Category: physics

AS AN UNDERGRADUATE at UC San Diego, I knew I wanted to work in science or engineering but I wasn’t sure what I specifically wanted to do “when I grew up.” That’s why I majored in physics–it’s versatile.

After earning a PhD in physics at UC Santa Barbara, I worked for years as an academic researcher at Lawrence Berkeley National Lab (LBNL). I later veered off this career path, merging my passions for science and writing. On the surface, my physics degrees may seem unnecessary for a science journalist, given that I mostly write about medical research. But my physics training is integral to how I research, interview, and write. So, I was intrigued to speak with several Berkeley Physics alumni doing non-academic jobs to see how they apply their physics degrees.

“Physics education and training will serve you well in whatever profession you want to pursue.”

Marc Peters is an intellectual property attorney at Turner Boyd LLP. He helps clients resolve disputes related to technology, including those involving patents, trade secrets, and copyrights.

According to Peters, “thinking like a physicist” means approaching issues with the right level of abstraction, which helps determine what matters, what does not, and what is “good enough.” It also requires the curiosity to always ask “why.” These are key skills for a successful litigator.

“I was fortunate to have Professor Marjorie Shapiro as my advisor and to work with the CDF group at LBNL. They taught me how to break down any problem into solvable chunks and how to work with a group of really smart people, which I am fortunate to still do,” says Peters. “And my electronics, semiconductor, programming, and teaching experience helps me understand my clients’ technology and helps me communicate it to non-technical judges and juries.”

Peters offers some advice to current students: “Physics education and training will serve you well in whatever profession you want to pursue. You’ll learn how to learn—and that is a huge advantage in any career, inside or outside of science.”

Erika Isomura is currently a fifth-grade elementary school teacher at the Hayward Unified School District. Although she initially thought she would teach high school physics, she’s spent the last 25 years teaching all grades between second and sixth grade.

When discussing her work, she sounds like an experimental researcher. “In teaching, you don’t know in advance how things are going to turn out. So, you think about the variables, potential outcomes, and desired outcomes. And then you try things out with the kids, reflect upon what you learned, refine, and use those modifications the next day,” says Isomura. “I tease my kids that I’m a scientist experimenting on them.” She also applies this experimental approach to teaching yoga to kids.

Isomura credits her methodical planning skills to her Berkeley Physics training. Teachers need to be able to identify an end goal, as well as break that goal into manageable chunks that help students feel successful, she says.

“My work has also benefited from the classes I took at Cal. I often tell my kids about Professor Clarke, my quantum mechanics professor. His tests were open. He said it was more important that you knew how to apply the concepts than memorize or just blindly derive things. And I’ve taken that to heart,” Isomura says. “I mostly use application-level exams, rather than asking students to memorize and regurgitate something; I think that’s benefited my students.”

David Brahm recently retired as a financial portfolio manager at Geode Capital Management. As a quantitative analyst, he typically spent his days programming mathematical financial models—using databases of financial statements from several thousand companies—that aimed to maximize stock returns and minimize risk. As he describes this big data optimization problem, he is clearly still thinking like a physicist.

“To a physicist, a stock portfolio is a vector of expected returns. And every stock has some volatility, but there are also strong correlations; for example, within the airline industry. So, risk is basically a covariance matrix. And we can put these together to solve a straightforward quadratic optimization problem, where we maximize the return and minimize the risk,” explains Brahm. “Like a physicist, we make simple, useful models. However, these models can fail during an extreme event like the pandemic.”

Jeffrey Hunt is a Senior Technical Fellow at the Boeing Company. He is essentially a professor in an international company. He publishes, gets patents, gives talks, and interfaces between the technical and managerial sides of the company—always pushing the forefronts of their technology.

According to Hunt, Berkeley Physics training contributed to his success in industry. “I learned how to see the big picture, be creative, and solve problems,” he says. “My training was also very broad—optics, electronics, computer algorithms, and more—which has enabled me to reinvent myself, move around, and advance at Boeing. A physics degree is the liberal arts degree for the new millennium.”

Hunt also appreciates that his Berkeley Physics group included students and postdocs from around the world, preparing him for global collaborations.

Nasreen Gazala Chopra is the Vice President of Systems Engineering and Sustainability at Applied Materials. She spends most of her time in meetings, where she relies on the fundamentals that she learned at Berkeley Physics to successfully understand and engage in technical discussions.

“Physics also helped me think more clearly and become a stronger problem solver,” she says. “Its generality helped me get an entry ticket to jobs. And I get a lot of respect as a capable person because physics is challenging.”

