Fermilab scientists and engineers have achieved a landmark result in an ongoing effort to design and build compact, portable particle accelerators. Our group successfully demonstrated a new, efficient way to cool superconducting accelerator components, cutting down on the bulk of the traditional cooling infrastructure needed for this technology.
The importance of this advance is apparent if you happen to walk around the Fermilab site. You really can’t miss it: Particle accelerators built for discovery are big machines. They stretch for hundreds of meters, even kilometers. They also require large and complex infrastructure, which restricts their use primarily to science research laboratories.
And yet, particle accelerators are very useful tools outside science research labs. They have applications in security, medicine, manufacturing, and roadways. And their impact might be even greater if we could make these traditionally giant machines compact. Miniaturize them. Design high-power accelerators that could fit, literally, inside the back of a truck.
For the first time, a team at Fermilab has cooled and operated a superconducting radio-frequency cavity — a crucial component of superconducting particle accelerators using cryogenic refrigerators — with cryocoolers, breaking the tradition of cooling cavities by immersing them in a bath of liquid helium. It achieved an accelerating gradient of 6.6 million volts per meter. Photo: Marty Murphy
At Fermilab, we relish such practical physics challenges. And last month, our team rose to the challenge, achieving a major milestone in our quest to realize powerful, compact accelerators that have an impact on our everyday lives. The core team included Ram Dhuley, Michael Geelhoed, Sam Posen and Charles Thangaraj.
Combining a verve for practicality with cutting-edge science, our team successfully demonstrated a new, revolutionary method for cooling a superconducting accelerator cavity without using liquid helium — counterintuitive for most in accelerator science.
This new method — based on a Fermilab idea patented five years ago — uses cryogenic refrigerators, or cryocoolers, for removing the heat dissipated by a superconducting accelerator cavity. By compressing and expanding helium gas across a regenerative heat exchanger in a “closed” cycle, the cryocoolers produce cooling without letting the helium out. This closed-cycle operation of cryocoolers makes our system very compact — more so than the standard liquid helium cooling equipment used by traditional accelerator cavities.
Superconducting cavities are crucial components in particle accelerators, propelling the particle beam to higher energies by giving it an electromagnetic push. We used a 650-megahertz niobium cavity, and we all watched with pride the first successful results delivered by our new method: an accelerator gradient of 6.6 million volts per meter. That is already sufficient for the applications we have in mind, and still, we know we can do better.
Superconducting cavities used in large accelerators are usually cooled to around 2 kelvins, colder than the 2.7 kelvins (minus 455 degrees Fahrenheit) of outer space. The typical way to achieve this is by immersing the cavities in liquid helium and pumping on the helium to lower its pressure, and therefore its temperature. All of this requires large and complex cryogenic systems – a factor that severely limits the portability and therefore the potential applications of superconducting accelerators in industrial and other environments.
Celebrating the success of the first results from the conduction-cooling project are, from left: Michael Geelhoed, Ram Dhuley, Sam Posen and Charles Thangaraj. Photo: Laura Rogas
Our team broke this barrier by successfully realizing a technique conceptualized by Fermilab physicist Bob Kephart, now retired. The technique proposed to make superconducting accelerators practical by 1) coating a thin layer of a material called niobium-tin to the inside of the niobium cavities, and 2) cooling the coated cavities using cryocoolers via conduction links connecting the two. The cryocooler-cavity setup dispenses with a bath of cryogenic liquid and any need for a cryogenic plant to achieve superconductivity.
The demonstration also shows how this method could simplify superconducting accelerators and make them accessible for broader needs beyond basic science – better pavements, wastewater treatment, medical device sterilization, and advanced manufacturing.
Applying the scientific breakthroughs at Fermilab and transforming them to solve challenges outside fundamental science involves systematic entrepreneurial thinking – identifying an opportunity and asking and answering a whole host of questions to validate the opportunity. A great value in all of this is converting DOE’s investment in science and technology into innovation that could allow new industries to emerge.
At Fermilab, we will continue to apply our frontier technologies for novel applications beyond discovery science. This major breakthrough is an exciting step in that direction, and we will continue to push the envelope.
