Searching for the Quantumness of Gravity

Brian Swingle’s first passion was condensed-matter physics. As a graduate student, he performed calculations to uncover and understand new quantum phases of matter, such as topological insulators and spin liquids. But then Swingle signed up for a string theory class. There he realized that the condensed-matter tools he was developing could be used to answer questions in quantum gravity, the theory that could reconcile Einstein’s general theory of relativity with quantum mechanics. Read his interview with Physics magazine's Matteo Rini. 

A New Way to Measure Energy in Microscopic Machines

What drives cells to live and engines to move? It all comes down to a quantity that scientists call “free energy,” essentially the energy that can be extracted from any system to perform useful work. Without this available energy, a living organism would eventually die and a machine would lie idle.

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Life at the Edge of the World

Close-up photo of a trencher, which digs grooves in the ice for power and data cables. (Credit: Liz Friedman/UMD)

What's it like living and working in Antarctica? Upon returning from a five-week trip to the Amundsen-Scott South Pole Station, UMD graduate student Liz Friedman sat down with Chris and Emily to chat about her experience. In this episode, Friedman shares some of her memories of station life and explains how plans at the pole don't always pan out.

This episode of Relatively Certain was produced by Chris Cesare, Emily Edwards and Dina Genkina. It features music by Dave Depper. Relatively Certain is a production of the Joint Quantum Institute, a research partnership between the University of Maryland and the National Institute of Standards and Technology, and you can find it on iTunes, Google Play or Soundcloud.

New Research Reveals How Energy Dissipates Outside Earth’s Magnetic Field

Earth’s magnetic field provides an invisible but crucial barrier that protects Earth from the solar wind—a stream of charged particles launched from the sun’s outer layers. The protective properties of the magnetic field can fail due to a process known as magnetic reconnection, which occurs when two opposing magnetic field lines break and reconnect with each other, dissipating massive amounts of energy and accelerating particles that threaten air traffic and satellite communication systems.

In this visualization, as the supersonic solar wind (yellow haze) flows around the Earth's magnetic field (blue wavy lines), it forms a highly turbulent boundary layer called the “magnetosheath” (yellow swirling area). A new research paper describes observations of small-scale magnetic reconnection within the magnetosheath, revealing important clues about heating in the sun's outer layers and elsewhere in the universe. Image credit: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith (Click image to download hi-res version.)
In this visualization, as the supersonic solar wind (yellow haze) flows around the Earth's magnetic field (blue wavy lines), it forms a highly turbulent boundary layer called the “magnetosheath” (yellow swirling area). A new research paper describes observations of small-scale magnetic reconnection within the magnetosheath, revealing important clues about heating in the sun's outer layers and elsewhere in the universe. Image credit: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith (Click image to download hi-res version.)

Just outside of Earth’s magnetic field, the solar wind’s onslaught of electrons and ionized gases creates a turbulent maelstrom of magnetic energy known as the magnetosheath. While magnetic reconnection has been well documented closer to Earth, physicists have sought to determine whether reconnection also happens in this turbulent zone.

A new research paper co-authored by University of Maryland Physics Professor James Drake suggests that the answer to this question is yes. The observation 

A new research paper co-authored by James Drake, a University of Maryland Distinguished University Professor of Physics, suggests that the answer to this question is yes. The observations, published in the May 10, 2018 issue of the journal Nature, provide the first evidence of magnetic reconnection occurring at very small spatial scales in the turbulent magnetosheath. However, unlike the reconnection that occurs with the Earth’s magnetic field, which involves electrons as well as ions, turbulent reconnection in the magnetosheath involves electrons alone. 

“We know that magnetic energy in churning, turbulent systems cascades to smaller and smaller scales. At some point that energy is fully dissipated. The big question is how that happens, and what role magnetic reconnection plays at such small scales,” Drake said. “This study shows that reconnection indeed can happen at the electron scale, with no ions involved at all, suggesting that reconnection may help dissipate magnetic energy at very small scales.” 

By drawing a clearer picture of the physics of magnetic reconnection, the discovery promises to advance scientists’ understanding of several open questions in solar physics. For example, electron-scale magnetic reconnection may play a role in heating of the solar corona—an expansive layer of charged particles that surrounds the sun and reaches temperatures hundreds of times higher than the sun’s visible surface. This in turn could help explain the physics of the solar wind, as well as the nature of turbulent magnetic systems elsewhere in space.

