Students in a trial classroom undertake the IBMQ exercises in May 2019. Photo: Ranbel Sun
Fermilab regularly makes fundamental science discoveries and is a world leader in quantum physics. In 2019, it launched the Fermilab Quantum Institute, which conducts world-class research at the leading edge of quantum computing and information science, laying the groundwork for critical physics calculations to be performed on quantum computers. As such, Fermilab is an ideal place to bring together particle physics and quantum computing as two complementary fields.
During the summer of 2018, three of us in the Fermilab Theoretical Physics Department applied to mentor two high school teachers, Anastasia Perry and Ranbel Sun. With STEM education in mind, we thought this was an ideal opportunity to share the exciting and disruptive technology of quantum computing.
After surveying the available resources on quantum computing, we discovered that while popular science articles and advanced textbooks existed in abundance, the material for high school students was decidedly lacking.
We decided to fill the gap: During the summer, Anastasia and Ranbel met with us several times a week to discuss the foundations of quantum mechanics, quantum computing and how to best present this information to a high school level audience. They read a vast amount of quantum computing material, distilled it to the simplest parts and created the module at an appropriate comprehension level. Together, we decided students should learn about quantum concepts including superposition, qubits, encryption, quantum measurement, entanglement, teleportation and their real-world applications.
Ranbel Sun and Anastasia Perry show the craft version of quantum tic-tac-toe during their June 2018 summer project. Photo: Jessica Turner
Once the summer was over, all of us continued to work on the material, creating attractive figures, improving readability and adding information on recent quantum computing developments (research really does change that quickly!). Finally, the information was collected into a single book. Working together with such a motivated and intelligent group ensured the whole process was exciting and fun.
Our group developed a course, “Quantum Computing as a High School Module,” which is available on the open-access archive arXiv. The course is the first on quantum computing designed for U.S. high school students, but it is also useful for a quantum-computing-curious public. The teachers ensured that the material is at the appropriate level, and we ensured that the science is sound.
We created the course to guide students through various aspects of quantum computing without relying on prior knowledge of quantum mechanics. Conceptual ideas are reinforced with active learning techniques, such as interactive problem sets and simulation-based labs at various levels. We’ve heard that the walkthrough exercises that use IBM’s real quantum computer to build a Schroedinger’s worm (equivalent to the cat) have been a real hit.
We tested the material through trial runs and received positive feedback from multiple sources. In the trial runs, we conducted surveys before and after the students took the course and found that they successfully learned about quantum computing and had a high level of enthusiasm for it. One student even commented “we should replace special relativity with quantum computing next year.”
This spring, we submitted to journal The Physics Teacher an article in which we analyze student feedback.
The course has seen remarkable success since its inception. We have been contacted by people from all over the world, including high school teachers in Brazil and education researchers in the Netherlands. The American Association of Physics Teachers is excited to collaborate with us on future quantum computing pedagogy workshops and to create nationwide impact in quantum computing education for high schoolers.
Quantum computing will affect the future of every area of science, so the need for a quantum-fluent workforce is great. With this quantum computing course, Fermilab scientists are breaking new ground in both quantum computing research and ensuring the competitiveness of the STEM workforce in the quantum era.
Ciaran Hughes, Joshua Isaacson and Jessica Turner are theoretical physicists at Fermilab.
What makes for a good dark matter detector? It has a lot in common with a good teleconference setup: You need a sensitive microphone and a quiet room.
Scientists working on the SENSEI experiment at the Department of Energy’s Fermilab now have demonstrated for the first time a particle detector — based on charge-coupled device, or CCD, technology — with both the sensitivity and reduced background rates needed for an effective search for low-mass particles of dark matter, the mysterious substance that accounts for about 80 percent of all matter in the universe.
The demonstration is important in two ways. First, the background rates measured by the SENSEI detector are record lows for a silicon detector. They set the world’s strongest limits on dark matter interactions with electrons, across a wide range of models. Second, it shows the high quality of the detectors that will be used in the full-scale SENSEI experiment under construction. SENSEI will run at the Canadian SNOLAB deep underground laboratory.
