A search for the dimuon decay of the Higgs boson is presented based on $pp$ collision data recorded by ATLAS during Run 3 of the Large Hadron Collider, corresponding to an integrated luminosity of $165{\mathrm{fb}}^{-1}$ at $\sqrt{s}=13.6\mathrm{TeV}$. To enhance the sensitivity, the results are combined with those from Run 2. An excess of events over the background is observed with a significance of $3.4\sigma$ ($2.5\sigma$ expected). The best-fit signal strength is $\mu =1.4\pm 0.4$. This result provides evidence for the $H\to \mu \mu$ decay with ATLAS data and offers a direct probe of the Higgs-boson Yukawa coupling to second-generation fermions.

The observation of a wide peaking structure in the $B_c^{+}\gamma$ mass spectrum is reported using proton-proton collision data collected by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of $9{\mathrm{fb}}^{-1}$. The statistical significance over the background-only hypothesis exceeds seven standard deviations. The width of the observed structure is larger than the expectation from a single-peak hypothesis, and is well described by an effective minimal model consisting of two narrow peaks located at $6704.8\pm 5.5\pm 2.8\pm 0.3\mathrm{MeV}/c^2$ and $6752.4\pm 9.5\pm 3.1\pm 0.3\mathrm{MeV}/c^2$. The uncertainty terms are statistical, systematic, and associated to the knowledge of the $B_c^{+}$ mass, respectively. The measured peak locations are in line with theoretical predictions for lowest excited $P$-wave $B_c^{+}$ states, marking the first observation of orbitally excited beauty-charm mesons and providing important insights into the internal dynamics of hadrons containing two heavy quarks.

In 1927, during the fifth Solvay Conference, Einstein and Bohr described a double-slit interferometer with a “movable slit” that can detect the momentum recoil of one photon. Their debate centered on this Gedankenexperiment has provided profound insights into the central concepts of quantum mechanics. Despite many efforts to reproduce this conceptual experiment, a linear-optical version with a movable, quantum-limited slit and tunable momentum width remained challenging. Here, we report a realization of the Einstein-Bohr interferometer using a single atom in an optical tweezer, which is cooled to the motional ground state in three dimensions such that its momentum uncertainty is comparable to that of a single photon. We design an interferometric configuration where the single atom serves as an ultralight, quantum-limit beam splitter that is momentum entangled with the input photon. By varying the trap depth of the optical tweezer, we dynamically tune the atom’s intrinsic momentum uncertainty, thus enabling the observation of a gradual shift in the visibility of single-photon interference. The interferometer also allows us to distinguish the classical noise caused by atom heating from the quantum-limited noise due to the momentum transfer, illustrating a quantum-to-classical transition.

In 1914, Ramanujan unveiled 17 extraordinary infinite series for $1/\pi$. In this Letter, we uncover their physics origin by relating them to 2D logarithmic conformal field theories (LCFTs), which emerge in diverse settings such as the fractional quantum Hall effect, percolation, polymers, and even holography. Through this LCFT connection, we reinterpret such infinite series in terms of fundamental CFT data-the operator spectrum and OPE coefficients. This perspective leads to novel physics-inspired approximations for $1/\pi$. Drawing lessons from Ramanujan’s formulas, we construct a new family of bases for expanding LCFT correlators that converge far more rapidly than the standard conformal block decomposition. This is achieved using recently developed stringy/parametric crossing-symmetric dispersion relations. Remarkably, when working with these new expansions, the action of a certain differential operator (which arises naturally from the Ramanujan connection) dramatically enhances convergence, with the entire contribution collapsing to that of the logarithmic identity operator. This striking simplification hints at a universal property of LCFTs. Finally, we discuss a new holographic interpretation of this unexpected mathematics-physics connection.

A key challenge in ultrafast science has been to directly track the coupled motions of electrons and nuclei in real space and real time. This Letter presents a significant step toward this goal by demonstrating the feasibility of time-resolved real-space tracking of valence electron and hydrogen dynamics during the photodissociation of ammonia (${\mathrm{NH}}_3$) using MeV ultrafast electron diffraction. It is demonstrated that the enhanced temporal resolution, in conjunction with the analysis of the charge-pair distribution function, enables the disentanglement of the correlated motion of valence electrons and hydrogens in a photoexcited ammonia molecule. The methodology employed in this Letter, which utilizes the charge-pair distribution function from ultrafast electron scattering to retrieve intertwined electron and nucleus dynamics, may open up new opportunities in the study of quantum dynamics for a wide range of molecules.

