Resilient Entanglement Distribution in a Multihop Quantum Network

TL;DR

This work addresses the challenge of resilient, on-demand entanglement distribution in quantum networks by implementing a multihop architecture controlled via software-defined networking. It demonstrates a six-node, campus-scale entanglement distribution across three buildings, using wavelength-selective switches and a quantum data plane integrated with a classical control plane to dynamically allocate spectral resources. The system exhibits resilience through redundant fiber paths and reconfigurable routing, achieving high-fidelity entanglement (up to the mid-0.9s) and measurable entanglement rates, with Bayesian quantum state tomography validating the results. The findings highlight the practicality of scalable, robust quantum networks and provide a blueprint for future global quantum internet deployments that require multihop connectivity and rapid link recovery.

Abstract

The evolution of quantum networking requires architectures capable of dynamically reconfigurable entanglement distribution to meet diverse user needs and ensure tolerance against transmission disruptions. We introduce multihop quantum networks to improve network reach and resilience by enabling quantum communications across intermediate nodes, thus broadening network connectivity and increasing scalability. We present multihop two-qubit polarization-entanglement distribution within a quantum network at the Oak Ridge National Laboratory campus. Our system uses wavelength-selective switches for adaptive bandwidth management on a software-defined quantum network that integrates a quantum data plane with classical data and control planes, creating a flexible, reconfigurable mesh. Our network distributes entanglement across six nodes within three subnetworks, each located in a separate building, optimizing quantum state fidelity and transmission rate through adaptive resource management. Additionally, we demonstrate the network's resilience by implementing a link recovery approach that monitors and reroutes quantum resources to maintain service continuity despite link failures -- paving the way for scalable and reliable quantum networking infrastructures.

Figures (6)

• Figure 1: Classical network topologies. (a) Single hop, where a single hub relays signals between nodes. (b) Multihop, where intermediate nodes also act as hubs to relay traffic. (c) Multihop mesh, where additional node-to-node connections create redundant pathways between any given node and the hub.
• Figure 2: Clock distribution and classical communications across subnetworks using White Rabbit, with each subnetwork located in a seperate building. CLK: output 10 MHz reference clock signal. PPS: output pulse per second. Rb CLK: rubidium frequency standard atomic clock. Switch: ethernet switch. WRN: White Rabbit node. WRS: White Rabbit switch. Black lines: ethernet signals (electrical). Blue lines: timing signals (electrical). Red lines: WR signals (optical).
• Figure 3: Multihop network on ORNL campus. Bottom insets show the experimental setups in each building: blue (orange) lines represent the optical classical (quantum) signals, and black lines show the electrical timing and control signals. Top insets summarize the basic network configurations: red (gray) lines show active (inactive) signals for (a) direct connections from Alice to Bob and Charlie, (b) link recovery for building C, and (c) link recovery for building B. [APD: avalanche photodiode. AWG: arbitrary waveform generator. Ctrl: controller system. FPC: fiber polarization controller. FPGA: field-programmable gate array. MC: motion controller. OC: optical circulator. Panel: fiber-optic patch panel. PPLN: periodically poled lithium niobate. PPS: pulse-per-second. Pump: continuous-wave laser. SNSPD: superconducting nanowire single-photon detector. TDC: time-to-digital converter. WDM: Wavelength division multiplexer. WRN: White Rabbit node. WRS: White Rabbit switch. WSS: wavelength-selective switch. 2$\times$1: 2$\times$1 MEMS optical switch. 2$\times$2: 2$\times$2 MEMS optical switch.]
• Figure 4: Direct links from building A to B and C. (a) Optical lightpaths. (b) Spectral allocation. Colors indicate the terminating hubs for all frequency slots, whose center frequencies increase from 192.125 THz (idler Ch. 8) to 192.500 THz (signal Ch. 8) in 25 GHz steps. Density matrices, fidelities, and coincidence rates are estimated by Bayesian tomography for nodes connected to the same (c) and different (d) hubs. The frequency slots (left to right) in (c,d) correspond to the top-to-bottom ordering in (b), with user labels denoting the specific slots measured for the respective density matrix.
• Figure 5: Link recovery via building B when the A$\rightarrow$C connection has been broken. (a) Optical lightpaths. Spectrum addressed to C is now rerouted via B. (b) Experimental results. The spectral allocation is identical to Fig. \ref{['fig:Direct_Links']}(b).