It’s colossal: Creating the world’s largest dilution refrigerator

While the refrigerator in your kitchen gets cold enough to prevent your leftovers from spoiling, dilution refrigerators used for quantum computing research cool devices near the coldest physical temperature possible. Now at the U.S. Department of Energy’s Fermi National Accelerator Laboratory, researchers are building Colossus: It will be the largest, most powerful refrigerator at millikelvin temperatures ever created.

Fermilab is known for its massive experiments, and Colossus will fit right in. Researchers from the Fermilab-hosted Superconducting Quantum Materials and Systems Center need lots of room at cold temperatures to achieve their goal of building a state-of-the-art quantum computer.

Unlike a kitchen refrigerator, which compresses gases called refrigerants to cool food, a dilution refrigerator uses a mixture of helium isotopes to create temperatures close to absolute zero, or zero kelvin: the coldest temperature imaginable in physics, which is physically impossible to reach.

“With the cooling power and volume that Colossus will provide, SQMS researchers will have unprecedented space for our future quantum computer and many other quantum computing and physics experiments,” said Matt Hollister, the lead technical expert on this project. “Colossus is named after the first electronic programmable computer, which was constructed in the 1940s for codebreaking. It was a historic milestone in the history of computing and seemed like an appropriate name for the size of our new refrigerator.”

SQMS scientists and engineers are tackling a challenge called quantum decoherence. Decoherence is a phenomenon that occurs when quantum information is obscured by signal noise or lost through the materials that make up the physical qubits, the basic units of a quantum computer.

The metallic, niobium cavities used by SQMS to develop better physical qubits are rooted in Fermilab’s renowned particle accelerator program. The lab’s expertise in superconducting cavities and cryogenics, essential in building modern, powerful particle accelerators, made Fermilab a prime location for hosting one of DOE’s national quantum information science research centers.

“Once we accomplish our goal of building this massive machine, we look forward to seeing the incredible physics and quantum computing experiments our fellow researchers have planned with Colossus.” – Matt Hollister, project lead technical expert

To make a quantum computer, researchers don’t just need high-quality qubits connected to each other, they also need a large quantity of these devices, too.

Most dilution refrigerators that operate at millikelvin temperatures offer only a fraction of the space compared to Colossus, which makes scalability a big hurdle for constructing a useful quantum computer. Colossus will be so large that it will be able to house hundreds to thousands of highly coherent cavities and qubits.

The new dilution refrigerator will be constructed around a repurposed facility originally used to test components for Fermilab’s Mu2e experiment at temperatures around 4K. When Colossus is fully built, it will offer 5 cubic meters of space and cool components to around 0.01K. That is 10 times the cooling power and 15 times the volume at that temperature than standard commercial dilution refrigerators.

“At SQMS, we use metallic cavities made of superconducting materials to perform our research. Superconducting materials are great at storing electromagnetic energy with very low losses, but the big caveat is they must be very cold,” Hollister said. “Thankfully, we are constructing a space to store hundreds to thousands of cavities and qubits, depending on the geometry and sizes of course.”

The construction of Colossus faces many challenges related to its large diameter of around 2 meters. Like an upside-down wedding cake, around seven plates with smaller and smaller diameters and lower and lower temperatures will be suspended from each other and will form the cryogenic structure of Colossus.

“A dilution refrigerator of this size-scale has never been built before. This presents numerous technical challenges our team is working through,” said Grzegorz Tatkowski, an SQMS cryogenic engineer. “We are designing Colossus for a rather large payload in terms of mass, and ensuring each plate reaches the right temperature specifications needed for this project is a challenge.”

To build it, technicians will repurpose the cryogenic plant and a control room originally used for the famed Collider Detector at Fermilab experiment, which provided data for researchers to discover the top quark and also provided a recent measurement on the mass of the W-boson.

“This is a much different cryogenics challenge than what I faced when I worked in the Neutrino Division at Fermilab,” said Chris James, a cryogenic engineer. “There we were working with massive tanks that could hold several tons of ultra-pure liquid argon to detect tiny particles called neutrinos. Here I am working with liquid helium that is around 0.01K, which is around 10,000 times colder than liquid argon.”

To finalize the design and specifications of Colossus, the SQMS team conducted an in-depth review process on the components for the fridge. The team expects to start major procurements in summer 2023.

“Once we accomplish our goal of building this massive machine, we look forward to seeing the incredible physics and quantum computing experiments our fellow researchers have planned with Colossus,” said Hollister. “The Colossus team is excited to build a first-of-its-kind machine to enable our upcoming experiments and create computational devices that will advance knowledge and capabilities.”