This picture shows the the new SENSEI skipper-CCD module. Image: SENSEI collaboration
The SENSEI detector is a 5.4-megapixel CCD made of 2 grams of silicon currently operating about 100 meters underground at Fermilab. If a dark matter particle collides with one of the electrons in the silicon, the energy transferred to the electron may be enough to liberate it from the crystal structure of the silicon. If there is enough energy, additional electrons will be freed. This charge is the signal SENSEI scientists are looking for. The smaller the signal SENSEI can detect, the broader the range of dark matter models it can test.
This shows the SENSEI CCD module in the detector vessel. Photo: SENSEI collaboration
To observe small dark matter signals, the first thing scientists need is a sensitive detector. In other words, they must be able to detect a small signal and consistently distinguish it from a truly empty detector. As demonstrated in previous work, SENSEI’s skipper-CCDs, designed by Lawrence Berkeley National Laboratory, can count the exact number of electrons in each pixel.
In this test data, taken with a very long acquisition time, we plotted the measured charge in each pixel. The true charge is of course always an integer number of electrons. The measurement precision is a small fraction of an electron, so the 0-electron and 1-electron pixels are well separated, and there is no possibility of miscategorizing an empty pixel. Image: SENSEI collaboration
Second, scientists need low background — the rate of signal-like events from causes other than dark matter has to be small. A sensitive detector with high background is like a studio microphone in a noisy room. Even if the microphone can pick up a whisper, your soft voice might be drowned out by the noise of the washing machine in the background. The only way to improve the recording is to eliminate the noise of the washing machine.
The SENSEI collaboration now has demonstrated for the first time that it has a sensitive dark matter detector and can reduce background rates. It’s important to demonstrate that a detector can achieve low background rates before you scale up to a larger experiment with the same technology, because otherwise you are just going to scale up your background rate. Previous dark matter searches by SENSEI used prototype CCDs, which had high sensitivity but also high backgrounds because they were not made with the highest-quality silicon.
SENSEI rules out the blue regions, where the rate of dark matter interactions would be larger than the event rate that SENSEI observes.
Gray regions are ruled out by other experiments. The orange bands are favored by theoretical models and are targets for the full-scale SENSEI experiment. Image: SENSEI collaboration
SENSEI’s new dark matter search has yielded the first result from its new science-grade CCDs, which were fabricated in a dedicated production run for SENSEI with high-quality silicon. The collaboration also reduced the amount of radiation that hits the CCD by adding extra shielding around the experiment. The result was a decrease in background event rates compared to the previous search with a prototype CCD. The rate of single-electron events decreased from 33,000 to 450 events/gram-day, and we see fewer two-electron events (five, down from 21) in a much larger exposure (2.09 gram-days, up from 0.043). We also see no three- or four-electron events — just as in the previous search, but with a larger exposure.
The science-grade CCDs work as well as could have been hoped, and SENSEI expects background rates to be even lower at SNOLAB. There will likely be more great science from SENSEI in the near future!
Learn more from SENSEI’s preprint or the collaboration’s presentation at a seminar at Fermilab.
Sho Uemura of the SENSEI collaboration is a scientist at Tel Aviv University and is supported in part by the Zuckerman STEM Leadership Program.
U.S. work on SENSEI is supported by the DOE Office of Science. This work is also funded by the Heising-Simons Foundation.
Fermilab 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, visit science.energy.gov.
Editor’s note: The Dark Energy Spectroscopic Instrument seeks to further our cosmic understanding by creating the largest 3-D map of galaxies to date. Below is a press release issued by the DESI collaboration announcing that DESI project completion is now formally approved. The U.S. Department of Energy’s Fermi National Accelerator Laboratory is a key player in the construction of this instrument, drawing on more than 25 years of experience with the Sloan Digital Sky Survey and the Dark Energy Survey.
