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The experimental value of the muon’s magnetic moment disagrees with theoretical predictions, but some of those predictions also disagree with each other—a problem theorists are working to resolve.

The magnetic moment of the muon, which describes how this electron-like particle wobbles in a magnetic field, has been a stubborn nut for particle physicists to crack. The experimentally determined values of this parameter have long disagreed with those from theoretical predictions, a trend that continued with a recent result from the Muon g-2 experiment at Fermi National Accelerator Laboratory in Illinois (see Research News: Mismatch with Standard-Model Predictions Reaches 5 Sigma). Such a discrepancy is exciting, as it could provide a hint of new physics that might resolve some of the outstanding problems in particle physics. However, the size of the discrepancy depends on which group of theorists you talk to. Resolving that theoretical discrepancy is currently the top goal for researchers in the muon-moment community.

“On the theory side, we have a lot of work to do,” says Aida El-Khadra from the University of Illinois at Urbana-Champaign. She is the chair of the Muon g-2 Theory Initiative—a collective of theorists and experimentalists working to determine what value the standard model of particle physics predicts for the muon’s magnetic moment. A few years back, the initiative seemed to be closing in on a single number [1]. But in 2021 a rift opened between the predictions of two separate methods for calculating the muon’s moment, leaving theorists without a clear prediction. “The ball is in our court, and we are working hard to get it back over the net,” El-Khadra says.

Understanding the nature of quantum objects’ behaviors is the premise for a reasonable description of the quantum world. Depending on whether the interference can be produced or not, the quantum object is endowed with dual features of a wave and a particle, i.e., the so-called wave-particle duality (WPD), which are generally observed in the so-called mutually exclusive experimental arrangements in the sense of Bohr’s complementarity principle.

Theoretical physicist John Wheeler proposed the delayed-choice experiment in the 1980s, pointing out that the methods used to observe photons will ultimately determine whether their behavior is like particles or waves.

In 2011, Ionicioiu and Terno proposed a quantum version of the delayed-choice experiment, by which the photon can be forced into a superposed state of the particle and wave and exhibits continuous morphing between those two sides with changing the controlling parameter of the ancilla.

A new study led by scientists from Spain and Germany has found a fundamental asymmetry showing that heating is consistently faster than cooling, challenging conventional expectations and introducing the concept of “thermal kinematics” to explain this phenomenon. The findings are published in Nature Physics.

Traditionally, heating and cooling, fundamental processes in thermodynamics, have been perceived as symmetric, following similar pathways.

On a microscopic level, heating involves injecting energy into individual particles, intensifying their motion. On the other hand, cooling entails the release of energy, dampening their motion. However, one question has always remained: Why is heating more efficient than cooling?

Atoms can absorb and reemit light—this is an everyday phenomenon. In most cases, however, an atom emits a light particle in all possible directions—recapturing this photon is, therefore, quite hard.

A research team from TU Wien in Vienna (Austria) has now been able to demonstrate theoretically that using a special lens, a single photon emitted by one atom can be guaranteed to be reabsorbed by a second atom. This second atom not only absorbs the photon though, but directly returns it back to the first atom. That way, the atoms pass the photon to each other with pinpoint accuracy again and again—just like in ping-pong.

An experiment outlined by a UCL (University College London)-led team of scientists from the UK and India could test whether relatively large masses have a quantum nature, resolving the question of whether quantum mechanical description works at a much larger scale than that of particles and atoms.

Quantum theory is typically seen as describing nature at the tiniest scales, and quantum effects have not been observed in a laboratory for objects more massive than about a quintillionth of a gram, or more precisely 10^-20 g.

The new experiment, described in a paper published in Physical Review Letters and involving researchers at UCL, the University of Southampton, and the Bose Institute in Kolkata, India, could, in principle, test the quantumness of an object regardless of its mass or energy.

Princeton physicists have uncovered a groundbreaking quantum phase transition in superconductivity, challenging established theories and highlighting the need for new approaches to understanding quantum mechanics in solids.

Princeton physicists have discovered an abrupt change in quantum behavior while experimenting with a three-atom.

An atom is the smallest component of an element. It is made up of protons and neutrons within the nucleus, and electrons circling the nucleus.

Heat is the enemy of quantum uncertainty. By arranging light-absorbing molecules in an ordered fashion, physicists in Japan have maintained the critical, yet-to-be-determined state of electron spins for 100 nanoseconds near room temperature.

The innovation could have a profound impact on progress in developing quantum technology that doesn’t rely on the bulky and expensive cooling equipment currently needed to keep particles in a so-called ‘coherent’ form.

Unlike the way we describe objects in our day-to-day living, which have qualities like color, position, speed, and rotation, quantum descriptions of objects involve something less settled. Until their characteristics are locked in place with a quick look, we have to treat objects as if they are smeared over a wide space, spinning in different directions, yet to adopt a simple measurement.

Computer simulations of complex systems provide an opportunity to study their time evolution under user control. Simulations of neural circuits are an established tool in computational neuroscience. Through systematic simplification on spatial and temporal scales they provide important insights in the time evolution of networks which in turn leads to an improved understanding of brain functions like learning, memory or behavior. Simulations of large networks are exploiting the concept of weak scaling where the massively parallel biological network structure is naturally mapped on computers with very large numbers of compute nodes. However, this approach is suffering from fundamental limitations. The power consumption is approaching prohibitive levels and, more seriously, the bridging of time-scales from millisecond to years, present in the neurobiology of plasticity, learning and development is inaccessible to classical computers. In the keynote I will argue that these limitations can be overcome by extreme approaches to weak and strong scaling based on brain-inspired computing architectures.

Bio: Karlheinz Meier received his PhD in physics in 1984 from Hamburg University in Germany. He has more than 25years of experience in experimental particle physics with contributions to 4 major experiments at particle colliders at DESY in Hamburg and CERN in Geneva. For the ATLAS experiment at the Large Hadron Collider (LHC) he led a 15 year effort to design, build and operate an electronics data processing system providing on-the-fly data reduction by 3 orders of magnitude enabling among other achievements the discovery of the Higgs Boson. Following scientific staff positions at DESY and CERN he was appointed full professor of physics at Heidelberg university in 1992. In Heidelberg he co-founded the Kirchhoff-Institute for Physics and a laboratory for the development of microelectronic circuits for science experiments. In particle physics he took a leading international role in shaping the future of the field as president of the European Committee for Future Accelerators (ECFA). Around 2005 he gradually shifted his scientific interests towards large-scale electronic implementations of brain-inspired computer architectures. His group pioneered several innovations in the field like the conception of a description language for neural circuits (PyNN), time-compressed mixed-signal neuromorphic computing systems and wafer-scale integration for their implementation. He led 2 major European initiatives, FACETS and BrainScaleS, that both demonstrated the rewarding interdisciplinary collaboration of neuroscience and information science. In 2009 he was one of the initiators of the European Human Brain Project (HBP) that was approved in 2013. In the HBP he leads the subproject on neuromorphic computing with the goal of establishing brain-inspired computing paradigms as tools for neuroscience and generic methods for inference from large data volumes.

A team of researchers from the Structured Light Laboratory at the University of the Witwatersrand, South Africa, has made a significant breakthrough regarding quantum entanglement.

Led by Professor Andrew Forbes, in collaboration with renowned string theorist Robert de Mello Koch, now at Huzhou University in China, the team has successfully demonstrated a novel method to manipulate quantum entangled particles without altering their intrinsic properties.

This feat marks a monumental step in our understanding and application of quantum entanglement.