The Superconducting Quantum Materials and Systems Center at Fermilab is supported by the DOE Office of Science.

The Superconducting Quantum Materials and Systems Center is one of the five U.S. Department of Energy National Quantum Information Science Research Centers. Led by Fermi National Accelerator Laboratory, SQMS is a collaboration of 23 partner institutions — national labs, academia and industry —working together to bring transformational advances in the field of quantum information science. The center leverages Fermilab’s expertise in building complex particle accelerators to engineer multiqubit quantum processor platforms based on state-of-the-art qubits and superconducting technologies. Working hand in hand with embedded industry partners, SQMS will build a quantum computer and new quantum sensors at Fermilab, which will open unprecedented computational opportunities. For more information, please visit sqms.fnal.gov.

Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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Editor’s note: This article originally was published by Sanford Underground Research Facility.

Traveling by rail, sea, interstates and shafts, the first components of the international Deep Underground Neutrino Experiment have arrived at the Sanford Underground Research Facility in Lead, South Dakota. The anode plane assemblies, or APAs, will one day capture data left in the wake of neutrino collisions in DUNE’s Far Detector.

“This APA arrival and test lift marks the start of DUNE onsite activities at SURF,” said Mike Headley, executive director of SURF. “I’d like to congratulate the CERN, Fermilab, University of Manchester and SURF joint team for making this first experiment lift a major success.”

DUNE will paint a clearer picture of the origin of matter and how the universe came to be by studying neutrinos, strange subatomic particles that rarely interact with matter. A beam of neutrinos will travel 800 miles through the earth, from the U.S. Department of Energy’s Fermi National Accelerator Laboratory near Chicago to DUNE’s massive underground detectors at SURF.

More than 1,400 scientists and engineers in over 30 countries contribute to the experiment, which is hosted by Fermilab.

“This was a test of the entire logistics chain — from the UK, to Switzerland, to Illinois, and finally to South Dakota,” said Joe Pygott, deputy head of the Fermilab South Dakota Services Division. “After a year of planning, it was satisfying to see the global effort come together.”

Making things awkward

Standing a staggering 19.7 feet tall and 7.5 feet wide (6.0 meters tall; 2.3 meters wide), the APAs are the largest and one of the most fragile components of DUNE. Researchers outfit the APAs’ large steel frames with hundreds of electronic read-out boards. Then, 15-miles of hair-thin copper-beryllium wire is wrapped around the frame, creating a fine, mesh-like appearance.

In total, 150 APAs will be built for DUNE: 136 from the UK and 14 from the US.

“Because of their size, fragility and cost, the APAs are classified as a ‘critical transport,’” said Olga Beltramello, a mechanical engineer at CERN.

To tackle the logistics and transport of unusual components like the APAs, the project formed the appropriately named Awkward Material Transport Team.

Beltramello, a member of the AMTT, led the creation of the frames that would cradle the APAs during transport. Throughout the design phase, she anticipated the dynamics of the journey ahead — the jostle of the rail car, the lurch of ocean waves, the sway of an overhead crane.

“We run analysis to understand how the APA would withstand the dynamics of the transport,” Beltramello said. “The calculations are complex, as vibrations from track transport in Europe are different from the tire transport in the U.S., which are different from sea transport.”

With mass production of APAs underway, the team used the delivery of two prototype APAs to SURF to stress-test their transportation plan. Accelerometers and vibration detectors monitored every wobble along the way, telling researchers just how much stress the components actually experienced during the journey.

By land and sea

The APAs were constructed at the UK’s Science and Technology Facilities Council’s Daresbury Laboratory, then shipped to CERN, the European laboratory for particle physics. There, the APAs were installed and tested in ProtoDUNE. A massive detector in its own right, ProtoDUNE is a prototype of the DUNE detectors to be built at SURF. Researchers wanted to ensure that the APAs could withstand the extreme cold of liquid argon (minus 200 degrees Celsius) and to see if they would yield clear data signals, unobscured by background noise.

“In ProtoDUNE, we saw lovely, clean images,” said Justin Evans, professor of physics at the University of Manchester and academic lead of the UK project for APA production.

The APAs then journeyed by rail to the seaside; by cargo ship across the Atlantic; and 1,600-miles by semitruck across the U.S. The final leg of the journey was down the mile-deep Ross Shaft, to the level where crews are excavating the large caverns that will house the DUNE Far Detector. Due to their size, the APAs will not fit on the elevator-like conveyance used to transport people and materials through the shaft. Instead, the APAs were suspended beneath the cage to lower them underground.