Since getting her PhD in physics at Berkeley, Chopra has worked in various roles, industries, and companies, including a Silicon Valley startup, Apple, the solar industry, and the semiconductor industry. She is now excited to share this industry experience as a new member of Berkeley’s College of Letters and Science Advisory Board.

“I’m looking forward to brainstorming with my fellow board members on how we can enrich the students’ curricula and experiences,” she says. “Berkeley has a reputation for being a leader in change. I’m interested in having a frontline seat to see how that’s being implemented.”

This is a reposting of my magazine feature courtesy of UC Berkeley’s 2023 Berkeley Physics Magazine.

BERKELEY PHYSICS FACULTY ARE DRIVEN to understand the fundamental physics of materials. Theorists hypothesize the existence of new forms of matter and behaviors, and their experimentalist colleagues develop novel materials and tools to observe these exotic properties.

“We can now control parameters to systematically study how a material goes from one quantum phase to another quantum phase,” says Berkeley Physics Professor Feng Wang, the Williams H. McAdams Chair in Physics. “Instead of solving equations in a computer, we can design model systems in our lab to test and understand the underlying mechanisms of phase formation and the properties of different phases.”

The community of condensed matter physicists researching exotic materials includes experimentalists Mike Crommie, Alessandra Lanzara, and Wang, who are physics professors at Berkeley and senior faculty scientists at Lawrence Berkeley National Lab.  

Although understanding the fundamental physics is what most excites Berkeley physicists, they also expect exotic materials to lead to important applications.

“People talk about using these new materials for future quantum technology—either in quantum sensing or quantum computation—where switching is done by alternating between quantum states,” says Wang. “People are also exploring whether they can replace silicon, allowing transistors and electronics to become even more miniaturized.”

BUILDING EXOTIC 2D MATERIALS

How to create exotic 2D materials is not obvious, but Crommie offers some guidance. “In most conventional materials, the periodicity—the distance between the atoms and how they’re arranged in the lattice—determines the behavior. Electron-electron interactions and topology don’t play a big role,” says Crommie. “We make so-called exotic 2D materials by modifying these properties using techniques developed in recent years, using three general approaches.”

In the first approach, the researchers stack and rotate atomically-thin layers of different materials to create what is called a 2D moiré superlattice. Strong covalent bonds provide in-plane stability, whereas relatively weak van der Waals forces hold the layers together. And a small mismatch in the spacing of the atoms between the layers produces an interference pattern—like when you put two screens together and rotate one—thus creating a new superlattice periodicity.

“Moiré superlattices allow us to engineer new lattices for electrons and to control their correlation behavior,” says Wang. “We’re building quantum materials by design with an unprecedented control that doesn’t exist in nature.”

In the second approach, the scientists induce exotic behavior from conventional 2D materials by very carefully controlling the electron density and screening environment.

“For example, if we take a single layer of a transition metal dichalcogenide (TMD) and put electrons in it at a very low density, then the electrons crystallize into a pattern called a Wigner crystal,” says Crommie. “That’s a very exotic behavior where the electrons freeze like ice into a new crystalline phase, because the potential energy dominates over the kinetic energy. Wigner crystals were predicted almost 90 years ago, but we can image them now in new 2D materials.”

In the third approach, they create novel excitonic states in topological insulators, materials that behave like an insulator in their interior but conduct electricity along their surfaces.

“On the surface of a topological insulator, it’s like there are two freeways for electrons. Electrons with one spin move in one direction, and electrons with the other spin move in the opposite direction,” says Lanzara, the Charles Kittel Chair in Physics. “Our goal is to use optical pulses and leverage the topology and bulk/surface properties of these materials to engineer new quasiparticles.

“Having access to higher resolution tools and new ways of probing materials is how we make new discoveries. It’s a must if you want to lead the way to new science.”

DEVELOPING NOVEL TOOLS

To build and investigate a diverse range of exotic 2D materials, Berkeley physicists are pioneering new techniques. “Having access to higher resolution tools and new ways of probing materials is how we make new discoveries. It’s a must if you want to lead the way to new science,” Lanzara says.

These experimentalists have favorite tools; for example, Wang specializes in studying how light interacts with materials.

“We use optical photons from near microwave to UV,” says Wang. “The combination of optical modalities depends on the material and the specific questions we’re trying to answer.”

