SingAREN-ESnet Tech Talks: “QUANT-NET: A Quantum Networking Testbed Exploring Distributed Quantum Communications” – 27 Sep 2024 by Chin Guok
16 Oct 2024 – In the past two years, research on quantum computing and networking has advanced quickly on a global scale. We were delighted to welcome Chin Guok, Chief Technology Officer of the Energy Sciences Network (ESnet), back to SingAREN this year to educate our members on this fascinating topic. This time, on 27 Sep 2024, he gave an overview of quantum networking fundamentals to our members and associates and delved further into the project status of the QUANT-NET1 testbed in Berkeley, California, and its initial findings.

Figure 1 Chin Guok opening the session

Figure 2 Participants from SingAREN members and CQT associates
In this lecture, Guok explained the principles, applications, and advantages of quantum networks, outlining the quantum mechanism and properties of major building blocks, including qubits and photon qubits.

Figure 3 Major elements in a quantum network (Diagram credit to ESnet)
Figure 3 illustrates the major elements in a quantum network:
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- Quantum nodes, which are physical quantum systems (e.g., trapped ions, quantum dots) connected to the quantum network. Matter qubits are typically defined and created from these physical quantum systems. Quantum information is generated, processed, and stored locally by matter qubits in quantum nodes. Matter qubits, often referred to as stationary qubits, are typically isolated from the surrounding environment to minimize decoherence and facilitate various quantum operations.
- Quantum channels, which connect physically separated quantum components in the quantum network and transfer quantum states faithfully from place to place using the flying qubits. Optical fibers and free-space communications are typically implemented as quantum channels because they have a reduced chance of decoherence and loss. Photons with polarization or time-bin encoding are the flying qubit of choice. The implementation of quantum channels also requires that information encoded in a stationary qubit is reliably transferred to a flying qubit, and vice versa.
- Quantum repeaters, which allow the end-to-end generation of quantum entanglement and thus the end-to-end transmission of qubits by using quantum teleportation. Quantum repeaters typically implement entanglement-related operations such as entanglement swapping and entanglement purification.
It may be reassuring to know that quantum networks are not likely to replace classical networks but will co-exist, supplementing classical networks with their quantum capabilities.
The next section of his lecture focused on the current state of the QUANT-NET testbed development, as well as highlights and challenges. This DOE/ASCR funded program1 aimed to develop a three-node quantum networking testbed system in Berkeley that will demonstrate the fundamentals of distributed quantum computing, quantum repeaters, and quantum hybrid systems using trapped ion and color center technologies. The QUANT-NET research efforts are focused on three areas:
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- Repeater-friendly quantum-node technologies, which include researching and developing trapped-ion processor nodes and color-center based single-photon sources;
- Quantum frequency conversion (QFC) of ion-compatible narrow-bandwidth photons at near-infrared 854 nm to the telecom C-band at 1550 nm; and
- Quantum network control, architecture and protocol stacks.

Figure 4: A three-node distributed quantum computing network at Berkeley (Photo credit to ESnet)
QUANT-NET testbed runs as a distributed system where a Quantum Network server coordinates all activities, controls and manages the underlying quantum devices . Device models were then developed for each class of testbed nodes. ARTIQ2-based quantum devices form the underlying quantum plane.

Figure 5 QUANT-NET testbed system diagram (Diagram credit to ESnet)
The QUANT-NET project has completed its third year of effort, and significant progress has been made in the design and implementation of the testbed. For example, the design and implementation of the quantum testbed infrastructure has been completed, which includes the fiber construction between University of California, Berkeley (UC Berkeley) and Lawrence Berkeley National Laboratory (Berkeley Lab), and building a quantum lab at LBNL. The research team is constructing a trap-cavity system and exploring a new Raman excitation scheme to optimize the cavity-assisted ion-photon generation. Guok summarized the project status saying “Making progress; still far to go.”

Figure 6 Engaging Q&A session
Many participants found the topic intriguing. Even though most of us do not comprehend the complex physics underlying quantum research, it has opened our eyes to the possibilities of future technology. Richard Feynman’s wise remark perfectly echoed the attendees’ sentiment: “Nobody understands quantum mechanics.“
We would like to thank Guok for spending time with our SingAREN members. Special thanks to our participants, especially friends from the Centre for Quantum Technologies (CQT).
This article was co-edited by Chin Guok, Wenji Wu (QUANT-NET), and Vee Len (SingAREN)
Reference and Further Readings:
- QUANT-NET (Quantum Application Network Testbed for Novel Entanglement Technology) is a DOE/ASCR funded quantum network research project with collaboration between Berkeley Lab, UC Berkeley, University of Innsbruck, and Caltech. QUANT-NET research is focused on building a software-controlled quantum computing network, linking Berkeley Lab and UC Berkeley.
- ARTIQ (Advanced Real-Time Infrastructure for Quantum Physics) is a leading-edge control system for quantum information experiments. It was initiated and developed in partnership with the Ion Storage Group at NIST, and is now used and supported by a growing number of research institutions worldwide. While ARTIQ is currently mostly used by atomic physics groups, its applicability reaches beyond ion trapping. Read more from https://m-labs.hk/experiment-control/artiq/
- Physics World report: QUANT-NET’s testbed innovations: reimagining the quantum network
- QuNet’23 paper: QUANT-NET: A testbed for quantum networking research over deployed fiber