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Some of the most exciting advances in modern scientific research are in the field of quantum science and technology. Among them is quantum computing, a novel data-crunching technique that could revolutionize everything from biochemistry to codebreaking.

The Department of Energy’s Fermilab is positioning itself to be a forerunner in the hugely exciting field, with a new lab on site dedicated to its research and development. Favorable to Fermilab is its expertise with particle accelerator technology, which scientists are now adapting to produce game-changing quantum systems. Specifically, the superconducting radio-frequency (SRF) technology developed at the lab could help push quantum computing into a new realm.

As part of the DOE Office of Science Quantum Information Science-Enabled Discovery (QuantISED) program, a consortium of three institutions under the leadership of Fermilab scientist Alexander Romanenko has been awarded $3.9 million over two years to further SRF technology for quantum science, potentially boosting the processing speed and storage capacity of quantum devices, including quantum computers and sensors.

Beyond binary

The device you’re reading this on right now is based, at the lowest levels, on binary code – 1s and 0s. Each 1 or 0 is called a bit, and this has been the basis for all computing, right from the very first prototypes in the early 20^th century. But quantum computing works differently, by exploiting strange effects that arise at the subatomic level, such that a quantum bit – or qubit – can exist as a combination of both 1 and 0.

A big stumbling block with current attempts at quantum systems is keeping this fragile superposition of 1 and 0 stable long enough to make it useful. Leading groups have managed to maintain superpositions in quantum computers for only a few milliseconds, which severely limits the potential applications of the technology. Fermilab scientists, along with collaborators at the National Institute of Standards and Technology and the University of Wisconsin – Madison, are aiming to make a big improvement on that, keeping the systems stable much longer, up to a few seconds at a time.

“The longer this stability time, the more you can do with a quantum computer. If it’s very short, you can do nothing,” said Romanenko, head of SRF technology at Fermilab. “We’re aiming to stabilize it for substantially longer than the current best. That’s the big impact we’re after.”

Home advantage

With 50 years of experience operating particle accelerators, Fermilab is home to some of the world’s leading experts in accelerating technologies, including structures called resonating cavities that use extremely low-temperature SRF technology to boost particles as they pass through them.

“Here, we really have among the best experts worldwide in different areas all together, so we are the place where integration can occur. That’s the exciting thing,” said Anna Grassellino, Fermilab scientist and deputy head of the lab’s Applied Physics and Superconducting Technology Division.

By lowering the energy of its electric and magnetic fields and operating it at near absolute zero temperatures — thousandths of a Kelvin — an accelerating cavity can be converted into a quantum device.

A special computer chip – essentially a tiny electrical circuit – is placed inside the cavity. The circuit is made of a special material that, at extremely cool temperatures, allows pairs of electrons to flow freely around — to superconduct.

The surrounding cavity gives the chip a pulse of photons, transferring a tiny amount of energy to the electrons in the chip’s circuit. But because this all takes place in the strange quantum world, the electrons become both energized and not at the same time – a superposition. Together, the chip and the cavity represent a single qubit.

A further pulse then allows the scientists to gain information from the chip.

If some of the energy of the pulse is absorbed by the cavity walls, the quantum superposition collapses, and the quantum computer becomes useless, which is one of the major problems faced by quantum groups. One of the key reasons Fermilab may be able to produce quantum systems that last longer than any other is the specialized manufacture of the cavity itself, which reduces pulse absorption and was developed at the laboratory.

“Fermilab is one of the world leaders in SRF technology,” said Fermilab Deputy Director Joe Lykken. “That’s why our research has delved into this quantum world — because we know we can make an impact based on our unique strengths in these and other areas.”

A quantum future

Quantum computers are not likely to replace current technology any time soon. The techniques are not directly comparable, and while a quantum approach is better suited for carrying out certain tasks, classical computing still maintains advantages.

“Quantum computing is different, not always better,” Romanenko explained.

The tasks that quantum computing could excel at include simulating the quantum systems that underlie high-energy physics. With its superposition advantage, a quantum computer may be able to carry out many more calculations in a given time than a classical system, rendering complex codes breakable and protein-folding far easier to model.

The quantum technology under development at Fermilab even has potential applications outside of computing. Fermilab is developing quantum sensors, such as the high-quality cavities, to detect candidate dark matter particles called dark photons.

These future possibilities may not even be too far off. The team behind the quantum effort are optimistic about the timescale.

“If all goes well, there should be the world’s best superconducting qubit here in just a few months,” Romanenko said.

 

Take a walk along the hall that houses Fermilab’s linear accelerator, and you’ll see tall sets of brightly lit shelves that resemble fancy vending machines. But instead of snacks and beverages, they hold boxy structures that resemble gleaming car batteries. Arranged in neat columns and rows, these cells — known as Marx cells and installed during the last 36 months — have rejuvenated the aging Fermilab linear accelerator, or Fermilab Linac, and help guarantee its exceptional performance for the decade to come.

The installation of five new Marx modulators — each comprising 54 Marx cells — marks the conclusion of a five-year-long project to modernize critical components of the Linac. They replace equipment that had helped power accelerator components since the late 1960s.

“We needed a long-term replacement,” said Fermilab engineer Howie Pfeffer, who began designing the lab’s Marx modulator system in 2013. “We did a lot of modeling and experiments to see if the Marx structure would work. It wasn’t obvious that it would. And we determined that, yeah, we can do it. Along the way we built a number of circuits with smaller numbers of cells before committing to the full 54-cell modulators. Each circuit led us to important changes in the next.”