Optical spectroscopy is Wang’s primary technique. But his group also uses scanning tunneling microscopy (STM), including a novel non-invasive spectroscopy technique he developed with Berkeley Physics Professors Alex Zettl and Michael Crommie.

Together they built a moiré superlattice from single layers of tungsten diselenide and tungsten disulfide and then added a spacer layer of boron nitride capped by a top layer of graphene. The graphene layer enabled them to sense a delicate crystal of electrons within the TMD moiré structure without destroying it with the STM tip. The spacer layer prevented electrical shorting and permitted independent doping for the TMD and graphene layers.

“We made the first real-space images of 2D Wigner crystals in our moiré superlattice by actually imaging a lattice formed by electrons. We were able to see the correlated ground state and interesting excited state properties,” Wang says.

This approach could also be used to image electron lattices in other materials, rather than relying on a “magic angle” between the layers to control the correlations. “Our TMD moiré superlattices exist even at zero twist angle due to the lattice mismatch, and the correlation effects remain strong,” says Wang.

Berkeley physicists are also directly measuring electrons and spin in momentum space using novel spin-, time-, and angle-resolved photoemission spectroscopy pioneered by Lanzara and her coworkers. In this technique, a material is irradiated with a beam of ultrafast photons and the spin, speed, and direction of the ejected photoelectrons are measured with incredible sensitivity to figure out what’s happening inside the material. Lanzara’s latest instrument, named the momentum nanoscope, can also look at real space.

Lanzara recently used her state-of-the-art system on the topological insulator bismuth telluride to search for novel types of excitons, which are charge-neutral quasiparticles created when light is absorbed in a semiconductor. Her team discovered and characterized the first spatially indirect topological exciton state. “The electron trapped on the surface is coupled to a hole confined in the bulk, generating a long-lasting spatially-separated exciton that retains the special spin properties inherent to topological states,” she says.

One potential application of exotic materials is sustainable electronics that stays cool. “Your cell phone and computer heat up because charges bounce into each other as they move,” explains Lanzara. “Some of these new 2D and topological materials allow information to be transported instead through spin, minimizing interactions and eliminating heating issues. Moreover, they can be combined as Lego-like blocks, enabling easy assembly of materials on demand that are reusable and recyclable.”

Just think, you might have an exotic 2D material in your pocket someday.

This is a reposting of my magazine feature, courtesy of UC Berkeley’s 2023 Berkeley Physics Magazine.

Berkeley Physics was delighted to host the 2023 Rising Stars in Physics Workshop this spring, sponsored by the Heising-Simons Foundation. This event brought together 24 outstanding women physicists and astronomers for two days of scientific talks and informal discussions aimed at helping them navigate the early stage of their academic careers.

The workshop was led by Pablo Jarillo-Herrero, associate professor of physics at MIT and founder of the workshop series, and Alessandra Lanzara, professor and Charles Kittel Chair in Physics at UC Berkeley. Lanzara’s personal experiences motivated her to help organize it. “My first years at Berkeley were difficult with too few role models in my department. I often felt lonely and like I didn’t belong,” says Lanzara. “These types of workshops help create a network for young women to share experiences, challenges, and ideas with their peers and senior colleagues to help them succeed.”

The highlight of the workshop for many of the participants was getting to know each other—through workshop sessions and casual interactions over meals or in an airport shuttle. “Meeting my physics peers from different fields was amazing,” says Veronika Sunko, Miller Postdoctoral Fellow. “The atmosphere was different with 80% of the people in the room being women. It was fun.” Sunko is a condensed matter experimentalist studying quantum materials with Berkeley Physics Professors Joe Orenstein and James Analytis. “We use lasers to learn about the magnetism of materials that exhibit an interesting interplay of magnetic and electronic degrees of freedom, yielding new phenomena that we’re working to understand,” she says.

Weishuang (Linda) Xu, postdoctoral researcher at the Berkeley Center for Theoretical Physics, enjoyed the keynote speeches by senior investigators. “Very accomplished people talked in-depth about their career trajectory and the massive-scale projects they’re overseeing,” says Xu. “I also appreciated the participants’ talks. I rarely hear about research outside my narrow niche of theoretical particle physics.” Xu works on various projects with different collaborators, using astrophysics and cosmology tools to study the particle nature of dark matter. “For example, I collaborate with Berkeley Physics Assistant Professor Ben Safdi. We’re analyzing data of gamma rays that come from the middle of our galaxy to search for Higgsino dark matter,” explains Xu.

