Building a better trap for the elusive neutrino

Jennifer Ngadiuba has been fascinated by the universe since a young age. “I had binoculars to watch the stars,” said Ngadiuba, a Wilson Fellow at the Department of Energy’s Fermi National Accelerator Laboratory. But it was fundamental physics which grabbed her heart. “In high school the teacher gave us a book by Stephen Hawking, and I decided that’s what I wanted to do.”

Recently, Ngadiuba’s contributions to particle physics were recognized by the International Union of Pure and Applied Physics, who awarded Ngadiuba the 2024 Early Career Scientist Prize in Particle Physics.

“This award is one of the most prestigious worldwide,” said Anadi Canepa, the head of the Fermilab CMS group and the incoming deputy spokesperson of the CMS experiment. “It’s a testament to Jennifer’s vision, drive and her interdisciplinary approach to physics. She is a trail blazer and an outstanding physicist, and we are extremely proud of her achievement.”

Ngadiuba received the award on July 24, 2024, during a ceremony at the International Conference on High Energy Physics in Prague. In the announcement, IUPAP cited Ngadiuba’s contributions to ultra-fast machine learning techniques and their application to anomaly detection.

“Jennifer is using AI to reshape collider physics,” said Maurizio Pierini, the CMS physics coordinator. “I expect that in ten years from now, CMS and ATLAS will do things very differently from the way we do today and, looking back, we will track much of this evolution — which is actually an AI revolution — back to her work.”

During college, Ngadiuba developed a passion for experimental tools. “When I was studying physics, it was a lot of math, a lot of theory, and a lot of quantum mechanics,” she said. “I thought, I need to understand how we actually see all this. What is the instrument that allows us to make a theory not a theory?”

This curiosity led Ngadiuba to Fermilab, where as a master’s student she worked on tracking detectors R&D for the future upgrade of the Compact Muon Solenoid experiment, one of the two general purpose detectors at the Large Hadron Collider. But it was during a fellowship at CERN when she was captivated by machine learning.

“Things were changing in society,” she said. “There was this explosion of data in both science and industry.”

Machine learning has been used in physics analyses since the 1980s, but Ngadiuba was curious about its implementation in a new realm: the data collection itself. The LHC generates around 1 billion collisions a second, and physicists only have a few microseconds to decide which events are noteworthy and which can be discarded.

Ngadiuba wanted to integrate machine learning into this decision-making process but was at first hesitant. “I thought the LHC is too fast for machine learning,” she said. But this did not deter Ngadiuba and her colleagues. “The tools available from industry were not OK for us,” she said. “So let’s build our own.”

The result was a new tool called hls4ml, which allows physicists to program machine learning algorithms onto a type of chip called field-programmable gate arrays. Because FPGAs use parallel processing, they can analyze and reconstruct collision events much faster than traditional CPUs. The next step was finding a project in which they could deploy it.

“What’s the most interesting problem we want to tackle?” Ngadiuba said.  “That’s why we decided to do anomaly detection.”

Most physics searches start with a theoretical model and then look for evidence to support that theory. In anomaly detection, physicists start by looking for odd things in the data.

“It’s a paradigm shift,” Ngadiuba said.

This past spring, Ngadiuba and her colleagues installed their anomaly detection tool in the CMS trigger system and have already collected their first data set.

“Many people write very interesting papers on what ATLAS and CMS could do with AI,” said Pierini, who has been working with Ngadiuba since she was a PhD student. “Jennifer doesn’t stop there. She pushes her idea forward, to real-life applications that change things for real, not just in principle.”

In addition to her work on CMS, Ngadiuba is currently partnering with physicists on the Deep Underground Neutrino Experiment to integrate the techniques developed by CMS into neutrino research.

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.

Construction workers have finished the excavation of the huge caverns that will house the international Deep Underground Neutrino Experiment. While engineers and technicians are preparing for the installation of the gigantic neutrino detectors into these caverns a mile underground, scientists around the world are working to optimize DUNE’s particle detector technology.

From new photon detection systems to improved detector designs, researchers are refining devices and technologies to make DUNE’s neutrino detectors — liquid-argon time projection chambers — the best they can be for the most precise neutrino measurements.

The purity of the liquid argon inside the DUNE cryostats, which is crucial to observing particles and light created by neutrino interactions in the liquid, might get an upgrade too. An interdisciplinary team of researchers in Brazil discovered that a filter media typically used in industrial applications can filter out nitrogen contamination in liquid argon. Future large-scale tests will help determine whether this promising method might be applicable for DUNE.

