Quantum Key Distribution with Time-Bin Encoding for Space Quantum Communications.

This work presents a quantum key distribution (QKD) system that uses time-bin encoding and a modified BB84 protocol, optimized for space-based quantum communications. Bennett and Brassard (1984) and Boarón et al. (2018) encoded qubits using the presence or absence of photons in discrete time intervals instead of traditional polarization.

The objective is to develop a secure and efficient system for free-space quantum transmission. An attenuated continuous-wave laser, photon detectors, and a synchronization system were implemented to properly align time intervals between Alice and Bob. The random states sent by Alice are generated through a binary file stored on a USB drive connected to a function generator, creating pulses with 1 µs time widths. These pulses, along with an amplitude modulator, adjust the amplitude of the continuous-wave laser to replicate the same 1 µs pulses. A phase shifter is used to establish two mutually unbiased state bases. The results suggest that this approach is robust against adverse conditions and attacks, highlighting its potential to improve security in space environments, making it unique and relevant in its field.