Fermilab contributed key elements to DESI, including the online databases used for data acquisition and the software that will ensure that each of the 5,000 robotic positioners are precisely pointing to their celestial targets, to within a tenth of the width of a human hair. Fermilab also contributed the corrector barrel, hexapod and cage. The corrector barrel – designed, built and initially tested at Fermilab – aligns DESI’s six large lenses. The hexapod, designed and built with partners in Italy, moves and focuses the lenses. Both the barrel and hexapod are housed in the cage, which was also designed and built by Fermilab. Additionally, Fermilab carried out the testing and packaging of DESI’s charge-coupled devices, or CCDs. The CCDs convert the light passing through the lenses from distant galaxies into digital information that can then be analyzed by the collaboration.
The Dark Energy Spectroscopic Instrument, which will map millions of galaxies in 3-D, reaches final milestone toward its startup.
Even as the Dark Energy Spectroscopic Instrument, or DESI, lies dormant within a telescope dome on a mountaintop in Arizona, due to the COVID-19 pandemic, the DESI project has moved forward in reaching the final formal approval milestone prior to startup.
DESI is designed to gather the light of tens of millions of galaxies, and several million ultrabright deep-sky objects called quasars, using fiber-optic cables that are automatically positioned to point at 5,000 galaxies at a time by an orchestrated set of swiveling robots. The gathered light is measured by a group of 10 devices called spectrographs, which split the light into its spectrum, or separate colors.
The measurements will help scientists map the universe in 3-D and learn more about mysterious dark energy — which drives the universe’s accelerating expansion — and could also provide new insight about the life cycle of galaxies and about the cosmic web that connects matter in the universe.
DESI Begins from Berkeley Lab on Vimeo.
After DESI passed a federal review in March, members of a federal advisory board formally approved the completion of the project on Monday, May 11. DESI was designed and built through the efforts of a large international collaboration that now numbers about 500 researchers at 75 institutions in 13 nations.
“Congratulations to the DESI team of U.S. and international labs and universities in developing this amazing, state-of-the-art spectroscopic instrument,” said Kathleen Turner, DESI program manager at the Department of Energy’s Office of High Energy Physics. “We are all looking forward to using DESI’s exquisite precision to map the expansion of the universe over time.”
Michael Levi, DESI project director and a scientist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), which is the lead institution in the project, said, “This is the culmination of 10 years of hard work by an incredibly dedicated and talented team and a major accomplish for all involved.”
He added, “We understand and appreciate the extraordinary privilege we have been given to work with this instrument – and even more so during this challenging time, as we continue as scientists to explore what lies beyond our world.”
The completion of the DESI Project was formally approved on May 11. DESI is designed to gather the light of tens of millions of galaxies, and several million ultrabright deep-sky objects called quasars, using fiber-optic cables that are automatically positioned to point at 5,000 galaxies at a time by an orchestrated set of swiveling robots. Photo: Marilyn Chung/Lawrence Berkeley National Laboratory
Preparing for a restart in DESI testing
In mid-March it became clear that a final testing phase of the instrument would be abruptly suspended due to the temporary shutdown of most activities at Kitt Peak National Observatory, or KPNO, where DESI is located, to reduce the risk of spreading COVID-19.
Project participants moved quickly to capture a large, last batch of sky data during the March 14-15 weekend before the instrument was temporarily shuttered the following week, and that data proved useful in the project’s review for the construction completion milestone, known as Critical Decision 4, or CD-4.
In the months leading up to the temporary reduction in operations at KPNO, which is a program of the National Science Foundation’s NOIRLab, researchers had engaged in DESI observing runs to troubleshoot technical snags and ensure its components are functioning properly.
Now, project participants say they are looking forward to a return to DESI testing in preparation for its startup and five-year mission.
“The early returns from the instrument were very gratifying after years of development,” said Daniel Eisenstein, a DESI spokesperson and Harvard University astronomy professor. “Now the whole team is eager to learn what DESI data will teach us about the universe.”
Founded in 1931 on the belief that the biggest scientific challenges are best addressed by teams, Lawrence Berkeley National Laboratory and its scientists have been recognized with 13 Nobel prizes. Today, Berkeley Lab researchers develop sustainable energy and environmental solutions, create useful new materials, advance the frontiers of computing, and probe the mysteries of life, matter, and the universe. Scientists from around the world rely on the lab’s facilities for their own discovery science. Berkeley Lab is a multiprogram national laboratory, managed by the University of California for the U.S. Department of Energy’s Office of Science.