NASA’s Magnetospheric Multiscale (MMS) mission gathered the data for the analysis. Flying in a pyramid formation with as little as 4.5 miles’ distance between four identical spacecraft, MMS imaged electrons within the pyramid once every 30 milliseconds. These highly precise measurements enabled the researchers to capture turbulent, electron-only magnetic reconnection, a phenomenon not previously observed. 

“MMS discovered electron magnetic reconnection, a new process much different from the standard magnetic reconnection that happens in calmer areas around Earth,” said Tai Phan, a senior fellow in the Space Sciences Laboratory at the University of California, Berkeley and the lead author of the paper. “This finding helps scientists understand how turbulent magnetic fields dissipate energy throughout the cosmos.”

Because turbulent reconnection involves only electrons, it remained hidden from scientists looking for the telltale signature of standard magnetic reconnection: ion jets. Compared with standard reconnection, in which broad jets of ions stream out tens of thousands of miles from the site of reconnection, turbulent reconnection ejects narrow jets of electrons only a couple miles wide.

But MMS scientists were able to leverage the design of one instrument, the Fast Plasma Investigation, to create a technique that allowed them to read between the lines and gather extra data points to resolve the jets.

“The key event of the paper happens in 45 milliseconds. This would be one data point with the regular data,” said Amy Rager, a graduate student at the Catholic University of America in Washington, D.C., who worked at NASA’s Goddard Space Flight Center to develop the technique. “But instead we can get six to seven data points in that region with this method, allowing us to understand what is happening.”

With the new method, MMS scientists are hopeful they can comb through existing data sets to find more of these events and other unexpected discoveries as well. 

“There were some surprises in the data,” Drake said. “Magnetic reconnection occurs when you have two magnetic fields pointing in opposite directions and they annihilate each other. In the present case a large ambient magnetic field survived after annihilation occurred. Honestly, we were surprised that turbulent reconnection at very small scales could occur with this background magnetic field present.”

Magnetic reconnection occurs throughout the universe, so whatever scientists learn about it near Earth can be applied to other phenomena. For example, the discovery of turbulent electron reconnection may help scientists understand the role that magnetic reconnection plays in heating the inexplicably hot solar corona—the sun’s outer atmosphere—and accelerating the supersonic solar wind. NASA’s upcoming Parker Solar Probe mission will travel directly toward the sun in the summer of 2018 to investigate these questions—armed with a new understanding of magnetic reconnection near Earth.

VIDEO: NASA Spacecraft Discovers New Magnetic Process in Turbulent Space:



This release was adapted from text provided by the University of California, Berkeley, and NASA. 

The research paper, “Electron Magnetic Reconnection Without Ion Coupling in Earth’s Turbulent Magnetosheath,” Tai Phan et al., was published in the journal Nature on May 10, 2018.

This work was supported by NASA (Award Nos. NNG04EB99C and NNX08AO83G), the UK Science and Technology Facilities Council (Award No. ST/N000692/1), the French Centre National d'Études Spatiales and the French Centre National de la Recherche Scientifique. The content of this article does not necessarily reflect the views of these organizations.

Original story.

Atoms May Hum a Tune from Grand Cosmic Symphony

Researchers playing with a cloud of ultracold atoms uncovered behavior that bears a striking resemblance to the universe in microcosm. Their work, which forges new connections between atomic physics and the sudden expansion of the early universe, will be published in Physical Review X and highlighted by Physics.

"From the atomic physics perspective, the experiment is beautifully described by existing theory," says Stephen Eckel, an atomic physicist at the National Institute of Standards and Technology (NIST) and the lead author of the new paper. "But even more striking is how that theory connects with cosmology."

In several sets of experiments, Eckel and his colleagues rapidly expanded the size of a doughnut-shaped cloud of atoms, taking snapshots during the process. The growth happens so fast that the cloud is left humming, and a related hum may have appeared on cosmic scales during the rapid expansion of the early universe—an epoch that cosmologists refer to as the period of inflation.

The work brought together experts in atomic physics and gravity, and the authors say it is a testament to the versatility of the Bose-Einstein condensate (BEC)—an ultracold cloud of atoms that can be described as a single quantum object—as a platform for testing ideas from other areas of physics.