As a new postdoc at the Harvard Society of Fellows, Carolyn Zhang soaked in career tips from workshop panelists on how to apply for faculty positions, build a research group, and balance commitments. “It was helpful to hear about different people’s unique journeys to where they are today. And it was cool to see so many women physics professors in one room,” she says. As a condensed matter theorist, Zhang studies the quantum phases of matter and the transitions between them. But her interests are broad and her fellowship is not tied to a single department.

Zhang also appreciates the volunteers who devoted time to organize the workshop. “They seemed genuinely passionate about supporting women entering the physics field, which was very encouraging.”

This is a reposting of my Department News story, courtesy of UC Berkeley’s 2023 Berkeley Physics Magazine.

A zoom-in of axion strings in a simulation of axion dark matter in the early universe. The strings throw off axions that go on to become that dark matter. These simulations are used to predict the properties of the axion, which informs laboratory detection efforts. (Ben Sadfi, UC Berkeley)

SCIENTISTS HAVE BEEN STUDYING THE COSMOS for centuries, but we still don’t know what makes up 85% of all matter in the universe. Unlike ordinary matter that we can see and feel, dark matter hasn’t been observed directly by even our most advanced scientific instruments. These invisible particles may be zipping through us all the time without interacting.

But scientists believe our world wouldn’t exist without dark matter. Its gravitational pull holds galaxies together, gathers them into clusters, bends light around them, and affects how they rotate. Dark matter also played a crucial role as galaxies initially formed.

“Lots of observational data show us that dark matter is a real particle, but we don’t know what kind. Its possible mass has a huge range, and there might be multiple types of dark matter particles,” says Berkeley Physics Professor Dan McKinsey, the Georgia Lee Chair in Physics. “We’re working hard to detect dark matter in the lab to open a window into new physics. It’s the only particle we know to exist outside the standard model.”

Berkeley Physics is one of the top places in the world to study dark matter. Experimental and theoretical physicists at Berkeley are leading far-reaching searches—hunting for dark matter candidates ranging from 1 TeV weakly interactive massive particles (WIMPs) to 1 MeV light dark matter particles down to 10 μeV axions.

Berkeley faculty are conducting, building, and designing next-generation dark matter experiments, including the LZ, SuperCDMS, TESSERACT, and ALPHA plasma haloscope. These innovative experiments are guided by models developed by Berkeley Physics theorists, including professors Hitoshi Murayama, Lawrence Hall, and Ben Safdi. We highlight only a few of these comprehensive efforts here.

HUNTING FOR WIMPS WITH LZ

One promising candidate is WIMPs, weakly interacting but heavy dark matter particles with a predicted mass of about 10 GeV to 100 TeV. A GeV is roughly the mass of a proton.

Hunting for WIMPs over 9 GeV is the aim of LZ, the larger and more sensitive successor of the LUX experiment. After 60 days of running, LZ recently became the most sensitive dark matter detector in the world. Berkeley Physics Professor and Berkeley Lab Director Mike Witherell, Emeritus Professor Bob Jacobsen, and McKinsey contributed to this success.

Because dark matter particles rarely interact with ordinary matter, their signal is easily drowned out by background noise. To shield from cosmic rays, LZ is located nearly a mile underground at the Sanford Underground Research Facility (SURF) in South Dakota. To reduce radioactive contamination, it uses ultra-clean detector materials. And to lower environmental backgrounds, it is built in several layers like an onion.

At the center of LZ is a time projection chamber (TPC)—a tank filled with seven tons of highly-purified liquid xenon. If a dark matter particle strikes a xenon nucleus, a flash of light and an electric charge are produced as the nucleus recoils. A strong electric field drifts the charge to the top surface of the TPC, where the electrons create a much larger flash of light that is measured by photomultiplier tubes on top and bottom.

The pattern and timing of the two flashes pinpoint the position and energy of the event. And the ratio of the two scintillation signals determines if the event was caused by a nuclear or electron recoil.

Outside the TPC are two veto detectors—a “skin” hold- ing three tons of liquid xenon and then an “outer detector” of gadolinium-loaded liquid scintillator—which are used to reject signals from gamma rays and neutrons, respectively. The whole thing lives inside a massive tank of water.

LZ is 25 times larger than the previous generation LUX experiment, which helps suppress backgrounds. But this increase also created a major challenge for McKinsey: designing and building a much higher high-voltage system to get the correct drift electric field, without the xenon lighting up like a neon lamp.