DOE’s 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, visit science.energy.gov.
The National Science Foundation’s NOIRLab, the U.S. center for ground-based optical-infrared astronomy, operates multiple research facilities including Kitt Peak National Observatory, a program of NSF’s NOIRLab. The laboratory is operated by the Association of Universities for Research in Astronomy under a cooperative agreement with NSF’s Division of Astronomical Sciences. The National Science Foundation is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.
The Heising-Simons Foundation is a family foundation based in Los Altos, California. The foundation works with its many partners to advance sustainable solutions in climate and clean energy, enable groundbreaking research in science, enhance the education of our youngest learners, and support human rights for all people.
The Gordon and Betty Moore Foundation, established in 2000, seeks to advance environmental conservation, patient care and scientific research. The foundation’s science program aims to make a significant impact on the development of provocative, transformative scientific research and increase knowledge in emerging fields.
The Science and Technology Facilities Council is part of UK Research and Innovation – the United Kingdom body that works in partnership with universities, research organizations, businesses, charities and government to create the best possible environment for research and innovation to flourish. STFC funds and supports research in particle and nuclear physics, astronomy, gravitational research and astrophysics, and space science and also operates a network of five national laboratories as well as supporting UK research at a number of international research facilities including CERN, Fermilab and the ESO telescopes in Chile. STFC is keeping the UK at the forefront of international science and has a broad science portfolio and works with the academic and industrial communities to share its expertise.
Established in 1958 and aiming at the forefront of astronomical science, the National Astronomical Observatories of the Chinese Academy of Sciences conducts cutting-edge astronomical studies, operates major national facilities and develops state-of the-art technological innovations.
In the late 2020s, Fermilab will begin sending the world’s most intense beam of neutrinos through Earth’s crust to detectors in South Dakota for the international Deep Underground Neutrino Experiment, or DUNE. When the new PIP-II particle accelerator comes online, an intense beam of protons will travel near the speed of light through a series of underground accelerator components before passing through metallic windows and colliding with a stationary target to produce the neutrinos. Researchers intend to construct the windows out of a titanium alloy and are testing the fatigue endurance of samples exposed to proton beams to see how well they will perform in the new accelerator complex.
Right on target
When Fermilab scientists set out to produce neutrinos for DUNE, they have to be incredibly precise. The PIP-II accelerator will use superconducting structures and powerful magnets to accelerate rapid microsecond bursts of protons that are focused and steered in the right direction, aimed at the DUNE detectors in South Dakota, before they smash into the neutrino-producing target on the Fermilab site.
The target — which consists of graphite rods roughly 1.5 meters in total length — is separated from the rest of the accelerator in a vessel filled with helium to help keep temperatures down.
The protons, traveling at their maximum energy, enter the vessel through a window, then hit the bull’s eye to produce a cascade of rapidly decaying pions — short-lived subatomic particles — that exit through a second window in the back. In less than a second, the pions will not only have decayed into neutrinos, but those neutrinos — which have almost no mass and travel close to the speed of light — will have reached their destination in South Dakota, a journey of 800 miles.
To create neutrinos, a beam of particles smashes into a target, which is contained in a chamber. The beam enters and exits the chamber (seen here on a carrier frame) through highly resilient metallic windows (the dark disk at the front of the chamber), which must be able to withstand a pummeling from the high-intensity beam. Fermilab researchers are currently testing a titanium alloy for these windows in preparation for an upcoming increase in beam intensity as part of the PIP-II program. Photo: Mike Stiemann
Designing the target array is no easy task, which is especially true of the windows. They need to have the stamina to withstand the high-power proton beam and temperatures in excess of 200 degrees Celsius, all while maintaining enough structural integrity to hold up against pressure differences across the window. Not only that, but they need to be made as thin as possible to minimize the interaction with the proton beam. Because of these extreme conditions, accelerator windows are made not of glass but of metal.
