The smallest bits of matter and energy are the building blocks of a radically new paradigm for sensing and relaying information.
Imagine sensors so sensitive that they can track the motion of a single atom. Or other sensors arranged in arrays to detect underground motions that may be precursors to earthquakes. Imagine new technologies to send information securely over specialized networks that are impossible to hack. Some of these ideas remain glimmers in the eyes of science -; but then, so were tiny, portable computers just a few decades ago.
Researchers around the world are exploring how the smallest bits of matter and energy, such as atoms, electrons and photons, can relay information by making essential use of their quantum properties. These unique properties are described by a branch of physics called quantum mechanics, which was originally devised to explain phenomena at the atomic and subatomic scales, but is now central to our understanding of all matter. At the U.S. Department of Energy's (DOE) Argonne National Laboratory, quantum information science (QIS) is a burgeoning discipline that stands to revolutionize computing, science and communication.
Argonne is leading the way toward a quantum future, conducting cross-disciplinary research through its quantum information initiative and via Q-NEXT, one of five national QIS research centers DOE established in August 2020. Through these efforts, Argonne scientists are laying the groundwork for quantum technologies, such as highly refined sensors and simulations that could eventually help detect disease, open the way toward new medicines, and keep our infrastructure secure, among other uses.
"It would be next to impossible to predict the most important things a new technology will bring to bear on the world. The only thing I think we can say with confidence is that it will have an enormous impact, as all new discoveries do." -; David Awschalom, director of Q-NEXT
"What's really helped drive and accelerate this field in the last 10 years is the ability of scientists and engineers around the world to create and manipulate individual quantum states of matter," said Argonne and University of Chicago's David Awschalom, director of Q-NEXT.
At Argonne, that ability rests on a 75-year foundation of pivotal discoveries and powerful facilities, including the Advanced Photon Source, Center for Nanoscale Materials and Argonne Leadership Computing Facility, all DOE Office of Science user facilities at Argonne that will help make the quantum revolution possible.
A Different Way of Handling Information
Traditional computers traffic in combinations of 1s and 0s -; binary units known as bits. Packed by the tens of billions onto ever smaller devices, bits are units of information that enable everything from simulating a nuclear reactor to watching memes on social media.
In the quantum world, information is represented by quantum bits, or qubits. A qubit might be based on the properties of a fundamental particle such as a photon -; the smallest unit of light. It might also be an electron or a microengineered construct in the lab.
A classical bit is either a 0 or a 1. But because of its quantum nature, a qubit can exist in a superposition of states, which means it has different probabilities of being in one state or another. The act of reading, or observing, the qubit determines which state it's in. Qubits can also be entangled, which means that even across long distances, they can be linked with each other.
Their quantum properties make qubits appealing for a variety of purposes in information processing and communication, such as performing certain complex calculations at lightning speed -; in some cases, much faster than possible on the biggest supercomputers -; or sending information through super secure channels. At Argonne, a 52-mile fiber-optic testbed is being used to test the concept of sending unhackable information across long distances.
"What makes a good quantum bit- There are lots of different ideas about designs and architectures," said JoAnne Hewett, deputy director of Q-NEXT and chief research officer at DOE's SLAC National Accelerator Laboratory, which is a Q-NEXT partner. "It's a horse race right now to solve the difficulties of making a qubit and keeping it in this qubit state."
Today's quantum computers might have tens or hundreds of qubits, which is just a tiny fraction of the number of bits available on traditional computers. But their existence is a remarkable achievement, considering that as recently as the 1980s, quantum computers were essentially a thought exercise -; one that physicist Paul Benioff enjoyed contemplating in his spare time while he was a scientist at Argonne.
Benioff's Fateful Side Project
In 1979, Benioff submitted a groundbreaking publication showing that quantum computers were theoretically possible. Up until then, it was a commonly held belief that a computer could not fully operate under the laws of quantum mechanics. For instance, the "read" function, where computers keep track of computational steps, would invoke a measurement. In a quantum computer, the act of measuring would disrupt the computational state and destroy the computation. And it would release energy from the closed quantum computer system, potentially preventing the computer from operating under the laws of quantum mechanics.
Benioff realized that a quantum mechanical version of a computer would necessarily be reversible -; a central requirement of quantum mechanics. A reversible computer would be able to return to the starting point of a calculation by reversing the computation steps, with no change (such as energy loss) to the surrounding system. It so happened that physicist Charles Bennett, known for his theoretical work on information and computation, visited Argonne in the late 1970s, and Benioff was able to talk with him about this quantum computer problem. Bennett told him about research he had published a few years earlier showing that a type of computational model called a Turing machine could be reversible.