McKinsey also led the data analysis effort to reduce “accidental backgrounds” with support on backgrounds from Berkeley Physics postdoc Ibles Olcina and graduate students Jose Soria, Yue Wang, Ryan Gibbons, Ryan Smith, and James “Reed” Watson. “Occasionally, isolated first and second scintillation pulses randomly pair up to look like a dark matter event,” explains McKinsey. “My group combed through data, produced a statistical model, and developed cuts to reduce these accidentals without cutting into our dark matter acceptance.”

So far, LZ has found no evidence of WIMPs, but it set the most stringent limits on WIMP cross-sections and masses to date. And the second 1000-day run is underway.

“LZ is performing to specification, which is a big deal since we’ve been working on it for a decade,” says McKinsey. “We’re now poised to push through more dark matter parameter space over the next few years.”

McKinsey is also helping to design the next-generation of LZ, a scaled-up 80-ton xenon experiment called XLZD.

SEARCHING FOR LOW-MASS WIMPS WITH SUPERCDMS

SuperCDMS, the next-generation of the CDMS experiment, is located deep underground at SNOLAB near Sudbury, Canada. It plans to detect dark matter particles with a mass between 10 GeV and 0.5 GeV. Berkeley Physics Professor Emeritus Bernard Sadoulet led the NSF-funded part of its construction.

Searching for dark matter with lower mass requires more sensitive detectors. SuperCDMS uses germanium or silicon crystals attached to sensors on both faces. When a dark matter particle interacts with either semi-conductor, its nucleus recoils and creates minute crystal vibrations (phonons) and ionization (charge). An electric field causes the charge to drift and shed lots of phonons.

“Measuring both phonons and ionization gives us discrimination capability against backgrounds. And drifting the charges in the high-voltage detector increases our energy sensitivity by a factor of 100, allowing us to search for lower masses,” says Sadoulet.

However, measuring these phonon signals is challenging. Berkeley Physics Assistant Professor Matt Pyle played a major role in developing this unique sensor technology with the help of Berkeley’s associate research physicist Bruno Serfass and former postdoctoral fellow William Page.

At its core are transition-edge sensors (TES)—materials stabilized in the middle of their superconducting transition—attached to aluminum fin antennas. The fin absorbs the energy of the vibrations, concentrates it, and pushes it into the TES. The resulting increase in TES temperature changes its resistance, which is measured by cryogenic electronics.

“These phonon sensors need to be small to reduce their heat capacity. But if they’re attached directly to a giant crystal, an athermal phonon bounces around for a long time before it interacts with the TES. By using fins, we increase the interaction probability and area coverage,” says Pyle, the Michael M. Garland Chair in Physics.

He adds, “Only about 30% of the energy is transferred to the TES using the fins, but that’s more than made up for by collecting the phonons quickly before they thermalize.”

The collaboration is currently installing the experiment at SNOLAB. Meanwhile, they have been commissioning the SuperCDMS detectors, software, and operations at CUTE, a nearby cryogenic underground test facility at SNOLAB.

Sadoulet notes that Berkeley Physics collaborations encourage technology and data analysis transfer between various groups. The core athermal phonon sensor technology and discrimination methods are being used in multiple experiments, including SuperCDMS and TESSERACT.

“We’re giving a single solution that will hopefully be employed many times by many different experiments, all searching for slightly different things,” says Pyle.

SEEKING LIGHT DARK MATTER WITH TESSERACT

TESSERACT intends to take the dark matter search a step further. This umbrella of two experiments is being designed to detect light dark matter particles from both nuclear and electron recoils, in the mass range of the proton to the electron—1 GeV down to 1 keV.

The entire project will use identical Berkeley Physics next-generation sensors, readout technology, and operations—and no electric field for signal amplification.

“What makes TESSERACT unique is that every detector is designed to have multiple signal channels that have to be in coincidence for dark matter events. That’s the secret idea sauce of TESSERACT,” says Pyle. “We’re also eliminating a whole class of backgrounds by going to zero field, which means we need very highly sensitive detectors.”

McKinsey’s group is helping develop TESSERACT’s HeRALD experiment with assistance from Assistant Project Scientist Junsong Lin and graduate students Roger Romani, Will Matava, and Wang. HeRALD uses purified liquid helium as the target for nuclear recoil dark matter. Its silicon athermal phonon detectors are submerged in the vat of liquid helium and suspended in a vacuum above it.