Most of the power that is fed to an accelerator is used to propel particles. The job of the modulator is to regulate those pulses of power — to shape them in a way that helps kick the particle beam forward at just the right time and right energies.

At Fermilab, the Marx modulators shape the pulses from a 5-million-watt amplifier, and the amplifier’s modulated power is used to accelerate protons in the Fermilab Linac. The specially formed waves propel the proton beam at a pulse rate of 15 times per second.

“The beam energy has to be exact, and most of the task of power regulation is to make sure that, as the particle beams accelerate through the Linac, they settle quickly to within one 10th of one percent of the accuracy level we want,” said Bill Pellico, leader of the Fermilab Proton Improvement Project, under which the Marx modulators were design and installed.

Capitalizing on the beam-tuning flexibility of the Marx modulators, Pfeffer and his engineering team perfectly filled the pulse prescription — a superfast, 350-microsecond pulse with a special shape specifically for injecting beam into the Linac. They also designed the modulators to make real-time corrections during the pulse, ensuring its shape would meet the accelerator’s stringent requirements. These machine learning capabilities enable the modulators to use past beam performance in improving pulse generation.

“This may be the first high-power Marx modulator with real-time pulse shaping feedback,” Pellico said.

The new modulators have improved regulation of the beam energy and also resulted in a nearly 50 percent savings in power over the older power-hungry modulators.

Marx modulators replace technology once common in analog radios and televisions — vacuum tube systems — with solid-state technology. Industry began using Marx modulators in the 1990s. Scientists, engineers and technicians have since developed a number of Marx modulators for particle accelerators, taking advantage of their efficient power use and better beam regulation.

“A lot of the old tubes in our accelerator had become obsolete. We couldn’t buy some of that stuff anymore,” Pellico said. “But now, we have not only a modern system, but also one where you can turn various cells on or off to modulate the power as desired. The design will have lots of applications in powering future particle accelerators — not just at Fermilab, but at other labs and facilities, too.”

The new, easy-to-maintain system enables the lab to generate easy-to-control particle beams, just one part of Fermilab’s effort to modernize its accelerator complex.

“Fermilab’s science program entirely depends on this working,” Pfeffer said. “It was a big responsibility. If we hadn’t gotten this work done, there’s no beam anywhere. So it feels great to see the Marx modulators completely installed and running. And thanks to our people who put it together, it’s the most beautiful circuit I’ve ever seen.”

The Proton Improvement Project is supported by the U.S. Department of Energy Office of Science.

Editor’s note: This is a version of an article that appeared in University of Chicago News.

The U.S. Department of Energy has awarded more than $22 million to scientists at the University of Chicago, Argonne National Laboratory and Fermi National Accelerator Laboratory for quantum science research, spanning the search for dark matter to more powerful computing.

The funding for more than a dozen projects will help scientists explore quantum engineering, which is rapidly becoming reality after decades consigned to theory.

“These are exciting new research programs aimed at creating the foundations of a new technology grounded in the laws of quantum mechanics,” said David Awschalom, the Liew Family Professor at the Institute for Molecular Engineering at the University of Chicago and a scientist at Argonne. “The projects offer a unique opportunity to not only deepen our knowledge of quantum science and what it has to offer across many fields, but also to continue building a framework of collaboration for quantum science between academic institutions and the national laboratories.”

Awschalom heads the Chicago Quantum Exchange — a partnership between all three institutions to foster an emerging Chicago-area ecosystem of quantum research and commercialization.

Among the projects funded:

• At the University of Chicago, Professor Cheng Chin will build a system called a “quantum matter synthesizer,” designed to achieve a dream long held by quantum physicists: to fully control individual atoms in a quantum system. This system will help scientists understand and harness the physics of quantum materials, as well as offer promising ways to process information using quantum technology.
• Argonne scientists will explore how to connect light particles via quantum entanglement, test long-distance entanglement, search for bosonic dark matter — a possible explanation for the mysterious phenomenon known as dark matter—and partner with the National Institute of Standards and Technology to tap quantum to improve scientists’ ability to measure very tiny effects, a field called quantum metrology.
• At Fermilab, scientists will explore applications and theory behind quantum computing, particularly for use in particle physics and accelerators, and use superconducting qubits to search for two other hypothetical particles proposed as explanations for dark matter: axions, extremely tiny particles with no spin, and dark photons, the dark “twins” of regular light particles.

“Scientists have understood the practical potential of quantum physics for decades, but only recently has the technology advanced to the point that we could tap into it,” said Joe Lykken, Fermilab chief research officer and deputy director. “Quantum physics has been Fermilab’s bread and butter for a half-century. With that accumulation of expertise and the technological innovation that comes with it, there’s hardly a place better positioned to explore — as a focused, dedicated program — the ways we can take full advantage of nature’s quantum behavior.”

“This is an opportunity to respond to a major emerging scientific challenge, which the national laboratories are uniquely positioned to do,” said Supratik Guha, a professor in University of Chicago’s Institute for Molecular Engineering and director of the Center for Nanoscale Materials at Argonne. “By delving into the fundamental science and then building devices and systems that exploit quantum mechanics, we expect enormous advantages in many fields.”

More information and the full list of funded quantum projects is available from the Department of Energy.