What Is A Quantum Repeater

Introduction to Quantum Computing

Quantum Repeater

Quantum Repeaters are used to overcome the limits imposed by attenuation and the no-cloning theorem in quantum mechanics.  Thus, a quantum repeater provides for the end-to-end generation of quantum entanglement, and the end-to-end transmission of qubits. 

Optical fibers are made of silica.  Silica has two leading loss mechanisms.  At short wavelengths, the dominant loss mechanism is elastic scattering. Elastic scattering can change the propagation direction of the light enough to allow it to escape the optical fiber.  At long wavelengths, the dominant loss mechanism becomes absorption by the material.   Also, it should be noted that the fiber loss is approximately constant.  Thus, loss becomes proportional to the distance of transmission.  

To provide context, 95% of the initial signal power remains after a transmission distance of 1km; whereas, 1% of the initial signal power remains after a transmission distance of 100 km. Thus, the transmitted power scales very poorly with distance requiring some form of repeaters.