"As soon as he told me that, I read his paper and said, that's fine. Now I will just make a quantum mechanical version of what his reversible classical model is," Benioff recalled. "And, so to speak, the rest is history."
Benioff continued to develop the theoretical concept of a quantum computer in subsequent papers.
Creating a Quantum Roadmap
Quantum computers could someday perform calculations that not even a supercomputer could handle, but the power of QIS goes far beyond computing. It represents an entirely different way of thinking about information, subject to different rules than discussed in traditional computer science.
"When quantum mechanics came along, people thought, well, that's how nature works -; but no one thought that it had anything to do with information or how you actually compute," said Salman Habib, director of Argonne's Computational Science division and an Argonne Distinguished Fellow. "Right now, we are driven by the excitement of this new paradigm, and we are waiting for technology to catch up, in some sense."
A few innovations, such as city-scale quantum networks, are already underway, driven in part by testing now occurring at Argonne. Other developments, like a national or global quantum internet, are much further off. The question is, when will using quantum systems make sense, and what will that look like-
"Just because something is quantum doesn't necessarily mean it's better," Habib said. "There is a lot of complexity that comes with a quantum network. So is the management of complexity going to be commensurate with the advantages-"
A wide range of activities at Argonne, spanning roughly 40 research projects, are dedicated to envisioning the realities of QIS and quantum computing. These include "roadmapping" sessions, led by Q-NEXT, to determine a path for bringing quantum technologies to the public in 10 to 15 years. Researchers at Argonne are pioneering the materials needed to build quantum information networks and working on error correction mechanisms akin to the ones that keep traditional computers running smoothly.
Foundries for Quantum Materials
Q-NEXT will also be supported by two national foundries for quantum materials -; one being built at Argonne and one at SLAC -; and will develop a National Quantum Devices Database. Together, its 20-plus partner institutions spanning universities and industries are developing capabilities for building unhackable quantum networks, ultrasensitive quantum sensors and testbeds for simulating the full gamut of quantum devices and systems.
"We are driving technologies to the level of single atom control," Awschalom said. "How can you fabricate billions of quantum bits based on individual atoms, photons or electrons, and how do you place them precisely -; and on demand- That's a major challenge for the field."
Meeting this challenge could open up a huge array of possibilities for quantum sensors that can detect the motion of one atom. Awschalom suggests the possibility of sensors that could enable telescopes far more powerful than what we have today or cancer detection at the level of a single cell.
But many hurdles lie along the way to designing these minuscule sensors and carriers of information. It requires the ability to design, synthesize and observe systems at the atomic level. These systems are easily disrupted by noise in the environment, such as interactions with light or magnetic fields.
Partners in Quantum
A key strength of Q-NEXT, Hewett added, is its blend of partners from national research labs, academia and industry, all of which have developed the tools and capabilities needed to tackle different aspects within this vast endeavor of building quantum information systems.
"The Q-NEXT partners really complement each other in terms of their expertise and their goals," she said. "It's a perfect example of how the whole is more than just a sum of the parts."
Innovation on this scale requires a scientific ecosystem and a complete technology supply chain, which Argonne is helping to build. It is a partner in Duality, a quantum accelerator which currently supports six startups as part of its first cohort. These startups will be able to develop their products, which include simulation software and a manufacturing process for quantum materials, using expertise and state-of-the-art facilities at Argonne, the University of Chicago and the University of Illinois at Urbana-Champaign.
One of the biggest challenges faced by the United States, and one that the national labs can help address, is creating a quantum-ready workforce. Q-NEXT partners are tackling the challenge by hosting traineeships in which students and early-career professionals are embedded side by side with experts in QIS research programs.
In many ways, the quantum devices and information systems being built today are analogous to the earliest days of computing in the late 1930s. For those old enough to remember the simple blinking cursor on a dark screen that greeted any home computer user as late as the 1970s and 1980s, it seemed unimaginable even then that the same technology would eventually deliver us pocket-sized computers capable of taking pictures and calling people anywhere in the world.
"It would be next to impossible to predict the most important things a new technology will bring to bear on the world," Awschalom said. "The only thing I think we can say with confidence is that it will have an enormous impact, as all new discoveries do. That's part of the excitement of the field."