Purdue builds quantum network testbed for breakthrough experiments and innovation
Purdue University has successfully demonstrated a functioning quantum network that distributes photonic entanglement between multiple laboratories, marking a significant milestone that positions the university alongside top quantum research institutions.
"It gives Purdue a new capability in the toolkit to expand its quantum program and to really compete with leading institutions around the world in quantum networking," said Joseph M. Lukens, associate professor in the Elmore Family School of Electrical and Computer Engineering, who led the development of the network after joining Purdue in January 2025.
Technical achievement and innovation
The quantum network builds on expertise Lukens developed during his previous research positions at Oak Ridge National Laboratory and Arizona State University. At Oak Ridge, he pioneered key technologies including flex-grid wavelength-division-multiplexing for quantum systems and White Rabbit time distribution systems for precise timing synchronization.
But what exactly is a quantum network? Lukens describes it as a system that uses quantum phenomena like entanglement to send information in the form of quantum bits, or qubits, between different locations. In quantum physics, entanglement means that particles become linked so that measuring one instantly affects the other, no matter how far apart they are. This phenomenon, which has no equivalent in classical physics, is what gives quantum networks their unique power.
An entanglement-based quantum network requires three essential components: a source that generates entanglement, infrastructure to route and measure photons with precise timing, and at least three connected nodes, Lukens explained. These networks rely on photons because they are "really the only viable flying qubit" — particles that travel at the speed of light while maintaining their quantum properties.
Purdue's quantum network connects three laboratories in the subbasement of the Materials Science and Electrical Engineering Building, where entangled photons travel through optical fiber connections. "We've shown entanglement between those three, so we can say we have a quantum network," Lukens confirmed.
Each requirement presented unique challenges that Lukens solved through innovations developed at Oak Ridge. To control entangled photon sources, he leveraged flexible-grid wavelength division multiplexing, which allows the network to dynamically route different quantum channels as needed. For precise measurement, he implemented White Rabbit timing systems that can timestamp photon arrivals within picoseconds — trillionths of a second — to confirm entanglement across locations. The system also features real-time adaptivity to automatically detect and correct disruptions caused by temperature changes or even people walking through the building.
Current capabilities and future opportunities
The quantum network serves as more than just a demonstration — it's a research platform that enables new possibilities. Lukens emphasizes the critical value of having local testbeds where researchers can push quantum networking to its limits. "We can try to entangle new types of qubits. We can implement new protocols," he said.
Currently, the network enables several quantum applications. The system can perform quantum key distribution protocols that create secret keys known only to authorized users. It also enables advanced research techniques such as ancilla-assisted quantum process tomography, an approach that allows researchers to characterize quantum channels using entanglement. The team is preparing their first paper on this technique, which represents part of their initial network demonstration.
The discovery of existing fiber connections to Wang Hall has accelerated collaborative possibilities. One unique opportunity involves microwave photonics, a technique that uses optical systems to carry high-frequency radio signals through fiber optics. "Sometimes you can do things with higher bandwidth in the optical domain than you can in the RF domain," Lukens noted. This capability allows radio frequency signal processing to occur in the same fibers carrying quantum information — a combination that hasn't been demonstrated over a network before.
Beyond photonic applications, the infrastructure opens doors to experiments with different quantum systems. Faculty working on cold atoms and other matter-based qubits can now be connected through the network, enabling demonstrations that go "beyond photons."
The network provides a foundation for exploring quantum applications that require distributed systems, from computing to sensing, as the field continues to evolve from theoretical research toward practical implementation. "It takes Purdue's strengths in photonics and provides the infrastructure, the capabilities needed to move from the lab to the field," Lukens said.
