Kevin McCabe

Optical networking for quantum key distribution and quantum communications

Modern optical networking techniques have the potential to greatly extend the applicability of quantum communications by moving beyond simple point-to-point optical links and by leveraging existing fibre infrastructures. We experimentally demonstrate many of the fundamental capabilities that are required. These include optical-layer multiplexing, switching and routing of quantum signals; quantum key distribution (QKD) in a dynamically reconfigured optical network; and coexistence of quantum signals with strong conventional telecom traffic on the same fibre. We successfully operate QKD at 1310 nm over a fibre shared with four optically amplified data channels near 1550 nm. We identify the dominant impairment as spontaneous anti-Stokes Raman scattering of the strong signals, quantify its impact, and measure and model its propagation through fibre. We describe a quantum networking architecture which can provide the flexibility and scalability likely to be critical for supporting widespread deployment of quantum applications.

Dense wavelength multiplexing of 1550 nm QKD with strong classical channels in reconfigurable networking environments

To move beyond dedicated links and networks, quantum communications signals must be integrated into networks carrying classical optical channels at power levels many orders of magnitude higher than the quantum signals themselves. We demonstrate the transmission of a 1550 nm quantum channel with up to two simultaneous 200 GHz spaced classical telecom channels, using reconfigurable optical add drop multiplexer (ROADM) technology for multiplexing and routing quantum and classical signals. The quantum channel is used to perform quantum key distribution (QKD) in the presence of noise generated as a by-product of the co-propagation of classical channels. We demonstrate that the dominant noise mechanism can arise from either four-wave mixing or spontaneous Raman scattering, depending on the optical path characteristics as well as the classical channel parameters. We quantify these impairments and discuss mitigation strategies.

Practical long-distance quantum key distribution system using decoy levels

Quantum key distribution (QKD) has the potential for widespread real-world applications, but no secure long-distance experiment has demonstrated the truly practical operation needed to move QKD from the laboratory to the real world due largely to limitations in synchronization and poor detector performance. Here, we report results obtained using a fully automated, robust QKD system based on the Bennett Brassard 1984 (BB84) protocol with low-noise superconducting nanowire single-photon detectors (SNSPDs) and decoy levels to produce a secret key with unconditional security over a record 140.6 km of optical fibre, an increase of more than a factor of five compared with the previous record for unconditionally secure key generation in a practical QKD system.

Experience with a Hybrid Processor: K-Means Clustering

We discuss hardware/software co-processing on a hybrid processor for a compute- and data-intensive multispectral imaging algorithm, k-means clustering. The experiments are performed on two models of the Altera Excalibur board, the first using the soft IP core 32-bit NIOS 1.1 RISC processor, and the second with the hard IP core ARM processor. In our experiments, we compare performance of the sequential k-means algorithm with three different accelerated versions. We consider granularity and synchronization issues when mapping an algorithm to a hybrid processor. Our results show that speedup of 11.8X is achieved by migrating computation to the Excalibur ARM hardware/software as compared to software only on a Gigahertz Pentium III. Speedup on the Excalibur NIOS is limited by the communication cost of transferring data from external memory through the processor to the customized circuits. This limitation is overcome on the Excalibur ARM, in which dual-port memories, accessible to both the processor and configurable logic, have the biggest performance impact of all the techniques studied.

Demonstration of 1550 nm QKD with ROADM-based DWDM Networking and the Impact of Fiber FWM

We demonstrate compatibility of 1550 nm QKD with a MEMS-based ROADM and also show that four-wave mixing resulting from copropagating DWDM signals can become the dominant source of background noise within the QKD channel passband.

Experimental characterization of the separation between wavelength-multiplexed quantum and classical communication channels

Quantum key distribution (QKD) is a new technique for secure key distribution based on the laws of physics rather than mathematical or algorithmic computational complexity used by current systems. Understanding the compatibility of QKD at 1310 nm with the existing commercial optical networks bearing classical wavelength-division-multiplexed (WDM) channels at 1550 nm is important to advance the deployment of QKD systems in such networks. The minimum wavelength separation for multiplexing QKD and WDM channels on a shared fiber is experimentally determined for impairment-free QKD+WDM transmission.

An applications approach to evolvable hardware

We discuss the use of Field Programmable Gate Arrays (FPGAs) as hardware accelerators in genetic algorithm (GA) applications. The research is particularly focused on image processing optimization problems where fitness evaluation is computationally demanding and poorly suited to micro-processor systems. This research identifies key design principles for FPGA based GA and suggests a novel 2 stage reconfiguration technique. We demonstrate its effectiveness in obtaining significant speed-up; and illustrate the unique hardware GA design environment where representation is driven by a combination of hardware architecture and problem domain.

Impact of spontaneous anti-Stokes Raman scattering on QKD+DWDM networking

This study presents an experimental demonstration of 1310 nm QKD multiplexing and transmission with amplified DWDM signals over a shared 10 km fiber span. This work identifies anti-Stokes Raman scattering generated during fiber propagation as the primary contributor of crosstalk noise at the QKD receiver. New results are presented on the characterization of spontaneous anti-Stokes Raman noise (SASRN), generated within the fiber by the high-power DWDM signals, and implications for QKD+DWDM networking architectures are also discussed.

Progress toward quantum communications networks: opportunities and challenges

Quantum communications is fast becoming an important component of many applications in quantum information science. Sharing quantum information over a distance among geographically separated nodes using photonic qubits requires a reconfigurable transparent networking infrastructure that can support quantum information services. Using quantum key distribution (QKD) as an example of a quantum communications service, we investigate the ability of fiber networks to support both conventional optical traffic and single-photon quantum communications signals on a shared infrastructure. The effect of Raman scattering from conventional channels on the quantum bit error rate (QBER) of a QKD system is analyzed. Additionally, the potential impact and mitigation strategies of other transmission impairments such as four-wave mixing, cross-phase modulation, and noise from mid-span optical amplifiers are discussed. We also review recent trends toward the development of automated and integrated QKD systems which are important steps toward reliable and manufacturable quantum communications systems.

A power-aware, satellite-based parallel signal processing scheme

Satellite subsystem power budgets typically have strict margin allocations that limit the on-board processing capability of the spacecraft. Subsystems are assigned a fixed, maximum power allocation and are managed in an on/off manner according to available power and operations schedule. For a remote-sensing satellite, this limitation can result in poorer detection performance of interesting signal events as well as static instrument or data collection settings. Power-aware computation techniques can be utilized to increase the capability of on-board processing of science data and give the remote-sensing system a greater degree of flexibility.We investigate a power-aware, signal processing scheme used to study signals from lightning events in the Earths atmosphere. Detection and analysis of these lightning signals is complicated by the frequency dispersion experienced by the signal in the ionosphere as well as the interfering anthropogenic signals. We outline a method using multiprocessor architecture to run processing algorithms which have varying rates of power consumption. A 6 order magnitude spectrum of energy usage for these algorithms is obtained from experiment results.