One of the profound consequences of the fractional quantum Hall (FQH) effect is the notion of fractionally charged anyons. In spite of extensive experimental study, puzzles remain, however. For example, both shot-noise and Aharonov-Bohm interference measurements sometimes report a charge that is a multiple of the elementary charge. We report here high-precision microscopic calculations that reveal the surprising result that the FQH anyons often bind together into stable clusters, which we term molecular anyons. This is counterintuitive, given that the elementary anyons carry the same charge and are, therefore, expected to repel one another. The number of anyons in a cluster, its binding energy, and its size depend sensitively on the parent FQH state and the interaction between electrons (which is experimentally tunable, e.g., by varying the quantum well width). Our calculations further suggest that the charge-$1/4$ non-Abelian anyons of the $5/2$ FQH state may also bind to form charge-$1/2$ Abelian clusters. The existence of molecular anyons not only can provide a natural explanation for the observed charges, but also leads to a host of new predictions for future experiments and invites a reanalysis of many past ones.

Quantum Monte Carlo (QMC) methods offer exact solutions for quantum many-body systems but face severe limitations in fermionic systems like atomic nuclei due to the sign problem. While sign-problem-free QMC algorithms exist and provide valuable insights across disciplines, they have been restricted to simple models with limited quantitative predictive power. Here we overcome this barrier by developing a novel lattice nuclear force that is rigorously sign-problem-free for even-even nuclei. This interaction achieves a standard deviation of $\sigma =2.932\mathrm{MeV}$ from experimental binding energies for 76 even-even nuclei ($N,Z\le 28$), matching state-of-the-art phenomenological mean-field models. Key innovations include the first sign-problem-free implementation of spin-orbit coupling for shell evolutions and an efficient QMC-optimized framework for global parameter fitting. Using this approach, we compute binding energies from ${}^4\mathrm{He}$ to ${}^{132}\mathrm{Sn}$ with unprecedented one-thousandth level numerical precision, reproduce symmetric nuclear matter saturation, and reveal novel spin-orbit-driven clustering in light nuclei. This Letter transforms sign-problem-free QMC simulation into a scalable and predictive nuclear structure tool, while establishing a high-fidelity, nonperturbative foundation for ab initio calculations of heavy nuclei.

Multiferroics are known to be classified into two types. However, type I lacks sufficient magnetoelectric coupling and type II lacks sufficient electric polarization, making both practically difficult. In this Letter, we explore the possibility of type-III multiferroics, where the origins of ferroelectricity and magnetism are highly intertwined but not causally related, with a combination of strong magnetoelectric coupling and large polarization. Our first-principles calculations predict that monolayer ${\mathrm{TiCdO}}_4$ is such a type-III ferroelectric-ferromagnetic multiferroic with both electronic and magnetic orders originating from competing electron populations on oxygen atoms. It shows an electric polarization of $50\mathrm{\mu }\mathrm{C}/{\mathrm{cm}}^2$, while the maximum linear and quadratic magnetoelectric response are as high as $35000\mathrm{ps}/\mathrm{m}$ and $1.59\times {10}^{-14}\mathrm{s}/\mathrm{A}$, respectively. Our Letter opens up new perspectives for the discovery and design of much-anticipated multiferroics that can be used for cross-modulation.

We show that long-wavelength interfacial fluctuations are strongly suppressed in nonequilibrium phase coexistence between bulk hyperuniform systems. Using simulations of three distinct microscopic models, we demonstrate that hyperuniform interfaces are much smoother than equilibrium ones, with a universal reduction of height fluctuations at large scale. We derive a nonequilibrium interface equation from the field theory of the bulk order parameter, and predict a reduction in height fluctuations, $S_h(\mathit{k})\equiv ⟨|h(\mathit{k}){|}^2⟩\sim |\mathit{k}{|}^{-1}$, in stark contrast to equilibrium capillary wave theory where $S_h(\mathit{k})\sim |\mathit{k}{|}^{-2}$. Our results establish a new universality class for nonequilibrium interfaces, highlighting the fundamental role of suppressed bulk fluctuations in shaping interfacial dynamics far from equilibrium.

