Quantum Networking Basics With ESnet’s Wenji Wu

Quantum networks may provide new capabilities for information processing and transport, potentially transformative for science, economy and natural science uses. These capabilities, provably impossible for existing “classical” physics based networking technologies, are of key interest to many U.S. Department of Energy (DOE) mission areas, such as climate and Earth system science, astronomy, materials discovery, and life sciences, etc.

In August of 2021, the Advanced Scientific Computing Research (ASCR) division of the US Department of Energy’s Office of Science announced a funding award for several quantum information system projects in support of the U.S. National Quantum Initiative. One of these projects is QUANT-NET (Quantum Application Network Testbed for Novel Entanglement Technology), a 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. ESnet executive director Inder Monga is the project principal investigator. The idea for QUANT-NET was born out of the 2020 DOE Quantum Internet Blueprint workshop, where representatives from DOE national laboratories, universities, industry, and other U.S. agencies came together to define a roadmap for building the first nationwide quantum Internet.

In this post, Dr. Wenji Wu, an ESnet networking researcher who is part of the QUANT-NET team, describes what future capabilities quantum networking may provide and why researchers believe quantum networks will transform scientific activities. 

Why Quantum Networks?

In the past thirty years, significant progress has been made in the fields of quantum technologies. The combination of quantum mechanics and information science forms a new area – quantum information science (QIS). In the broad context of QIS, quantum networks have an important role for the physical implementation of quantum computing, communication, and metrology. Quantum networks are envisioned to achieve novel capabilities that are provably impossible using classical networks and could be transformative to science, the economy, and national security. These novel capabilities range from cryptography, sensing and metrology, distributed systems, to secure quantum cloud computing. 

A few examples of this include: 

  • Secure Quantum Communication: Quantum networks take advantage of the laws of quantum physics (i.e., superposition and entanglement) to transmit information, potentially achieving a level of privacy and security that is impossible to achieve with today’s Internet. See Figure 1a.
  • A Quantum Network of Clocks: Recent research shows that a quantum network of atomic clocks can result in a substantial boost of the overall precision if multiple clocks are properly connected by quantum mechanical means. Compared to a single clock, the ultimate precision will improve as much as 1/K, where K is the number of clocks. If the same clocks are connected via a classical network, the precision scales as much as 1/SQRT(K). Ultimately, a quantum network of atomic clocks can surpass the Standard Quantum Limit (SQL) to reach the ultimate precision allowed by quantum theory — the Heisenberg limit. See Figure 1b.
  • Upscaling Quantum Computing: An individual quantum computer is typically limited in size. Connected by quantum networks, multiple quantum computers can work together as one big quantum computer to address larger problems. See Figure 1c.

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Figure 1a: Secure quantum communication (credit: Chen et al. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.070501).Figure 1b: A quantum network of clocks (credit: Komar, Peter et al. “A quantum network of clocks.” Nature Physics 10.8 (2014:582-587).Figure 1c: Upscale quantum computing (credit: Thor Swift, Berkeley Lab).

Quantum Network Basics

Quantum networks are distributed systems of quantum systems, which are able to exchange quantum bits (qubits) and generate and distribute entangled quantum states. As illustrated by Figure 2, a quantum network conceptually consists of three essential quantum components: 

  1. Quantum nodes, which are physical quantum systems (e.g., trapped ions, quantum dots, Nitrogen-vacancy centers) connected to the quantum network. Well-characterized 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. 
  2. 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. 
  3. 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.

Figure 2: A quantum network consists of three essential quantum systems

In quantum networks, qubits cannot be copied due to the no-cloning theorem, which forbids the creation of identical copies of an arbitrary unknown quantum state. Therefore, qubits can not be physically transmitted over long distances without being hindered by the effects of signal loss and decoherence inherent to most transport mediums such as optical fiber. However, qubits can share a special relation known as entanglement. Entangled qubits have interesting non-local properties, even if they are located at distant nodes. Consuming an entangled qubit pair, a data qubit can be sent deterministically to a remote node. Entanglement is the fundamental building block of quantum networks. 

As illustrated in Figure 3, key entanglement-related operations include: 

  • Entanglement Purification: Multiple low-quality entanglements can be purified into a high-quality entanglement. 
  • Entanglement Swapping: Long-distance entanglement can be built from shorter segments, with flying qubits transmitted locally.
  • Teleportation: to enable the end-to-end transmission of qubits.

Figure 3: Key entanglement-related operations

Classic networks typically concern the performance metrics such as bandwidth, throughput, and latency. Likewise, quantum networks care for performance metrics related to quantum operations. Critical quantum quality metrics include entanglement generation rate, decoherence rate, and fidelity. In quantum networks, fidelity is a key indicator to characterize the quality of quantum states or operations. In general, a minimum fidelity (Fmin) is required to support quantum operations.

It is envisioned that quantum networks will operate in parallel with classic networks. Quantum networks are not meant to replace classic networks but rather to supplement them with quantum capabilities.

Current Status

Today, quantum networks are in their infancy. Like the Internet, quantum networks are expected to undergo different stages of research and development until they reach their full functionality. There are many promising R&D efforts underway looking to develop quantum network technologies. The DOE unveiled a quantum Internet blueprint in 2020 to accelerate research in quantum science and technology, with the emphasis on the creation of a quantum Internet.

Q&A with Jessy Schmit, ESnet’s Network Engineering Group Lead!

