# US 2025/0168632 A1 · Innovative Quantum Key Distribution Transmission System > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2025/0168632 A1 - Document ID: US20250168632A1 - Status: Published application - Kind: A1 - Application number: 18/954,999 - Filed: 2024-11-21 - Published: 2025-05-22 - Earliest claimed: 2023-11-22 - Assignees: Thales Alenia Space Italia S.p.A. Con Unico Socio - Applicants: Thales Alenia Space Italia S.p.A. Con Unico Socio - Inventors: Tommaso Catuogno; Mattia Verducci; Cristian Iacurto; Andrea Geraldi - Web page: https://patentgrep.com/patent/US20250168632A1 ## CPC - H04L 9/0852: {Quantum cryptography (transmission systems employing electromagnetic waves other than radio waves, e.g. light, infrared H04B10/00; wavelength-division multiplex systems H04J14/02; WDM arrangements H04J14/03)} - H04W 12/0431: Key distribution or pre-distribution; Key agreement - H04B 10/70: Photonic quantum communication - H04L 9/0858: {Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding} - H04W 12/122: Counter-measures against attacks; Protection against rogue devices - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) - H04B: TRANSMISSION ## Abstract The present invention concerns a Quantum Key Distribution transmission system comprising a transmitter and a receiver, wherein the transmitter is configured to transmit a multiphoton pulse to the receiver through a trusted area that extends from the transmitter towards the receiver up to a trusted distance from the transmitter; wherein the transmitter is configured to transmit the multiphoton pulse with a transmission power such that a single-photon pulse propagates out from the trusted area up to reach the receiver. ## Claims ### Claim 1 A Quantum Key Distribution (QKD) transmission system (2, 3) comprising transmitter (31) and a receiver (32), wherein the transmitter (31) is configured to transmit a multiphoton pulse to the receiver (32) through a trusted area (23, 33) that extends from the transmitter (31) towards the receiver (32) up to a trusted distance (D) from the transmitter (31); wherein the transmitter (31) is configured to transmit the multiphoton pulse with a transmission power such that a single-photon pulse propagates out from the trusted area (23, 33) up to reach the receiver (32). ### Claim 2 (depends on 1) The Quantum Key Distribution transmission system of claim 1, wherein the transmitter (31) is configured to: a) determine the trusted distance (D) thereby defining a trusted area's size; b) assess security of the trusted area (23, 33); c) if the trusted area (23, 33) is secure, i. determine a transmission power such that, by transmitting a multiphoton pulse with said transmission power, a single-photon pulse propagates out from the trusted area (23, 33) up to reach the receiver (32), and ii. transmit a multiphoton pulse with the determined transmission power; d) if the trusted area (23, 33) is not secure, carry out the steps a), b), and c) or d) by determining a different trusted distance (D). ### Claim 3 (depends on 2) The Quantum Key Distribution transmission system of claim 2, wherein: the trusted distance (D) is determined based on priority and performance requirements related to a requested encryption service and, optionally, also on a class of service of said encryption service; the security of the trusted area (23, 33) is assessed based on a continuous monitoring of the trusted area (23, 33) or of an area around the transmitter (31); the transmission power is determined such that propagation of N transmitted photons through the trusted area (23, 33) leads statistically to a number of photons equal to one at the trusted distance (D) with a probability higher than a predefined threshold, N being a positive integer higher than one; the transmitted multiphoton pulse carries the N photons. ### Claim 4 (depends on 3) The Quantum Key Distribution transmission system of claim 3, wherein the transmission power is determined based on the following mathematical formula: P ⁢ { Nphotons ⁡ ( N , D , P Tx , Channel_Model ) = 1 } > Threshold , where D denotes the trusted distance, PTx denotes the transmission power, N denotes the number of photons transmitted with the transmission power PTx, Channel_Model denotes a predefined channel model assumed for the transmission channel and modelling channel losses during photon propagation, Nphotons denotes a function providing the number of photons present at the trusted distance D from the transmitter (31) based on the number of transmitted photons N, the trusted distance D, the transmission power PTx and the predefined channel model Channel_Model, P denotes the probability that the function Nphotons is equal to one, and Threshold denotes a predefined threshold. ### Claim 5 (depends on 3) The Quantum Key Distribution transmission system according to claim 3, wherein