The Illinois Express Quantum Network (IEQNET) is a program to realize metro-scale quantum networking over deployed optical fiber using currently available technology. IEQNET consists of multiple sites that are geographically dispersed in the Chicago metropolitan area. Each site has one or more quantum nodes (Qnodes) representing the communication parties in a quantum network. Q-nodes generate or measure quantum signals such as entangled photons and communicate the results via standard, classical, means. The entangled photons in IEQNET nodes are generated at multiple wavelengths, and are selectively distributed to the desired users via optical switches. Here we describe the network architecture of IEQNET, including the Internet-inspired layered hierarchy that leverages software-defined-networking (SDN) technology to perform traditional wavelength routing and assignment between the Q-nodes. Specifically, SDN decouples the control and data planes, with the control plane being entirely classical. Issues associated with synchronization, calibration, network monitoring, and scheduling will be discussed. An important goal of IEQNET is demonstrating the extent to which the control plane can coexist with the data plane using the same fiber lines. This goal is furthered by the use of tunable narrow-band optical filtering at the receivers and, at least in some cases, a wide wavelength separation between the quantum and classical channels. We envision IEQNET to aid in developing robust and practical quantum networks by demonstrating metro-scale quantum communication tasks such as entanglement distribution and quantum-state teleportation.
Low-loss nano- and micro-photonic platforms provide strong optical confinement and as a result enhance the effective material nonlinearity by several orders of magnitude, making them appealing candidates for quantum nonlinear photonics. One such platform is based on high-Q crystalline whispering-gallery-mode (WGM) microresonators, which can provide for highly efficient three-wave mixing, where even a single photon has a strong effect. We present experimental progress on the fabrication of small microresonators (R⪅100 μm) with Q-factors ≥ 106 that are capable of supporting such strong coupling. We also demonstrate direct imaging of the spatial profiles of the WGMs, which is useful for identifying the phase-matched resonances of three-wave-mixing processes. Additionally, we present theoretical modeling of the cavity dynamics which suggests that single-photon-driven nonlinear processes are feasible in these crystalline microresonators. This crystalline WGM microresonator platform, therefore, can enable deterministic generation of non-classical light, including entangling gates for quantum information processing.
Optically active rare-earth Neodymium (Nd) ions are integrated in Niobium (Nb) thin films forming a new quantum memory device (Nd:Nb) targeting long-lived coherence times and multi-functionality enabled by both spin and photon storage properties. Nb is implanted with Nd spanning 10-60 keV energy and 1013-1014 cm-2 dose producing a 1- 3% Nd:Nb concentration as confirmed by energy-dispersive X-ray spectroscopy. Scanning confocal photoluminescence (PL) at 785 nm excitation are made and sharp emission peaks from the 4F3/2 -< 4I11/2 Nd3+ transition at 1064-1070 nm are examined. In contrast, un-implanted Nb is void of any peaks. Line-shapes at room temperature are fit with Lorentzian profiles with line-widths of 4-5 nm and 1.3 THz bandwidth and the impacts of hyperfine splitting via the metallic crystal potential are apparent and the co-contribution of implant induced defects. With increasing Nd from 1% to 3%, there is a 0.3 nm red shift and increased broadening to a 4.8 nm linewidth. Nd:Nb is photoconductive and responds strongly to applied fields. Furthermore, optically detected magnetic resonance (ODMR) measurements are presented spanning near-infrared telecom band. The modulation of the emission intensity with magnetic field and microwave power by integration of these magnetic Kramer type Nd ions is quantified along with spin echoes under pulsed microwave π-π/2 excitation. A hybrid system architecture is proposed using spin and photon quantum information storage with the nuclear and electron states of the Nd3+ and neighboring Nb atoms that can couple qubit states to hyperfine 7/2 spin states of Nd:Nb and onto NIR optical levels excitable with entangled single photons, thus enabling implementation of computing and networking/internet protocols in a single platform.
We present the design and construction of a high-speed telecom-band (1.5 μm) single-photon counting system based on an InGaAs/InP avalanche photodiode (APD) operating in the gated Geiger mode. The detector can be gated at high speeds (we examine its performance up to 25 MHz) to maximize the counting rate in long-distance, telecom-band, fiber-optic quantum communication applications. Narrow gate pulses (250 ps full width at half maximum) are used to reduce the dark-count and the after-pulse probability. In order to count the avalanche events, we employ a high-speed comparator to sample the unfiltered and unamplified avalanche photocurrent. The APD and all the associated electronics are integrated onto a printed circuit board with a computer interface. In addition, we cool the APD to -27°C to reduce the dark-count probability.
We will describe keyed communication in quantum noise (KCQ) and how it can be used for either data encryption or key generation. Specifically, we will focus on the AlphaEta protocol for data encryption where the role of quantum noise will be discussed. Additionally, the potential of using classical noise to enhance security via deliberate signal randomization (DSR) will be investigated. We will also investigate the effect of unwanted impairments, such as nonlinearities in a wavelength-division-multiplexed fiber transmission system, and how they affect the ultimate allowable propagation distance. Our simulations and experiments suggest that AlphaEta-protocol based physical-layer encryption is compatible with long-haul optical transmission systems operating at Gb/s data rates.
We demonstrate quantum-noise protected data encryption over a 200km-long inline optically-amplified fiber line at 650Mbps rate using off-the-shelf components. In contrast to our previous implementation, this demonstration uses phase-encoded coherent states, resulting in a polarization independent system that is compatible with the existing WDM infrastructure. Security calculations are presented for individual attacks on both the encrypted data as well as the secret key. This demonstration paves the way for widespread deployment of quantum cryptography in WDM networks.
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