  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 (Q-nodes) 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.