Jeff Barthel, SURF’s rigging supervisor who led the maneuver, said the test lift of the nearly 6,400-pound load “couldn’t have gone smoother.”

Assured by the APA performance in ProtoDUNE and the successful test transport, researchers have started mass producing APAs for DUNE.

“For me, even more important than reaching this technical goal, is the excellent collaboration between groups,” Beltramello said. “This was our first collaboration across these groups, and it was extremely successful. It’s good for the future.”

A neutrino trap

When excavation is complete, the caverns will provide space for detector modules filled with a combined 70,000 tons of liquid argon. The APAs will be submerged side-by-side in the frigid liquid argon, forming a series of net-like walls across the width of the detector.

When neutrinos collide with an argon nucleus, the collisions create a cascade of charged particles. These particles, in turn, knock loose electrons from the shells of argon atoms. An electric field will push the free-floating electrons toward a wall of APAs. Like a spider’s web, the APA wires will ensnare the drifting electrons, sending shivers of data up the wires to the electrical read-out boards. Researchers see this data in the form of particle tracks.

“The electrons are hitting these miles and miles of wires, and we get information from that little pulse of electrical current on the wire,” Evans explained. “The pattern of particles that went through the detector is mirrored in the pattern of electrons colliding with the APAs.”

From these particle tracks, researchers derive information about neutrinos and their antimatter counterparts. The results will shed light on the role neutrinos played in the evolution of the universe.

Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Dark matter makes up about 27% of the matter and energy budget in the universe, but scientists do not know much about it. They do know that it is cold, meaning that the particles that make up dark matter are slow-moving. It is also difficult to detect dark matter directly because it does not interact with light. However, scientists at the U.S. Department of Energy’s Fermi National Accelerator Laboratory have found a way to look for dark matter using quantum computers.

Aaron Chou, a senior scientist at Fermilab, works on detecting dark matter through quantum science. As part of DOE’s Office of High Energy Physics QuantISED program, he has developed a way to use qubits, the main component of quantum computing systems, to detect single photons produced by dark matter in the presence of a strong magnetic field.

How quantum computers could detect dark matter

A classical computer processes information with binary bits set to either 1 or 0. The specific pattern of ones and zeros makes it possible for the computer to perform certain functions and tasks. In quantum computing, however, qubits exist at both 1 and 0 simultaneously until they are read, due to a quantum mechanical property known as superposition. This property allows quantum computers to efficiently perform complex calculations that a classical computer would take an enormous amount of time to complete.

“Qubits work by manipulating single excitations of information, for example, single photons,” said Chou. “So, if you’re working with such small packets of energy as single excitations, you’re far more susceptible to external disturbances.”

In order for qubits to operate at these quantum levels, they must reside in carefully controlled environments that protect them from outside interference and keep them at consistently cold temperatures. Even the slightest disturbance can throw off a program in a quantum computer. With their extreme sensitivity, Chou realized quantum computers could provide a way to detect dark matter. He recognized that other dark matter detectors need to be shielded in the same way quantum computers are, further solidifying the idea.

“Both quantum computers and dark matter detectors have to be heavily shielded, and the only thing that can jump through is dark matter,” Chou said. “So, if people are building quantum computers with the same requirements, we asked ‘why can’t you just use those as dark matter detectors?’”

Where errors are most welcome

When dark matter particles traverse a strong magnetic field, they may produce photons that Chou and his team can measure with superconducting qubits inside aluminum photon cavities. Because the qubits have been shielded from all other outside disturbances, when scientists detect a disturbance from a photon, they can infer that it was the result of dark matter flying through the protective layers.

“These disturbances manifest as errors where you didn’t load any information into the computer, but somehow information appeared, like zeroes that flip into ones from particles flying through the device,” he said.

So far, Chou and his team have demonstrated how the technique works and that the device is incredibly sensitive to these photons. Their method has advantages over other sensors, such as being able to make multiple measurements of the same photon to ensure a disturbance was not just caused by another fluke. The device also has an ultra-low noise level, which allows for a heightened sensitivity to dark matter signals.

Even the slightest disturbance can throw off a program in a quantum computer. With their extreme sensitivity, Aaron Chou realized quantum computers could provide a way to detect dark matter.

“We know how to make these tunable boxes from the high-energy physics community, and we worked together with the quantum computing people to understand and transfer the technology for these qubits to be used as sensors,” Chou said.

From here, they plan to develop a dark matter detection experiment and continue improving upon the design of the device.

Using sapphire cavities to catch dark matter

“This apparatus tests the sensor in the box, which holds photons with a single frequency,” Chou said. “The next step is to modify this box to turn it into kind of a radio receiver in which we can change the dimensions of the box.”