"Maybe this will one day inform future models of cosmology," Eckel says. "Or vice versa. Maybe there will be a model of cosmology that’s difficult to solve but that you could simulate using a cold atomic gas."

It’s not the first time that researchers have connected BECs and cosmology. Prior studies mimicked black holes and searched for analogs of the radiation predicted to pour forth from their shadowy boundaries. The new experiments focus instead on the BEC’s response to a rapid expansion, a process that suggests several analogies to what may have happened during the period of inflation.

The first and most direct analogy involves the way that waves travel through an expanding medium. Such a situation doesn’t arise often in physics, but it happened during inflation on a grand scale. During that expansion, space itself stretched any waves to much larger sizes and stole energy from them through a process known as Hubble friction.

In one set of experiments, researchers spotted analogous features in their cloud of atoms. They imprinted a sound wave onto their cloud—alternating regions of more atoms and fewer atoms around the ring, like a wave in the early universe—and watched it disperse during expansion. Unsurprisingly, the sound wave stretched out, but its amplitude also decreased. The math revealed that this damping looked just like Hubble friction, and the behavior was captured well by calculations and numerical simulations.

"It's like we're hitting the BEC with a hammer," says Gretchen Campbell, the NIST co-director of the Joint Quantum Institute (JQI) and a coauthor of the paper, "and it’s sort of shocking to me that these simulations so nicely replicate what's going on."

In a second set of experiments, the team uncovered another, more speculative analogy. For these tests they left the BEC free of any sound waves but provoked the same expansion, watching the BEC slosh back and forth until it relaxed.

In a way, that relaxation also resembled inflation. Some of the energy that drove the expansion of the universe ultimately ended up creating all of the matter and light around us. And although there are many theories for how this happened, cosmologists aren’t exactly sure how that leftover energy got converted into all the stuff we see today.

In the BEC, the energy of the expansion was quickly transferred to things like sound waves traveling around the ring. Some early guesses for why this was happening looked promising, but they fell short of predicting the energy transfer accurately. So the team turned to numerical simulations that could capture a more complete picture of the physics.

What emerged was a complicated account of the energy conversion: After the expansion stopped, atoms at the outer edge of the ring hit their new, expanded boundary and got reflected back toward the center of the cloud. There, they interfered with atoms still traveling outward, creating a zone in the middle where almost no atoms could live. Atoms on either side of this inhospitable area had mismatched quantum properties, like two neighboring clocks that are out of sync.

The situation was highly unstable and eventually collapsed, leading to the creation of vortices throughout the cloud. These vortices, or little quantum whirlpools, would break apart and generate sound waves that ran around the ring, like the particles and radiation left over after inflation. Some vortices even escaped from the edge of the BEC, creating an imbalance that left the cloud rotating.

Unlike the analogy to Hubble friction, the complicated story of how sloshing atoms can create dozens of quantum whirlpools may bear no resemblance to what goes on during and after inflation. But Ted Jacobson, a coauthor of the new paper and a physics professor at the University of Maryland specializing in black holes, says that his interaction with atomic physicists yielded benefits outside these technical results.

"What I learned from them, and from thinking so much about an experiment like that, are new ways to think about the cosmology problem," Jacobson says. "And they learned to think about aspects of the BEC that they would never have thought about before. Whether those are useful or important remains to be seen, but it was certainly stimulating."

Eckel echoes the same thought. "Ted got me to think about the processes in BECs differently," he says, "and any time you approach a problem and you can see it from a different perspective, it gives you a better chance of actually solving that problem."

Future experiments may study the complicated transfer of energy during expansion more closely, or even search for further cosmological analogies. "The nice thing is that from these results, we now know how to design experiments in the future to target the different effects that we hope to see," Campbell says. "And as theorists come up with models, it does give us a testbed where we could actually study those models and see what happens."

The new paper included contributions from two coauthors not mentioned in the text: Avinash Kumar, a graduate student at JQI; and Ian Spielman, a JQI Fellow and NIST physicist.

Story by Chris Cesare

RESEARCH CONTACTS: Stephen Eckel This email address is being protected from spambots. You need JavaScript enabled to view it.

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Stirring-up atomtronics in a quantum circuit
An ultracold landscape for atomtronics
Stirring Up New Physics in Toroidal BECs