“Using helium provides excellent background discrimination. If a dark matter event occurs in the helium, it lights up multiple pixels in coincidence, whereas a background event or microfracture in the silicon only lights up one pixel.” Helium is also cheap, easy to purify, easy to scale up, and naturally immune to some backgrounds. HeRALD will initially be sensitive to dark matter particles from 1 GeV to 100 MeV, but the scientists hope to reach the keV scale in the future.

Pyle’s group is helping develop TESSERACT’s SPICE experiment. It uses polar crystals—either gallium arsenide (GaAs) or sapphire (Al2O3)—as the target for both nuclear and electron recoil dark matter. A polar crystal has two types of ions with opposite charges. Some dark matter candidates may transform themselves, with low probability, into photons, which then nudge the different ions in opposite directions. This produces phonons that can be detected by the TES.

For the GaAs part of SPICE, the photons and phonons are collected in separate detectors, enabling photon-phonon coincidence to tag the unique dark matter signature, says Pyle. This scheme is designed to detect dark matter between 1 GeV to 1 MeV, caused primarily by electron scattering.

To detect dark matter with even lower mass, the second part of SPICE measures only the athermal phonon signal using sapphire detectors with even better energy sensitivity.

Pyle’s group is unraveling how to read out and calibrate these sapphire crystalline targets using his latest TES. Currently, the detectors are sensitive to dark matter in the GeV to MeV range, but the team hopes to get down to a keV.

McKinsey and Pyle are both enjoying their tabletop experiments. “If the detector is sensitive enough, then you can in principle detect light dark matter in your lab at the surface. It could happen,” McKinsey says. But TESSERACT will be installed underground in the next few years—at SURF or the Modane Underground Laboratory.

PROBING FOR AXIONS

Berkeley Physics Assistant Professor Ben Safdi studies other dark matter candidates, but he finds the ultra-light axions to be the most compelling because they explain more than dark matter. Axions were first theorized to explain the mystery of how neutrons behave in electric fields. And they have deep connections to the consistency of gravity at a quantum level.

“Axions are theoretically very well motivated, and they’re almost completely unexplored experimentally,” says Safdi, who holds the Henry Shenker Professor in Physics. “In the next decade or so, we’ll be able to say definitively whether or not these particles exist in nature.”

Although Safdi is a theoretical physicist, he looks for indirect signatures of dark matter in experimental data with his team, including graduate students Yujin Park and Joshua Benabou. “My work starts theoretically, with pencil and paper and then simulations. For a particular astrophysical system or precision laboratory experiment, we ask how axions would affect it and what data we need to test these predictions. Then, we get and analyze those data sets, determining if we find evidence for axions or not,” explains Safdi.

Additionally, Safdi spends much of his time simulating how axions were produced shortly after the Big Bang to determine what mass gives the correct abundance of dark matter. For this work, he uses advanced supercomputers at the National Energy Research Scientific Computing Center (NERSC) at Berkeley Lab, which just commissioned its faster and bigger Perlmutter supercomputer. “We have lots of jobs up the hill churning away. It’s a game changer for our mass prediction computations,” says Safdi.

One feature he needs to simulate in the early universe is axion strings, which are very violent but narrow regions of space—like tiny tornadoes—that whip around and emit lots of axions.

“During the simulations, a small part of the expanding universe is represented by a 3D grid over which the equations are solved,” explains Safdi. “But the axion strings are moving, so we have to dynamically update the grid. Despite running on supercomputers, computer memory is our limiting factor.”

Luckily, Safdi teamed up with the AMReX collaboration at Berkeley Lab, adapting their code framework designed to solve multi-scale problems. The key was using an adaptive mesh grid with a fine spatial resolution around the axion strings and sparse resolution elsewhere.

Using the biggest simulation of cosmology to date, they more precisely predicted the axion mass to be between 180 to 40 μeV, higher than expected. This claim implies axions from the early universe can’t be detected by the current experiments, which use a microwave resonance chamber to enhance the photon frequency coming from axions. The required chamber would be too small to get a measurable signal.

However, Safdi’s prediction excited Berkeley Nuclear Engineering Professor Karl van Bibber. He is building the ALPHA plasmonic haloscope, which creates resonant enhancement using parallel wires in a strong magnetic field. And van Bibber is waiting to tune his experiment using the more precise predictions Safdi is now calculating with the Perlmutter.

Overall, Berkeley Physics’ search for dark matter is casting an impressively wide net. “Berkeley might be the best place in the world for dark matter research. I can’t think of any place that’s stronger overall and better,” says McKinsey.

This is a reposting of my Berkeley Physics magazine feature, courtesy of UC Berkeley’s Physics Department.