From Atoms to Black Holes at the March Meeting’s Kavli Symposium

By Meredith Fore | April 13, 2023

Credit: The SXS Project

A computer simulation of two black holes merging, an event detected by LIGO in 2015.

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The APS March Meeting 2023 kicked off with a bang with the Kavli Symposium, where four speakers from four different fields, at four different scales, shared their work with attendees.

The Kavli Symposium is an annual tradition at the March Meeting, showcasing a variety of speakers and topics that have ranged over the years from cancer-detecting nanotechnology to cosmological observations and beyond. The theme this year, “Frontier Physics from Atomic to Astronomical Scales,” highlighted work that focused on the scales of atoms, 2D materials, the Earth, and black holes.

The scale of atoms

Monika Aidelsburger, a professor at the Ludwig Maximilian University of Munich, uses atoms as tools to investigate complex systems, imitating their physics with a technique called quantum simulation.

Classical simulations of many particles quickly become impractically complex. But understanding the interactions between quantum particles is key for many applications, including quantum computing.

“For these applications, we have to understand how many interacting quantum particles work together and understand their properties. That’s the challenge — but also, in some sense, exactly what we want to harness,” Aidelsburger said.

To create these simulations, the atoms are captured in a lattice of lasers, creating a “cloud” of atoms at very low temperatures. With experimental adjustment, Aidelsburger showed that this cloud of atoms can demonstrate the quantum Hall effect, which usually occurs in condensed matter rather than a group of individual particles.

This technique, however, can’t yet simulate the fields emitted by these systems, such as the electric field from a charged particle.

“What is apparent is that we are only simulating part of the physics,” Aidelsburger said. The next step, she said, is to integrate lattice gauge theory, a particular formulation of quantum field theory.

The scale of 2D materials

Pablo Jarillo-Herrero studies strongly correlated quantum materials, where powerful interactions within the system create unique phenomena like high-temperature superconductivity. But the complexity of these interactions makes it difficult to explain the materials’ exotic properties.

“The simplest model that we believe captures the essence of this phenomenology only captures the essence — we don’t know how to connect it to the phase diagram of the material,” Jarillo-Herrero said.

One solution, he says, is exactly what Aidelsburger does: simulating the system using atoms. But he works on a larger scale, using twistronics, two layers of 2D materials in which one is rotated relative to the other. With various angles and materials, the interactions of these systems can model topological, superconductive, magnetic, and strange metal phases of condensed matter. “We can realize all of these phases with just a few ingredients, and that is something that has attracted the attention of a lot of people,” Jarillo-Herrero said.

The scale of the Earth

For Brad Marston, professor of physics at Brown University, the two speakers that came before him perfectly set up his talk by talking about topological phases of matter, because “in some sense,” he said, “we’re living inside a topological insulator.”

In 1879, Lord Kelvin published a paper concluding that ocean waves couldn’t be modeled like waves in a still tub because the rotation of the Earth shapes the waves and tides. This paper contained an equation for an exponentially trapped boundary mode — the first topological wave in the literature, a century before it was rediscovered in the context of quantum matter.

Now, we have the technology to measure the size of waves at any point on Earth to millimeter resolution. Using this data, Marston shows that the equator acts as a topographic boundary for the ocean water in the northern and southern hemispheres, and that certain large-scale oceanic waves are topologically protected — more difficult for external forces to disrupt.

He ended by advising the audience to join the APS Topical Group on the Physics of Climate.

“We can gain a greater appreciation of our planet’s climate by thinking about it from the perspective of physics,” Marston concluded. “And this greater appreciation, I hope, will translate into a greater desire to understand it more deeply and perhaps solve some of the many pressing problems that face us.”

The scale of black holes

Gabriela Gonzalez, a professor of physics and astronomy at Louisiana State University and a member of LIGO, talked about research at the largest scales — of physics and of scientific collaboration.

“The original 2011 paper [for the first gravitational wave detection] had over a thousand authors,” she said. “It crashed the Physical Review Letters server because everyone wanted to read it at the same time.”

Since that groundbreaking discovery, detected from the merger of two black holes, the gravitational wave observatories have gone through several upgrades to increase sensitivity (LIGO is expected to finish its latest upgrade in May this year). This enabled more detections, including the first instance of multi-messenger astronomy, with the detection of a gamma ray burst from a neutron star merger in 2017.

“That gamma ray burst was actually not that big,” Gonzalez said. “Nobody would have paid attention to that gamma ray burst if it hadn’t come from the direction we detected the neutron star merger.”

She also highlighted the next generation of gravitational wave detectors, which will probe a wider range of gravitational frequencies: LISA, a space-based detector set to be launched in the 2030s, and the Cosmic Explorer, a proposed ground-based detector that would be ten times longer than LIGO.

Gonzalez said she likes thinking of gravitational waves as the music of the universe, since they are more akin to sound waves than light waves. And with these new experiments, she said, “we will have all kinds of different instruments to hear the orchestra of the universe.”

Meredith Fore is a science writer for the Chicago Quantum Exchange.