We report a daylight km-range free space QKD demonstration at 850nm obtaining a QBER of 1.9% and a raw key-rate of 14 kbit/s. We used the BB84 protocol with polarisation encoding and two supporting optical beams for classical communication and clock synchronisation.
Quantum Key Distribution (QKD) represents a groundbreaking cryptographic technology that enables theoretically unconditionally secure key generation between communication parties. With recent advancements in network integration, QKD systems have been successfully deployed across diverse complex scenarios. For last-mile access network applications, free-space optical channels emerge as an optimal transmission medium. In this work, we implement a free-space QKD system employing a high-repetition-rate phase-encoding BB84 protocol. The experimental setup incorporates a simplified, highly integrable synchronization apparatus and self-compensating phase drift correction mechanism, which enhances both system stability and secure key generation rate. Experimental results demonstrate robust performance over a 1.4-km free-space channel with approximately 13 dB attenuation, achieving a secure key rate (SKR) of 160.19 kbps while maintaining a quantum bit error rate (QBER) of 2.3%. These findings establish the feasibility and efficiency of phase-encoded free-space QKD for last-mile access network applications.
The goal of cryptography is to encode data in such a way that no one can decode it unless they are the intended recipient. With the emergence of quantum computing, classical cryptography is not reliable enough to protect sensitive information. Nevertheless, there are alternatives. Quantum Key Distribution (QKD) is a method to secure communication based on the laws of quantum physics. Due to being impossible to measure the quantum state of a system without disturbing it, QKD provides a way to communicate between two parties while being, in theory, immune to eavesdropping. In this work, a free-space high-speed QKD setup is proposed, with the objective of implementing the polarization three-state one-decoy variant of the BB84 protocol. An assessment of the best type of laser diode to use for free-space QKD is made between several options. The system’s performance was assessed, incorporating a quantitative analysis of system losses and an estimation of the number of photons traversing the quantum channel. The system achieved a Quantum Bit Error Rate (QBER) of 1.58% for the Z basis and 1.46% for the X basis, for an average reception of two photons per pulse. Preliminary QBER measurements were also undertaken in the context of Quantum Keyless Private Communication protocols, focusing on the average number of photons per pulse.
To enable global scale quantum key distribution1-3 (QKD), satellite based systems 4,5 are the most promising approach. So far, free-space QKD has already been demonstrated on communication channels with attenuation comparable to satellite downlinks,6 and classical laser communications with satellites and aircrafts is heavily explored.7-10 Here, combining both these challenges, we demonstrate an aircraft to ground QKD transmission obtaining a sifted key rate of 145 bit/s and a QBER, larglely dominated by background events and stray light, of 4:8 %.
In quantum key distribution (QKD) single-photon transmissions generate the shared, secret random number sequences, known as cryptographic keys that are used to encrypt and decrypt secret communications. Because the security of QKD is based on principles of quantum physics an adversary can neither successfully tap the key transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed an experimental QKD system that uses the four-state BB84 protocol with non-orthogonal photon polarization states and lowest-order adaptive optics to generate shared key material over multi-kilometer atmospheric, line-of-sight paths. I will present results of a daylight demonstration of this system. Key material is built up using the transmission of a photon-pulse per bit of an initial secret random sequence. I will describe the design and operation of the system, present an analysis of the system's security, efficiency, error rate, and secret key rate, as well as cryptographic testing of the key bits produced. I will describe the prospects for longer-distance applications of free-space QKD, particularly for satellite communications.