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Nanometer-Resolved Images from Superconducting Technology

An imaging method provides unprecedented resolution for studies of quantum materials by relying on superconductors’ extreme sensitivity to light.

The energy deposited in a superconductor by a single photon can register a detectable signal, which is why superconductors are employed in some extremely sensitive detectors. Now researchers have shown how to use this sensitivity to create maps of the superconducting properties of a material with nanometer resolution [1]. The technique can also detect polaritons—hybrid light–matter excitations that may be useful in quantum technologies—with higher resolution than earlier methods. The researchers expect the new technique to be useful in fields as diverse as quantum information and nanophotonics.

When a superconductor held just below its critical temperature absorbs a single photon, the superconductivity can be destroyed in a small region of the material, triggering a small electrical signal. Recent advances have expanded the operating temperatures of such detectors and improved their sensitivities to photons over a wide range of frequencies, enabling many new applications. Mengkun Liu of Stony Brook University in New York and colleagues wondered if the same sensitivity might be employed to build high-resolution spatial maps of the properties of superconducting samples. “Spatial variations often influence superconducting strength and coherence, so an ability to image these properties locally would bring valuable insight,” says Stony Brook team member Ran Jing.

Taming Heat in Quantum Tech

Many quantum technologies function only at ultralow temperatures. Managing the flow of heat in these systems is crucial for protecting their sensitive components. Now Matteo Pioldi and his colleagues at the CNR Institute of Nanoscience and the Scuola Normale Superiore, both in Pisa, Italy, have devised a thermal analogue of a transistor that could facilitate this heat management [1]. Just as a transistor can control electric currents, the new device has the potential to control heat currents in cryogenic quantum systems.

The most common type of transistor has three electrical terminals: the source, the gate, and the drain. Adjusting the voltage applied to the gate alters the strength of the electric current flowing from the source to the drain. In the proposed device, a semiconductor-based thermal reservoir serves as the source, and metallic thermal reservoirs serve as the gate and the drain. A second semiconductor-based reservoir exchanges heat with the source through photons and with the gate and the drain through electrons. Changing the gate’s temperature affects how easily heat flows through the device and, in turn, alters the strength of the heat current flowing from the source to the drain.

Pioldi and his colleagues performed numerical simulations of their device in a realistic setup at ultralow temperatures. They found that a small change in the strength of the heat current coming from the gate could cause the strength of the current between the source and the drain to increase by an amount that was 15 times larger. They say that their device could improve heat management in quantum circuits and thus help optimize quantum sensors, quantum computers, and other temperature-sensitive quantum systems.

Let’s Twist Again: Seeing Spin Spirals in Action

Using ultrafast x-ray pulses, researchers have probed the chirality of spin spirals in synthetic antiferromagnets.

Magnetism is a constant companion in our daily lives. Data storage, sensors, electric motors—none of these devices would function without it. Yet most technologies exploit only the simplest form of magnetic order: ferromagnetism, in which all magnetic moments within a domain align in the same direction. But magnetic order can be far more intricate. In conventional antiferromagnets (AFMs), the magnetic moments align in opposite directions to produce zero net magnetization, a type of order which has several advantages over ferromagnetism in many next-generation technological applications. In more exotic materials, the magnetic moments can twist into spirals, vortices, and other spin structures that might one day be used to store information. Occurring in both ferromagnets and AFMs, these spin structures are defined by their chirality, the direction in which the spins rotate relative to a fixed axis.

The chirality is a key fingerprint of the competing interactions at play in complex magnetic systems. However, observing the dynamics of chirality and magnetization in AFMs has been experimentally challenging, as both can evolve over nanometer length scales and on femtosecond timescales. In a new study, Zongxia Guo from the French National Centre for Scientific Research and colleagues have taken a major step forward by probing both quantities with ultrashort and ultrabright pulses from a free-electron laser (FEL) [1]. The researchers look specifically at spin spirals in an AFM, and they find that—under laser excitation—the chirality and magnetization evolve together in near unison and on significantly faster time scales than is observed for ferromagnets. Such fast spin dynamics in chiral spin structures offers a promising new route for how we will store, transfer, and compute information in the future.

Imaginary Time Delays Are For Real

The time delay experienced by a scattered light signal has an imaginary part that was considered unobservable, but researchers have isolated its effect in a frequency shift.

A scattering material, such as a frosted window or a thin fog, will cause light to travel slower than it would if no material were in its path. The mathematical formula for this time delay has a real part—which is well studied—and a lesser-known imaginary part. “The imaginary time delay has been largely ignored and disregarded as unphysical,” says Isabella Giovannelli from the University of Maryland. But she and her advisor Steven Anlage have now measured this abstract quantity by recording a corresponding frequency shift in scattered light pulses [1].

The real part of the time delay has been observed in many experiments, particularly slow-light setups where light pulses can become effectively trapped inside a scattering medium (see Focus: Light Nearly Stopped in a Waveguide). By contrast, the imaginary part has been stuck in the realm of mathematics. Theoretical work from 2016, however, showed that the imaginary time delay can be related to a potentially observable frequency shift [2].

Brain scans reveal parahippocampal cortex thinning in those with depression and neuroticism

Depression is a mental health disorder characterized by a recurrent or persistent sadness and a loss of interest in activities that were previously deemed pleasurable, sometimes accompanied by changes in sleep, appetite and perceived energy levels. One of the most debilitating types of depression is major depressive disorder (MDD), which entails a pervasive low mood for a prolonged time, which in turn adversely impacts people’s ability to engage in daily activities.

