Highlights of the Year

The United Nations designated 2025 as the International Year of Quantum Science and Technology, prompting ceremonies worldwide to highlight quantum science’s impact. Physics Magazine marked the year with features designed to deepen our readers’ appreciation of the quantum world. Teaming up with Physical Review editors, we prepared a collection of seminal papers that shaped the field (See Quantum Foundations Collection), published stories on the century’s major quantum breakthroughs (See IYQ Quantum Milestones Collection), introduced a mascot for the year, and chronicled the birth of quantum mechanics (See Special Feature: The Tumultuous Birth of Quantum Mechanics). But the year wasn’t only about past glory—quantum research, both applied and fundamental, was our most covered topic.

C. Lamman/DESI Collaboration

C. Lamman/DESI Collaboration

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The source of the Universe’s accelerating expansion, known as dark energy, may not exert a constant “force” on the cosmos, as previously assumed (see Research News: The Standard Cosmology Model May Be Breaking and Viewpoint: Rethinking Our Place in the Universe). The Dark Energy Spectroscopy Instrument (DESI) Collaboration reported that the rate of accelerated expansion peaked about two billion years ago and has been dropping since then, on the basis of their analysis of data from nearly 15 million celestial objects. In DESI’s three years of operation, the collaboration generated the most complete 3D map of the Universe ever recorded, and theorists hope that the five-year results will be able to significantly narrow down the viable models for dark energy.

Of the many ways that graphene sheets can be stacked, a simple staggered arrangement has attracted much of this year’s attention. The staggered sheets form so-called rhombohedral graphene, which may host exotic quantum phenomena owing to its unusually flat electronic bands. Indeed, researchers discovered two new superconducting states in rhombohedral graphene that exhibit both chirality and magnetism—a first for any superconductor (see Research News: Chiral Superconductivity in Rhombohedral Graphene). One exciting prospect is that subsequent experiments could reveal that the states are not just chiral but topological too. If that possibility pans out, rhombohedral graphene could serve as a platform for fault-tolerant quantum computers.

Retelling a story comes naturally to most of us. Whether it’s a favorite book or a cult film, we can easily summarize the main plot points, while also recounting specific scenes. To explain this story-recall ability, researchers have constructed a hierarchical model (see Focus: How We Remember Stories). The idea is that human memory organizes the elements of a story within a tree structure. The more abstract elements form the “trunk,” whereas the more specific details fill in the “branches.” To test this model, the research team asked study participants to recall a story that they had read. The responses were analyzed by artificial intelligence and revealed statistical features that supported the model’s predictions.

Neutrinos barely interact with anything, so a collective laser-like emission of neutrinos sounds like science fiction. But researchers believe that this so-called superradiance could be coaxed from a quantum condensate of radioactive atoms (see Viewpoint: Envisioning a Neutrino Laser). In the proposed scheme, ultracold rubidium-83 atoms—which emit a neutrino when they decay—are placed in the same quantum state. One atom’s decay triggers other decays, leading to emission from the whole condensate. Hurdles remain for realizing a radioactive condensate and channeling its emissions. But if generated, a coherent neutrino beam could potentially be used for interferometry and communications. That’s a bright future for the most abundant massive particle in the Universe.

ESA; Euclid; Euclid Consortium; NASA; image processing by J.-C. Cuillandre, E. Bertin, and G. Anselmi

ESA; Euclid; Euclid Consortium; NASA; image processing by J.-C. Cuillandre, E. Bertin, and G. Anselmi

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Looking into the cosmic past has gotten a little easier thanks to the debut of two new astronomy projects. “First light” for the Vera C. Rubin Observatory in Chile was celebrated over the summer with the release of images and videos (see Research News: First Takes of the Largest Astronomical Movie Ever). This 8.4-m telescope will survey the whole Southern Sky looking for things that go “bump” in the night, such as supernovae explosions and fast-moving asteroids. A more targeted view will be provided by the spaceborne Euclid mission, which regaled the public with its own first pics of faraway galaxies (see Research News: Lensing Candidates Stand Out in Euclid Mission’s First Data Release). Euclid astronomers aim to better understand dark matter and dark energy.

A decade after the first detection of gravitational waves, LIGO’s detectors delivered another landmark result, capturing the cleanest black-hole-merger signal ever recorded (See Viewpoint: Landmark Black Hole Test Marks Decade of Gravitational-Wave Discoveries). Although the merger event was remarkably similar to the one reported in 2015, detector advances over the past ten years have dramatically reduced noise. The unprecedented sensitivity of current detectors allowed the LIGO-Virgo-KAGRA Collaboration to hear signal “overtones” on top of the fundamental ringdown note. The analysis of these spectral features confirmed the nature of the merging objects and provided the most convincing verification yet of Stephen Hawking’s 1971 area theorem, which states that the total area of black hole horizons cannot decrease, even after a black hole merger.

The pasta sauce cacio e pepe has just three ingredients: pecorino Romano cheese, cracked black pepper, and the starchy water in which the pasta—typically spaghetti—cooks. Despite its simplicity, the dish is tricky to pull off, as the sauce can fail to form a smooth, glossy emulsion. Although advice abounds on how to make appetizing cacio e pepe, a team of Italian physicists resolved to understand the source of the sauce’s finicky formation. The researchers concluded that perfecting cacio e pepe requires a modest dose of cornstarch (see Research News: Cooking Flawless Pasta). The battery of experimental and theoretical techniques that the team brought to bear on the culinary conundrum earned its members this year’s Ig Nobel Prize in Physics.

If we want to reduce the harm to our planet caused by our fossil-fuel-based lifestyle, then it’s imperative to transition society to carbon-neutral energy systems. Physicists have long focused efforts on the technical problems of forecasting climate change and developing renewable energy sources. But to avoid physicists being perceived as naive, it is essential to foster relationships with political scientists, engineers, economists, and other experts, argues condensed-matter physicist Normand Mousseau (see Opinion: How Can Physicists Contribute to the Climate Challenge?). By learning the language of these specialists, physicists can have a more meaningful impact on our climate future. Mousseau issues a call to action for institutions to expand physicists’ training and to support their involvement in the energy transformation.

R. Lin et al., Phys. Rev. Lett. 135, 060602 (2025)

R. Lin et al., Phys. Rev. Lett. 135, 060602 (2025)

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Researchers created a cartoon video about Schrödinger’s cat using over 500 atoms as movable pixels (see Video: Cat Video Made with Atoms—one of our most viewed stories of the year). The animation was meant to demonstrate the record-breaking speed with which the researchers’ new artificial-intelligence system allowed them to manipulate atoms within an array of thousands of single-atom traps. The team could completely rearrange the atoms within 60 milliseconds, whereas previous systems have taken much longer thanks to the challenge of organizing traffic flow for so many atoms. Such speedy shuffling will be essential for future atom-based quantum computers.