choices and assess the overall achievable performance in terms of Secret Key Volume (SKV).
With the goal of a space-based quantum network is to have satellites distribute keys between any nodes on the ground, we consider an evolved quantum network from a near-term form, in which a space-based relay, satellite executes a sequence of satellite-based quantum key distribution (SatQKD) missions, allowing any two ground nodes to have a shared secure key. Accordingly, we develop a comprehensive framework for the dynamic simulation of SatQKD and consider scheduling QKD downlink in future space-based quantum communication network. The embedding of precise orbital model including beam diffractions and atmosphere effects makes our framework more realistic. Incorporated with the local meteorological data to channel loss model, the cloud cover contribution to transmission disturbance is quantified to realize a quasi-experimental scenario. We provide a trade-off consideration between the duration available for communications and its corresponding average link loss during one orbit, which could be used to support decisions involving the locations of ground stations and the selection of the orbital parameters for a quantum satellite. Our work also shows that satellite downlink schedule could allow for the possibility to consider strategies for different SatQKD missions such as extending connection for distant ground nodes, prioritized delivery, or promoting keys utilization, which can be used as a guideline to support decisions for future satellite application.