“We started with the goal of finding new materials that could capture oxygen and water in a more efficient way,” said lead researcher Pascoal Pagliuso, a physics professor at “Gleb Wataghin” Institute of Physics, Unicamp in Campinas-São Paulo. “We decided to try and find a way to capture nitrogen, too. And we succeeded.”

Neutrinos are the most abundant matter particles in the universe, yet they are hard to detect. For DUNE scientists to observe some of the neutrinos flying through their gigantic particle detectors, the neutrinos must interact with something. In the case of DUNE, hosted by the U.S. Department of Energy’s Fermi National Accelerator Laboratory, neutrinos will collide with argon atoms. The process creates secondary particles that knock loose electrons and emit brief flashes of scintillation light. Instruments can record the electrons and light so that scientists can identify and reconstruct the particles and tracks that the collisions produce. However, for this measurement to happen, the particles need to have a clear, unobstructed path through the liquid argon all the way to the detection devices. In particular, the liquid argon has to be ultra-pure and contain few atoms of other elements that could absorb electrons or light.

A tricky challenge

Researchers and engineers ensure that the liquid argon in the detectors is as pure as it can be by filtering out contaminants like water and oxygen. These are two of the most common impurities. However, there’s a third contaminant that is common: nitrogen. While neutrino researchers have well-established methods to filter out water and oxygen, reducing nitrogen levels below the levels provided by commercial providers has been a challenge.

Nitrogen can have a significant impact on the results of experiments — up to 20% of scintillation light can be lost even with just one part per million of nitrogen present in liquid argon. With ambitious experiments such as DUNE, ensuring the quality of all detector components and materials to produce the best results is critical to finding out more about neutrinos and their role in the subatomic world.

Fermilab currently uses a molecular sieve and a copper material to filter out water and oxygen, respectively, but neither can capture nitrogen from liquid argon.

Led by Pagliuso, researchers in Brazil discovered a way to reduce even small contamination levels of nitrogen in liquid argon. His interdisciplinary team of physicists and engineers found a material that removes both nitrogen and water.

Combined with a filter media like the copper material used by Fermilab, the media can remove the three most common liquid-argon contaminants, ensuring the argon is as pure as possible for neutrino experiments.

The material is known as Lithium-FAU, a Faujasite LiX zeolite. This type of aluminosilicate material has industrial applications in refining petroleum and purifying air. The Brazilian team discovered it also has the ability to remove nitrogen from liquid argon through adsorption. “It’s like when you have a medicine for one disease and discover that it also works for another disease,” Pagliuso said.

When zeolites are used as adsorbents to refine or purify liquids and gases, they attract particular particles that will stick to their surface while allowing others to pass through the crystalline structure. It’s the concept also applied when putting packets of silica gel in new shoes to capture moisture: water clings to the surface of the silica gel beads so that the humidity won’t damage the shoes. In this case, the nitrogen molecules interact with the positively charged ions in the zeolite; the size of the lithium molecules is small enough to leave room for the nitrogen to be captured and for the liquid argon to flow free of contaminants.

The chemical engineering branch of the research team at Unicamp developed simulations to predict how nitrogen would be adsorbed by Li-FAU, giving DUNE experimenters the necessary framework for testing how the media performs in the specific environment of liquid argon in a cryostat.

“Predicting the behavior of the filter is important to determine the capacity of the filter,” said Dirceu Noriler, a professor and Director of the School of Chemical Engineering at Unicamp. “We helped the engineers design the filter by specifying the saturation time and number of cycles needed to reach the required purity.”

Successful tests

Researchers and engineers initially tested the media in the relatively small Liquid Argon Purification Cryostat at Unicamp with approximately 90 liters of liquid argon. Their successful results matched the simulations Noriler and his team had developed. Further testing took place this past fall at the 3000-liter ICEBERG test stand in Fermilab’s Noble Liquid Test Facility, which was filled with 2,625 liters of liquid argon for this particular test. The results confirmed Li-FAU’s ability to remove nitrogen from liquid argon at a larger scale.

“The Noble Liquid Test Facility here at Fermilab supports all sorts of liquid argon detector R&D, and we were very happy with the results. We intend to add Li-FAU to the facility as soon as possible so that, in addition to DUNE, all projects working on improving light collection systems can benefit,” said Flor de María Blaszczyk, R&D coordinator and test facility manager at Fermilab.

