Learn more about breakthroughs pioneered at the University of Chicago
The quantum internet, explained
Editor’s note: This is part of a series called “The Day Tomorrow Began,” which explores the history of breakthroughs at UChicago. Learn more here.
The quantum internet is a network of quantum computers that will someday send, compute, and receive information encoded in quantum states. The quantum internet will not replace the modern or “classical” internet; instead, it will provide new functionalities such as quantum cryptography and quantum cloud computing.
While the full implications of the quantum internet won’t be known for some time, several applications have been theorized and some, like quantum key distribution, are already in use. It’s unclear when a full-scale global quantum internet will be deployed, but researchers estimate that interstate quantum networks will be established within the United States in the next 10 to 15 years.
The quantum internet is a theorized and much sought-after network of interconnected quantum computers that will one day allow people to send, compute, and receive information using quantum technology.
The purpose of the quantum internet is not to replace the internet we know today, but to instead create a co-existent network that can be used to solve specific types of problems.
Scientists think it will be particularly useful for problems that involve many variables, such as analyzing financial risk, encrypting data, and studying the properties of materials.
Researchers doubt that individuals will own personal quantum computers in near future. Instead, they’ll be housed at academic institutions and private companies where they can be accessed through a cloud service.
How does the quantum internet work?
Quantum computers use fundamental units of information similar to the bits used in classical computing. These are called “qubits.”
However, unlike conventional computer bits—which convey information as a 0 or 1—qubits convey information through a combination of quantum states, which are unique conditions found only on the subatomic scale.
For example, one quantum state that could be used to encode information is a property called “spin,” which is the intrinsic angular momentum of an electron. Spin can be thought of like a tiny compass needle that points either up or down. Researchers can manipulate that needle to encode information into the electrons themselves, much like they would with conventional bits—but in this case, the information is encoded in a combination of possible states. Qubits are not either 0 or 1, but rather both and neither, in a quantum phenomenon called superposition.
This allows quantum computers to process information in a wholly different way than their conventional counterparts, and therefore they can solve certain types of problems that would take even the largest supercomputers decades to complete. These are problems like factoring large numbers or solving complex logistics calculations (see the traveling salesman problem). Quantum computers would be especially useful for cryptography as well as discovering new types of pharmaceutical drugs or new materials for solar cells, batteries, or other technologies.
But to unlock that potential, a quantum computer must be able to process a large number of qubits—more than any single machine can manage at the moment. That is, unless several quantum computers could be joined through the quantum internet and their computational power pooled, creating a far more capable system.
There are several different types of qubits in development, and each comes with distinct advantages and disadvantages. The most common qubits being studied today are quantum dots, ion traps, superconducting circuits, and defect spin qubits.
What can the quantum internet do?
Like many scientific advances, we won’t understand everything the quantum internet can do until it’s been fully developed.
Few could imagine 60 years ago that a handful of interconnected computers would one day spawn the sprawling digital landscape we know today. The quantum internet presents a similar unknown, but a number of applications have been theorized and some have already been demonstrated.
Thanks to qubits’ unique quantum properties, scientists think the quantum internet will greatly improve information security, making it nearly impossible for quantum encrypted messages to be intercepted and deciphered. Quantum key distribution, or QKD, is a process by which two parties share a cryptographic key over a quantum network that cannot be intercepted. Several private companies already offer the process, and it has even been used to secure national elections.
At the same time, quantum computers pose a threat to traditional encrypted communication. RSA, the current standard for protecting sensitive digital information, is nearly impossible for modern computers to break; however, quantum computers with enough processing power could get past RSA encryption in a matter of minutes or seconds.
A fully-realized quantum network could significantly improve the precision of scientific instruments used to study certain phenomena. The impact of such a network would be wide-ranging, but early interest has centered on gravitational waves from black holes, microscopy, and electromagnetic imaging.
Creating a purely quantum internet would also relieve the need for quantum information to transition between classical and quantum systems, which is a considerable hurdle in current systems. Instead, it would allow a set of individual quantum computers to process information as one conglomerate machine, giving them far greater computational power than any single system could command on its own.
"The quantum internet represents a paradigm shift in how we think about secure global communication," said David Awschalom, the Liew Family Professor in Molecular Engineering and Physics at the University of Chicago, director of the Chicago Quantum Exchange, and director of Q-NEXT, a Department of Energy Quantum Information Science Center at Argonne. "Being able to create an entangled network of quantum computers would allow us to send unhackable encrypted messages, keep technology in perfect sync across long distances using quantum clocks, and solve complex problems that one quantum computer might struggle with alone--and those are just some of the applications we know about right now. The future is likely to hold surprising and impactful discoveries using quantum networks."