By altering the dimensions of the photon cavity, it will be able to sense different wavelengths of photons produced by dark matter.

“The waves that can live in the box are determined by the overall size of the box. In order to change what frequencies and which wavelengths of dark matter we want to look for, we actually have to change the size of the box,” said Chou. “That’s the work we’re currently doing; we’ve created boxes in which we can change the lengths of different parts of it in order to be able to tune into dark matter at different frequencies.”

The researchers are also developing cavities made from different materials. The traditional aluminum photon cavities lose their superconductivity in the presence of the magnetic field necessary for producing photons from dark matter particles.

“These cavities cannot live in high magnetic fields,” he said. “High magnetic fields destroy the superconductivity, so we’ve made a new cavity made out of synthetic sapphire.”

Developing these new, tunable sapphire photon cavities will lead the team closer to running dark matter experiments that combine aspects from both physics and quantum science.

Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Just as charged particles collide into one another in an accelerator, various branches of science ranging from physics and engineering to computer science collide to design, construct and operate particle accelerators. To help develop the next generation of researchers in accelerator science and technology, the U.S. Department of Energy’s Argonne National and Fermi National Accelerator Laboratories jointly run a prestigious summer undergraduate program to achieve this goal.

Established in 2008, the Lee Teng internship gives upper-level university students in the U.S. the opportunity to gain hands-on experience in accelerator science and technology while working with experts in the field. Every summer, 10 students participate in the competitive paid internship. These interns come from a wide range of disciplines, including physics, mathematics, materials science, electrical and mechanical engineering and computer science.

After a two-year pause due to COVID-19, the internship will resume in the summer of 2023. The 10-week program enables new college juniors, seniors and occasionally even talented sophomores to challenge themselves in the exciting world of particle accelerators at either Fermilab or Argonne.

“Accelerator science and technology has enabled countless scientific discoveries with transformative impacts on society and industry,” said Jonathan Jarvis, co-director of the Lee Teng Internship program and head of Fermilab’s Accelerator Research Department. “Programs like LTI are essential for developing the workforce that will produce the next generation of innovations and discoveries.”

“I was very fortunate to have the opportunity to be part of the Lee Teng Internship. The exposure to Fermilab was extremely positive and motivated me to continue working with the different national labs wherever possible.” – Ben Sims, former Fermilab LTI intern

The program fosters the ideas and potential of early-career individuals in this field in honor of theoretical physicist Lee Chang-Li Teng, who led and contributed to numerous global particle accelerator projects while educating those around him. Upon emigrating to the United States, Teng followed his passion for particle physics. He first earned his doctorate at the University of Chicago and then worked at Argonne and Fermilab for decades.

Ideal candidates for LTI show exceptional strength in the classroom but don’t need to have previous accelerator experience. Jarvis said the selection committee of five to six engineers and scientists want to see a promising student who is open and interested in relevant areas like electromagnetism.

The LTI program opens with a two-week trip to the rigorous U.S. Particle Accelerator School, where the interns take the course, “Fundamentals of Accelerator Physics and Technology with Simulations and Measurements Lab,” for academic credit. The interns then return to the labs to work on a collaborative research project alongside a mentor at Argonne or Fermilab.

“Being able to work at Argonne National Lab introduced me to the idea of working at national labs, which is now my goal. Participating in USPAS was also a great experience as it gave me an option for research in graduate school that I pursued,” said Cassandra Phillips, former Argonne LTI intern and Northern Illinois University graduate student. “Now I get to work at the Argonne Wakefield Accelerator facility as a graduate student performing research for structure-based wakefield acceleration.”

In the remaining eight weeks, students are assigned to a mentor and project at either national laboratory that appropriately matches their respective skill sets. For example, a student with interest and experience in machine learning or artificial intelligence might be paired with an accelerator engineer for a project on accelerator control systems. During the internship, interns will tour Fermilab and Argonne and visit the University of Chicago research facilities. They also receive guidance on building graduate school applications. Concluding the program, interns will summarize their summer research and present their projects at a joint research symposium.

“I was very fortunate to have the opportunity to be part of the Lee Teng Internship. The exposure to Fermilab was extremely positive and motivated me to continue working with the different national labs wherever possible. This has led to my current work as a graduate student on beamline simulations of the new low-emittance injector for LCLS-II-HE,” said Ben Sims, a former Fermilab LTI intern and current graduate student at Michigan State University. “I hope to continue my career by working at a national lab in the future.”

Applications for the Lee Teng Internship went live on Fermilab’s website in November 2022.

Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov