Comparison of commercial and next generation quantum key distribution: Technologies for secure communication of information

Battelle has been actively exploring emerging quantum key distribution (QKD) cryptographic technologies for secure communication of information with a goal of expanding the use of this technology by commercial enterprises in the United States. In QKD systems, the principles of quantum physics are applied to generate a secret data encryption key, which is distributed between two users. The security of this key is guaranteed by the laws of quantum physics, and this distributed key can be used to encrypt data to enable secure communication on insecure channels. To date, Battelle has studied commercially available and custom-built QKD systems in controlled laboratory environments and is actively working to establish a QKD Test Bed network to characterize performance in real world metropolitan (10-100 km) and long distance (>; 100 km) environments. All QKD systems that we have tested to date utilize a discrete variable (DV) binary approach. In this approach, discrete information is encoded onto a quantum state of a single photon, and binary data are measured using single photon detectors. Recently, continuous variable (CV) QKD systems have been developed and are expected to be commercially available shortly. In CV-QKD systems, randomly generated continuous variables are encoded on coherent states of weak pulses of light, and continuous data values are measured with homodyne detection methods. In certain applications for cyber security, the CV-QKD systems may offer advantages over traditional DV-QKD systems, such as a higher secret key exchange rate for short distances, lower cost, and compatibility with telecommunication technologies. In this paper, current CV- and DV-QKD approaches are described, and security issues and technical challenges fielding these quantum-based systems are discussed. Experimental and theoretical data that have been published on quantum key exchange rates and distances that are relevant to metropolitan and long distance network applications are presented. From an analysis of these data, the relative performance of the two approaches is compared as a function of distance and environment (free space and optical fiber). Additionally, current research activities are described for both technologies, which include network integration and methods to increase secret key distribution rates and distances.