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A research team led by Dominik Schneble, Ph.D., Professor in the Department of Physics and Astronomy, has uncovered a novel regime, or set of conditions within a system, for cooperative radiative phenomena, casting new light on a 70-year-old problem in quantum optics.

Their findings on previously unseen collective spontaneous emission effects, in an array of synthetic (artificial) atoms, are published in Nature Physics, accompanied by a theoretical paper in Physical Review Research.

Spontaneous emission is a phenomenon in which an excited atom falls to a lower-energy state and spontaneously emits a quantum of electromagnetic radiation in the form of a single photon. When a single excited atom decays and emits a photon, the probability of finding the atom in its excited state falls exponentially to zero as time progresses.

Imagine a thread so thin it’s invisible to the naked eye but packed with the mass of thousands of stars. This isn’t science fiction—it’s the theoretical description of cosmic strings, structures that may hold answers to the Universe’s greatest mysteries. If confirmed, researchers believe these theoretical strings could unlock the key to time travel.

Cosmic strings, if they exist, are thought to be incredibly slender. Some say they’d be long tubes, either stretching infinitely or looping back on themselves. Despite their thinness, a cosmic string’s mass could rival tens of thousands of stars, and it would gradually shrink over time, radiating gravitational waves as it “wiggles.”

Physicists have proposed two types of cosmic strings thus far. The first, “cosmic superstrings,” stems from string theory, a framework suggesting the Universe’s fundamental particles are vibrating strings. Superstrings could be stretched across the cosmos, providing clues about the fabric of reality and possibly holding the key to time travel, too.

Researchers propose that time is a result of quantum entanglement, the mysterious connection between particles separated by vast distances. Their findings, published in the journal Physical Review A, could offer a clue to solving the problem of time.

“There exists a way to introduce time which is consistent with both classical laws and quantum laws, and is a manifestation of entanglement,” explained Alessandro Coppo, a physicist at the National Research Council of Italy and the study’s lead author. “The correlation between the clock and the system creates the emergence of time, a fundamental ingredient in our lives.”

In quantum mechanics, time is a fixed phenomenon, an unchanging flow from past to present. It remains external to the ever-changing quantum systems it measures and can only be observed through changes in external entities, like the hands of a clock.

Scientists have developed a novel technique using high-energy particle collisions at the Relativistic Heavy Ion Collider (RHIC), a U.S. Department of Energy (DOE) Office of Science user facility for nuclear physics research located at DOE’s Brookhaven National Laboratory. Detailed in a newly published paper in Nature, this method complements lower-energy approaches for studying nuclear structure. It offers deeper insights into the shapes of atomic nuclei, enhancing our understanding of the building blocks of visible matter.

“In this new measurement, we not only quantify the overall shape of the nucleus — whether it’s elongated like a football or squashed down like a tangerine — but also the subtle triaxiality, the relative differences among its three principle axes that characterize a shape in between the ‘football’ and ‘tangerine,’” said Jiangyong Jia, a professor at Stony Brook University (SBU) who has a joint appointment at Brookhaven Lab and is one of the principal authors on the STAR Collaboration publication.

Deciphering nuclear shapes has relevance to a wide range of physics questions, including which atoms are most likely to split in nuclear fission, how heavy atomic elements form in collisions of neutron stars, and which nuclei could point the way to exotic particle decay discoveries. Leveraging improved knowledge of nuclear shapes will also deepen scientists’ understanding of the initial conditions of a particle soup that mimics the early universe, which is created in RHIC’s energetic particle smashups. The method can be applied to analyzing additional data from RHIC as well as data collected from nuclear collisions at Europe’s Large Hadron Collider (LHC). It will also have relevance to future explorations of nuclei at the Electron-Ion Collider, a nuclear physics facility in the design stage at Brookhaven Lab.

New work provides a good view of where the field currently stands.

Surfaces play a key role in numerous chemical reactions, including catalysis and corrosion. Understanding the atomic structure of the surface of a functional material is essential for both engineers and chemists. Researchers at Nagoya University in Japan used atomic-resolution secondary electron (SE) imaging to capture the atomic structure of the very top layer of materials to better understand the differences from its lower layers. The researchers published their findings in the journal Microscopy.

Some materials exhibit “surface reconstruction,” where the surface atoms are organized differently from the interior atoms. To observe this, especially at the atomic level, surface-sensitive techniques are needed.

Traditionally, scanning electron microscopy (SEM) has been an effective tool to examine nanoscale structures. SEM works by scanning a sample with a focused electron beam and capturing the SEs emitted from the surface. SEs are typically emitted from a shallow depth below the surface, making it difficult to observe phenomena like surface reconstruction, especially if only a single atomic layer is involved.

A new theory that explains how light and matter interact at the quantum level has enabled researchers to define for the first time the precise shape of a single photon.

Research at the University of Birmingham, published in Physical Review Letters, explores the nature of photons (individual particles of light) in unprecedented detail to show how they are emitted by atoms or molecules and shaped by their environment.

The nature of this interaction leads to infinite possibilities for light to exist and propagate, or travel, through its surrounding environment. This limitless possibility, however, makes the interactions exceptionally hard to model, and is a challenge that quantum physicists have been working to address for several decades.

Then, in the 1980s, neutrinos from this supernova were picked up by the Irvine-Michigan-Brookhaven detector deep underground in Ohio. The discovery marked one of the first measurements of neutrinos from beyond our solar system, helped kickstart the field of observational neutrino astronomy, and provided a starting point that next-generation neutrino detectors continue to build on.

But the discovery was also lucky: The detector was built primarily to study proton decay, rather than neutrinos. “When you build a new detector with new capabilities, you’re sensitive to things that you never expected,” says Henry Sobel, a physics professor at the University of California, Irvine, and one of IMB’s original collaborators. The unexpected supernova would shape the legacy of IMB, which was recently recognized as an APS Historic Site for its role in neutrino science.

In the mid-1970s, teams of physicists were racing to build detectors that could measure proton decay, a hypothesized phenomenon that would confirm Howard Georgi and Sheldon Glashow’s new Grand Unified Theory, one that sought to unite three of the four fundamental forces of nature. The winner emerged in Painesville, Ohio, a small city northeast of Cleveland: The IMB detector, the world’s first kiloton-scale nucleon decay detector, began collecting data in 1982.

Researchers have developed a method to precisely locate hydrogen atoms within nanofilams, a breakthrough with significant implications for superconductivity and other material properties.

Their study, employing nuclear reaction analysis and ion channeling, revealed how hydrogen and its isotopes are distributed within titanium nanofilms, offering insights into tuning the material properties for various applications including hydrogen storage and catalysis.

Impact of hydrogen on material properties.