Not only will the purification media improve the quality of the liquid argon that Fermilab uses for experiments, but it would also allow for the removal of nitrogen contaminants if air would accidentally be introduced into the cryostat due to the malfunction of equipment. Nitrogen is the most abundant element in air, so knowing how to filter it out will be crucial for ensuring DUNE and other experiments won’t be compromised.

The next step is working to scale up the testing with larger volumes of liquid argon to ensure the media performs as well as it has so far. Scientists hope that ultimately the method will be capable of removing nitrogen at the large scale required for DUNE, which will feature detector modules that each contain 17,500 tons of liquid argon.

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.

Scientists cannot observe dark matter directly, so to “see” it, they look for signals that it has interacted with other matter by creating a visible photon. However, signals from dark matter are incredibly weak. If scientists can make a particle detector more receptive to these signals, they can increase the likelihood of discovery and decrease the time to get there. One way to do this is to stimulate the emission of photons.

Scientists at the U.S. Department of Energy’s Fermi National Accelerator Laboratory and University of Chicago reported the ability to enhance the signals from dark matter waves by a factor of 2.78 using novel quantum techniques. This technology demonstrates how advances in quantum information science can be applied, not only to quantum computing applications, but also to new physics discoveries.

This exciting result was made possible by the DOE’s Quantum Information Science Enabled Discovery program, and the Heising-Simons Foundation. University of Chicago graduate student Ankur Agrawal conducted this research for his doctoral thesis supervised by Fermilab scientist Aaron Chou in collaboration with members of Professor David Schuster’s group at the University of Chicago. The results were recently published in Physical Review Letters.

For this experiment, the researchers first prepared a microwave cavity in a special quantum state. Then, they used superconducting quantum bits, or qubits, to increase the measurement sensitivity within that cavity so they could more easily detect any signals indicating the presence of dark matter.

“There are two ways to speed up an experiment; you can gather more signal or reduce noise,” said Schuster. “In this experiment we used a qubit to do both, preparing a quantum state of light that stimulates the creation of photons, and then using the qubit to probe the exact number of photons multiple times without destroying any to eliminate excess noise.”

The researchers prepared the microwave cavity using superconducting qubits in what is known as a Fock state. These quantum Fock states have a well-defined number of photons, and the higher the Fock state, the more likely it is that dark matter will interact. By preparing the cavity this way, as dark matter passes through the microwave cavity wall, the interaction will cause an extra photon produced by dark matter to be pumped into or removed from the cavity. The presence of one more or one less photon indicates that the photon was stimulated by dark matter.

“This experiment is a beautiful demonstration of one of the first things we learn in a quantum mechanics course about quantum states, and the results confirm what I learned,” said Agrawal.

The second part of the experiment involved engineering the interaction between the qubit and the cavity in such a way as to reduce the noise. At microwave frequencies, each photon has a tiny amount of energy which makes them very sensitive to the noise from the surrounding environment. To minimize the thermal photons from overwhelming the signal, researchers cool this cavity with a dilution refrigerator where the temperature is one-one-hundredth of a Kelvin—100 times colder than outer space.

Using superconducting qubits enabled them to engineer the interaction in such a way as to reduce the noise to extremely low levels, thereby increasing sensitivity.

“For this technique, we engineer the qubit-photon interaction so that the photon is not destroyed in the process of measurement,” said Akash Dixit, a scientist who was part of the research team at Fermilab. “This allows us to measure the same photon many times which reduces the influence of noise and increases our sensitivity to these rare events.”

The overall technique is like pushing a child on a swing. If the child is not swinging, you need to push her much harder to get her moving; but if the swing is already swinging, you don’t have to push as hard.

“What we do is take the electromagnetic field in our microwave cavity or detector — the swing — and get it to start swinging so that it can more easily take pushes from the dark matter that’s passing by,” said Chou. “This process of stimulated emission is actually exactly how lasers work.”

Previous experiments started with a zero, or ground-state, field inside the cavity, the equivalent of the swing standing still.

“Scientists can use this technique to increase sensitivity to advance their search for dark matter, saving time and resources and to explore other mysteries of fundamental science,” said Agrawal.

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.

