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Physicists used to think they had a good idea of the size of the proton. Values derived from measurements of hydrogen’s emission spectrum and from electron-scattering experiments agreed with a proton radius of around 0.88 femtometers (fm). Then, in 2010, confidence was shaken by a spectral measurement that indicated a proton radius of approximately 0.84 fm [1]. In the years since, this “proton radius puzzle” has become even more of a head-scratcher, with some experiments supporting the original estimate and others finding an even greater discrepancy. Simon Scheidegger and Frédéric Merkt at the Swiss Federal Institute of Technology (ETH), Zurich, have now made precise new measurements of the transition energies between one of hydrogen’s metastable low-energy states and several of its highly excited states [2] (Fig. 1). These measurements allow the researchers to derive some of the atom’s properties, such as its ionization energy, with greater confidence, which should help clear up some of the confusion.

The 2010 study that “shrank the proton” (as the title of the editorial summary in Nature jokingly stated) concerned the 2 S –2 P_1/2 Lamb shift [1]. According to Dirac’s predictions, the 2 S and 2 P_1/2 levels of atomic hydrogen should be degenerate. The Lamb shift refers to the lifting of this degeneracy by quantum electrodynamic (QED) effects, the largest contribution being the electron “self-energy” due to interactions with virtual photons. Once this and other QED effects are accounted for, a tiny shift of the bound-state energy levels remains, which can be attributed to the proton’s finite size. By measuring this residual energy shift, one can determine the proton radius directly. The authors of the 2010 study did so using hydrogen atoms in which the electron was replaced by its heavier cousin, the muon, since the finite-size effect is stronger in this system.

Ever since that surprise result, researchers have tried to pin down the proton radius both directly, via the finite-size effect, and indirectly, via the Rydberg constant. The Rydberg constant relates an atom’s energy levels to other physical constants and is one of the key inputs used in calculations of the proton radius. Determining its value requires painstaking measurements of the transition energies between hydrogen’s various states. Several groups have made monumental efforts in this regard, but the values they derive for the proton radius have been all over the place. A 2018 measurement of the 1 S –3 S transition by a group in France gave a value of about 0.88 fm [3], a 2019 measurement of the classic Lamb shift (this time in regular hydrogen) by a group in Canada came up with a value of about 0.833 fm [4], and a 2017 measurement of the 2 S –4 P transition by a group in Germany suggested a similarly low value of about 0.834 fm [5]. In 2020, the group in Germany arrived at a slightly higher value of 0.848 fm [6]. In 2022, finally, from measurements of the 2 S –8 D transition, a group at Colorado State University proposed a “compromise value” of about 0.86 fm [7].

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“Somewhere between one and ten million qubits are needed for a fault-tolerant quantum computer, whereas IBM has only just realized a 1,200-qubit computer,” says Aoki.

While this approach isn’t limited to any specific platform for quantum computers, it does lend itself to trapped ions and neutral atoms since they don’t need to be cooled to cryogenic temperatures, which makes them much easier to connect.

Continue reading “A fresh approach to quantum computers based on atoms and photons” »

The Short-Baseline Near Detector collaboration is preparing for an exciting year at the U.S. Department of Energy’s Fermi National Accelerator Laboratory. After nearly a decade of planning, prototyping and construction, the team is in the final stretch of commissioning of their detector.

In January, engineers began introducing gaseous argon into SBND to push air out of the cryostat. Now that the detector is mostly free of impurities, the team has begun filling it with liquid argon.

Continue reading “Scientists Get Ready to Observe Neutrinos with SBND” »

The Australian Synchrotron, a crown jewel of Australian scientific infrastructure, is making major strides towards sustainable energy independence. The nuclear research facility recently completed the installation of 3,200 solar panels which now blankets the facility’s rooftops. This move is expected to generate substantial savings and support Synchrotron’s world-class research.

The state-of-the-art particle accelerator has now gone green with a 1.59 MW/ 1,668 kWh rooftop solar system. The facility will save about $2 million in energy costs over the next five years.

China wants to set up a Higgs factory that can produce millions of Higgs boson and establish it as the world leader in high energy physics.

For over ten years, physicists have been able to pinpoint the exact positions of individual atoms with a precision finer than one-thousandth of a millimeter using a specialized microscope. However, this method has so far only provided the x and y coordinates. Information on the vertical position of the atom – i.e., the distance between the atom and the microscope objective – is lacking.

A new method has now been developed that can determine all three spatial coordinates of an atom with one single image. This method – developed by the University of Bonn and University of Bristol – is based on an ingenious physical principle. The study was recently published in the specialist journal Physical Review A.

“Opposites charges attract; like charges repel” is a fundamental principle of basic physics. However, a new study from Oxford University, recently published in the journal Nature Nanotechnology, has demonstrated that similarly charged particles in solution can, in fact, attract each other over long distances.

Just as surprisingly, the team found that the effect is different for positively and negatively charged particles, depending on the solvent.

Besides overturning long-held beliefs, these results have immediate implications for a range of processes that involve interparticle and intermolecular interactions across various length-scales, including self-assembly, crystallization, and phase separation.

MIT ’s breakthrough in integrating 2D materials into devices paves the way for next-generation devices with unique optical and electronic properties.

Two-dimensional materials, which are only a few atoms thick, can exhibit some incredible properties, such as the ability to carry electric charge extremely efficiently, which could boost the performance of next-generation electronic devices.

But integrating 2D materials into devices and systems like computer chips is notoriously difficult. These ultrathin structures can be damaged by conventional fabrication techniques, which often rely on the use of chemicals, high temperatures, or destructive processes like etching.

How much oxygen does Jupiter’s moon, Europa, produce, and what can this teach us about its subsurface liquid water ocean? This is what a study published today in Nature Astronomy hopes to address as an international team of researchers investigated how charged particles break apart the surface ice resulting in hydrogen and oxygen that feed Europa’s extremely thin atmosphere. This study holds the potential to help scientists better understand the geologic and biochemical processes on Europa, along with gaining greater insight into the conditions necessary for finding life beyond Earth.

For the study, the researchers used the Jovian Auroral Distributions Experiment (JADE) instrument onboard NASA’s June spacecraft to collect data on the amount of oxygen being discharged from Europa’s icy surface due to charge particles emanating from Jupiter’s massive magnetic field. In the end, the researchers found that oxygen production resulting from these charged particles interacting with the icy surface was approximately 26 pounds per second (12 kilograms per second), which is a much more focused number compared to previous estimates which ranged from a few pounds per second to over 2,000 pounds per second.

“Europa is like an ice ball slowly losing its water in a flowing stream. Except, in this case, the stream is a fluid of ionized particles swept around Jupiter by its extraordinary magnetic field,” said Dr. Jamey Szalay, who is a research scholar at Princeton University, a scientist on JADE, and lead author of the study. “When these ionized particles impact Europa, they break up the water-ice molecule by molecule on the surface to produce hydrogen and oxygen. In a way, the entire ice shell is being continuously eroded by waves of charged particles washing up upon it.”