US 12,149,615 B2
Long-distance quantum key distribution
Nikita Kirsanov, St. Gallen (CH); Nurbolat Kenbayev, St. Gallen (CH); Dmitry Kronberg, St. Gallen (CH); Valerii Vinokour, St. Gallen (CH); Gordey Lesovik, St. Gallen (CH); Pavel Sekatski, St. Gallen (CH); and Asel Sagingalieva, St. Gallen (CH)
Assigned to Terra Quantum AG, Rorschach (CH)
Filed by Terra Quantum AG, St. Gallen (CH)
Filed on Feb. 18, 2022, as Appl. No. 17/675,256.
Claims priority of application No. 21157942 (EP), filed on Feb. 18, 2021; and application No. 21166427 (EP), filed on Mar. 31, 2021.
Prior Publication US 2022/0278834 A1, Sep. 1, 2022
Int. Cl. H04L 9/08 (2006.01); G06N 10/20 (2022.01)
CPC H04L 9/0858 (2013.01) [G06N 10/20 (2022.01); H04L 9/0838 (2013.01)] 15 Claims
OG exemplary drawing
 
1. A method for determining a secret cryptographic key shared between a sending unit and a receiving unit that are connected via a communication channel comprising a plurality of spatially separated amplifiers, the method comprising: transmitting, at the sending unit, at least one electromagnetic test pulse to the receiving unit via the communication channel, and determining a signal loss (rE) in the communication channel caused by an eavesdropper based on the at least one electromagnetic test pulse detected at the receiving unit; transmitting, at the sending unit, a first sequence of electromagnetic pulses to the receiving unit via the communication channel for establishing a shared secret cryptographic key, wherein the transmitted first sequence of electromagnetic pulses along the communication channel are amplified by the spatially separated amplifiers; wherein each electromagnetic pulse of the first sequence of electromagnetic pulses corresponds to a bit of a random bit sequence according to a ciphering protocol; and determining at least one ciphering parameter of the ciphering protocol by maximizing an expected key generation rate (Lf/L) with respect to the at least one ciphering parameter using an information theory model for the expected key generation rate (Lf/L), wherein the determined signal loss (rE) and at least one amplification parameter of the spatially separated amplifiers are taken into account as input parameters to the information theory model.