the continuous monitoring of the trusted area (23, 33) or of the area around the transmitter (31) is carried out by means of one or more sensors and/or based on Earth monitoring. ### Claim 6 (depends on 3) The Quantum Key Distribution transmission system according to claim 3, wherein the transmitter (31) is configured to stop transmitting the multiphoton pulse if a potential threat to security of the trusted area (23, 33) is detected based on the continuous monitoring. ### Claim 7 (depends on 6) The Quantum Key Distribution transmission system of claim 6, wherein the transmitter (31) is configured to, if it stops transmitting due to a detected potential threat, carry out the steps a), b), and c) or d) by determining a different trusted distance (D). ### Claim 8 (depends on 1) The Quantum Key Distribution transmission system according to claim 1, wherein said Quantum Key Distribution transmission system is integrated into a space or satellite or terrestrial or space/satellite-earth communication system. ### Claim 9 (depends on 1) A transmitting system configured as the transmitter (31) of the Quantum Key Distribution transmission system (2, 3) as claimed in claim 1. ### Claim 10 A method for Quantum Key Distribution (QKD) transmission from a transmitter (31) to a receiver (32), comprising transmitting, the transmitter (31), a multiphoton pulse to the receiver (32) through a trusted area (23, 33) that extends from the transmitter (31) towards the receiver (32) up to a trusted distance (D) from the transmitter (31); wherein transmitting includes transmitting the multiphoton pulse with a transmission power such that a single-photon pulse propagates out from the trusted area (23, 33) up to reach the receiver (32). ### Claim 11 (depends on 10) The method of claim 10, including: a) determining the trusted distance (D) thereby defining a trusted area's size; b) assessing security of the trusted area (23, 33); c) if the trusted area (23, 33) is secure, i. determining a transmission power such that, by transmitting a multiphoton pulse with said transmission power by the transmitter (31), a single-photon pulse propagates out from the trusted area (23, 33) up to reach the receiver (32), and ii. transmitting, by the transmitter (31), a multiphoton pulse with the determined transmission power; d) if the trusted area (23, 33) is not secure, carrying out the steps a), b), and c) or d) by determining a different trusted distance (D). ### Claim 12 (depends on 11) The method of claim 11, wherein: the trusted distance (D) is determined based on priority and performance requirements related to a requested encryption service and, optionally, also on a class of service of said encryption service; the security of the trusted area (23, 33) is assessed based on a continuous monitoring of the trusted area (23, 33) or of an area around the transmitter (31); the transmission power is determined such that propagation of N transmitted photons through the trusted area (23, 33) leads statistically to a number of photons equal to one at the trusted distance (D) with a probability higher than a predefined threshold, N being a positive integer higher than one; the transmitted multiphoton pulse carries the N photons. ### Claim 13 (depends on 12) The method of claim 12, wherein the transmission power is determined based on the following mathematical formula: P ⁢ { Nphotons ⁡ ( N , D , P Tx , Channel_Model ) = 1 } > Threshold , where D denotes the trusted distance, PTx denotes the transmission power, N denotes the number of photons transmitted with the transmission power PTx, Channel_Model denotes a predefined channel model assumed for the transmission channel and modelling channel losses during photon propagation, Nphotons denotes a function providing the number of photons present at the trusted distance D from the transmitter (31) based on the number of transmitted photons N, the trusted distance D, the transmission power PTx and the predefined channel model Channel_Model, P denotes the probability that the function Nphotons is equal to one, and Threshold denotes a predefined threshold. ### Claim 14 (depends on 12) The method according to claim 12, wherein the continuous monitoring of the trusted area (23, 33) or of the area around the transmitter (31) is carried out by means of one or more sensors and/or based on Earth monitoring. ### Claim 15 (depends on 12) The method according to claim 12, further comprising stopping transmitting the multiphoton pulse if a potential threat to security of the trusted area (23, 33) is detected based on the continuous monitoring. ### Claim 16 (depends on 15) The method of claim 15, further comprising, if transmitting the multiphoton pulse is stopped due to a detected potential threat, carrying out the steps a), b), and c) or d) by determining a different trusted distance (D).