The addition of IBM as a new partner in the Superconducting Quantum Materials and Systems Center, a DOE National Quantum Information Science Research Center, hosted by Fermilab, has been approved by the U.S. Department of Energy Office of Science, Science Programs. As a major national and international research center, SQMS is dedicated to advancing critical quantum technologies, with a focus on superconducting quantum systems. IBM is an industry leader in developing superconducting quantum computing technology. This collaboration intends to leverage the strengths of these two organizations to address key hurdles in quantum computing, communication and large-scale deployment of superconducting quantum platforms.

“We welcome the addition of IBM to the SQMS collaboration, which brings together some of the world’s top experts in superconducting materials, devices and quantum systems. This collaboration aims to leverage our complementary technical strengths and shared goals to advance superconducting quantum systems for progressing toward a fault-tolerant quantum computer,” said Anna Grassellino, SQMS Center Director.

The SQMS Center brings together more than 30 partner institutions representing national labs, industry and academia. The diverse collaboration unites over 500 experts from around the world working together to bring transformational advances in quantum information science.

As part of the collaboration, IBM intends to focus on five critical areas: large-scale cryogenics, superconducting qubit noise sources, quantum interconnects, quantum computing applications for fundamental physics and quantum workforce development.

“Fermilab and the SQMS Center are the ideal places to develop these key technologies and produce them at scale,” said Lia Merminga, Fermilab director. “We have decades of experience building large, complex superconducting cryogenic systems for accelerators and adopting advanced instrumentation to further our science mission. The advancement of quantum information science is a national priority, and Fermilab is deeply engaged in that progress.”

Large-scale cryogenics

SQMS and IBM intend to work together to advance technologies critical for scaling up quantum computers to large-scale data centers. SQMS is already proposing novel solutions for higher efficiency large-scale milliKelvin cryogenics at Fermilab. These developments in cryogenics will include the world’s largest dilution refrigerator to host 3D superconducting radiofrequency (SRF)-based quantum computing and sensing platforms, called Colossus. IBM will provide practical information and specifications to broaden the impact of Colossus. This includes developing a large-scale cooling system based on LHe/N2 plants, which would suit IBM’s future large-scale commercial quantum computing systems.

High-quality and high-density quantum interconnects

SQMS is designing and prototyping high-quality and high-density quantum interconnects based on 3D SRF platforms for quantum computing platforms being developed at Fermilab. These developments are also applicable to scaling up chip-based modular systems. Fermilab and IBM aim to explore the feasibility and usability of quantum links as part of a commercial quantum system with a focus on high-quality microwave cables.

Noise reduction in qubits and processors

As part of the SQMS Center, IBM and SQMS partners intend to work together to further the scientific understanding of mechanisms limiting the performance of superconducting qubits and developing practical schemes for the so-called “1/f flux noise” abatement.

Development of scientific applications of quantum computing systems

SQMS partners and IBM plan to advance the study of physics-based applications of quantum computing systems. For example, in condensed matter physics, researchers aim to explore the use of IBM’s utility-scale processors to support a quantum many-body dynamics simulation, whose complexity approaches a quantum advantage regime. For high-energy physics, partners will explore simulations of lattice quantum field theories.

Quantum workforce development programs

To attract and train the next generation of a diverse quantum workforce, SQMS established several successful workforce development programs, including the U.S. Quantum Information Science School shared with the other four National Quantum Information Science Research Centers (NQISRC) funded by DOE. IBM has a robust quantum education program that has enabled millions of learners worldwide and helped provide industry and domain expertise at Fortune 500 companies, universities, laboratories and startups within the IBM Quantum Network by providing tools to build their quantum workforce. SQMS and IBM plan to join forces to strengthen national quantum workforce development programs.

“As we accelerate towards building a large-scale, fault-tolerant quantum computer, we need to solve and scale complex challenges such as efficient, large-scale refrigeration and high-density and low-loss quantum interconnects and advance our understanding of noise sources and how to reduce them,” said Jay Gambetta, IBM Fellow and Vice President, IBM Quantum. “The planned participation in the SQMS Center’s research is a pillar for progressing our roadmap towards large-scale quantum computing. Alongside the collaboration to break through quantum hardware barriers, IBM and Fermilab intend to work together to drive scientific applications of quantum computing and build a quantum-ready workforce.”

The start of the collaboration is pending final approval of a legal agreement between IBM and Fermi Research Alliance, LLC.

 

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 more than 30 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 sqmscenter.fnal.gov.

Fermi National Accelerator Laboratory is America’s premier national laboratory for particle physics research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC. Visit Fermilab’s website at https://www.fnal.gov and follow us on Twitter @Fermilab.