How far off is the quantum internet?
To date, no one has been able to successfully create a sustained quantum network on a large scale, but there have been major advances.
In 2017 researchers at the University of Science and Technology of China used lasers to successfully transmit entangled photons between a satellite in orbit and ground stations more than 700 miles below. The experiment showed the possibility of using satellites to form part of a quantum network, but the system was only able to recover one photon out of every 6 million—too few to be used for reliable communication.
In April of 2019, scientists with Brookhaven National Laboratory, Stony Brook University, and the United States Department of Energy’s Energy Sciences Network achieved entanglement over 10 miles using portable quantum entanglement sources and a fiber-optic network. Since then, their experiment has grown to include an 80-mile quantum network testbed.
In January 2020, researchers at the University of Chicago and Argonne National Laboratory successfully tested a 54-mile quantum loop that uses an existing fiber-optic cable buried beneath Chicago’s western suburbs. The project demonstrated the core functionality needed for a quantum network line by carrying optical pulses with a delay of only 200 milliseconds. With the loop in place, researchers began testing a broader array of quantum devices.
In June 2022, a 35-mile extension was added to the Chicago network, making it one of the longest in the nation. The network is now composed of six nodes and 124 miles of optical fiber—transmitting particles carrying quantum-encoded information between the U.S. Department of Energy’s Argonne National Laboratory in suburban Lemont and two buildings on the South Side of Chicago, one on the UChicago campus and the other at the CQE headquarters in the Hyde Park neighborhood.
The extended Chicago network represents a substantive jump in the scale of quantum networks and lays the foundations for even larger, interstate systems.
What else is needed to build the quantum internet?
While the quantum internet has moved beyond the theoretical, scientists are still perfecting much of its essential hardware, including the components responsible for generating, transmitting, and synchronizing qubits.
Qubits are encoded in the quantum states of subatomic particles, and those quantum states are easily disrupted by outside forces such as vibration or fluctuations in temperature. When a quantum state is disturbed, it loses whatever information it was carrying. Many types of quantum computers have to be isolated and cooled to near absolute zero in order to prevent this, which is costly.
One way of getting around cryogenic storage is to use a different type of qubit altogether—one that can function at room temperature, such as defect spin qubits. These are created from incredibly hard materials like diamond or silicon carbide and are manufactured with a particular defect in their molecular structure. A molecule within that defect is then used to hold quantum information. David Awschalom, Liew Family Professor in Molecular Engineering and Physics at the University of Chicago and senior scientist at Argonne National Laboratory, has made multiple breakthroughs in this area; for example, in February 2022, he and his team announced they were able to maintain a spin defect qubit’s quantum state for five seconds at 5K—a new record for that class of device—and to read information stored in the qubit on demand.
To go beyond a regional network, like the one being built in Chicago, scientists must find a way to amplify a quantum signal—a particularly difficult task given the nature of quantum states. With the classical internet, whenever a signal weakens, a repeater can capture and retransmit it. Unfortunately, capturing or attempting to duplicate an entangled photon will destroy it because of what’s known as the “no-clone theorem.”
Researchers are actively pursuing several methods to repeat a quantum signal without destroying it. For example, Tian Zhong, assistant professor at the Pritzker School of Molecular Engineering (PME) at UChicago, believes this can be done by deploying quantum memories that can shield quantum information from decoherence, essentially creating quantum relays to keep qubits intact until they reach their destination. Such a system would theoretically allow for quantum communication to travel across the globe.
Moving qubits from one place to another will require some form of physical connection, at least initially, and two options have emerged in recent years as the most likely candidates: satellite transmission and fiber-optic cable. Of the two, fiber optics are the far cheaper and more abundant option.
Already, laboratories around the world have begun testing fiber-optic networks, including a 124-mile loop in Chicago that links the Argonne National Laboratory in suburban Lemont, the University of Chicago in Hyde Park, the Chicago Quantum Exchange headquarters, and two other buildings in south Chicago. The network, which was expanded in the spring of 2022, is one of the largest in the world, with a further expansion planned that will link Fermi National Accelerator Laboratory.
—Prof. Jacqueline Stewart