As is estimated to be experienced by approximately 3.5% of people worldwide, understanding its neurophysiological underpinnings and its characteristic brain signatures is of utmost importance. Past studies have linked depression, particularly MDD, to structural changes in a brain region known as the medial temporal lobe, which has been implicated in the formation and retrieval of memories, as well as in emotional processing and decision-making.

Researchers at Aachen University and Forschungszentrum Jülich GmbH recently carried out a study aimed at exploring the link between the structure of a specific part of the MTL, namely the parahippocampal cortex (PHC), and MDD. Their paper, published in Translational Psychiatry, suggests that the thickness of the PHC is an indicator of both MDD and , a psychological trait marked by a pronounced tendency to feel (e.g., anxiety, guilt, anger, etc.).

Discovery of bumblebee medicine’s simple structure makes synthetic production viable

Researchers at the University of Chemistry and Technology, Prague have successfully developed a method to chemically synthesize callunene, a natural compound that protects bumblebees from a deadly gut parasite. In a recent discovery, the team also determined that the naturally occurring compound is a 50/50 mixture of its mirror-image forms, meaning the synthetic version can be used directly to safeguard vital pollinator colonies.

The study, published in the Journal of Natural Products, addresses the threat posed by the parasite Crithidia bombi. This protozoan infects bumblebees, impairing their ability to find nectar-rich flowers, which ultimately leads to starvation, reduced fitness, and death. The problem is especially acute in commercial indoor farming operations that rely on healthy pollinator colonies. Not only because of the farming effectiveness, but also because parasites might be spread from indoor pollinators to wild colonies.

Nature provides a defense in the form of callunene, a compound found in the nectar of heather (Calluna vulgaris). Bumblebees that forage on heather are prophylactically protected from Crithidia infection. However, the loss of heathland habitats and the difficulty of isolating the compound from natural sources have made this solution impractical on a large scale.

Study outlines alternative approach to detecting inelastic dark matter particles

It is now understood that all known matter, i.e., studied by science and harnessed by technology, constitutes only 5% of the content of the universe. The rest is composed of two unknown components: dark matter (about 27%) and dark energy (about 68%). This calculation, confirmed decades ago, continues to surprise both lay people and scientists alike.

In the case of dark matter (DM), there is abundant evidence that it really exists, all resulting from its with ordinary matter. This evidence comes from sources such as the rotation curves of stars in galaxies, discrepancies in the movement of galaxies in clusters, the formation of large-scale structures in the universe, and cosmic background radiation, which is distributed uniformly throughout space.

Despite knowing with a high degree of certainty that DM exists, we do not know what it is. Several models proposed thus far have failed.

AI can evolve to feel guilt—but only in certain social environments

Guilt is a highly advantageous quality for society as a whole. It might not prevent initial wrongdoings, but guilt allows humans to judge their own prior judgments as harmful and prevents them from happening again. The internal distress caused by feelings of guilt often—but not always—results in the person taking on some kind of penance to relieve themselves from internal turmoil. This might be something as simple as admitting their wrongdoing to others and taking on a slight stigma of someone who is morally corrupt. This upfront cost might be initially painful, but can relieve further guilt and lead to better cooperation for the group in the future.

As we interact more and more with and use it in almost every aspect of our modern society, finding ways to instill ethical decision-making becomes more critical. In a recent study, published in the Journal of the Royal Society Interface, researchers used to explore how and when guilt evolves in multi-agent systems.

The researchers used the “prisoners’ dilemma”—a game where two players must choose between cooperating and defecting. Defecting provides an agent with a higher payoff, but they must betray their partner. This, in turn, makes it more likely that the partner will also defect. However, if the game is repeated over and over, results in a better payoff for both agents.

Anticipation of a virtual infectious pathogen is enough to prompt real biological defenses

Researchers led by the University of Geneva and École Polytechnique Fédérale de Lausanne report that neural anticipation of virtual infection triggers an immune response through activation of innate lymphoid cells.

Innate lymphoid cells (ILCs) are a type of immune cell crucial for early immune responses. They do not rely on antigen recognition like adaptive immune cells but respond quickly and effectively to various inflammatory signals and pathogen-associated cues, playing an essential role in early defense.

Protecting the body from pathogens typically involves a multitude of responses after actual contact. An anticipatory biological immune reaction to an infection had not been previously demonstrated.

Study finds infant anesthesia exposure accelerates visual brain activity patterns

New research published in Proceedings of the National Academy of Sciences (PNAS) finds that prolonged and/or repeated exposure to gamma-aminobutyric acid (GABA) anesthetic agents (sevoflurane, propofol) for infants in the first two months of life resulted in an accelerated maturation of brain electrical activity patterns evoked by visual stimuli when recorded at 2–5 months of age, compared to infants who did not have early general anesthesia exposure.

These findings may suggest the use of non-GABA-active anesthetics for the newborn age-range. To address such concerns, a large multicenter clinical trial (called TREX) is currently in progress using a combination of agents in order to minimize exposure to GABA-active anesthetics.

The paper is the fourth in a series emerging from a prospective longitudinal study known as the General Anesthesia and Brain Activity (GABA) Study, led by researchers at Boston Children’s Hospital and Northeastern University.