When it comes to understanding how a cohesive object breaks up, there are two types of temptations: either seek detailed mechanisms (capillary instabilities for liquids, cracks, propagation in brittle solids...), or rely on a general principle to infer the multiplicity of the fragments’ sizes. Here we show that an original conservation law coupled with a maximal randomness principle provides new, unifying predictions. We explain when this principle is likely to apply, and why the fragment’s size distribution is a power law $p(d)\sim d^{-\beta }$, in that case, with exponent $\beta =D+1-\{{\pi }^{D/2}/[2^D(D/2)!]\},$ a function of the dimensionality of the breaking object $D$. Examples including crushed and grinned brittle materials like solid bars, plates, and shells; or cubes and spheroids; but also liquid drops and bubbles; exploding liquid shells; plastic debris in the ocean; and remnants from the cavemen industry are considered. The discussion is supplemented by an original experiment.

We study how simple eukaryotic organisms make decisions in response to competing stimuli in the context of phototaxis by the unicellular alga Chlamydomonas reinhardtii. While negatively phototactic cells swim directly away from a collimated light beam, when presented with two beams of adjustable intersection angle and intensities, we find that cells swim in a direction given by an intensity-weighted average of the two light propagation vectors. This geometrical law is a fixed point of an adaptive model of phototaxis and minimizes the average light intensity falling on the anterior pole of the cell. At large angular separations, subpopulations of cells swim away from one source or the other, or along the direction of the geometrical law, with some cells stochastically switching between the three directions. This behavior is shown to arise from a population-level distribution of photoreceptor locations that breaks front-back symmetry of photoreception.

In the early days of laser spectroscopy, Letokhov and Chebotayev proposed a scheme for measuring narrow spectral lines where the resolution is not restricted to Doppler effects because the molecules are entrained in a standing-wave light field. Now, such one-dimensional trapping in the intensity maxima of an intracavity field, slightly detuned from resonance, is experimentally demonstrated in the measurement of the very weak S(0) (2-0) quadrupole overtone transition in ${\mathrm{H}}_2$ at 1189 nm. The trapping manifests as an extremely narrow absorption feature at the predicted zero-recoil position, a 70 kHz shift from the blue-recoil component observed in Lamb-dip spectroscopy. A quantitative analysis of the saturation and trapping conditions supports the findings.

NbRe is a noncentrosymmetric superconductor that has been proposed as a candidate for intrinsic spin-triplet pairing. However, a conclusive demonstration of triplet pairing in NbRe is yet to be found. To probe the presence of spin-triplet Cooper pairs, we fabricated $\mathrm{Py}/\mathrm{NbRe}/\mathrm{Py}$ trilayers capped with an antiferromagnetic layer. Magnetic and electrical measurements reveal an inverse spin-valve effect, which could indicate equal-spin-triplet superconductivity. The minimal sample structure and the lack of ad hoc engineered interfaces clearly associate our observation to intrinsic triplet correlations of NbRe. The availability of NbRe in thin-film form and the simplicity of the heterostructure highlight its potential as a scalable platform for superconducting spintronics.

The violation of Leggett-Garg inequality (LGI) indicates general temporal correlations in quantum systems that cannot be explained classically. Under unitary dynamics and projective measurements, the violation of LGI is restricted up to the temporal Tsirelson’s bound (TTB). Here, we consider superposition of unitary time evolutions and find them to produce an enhancement in the violation of LGI beyond the TTB, growing monotonically with increasing superposition. We experimentally realize superposition of unitaries in NMR systems and demonstrate this enhanced violation. In the presence of noise, such superposition of unitaries remarkably extend the time of LGI violation, showcasing improved robustness against decoherence. This opens up possibilities of employing such nontrivial dynamical maps for robust quantum control, along with provoking research on characterizing correlations in general sequential measurement scenarios.

Small superconducting islands can exhibit charge quantization, where Coulomb interactions compete with Cooper pairing. Using scanning tunneling spectroscopy, we probe this interplay by measuring the charging energy ($E_C$) and the pairing energy ($\mathrm{\Delta }$) of individual Pb nanoislands. Below a critical island size, where $E_C>\mathrm{\Delta }$, we observe a crossover between even and odd parity ground states. By applying controlled voltage pulses, we continuously tune the island’s electrostatic potential and map the full charge-parity landscape. These results demonstrate tunable superconducting ground states, offering a potential platform for qubit design and control.