Jessy Schmit came to ESnet from Pilot Fiber in New York, NY, where for the last six years, she was the Senior Manager of Network Operations and Support. Before Pilot Fiber, Jessy worked at a creative advertising agency and spent several years in the arts as a performer and director. Her background includes strategic leadership in marketing, customer experience, design, and technology. 

Schmit recently earned her Master’s Degree in Technology Management from New York University’s Tandon School of Engineering. 

Originally from Seattle, she currently resides in Brooklyn and spent seven years in the San Francisco Bay Area getting her undergraduate degree. She looks forward to reconnecting with her West Coast roots at ESnet.  

Question 1: What brought you to ESnet?

I had the opportunity to work with Jay Stewart at my last company, his recommendation and an instant connection to the people I met during the interview process made the decision a no-brainer.  ESnet’s mission and values are something I can really get behind!

Question 2: What is the most exciting thing in your field right now?

I nerd out on customer experience and process improvements, so I am excited about the modernization of IT back office, technical support, and self-service for engineering organizations. Increasing automation strategically without sacrificing the beneficial human elements of customer and end-user support can speed execution and ease the burden on engineering and support teams. Network automations can also reduce error and improve availability and resilience. In other sectors, specifically healthcare, we’re seeing how self-service, increased resiliency and the improved application of technology can make people feel more connected to their provider or service.  

Question 3: What excites you most about your role?

The people! The candid and thoughtful approach to questions and discussion was really refreshing during my interview process. And now I have the opportunity to work beside those totally awesome ESnet folks everyday and they’ve surpassed my expectations. I am excited to continue collaborating with such a talented and dedicated team of performers across the organization and learning all I can in my new environment. Working to further such a worthy mission makes it pretty easy to feel passionate about my new job.

Question 4: What challenges/opportunities are you looking forward to tackling?

I’m excited to figure out what motivates my team. I’ve found that what drives an engineer is wildly different from what motivates an accountant or a professor or chef (or any other role). Creating an environment where everyone feels supported and enabled to perform exemplary work that betters the larger organizational goals but also, ideally, their own development goals, is a focus for me.  

Question 5: How do you feel your past experience will transfer to your role at ESnet?

Looking at the typical pedigree of a team lead in technology or science, the benefits of a background in the arts might not be immediately obvious. While traditional technical skills may get a candidate in the door, it’s really the interpersonal and communication skills that allow them to thrive in their role. Entering the realm of technology and science from another discipline provides me with a unique perspective that can add diversity to the viewpoints of the team. My previous role was at a startup ISP in Manhattan and the pace of progress on our network operations and engineering meant I had to be agile, speedy, creative, and responsive – around the clock – to emergencies and customer needs. I’m hopeful the transfer of my work ethic, adaptability, and empathy will allow me to provide individualized support for my team(s) and future customers. 

Question 6: What book, movie, or podcast would you recommend?

I could talk about movies for days, but I’d say “KIMI” for a little tech industry suspense. I would also recommend “The Woman King” for some stellar performances and an inspiring story, and “Severance” (TV show) for a fascinating, and sometimes super funny, dystopian drama.

Join ESnet at SC22!

The International Conference for High Performance Computing, Networking, Storage, and Analysis (SC22) is just around the corner and ESnet staff will be there to connect, learn, and share their knowledge with the HPC community. SC22 will take place November 13 – 18 in Dallas, Texas, and is primarily in person for the first time since 2019. 

Here are some staff highlights:

Sunday, November 13

  • 8:30 AM – 5:00 PM  INDIS 2022: Annual International Workshop on Innovating the Network for Data-Intensive Science, Mariam Kiran, Anu Mercian, Room C156 
  • 8:55 AM     INDIS 2022: Panel Discussion: Network Research Exhibition: the Future of Networking and Computing with Big Data Streams, Tom Lehman, C
  • 3:30 PM     INDIS 2022 Featured Technical Talk: Quantum Communication: A Physics Experiment of a Network Paradigm Shift, Inder Monga, Room C156
  • 4:10 PM     Paper: EJ-FAT Joint ESnet JLab FPGA Accelerated Transport Load Balancer, Stacey Sheldon, Yatish Kumar, Michael Goodrich, Graham Heyes, Room C156  

Tuesday, November 15

  • 10:30 AM – 12:00 PM    Paper: HPC Network Architecture, Mariam Kiran, Room C141-143-149
  • 12:00 PM – 1:00 PM    Demo: Global Petascale to Exascale Workflows for Data Intensive Science, Mariam Kiran, DOE Booth #1600
  • 3:15 PM    Featured DOE Booth Talk: ESnet6: How ESnet’s Next-Generation Infrastructure Will Enable Integrated Research Initiative Workflows, Inder Monga, DOE Booth #1600

Wednesday, November 16

  • 11:00 AM    SC22 Network Research Exhibition, SC22-NRE-15, SENSE and Rucio/FTS/XRootD Interoperation, Tom Lehman, Xi Yang, Caltech Booth #2820
  • 2:00 PM    SC22 Network Research Exhibition, SC22-NRE-13, AutoGOLE/SENSE: End-to-End Network Services and Workflow Integration, Tom Lehman, Xi Yang, Caltech Booth #2820

Thursday, November 17

  • 10:00 AM     Demo: Janus Container Management and the EScp Data Mover, Ezra Kissel, Charles Shiflett, Md Arrifuzzaman, DOE Booth #1600