Demonstrating BB84 quantum key distribution in the physical layer of an optical fiber based system

Abstract

Nowadays, widely spread encryption methods (e.g., RSA) and protocols enabling digital signatures (e.g., DSA, ECDSA) are an integral part of our life. Although recently developed quantum computers have low processing capacity, huge dimensions and lack of interoperability, we must underline their practical significance – applying Peter Shor’s quantum algorithm (which makes it possible to factorize integers in polynomial time) public key cryptography is set to become breakable. As an answer, symmetric key cryptography proves to be secure against quantum based attacks and with it quantum key distribution (QKD) is going through vast development and growing to be a hot topic in data security. This is due to such methods securely generating symmetric keys by protocols relying on laws of quantum physics. In this paper we introduce a fiber based QKD system that is being built in Hungary in a collaboration between Budapest University of Technology and Economics (BME), Wigner Research Centre for Physics and Ericsson Hungary. We demonstrate the first successful quantum key distribution over physical layer in accordance with the truth table of BB84 protocol in the country. We apply light pulses at 1550 nm wavelength, reducing their power to less than one photon per pulse level. We create two phases of operation including an initialization phase in which software and hardware solutions are proposed for synchronizing the units of the two communicating parties. We introduce a data processing and a timing mechanism and elaborate on the results of the demonstration. We also inspect the possibilities of efficiency enhancement and give an outlook on further development directions.