Organic semiconductors show complex phenomena due to their high energetic disorder. A striking example is the possibility of an increased effective temperature $T_{\mathrm{eff}}$ of the charge carrier distribution relative to the lattice temperature, which results from the slow charge carrier relaxation after excitation, either by high electric field or photon absorption. The increased effective temperature has been linked to conductivity enhancements and performance increases in actual devices, but a direct observation has been lacking. Here, we utilize nanoscopic tree-terminal devices to measure the Seebeck voltage arising in a doped organic polymer semiconductor due to a field-driven enhancement of the effective electronic temperature, providing direct proof of the existence of $T_{\mathrm{eff}}$. The results agree quantitatively with numerical predictions by a kinetic Monte Carlo model. The findings not only provide fundamental understanding but also indicate an avenue toward low-loss thermoelectric devices.

Recently, unconventional spin-orbit torques (SOTs) with tunable spin generation have opened new pathways for designing novel magnetization control for cutting-edge spintronics innovations. A leading research thrust is to develop field-free deterministic magnetization switching for implementing scalable and energy favorable magnetic recording and storage, which have been demonstrated in conventional ferromagnetic and antiferromagnetic material systems. Here, we extend this advanced magnetization control strategy to chiral antiferromagnet ${\mathrm{Mn}}_3\mathrm{Sn}$ using spin currents with out-of-plane canted polarization generated from low-symmetry van der Waals (vdW) material ${\mathrm{WTe}}_2$. Numerical calculations suggest that dampinglike SOT of spins injected perpendicular to the kagome plane of ${\mathrm{Mn}}_3\mathrm{Sn}$ serves as a driving force to rotate the chiral magnetic order, while the fieldlike SOT of spin currents with polarization parallel to the kagome plane provides the bipolar deterministicity to the magnetic switching in the absence of an external magnetic field. We further introduce scanning quantum microscopy to visualize nanoscale evolutions of ${\mathrm{Mn}}_3\mathrm{Sn}$ magnetic domains during the field-free switching process, corroborating the exceptionally large magnetic switching ratio up to 90%. Our results highlight the opportunities provided by hybrid SOT material platforms consisting of noncollinear antiferromagnets and low-symmetry vdW spin source materials for developing next-generation spintronic logic devices.

Quantum conductance effects start to appear as the size of electronic devices decreases and they are used in the next generation memristors and quantum calculations. Understanding the relationship between line width and resistance is crucial for developing quantized electronic devices. This Letter reports the development of an electromechanical testing device based on microelectromechanical systems integrated within a transmission electron microscope for in situ investigations at atomic resolution. The resistance changes of single crystalline gold (Au) wires, spanning from hundreds of nanometers down to several atoms are investigated. A transition in resistance from quasiballistic to ballistic transport states is uncovered. The experimental data fitted by calculation show that the ballistic transport limit for single crystal Au at room temperature is about 2.5 nm, beyond which the transmission probability experienced a rapid drop.

Optical tweezers are widely used as a highly sensitive tool to measure forces on micron-scale particles. One such application is the measurement of the electric charge of a particle, which can be done with high precision in liquids, air, or vacuum. We experimentally investigate how the trapping laser itself can electrically charge such a particle, in our case a $\sim 1\mathrm{\mu }\mathrm{m}$ ${\mathrm{SiO}}_2$ sphere in air. We model the charging mechanism as a two-photon process which reproduces the experimental data with high fidelity.

There are many exotic thermodynamic processes that are hard to study in nature. Here, we synthesize a structured environment to explore the extremes of thermodynamics. We present an engine running at extreme temperatures of above ten Megakelvin. Our underdamped engine is realised by electrically levitating and controlling a charged microparticle in vacuum. Giant fluctuations are observed in the engine’s heat exchange with the environment, while its efficiency shows stochastic events where more work is performed by the engine than heat consumed. Moreover, the nonuniformity of the synthetic environment leads to the particle experiencing position dependent diffusion, a critical phenomenon in microscale biological processes. We theoretically account for the effects of multiplicative noise and find excellent agreement with the observed behavior.