This project is supported by the Laboratory Directed Research and Development Program at Fermilab. The work is also supported by the DOE Office of Science.
Charles Thangaraj is the science and technology manager at Fermilab’s Illinois Accelerator Research Center.
See other science results from Fermilab.
Linear algebra is a field of mathematics that has been thoroughly investigated for many centuries, providing invaluable tools used not only in mathematics, but also across physics and engineering as well as many other fields. For years physicists have used important theorems in linear algebra to quickly calculate solutions to the most complicated problems.
This August, three theoretical physicists — Peter Denton, a scientist at Brookhaven National Laboratory and a scholar at Fermilab’s Neutrino Physics Center; Stephen Parke, theoretical physicist at Fermilab; and Xining Zhang, a University of Chicago graduate student working under Parke — turned the tables and, in the context of particle physics, discovered a fundamental identity in linear algebra.
From left: Xining Zhang of the University of Chicago, Peter Denton of Brookhaven National Laboratory and Stephen Parke of Fermilab have discovered a new mathematical identity that had eluded mathematicians for centuries. Photo: Reidar Hahn
The identity relates eigenvectors and eigenvalues in a direct way that hadn’t been previously recognized. Eigenvectors and eigenvalues are two important ways of reducing the properties of a matrix to their most basic components and have applications in many math, physics and real-world contexts, such as in analyzing vibrating systems and facial recognition programs. The eigenvectors identify the directions in which a transformation occurs, and the eigenvalues specify the amount of stretching or compressing that occurs.
Experts fully expected the identity to exist somewhere in the literature for centuries but couldn’t find any evidence for it online or in textbooks. The three of us were eventually directed to a similar result by UCLA mathematics professor Terence Tao, who has a Fields Medal and Breakthrough Prize to his name. When we presented Tao with our result, he cheerfully declared that it was, in fact, the discovery of a new identity, and he provided several mathematical proofs, which have now been published online. Tao also discussed the new identity in his math blog.
The physics usage case of this result stems from our investigations of neutrino oscillation probabilities in matter, which involve finding eigenvectors and eigenvalues, both of which are rather complicated expressions. While the eigenvalues are somewhat unavoidably tricky, this new result shows that the eigenvectors can be written down in a simple, compact, and easy-to-remember form, once the eigenvalues are calculated. For this reason, we called the eigenvalues “the Rosetta Stone” for neutrino oscillations in our original publication — once you have them, you know everything you want to know.
This work is supported by the DOE Office of Science.
Andrew Dzurak of the University of New South Wales gives the workshop’s keynote address. Photo: Edoardo Charbon
It’s a cold truth about quantum computing: To operate, the leading types of processing units that could lie at the heart of quantum computers must be maintained below a chilling 15 millikelvins, or minus 459 degrees Fahrenheit, close to absolute zero. And to be useful, the electronics that process and read the data have to be nearly as cold.
Leaders in quantum science converged this summer at Fermilab for the world’s first workshop on cryogenic electronics for quantum systems. As these fields are highly competitive, the hosts worked hard to attract key global allies and leaders in the field.
Scientists and engineers from academia and industry discussed the challenges of designing electronics for processors and sensors that will work in the ultracold environment.
It’s a fundamental problem facing the field of quantum computing, which holds immense possibility across multiple disciplines. Experts say that quantum computers could someday be powerful enough to solve problems that are impossible for classical computers, potentially redefining how we see the world.
And much of it rides on designing electronics that are up to the task.
“Quantum systems won’t exist without cryogenic electronics,” said Fermilab engineer Farah Fahim, workshop co-organizer and deputy head of quantum science at Fermilab. “That’s why our community needs to collaborate, and why we’re working to establish key partnerships with academia and industry, as well as manufacturing companies that would support the fabrication of cold chips.”
Researchers across multiple sectors have called for collaboration, and pioneers in the field turned out for the meeting. They included Edoardo Charbon (also workshop co-organizer) of the Advanced Quantum Architecture Lab at the Swiss Federal Institute of Technology Lausanne, or EPFL, in Switzerland and Andrew Dzurak of the University of New South Wales and Australia, a trailblazer in the field of silicon-based qubits who gave the workshop’s keynote address. Representatives from IBM, Intel, Global Foundries, Google and Microsoft also attended.