While metallic windows wouldn’t let much light into your home, they don’t pose much of a barrier to particle beams. Atoms are mostly made up of empty space, and high-energy protons travel through the interstices within and between the window’s atoms with relatively little interaction.
However, the beams passing through the windows are highly energetic, and the small fraction of protons that do rebound off nuclei in the windows deposit energy in the form of heat and vibrational waves, which pose the risk of rupturing the material and are a major source of concern for engineers and physicists.
Target windows need to have the stamina to withstand the high-power proton beam and temperatures in excess of 200 degrees Celsius, all while maintaining enough structural integrity to hold up against pressure differences across the window. Not only that, but they need to be made as thin as possible to minimize the interaction with the proton beam.
“These windows have to be able to sustain the heat generated by the beam interaction,” said Fermilab postdoctoral research associate Sujit Bidhar.
All of this heating and cooling causes the beam windows to rapidly contract and expand.
“The target material expands within 10 microseconds,” Bidhar said. “But the surrounding material isn’t expanding, because it’s not directly interacting with the beam. This causes a kind of hammering effect, which we call stress waves.”
The waves inside the material are analogous to a person swimming in a pool; moving through the water creates similar waves that would spread out to the edge and ricochet back to their point of origin. If the swimmer were to add extra energy by doing a cannonball into the water, the wave would increase in amplitude and might spill over the side.
Since target windows in accelerators are solid, however, strong waves passing through them weaken the material over time through a process called fatigue, and instead of being able to splash over the side of a pool, the induced stress will eventually cause the array to break. It’s not a question of if, but when.
Predicting the next big break
Physicists have a vested interest in knowing exactly how long each accelerator component can be expected to last. Unexpected equipment failures can lead to long delays and setbacks.
Many particle accelerators use target windows made of beryllium, a rare type of lightweight metal that, up until now, has shown the best results thanks to its exceptional durability. But physicists and engineers are constantly looking for ways to innovate, and those developing target windows for DUNE are investigating titanium alloys, which may have properties that allow them to hold up better than their beryllium counterparts.
“Titanium has a high specific strength as well as a high resistance to fatigue stress and corrosion,” said Kavin Ammigan, a senior engineer at Fermilab. “We’re testing to see how these critical properties change when titanium is exposed to proton beams.”
Titanium alloys have been used at the Japan Proton Accelerator Research Complex – known as J-PARC — for over a decade with promising results. With Fermilab’s PIP-II upgrade, the laboratory accelerator complex will accelerate a much higher-intensity beam than it does currently. In order to predict how long titanium windows will last at Fermilab, researchers needed to test samples using similar beam energies.
Small samples of titanium alloys were subjected to an intense proton beam at Brookhaven National Laboratory, after which they were tested for stress fatigue at Fermilab. Photo: Sujit Bidhar
Titanium fatigue samples provided by researchers at J-PARC were sent to Fermilab, where their mechanical properties were tested. The samples were then pummeled by an intense beam of protons at Brookhaven National Laboratory over the course of eight weeks, after which they were returned to Fermilab for another round of testing to determine exactly how the properties of the alloy had changed and degraded over time. By testing both before and after being bombarded by proton beams, researchers can roughly predict how long windows made out of titanium allows can be expected to last in the upgraded accelerator.
The data generated by the project will be useful not only for Fermilab and the PIP-II upgrade, but also for other institutions and future accelerators. The J-PARC accelerator facility, for example, has plans to increase the intensity of its particle beam and will be able to use the results from the current study to predict the lifespan of the titanium target window.
With this information in hand, Fermilab researchers will be able to proactively manage their beam devices. Titanium windows will be removed before the end of their projected life expectancies and replaced with fresh, unfatigued windows.
Ammigan, Bidhar and Fermilab colleagues have completed their first batch of titanium alloy sample measurements and plan to have a second batch completed in a few months’ time, after which they plan on publishing their results.
Particle accelerator research and construction at Fermilab is supported by the Department of Energy Office of Science.
Fermilab 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, visit science.energy.gov.