Lee Oesterling

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.

A multiplexed light-matter interface for fibre-based quantum networks

Processing and distributing quantum information using photons through fibre-optic or free-space links are essential for building future quantum networks. The scalability needed for such networks can be achieved by employing photonic quantum states that are multiplexed into time and/or frequency, and light-matter interfaces that are able to store and process such states with large time-bandwidth product and multimode capacities. Despite important progress in developing such devices, the demonstration of these capabilities using non-classical light remains challenging. Here, employing the atomic frequency comb quantum memory protocol in a cryogenically cooled erbium-doped optical fibre, we report the quantum storage of heralded single photons at a telecom-wavelength (1.53 μm) with a time-bandwidth product approaching 800. Furthermore, we demonstrate frequency-multimode storage and memory-based spectral-temporal photon manipulation. Notably, our demonstrations rely on fully integrated quantum technologies operating at telecommunication wavelengths. With improved storage efficiency, our light-matter interface may become a useful tool in future quantum networks.

Development of photon pair sources using periodically poled lithium niobate waveguide technology and fiber optic components

To support quantum technologies that require entangled photon pairs and/or heralded photons for operation, a photon pair source was developed that uses periodically poled lithium niobate (PPLN) waveguides that are coupled to optical fibers. Both Ti-indiffused and annealed proton-exchanged (APE) waveguide technologies were studied, and waveguide/fiber interfaces were designed to increase the coupling efficiency of the photon pairs into optical fiber. PPLN waveguide devices were fabricated and the optical loss, wavelength conversion efficiency, and heralding efficiency were measured. The maximum heralding efficiencies achieved were 75 and 68% for Ti-indiffused and APE waveguides, respectively. A compact photon pair source based on a packaged PPLN waveguide device and commercially available fiber optic components is presented.

Terahertz spectral signatures of explosive materials and precursors

Terahertz (THz) spectral signatures have been measured for a variety of explosive materials and precursors. These signatures were measured by THz Time Domain Spectroscopy, using ultrashort pulsed lasers coupled with electro-optic materials to generate and detect THz radiation. Transmission and reflection spectra were measured across a frequency range from 0.2 to 2.5 THz for solid and liquid materials. These spectra are reported in terms of index of refraction and absorption coefficient, both of which can be calculated from transmission or reflection data. The value of THz spectral signatures for the development of future explosives sensing systems is discussed.