“The Fermilab cryoelectronics workshop is a very important first step for the quantum computing community,” said Malcolm Carroll, research staff member at IBM Research. “Developing supporting electronics for future quantum computers is one of the next big hurdles. IBM looks forward to this series continuing and contributing to it as it has for this first one.”
The global cooling effort centers on accommodating the qubit — the fundamental unit of a quantum computer’s processor. Qubit information needs the extreme cold to survive — below 15 millikelvins — since any thermal energy can disturb the quantum computing operation.
“The core of any quantum-technology-based system is a very special and carefully designed electronics optimized for deep cryogenic temperatures. This is a brave new world for us electronics engineers.”
Current state-of-the-art systems use tens of qubits. But a quantum computer that surpasses the capabilities of today’s classical computer would in certain cases require millions or billions of qubits, each of which needs electronics, both to control the state of the qubit and to read out its signals.
And electronics means cables.
“As the system scales up, one bottleneck has been getting information out of the qubits and controlling the qubits themselves,” Fahim said. “It requires large numbers of wires.”
For larger systems, the qubits and the electronics need to be closely integrated. Otherwise, information can become degraded as it winds its way down lengthy wires to bulky systems. With tight integration, the electronics can deliver the fast, self-correcting feedback required to control the qubit state — on the order of ten-billionths of a second.
When you have the number of wires and cables required for a million- or billion-qubit system, close integration isn’t possible unless your electronics can operate in the cold, side-by-side with the qubit.
Fermilab engineer Farah Fahim, left, and Edoardo Charbon of the Advanced Quantum Architecture Lab at EPFL co-organized the world’s first workshop on cryogenic electronics for quantum systems. Photo: Davide Braga
“When you have lots of cables, after some point, you can’t expand in that direction anymore. You can’t integrate a million cold qubits with warm electronics,” Fahim said. “To scale up, cryogenic electronics is the only way to go. To be able to take it to the next level of integration, we need to move the room temperature control to cryogenic control. You want to be able to change the technology to meet the requirements.”
When the electronics live in the same space — the same refrigerated space — as the qubits, the system becomes practical and manageable, capable of providing accurate, real-time qubit control.
That is the challenge the workshop attendees took head-on: developing quantum-system electronics that don’t mind being left in the cold.
“Developments in cold electronics may hold the keys to scaling up quantum computing,” said Microsoft Quantum – Sydney Director David Reilly, also a professor at the University of Sydney. “As the community moves from the demonstration of single-qubit prototypes to scaled up machines that can address real problems, interest in this field is really taking off. Fermilab has deep expertise in cold electronics as well as a culture of filling the gap between academia and industry. It’s only fitting that the first workshop on this topic was at Fermilab — and I expect to see many more as government labs become pivotal players in the quantum ecosystem.”
Experts dream of a day when quantum computers can get out of the cold and sit comfortably atop your desk just like your current PC.
“We would like to reach a stage where nothing is cryocooled, but until we get there, the only way we get there is with electronics operating at very low temperatures,” Fahim said.
The workshop was a major, international step in that direction.
“Quantum technologies are the next frontier for many fields, including electronics. While quantum computers are certainly the pinnacle of such worldwide effort, many other applications are emerging, like quantum imaging, quantum sensing, quantum communications, quantum metrology, to name just a few,” Charbon said. “But the core of any quantum-technology-based system is a very special and carefully designed electronics optimized for deep cryogenic temperatures. This is a brave new world for us electronics engineers.”
To continue the dialogue on this key enabling technology, the second International Workshop on Cryogenic Electronics for Quantum Systems will be held in Neuchatel, Switzerland in 2020.
This work is supported by the DOE Office of Science.
Learn more about quantum science efforts at Fermilab.
Fermilab is a member of the IBM Q Hub at the Oak Ridge National Laboratory and part of joint research with the IBM Q Network in the context of the Chicago Quantum Exchange.