New Limits on Ultralight Axion Dark Matter with Gravitational Lensing

Researchers have used gravitational lensing data from the cosmic microwave background (CMB) to set the tightest limits to date on the abundance of ultralight axions (ULAs) within a specific mass range. ULAs are promising dark matter candidates that arise in various extensions of the Standard Model of particle physics. This study combines recent measurements from the Planck, Atacama Cosmology Telescope (ACT), and South Pole Telescope (SPT-3G) with a nonlinear clustering model calibrated by state-of-the-art simulations for ULAs. Ultralight axions with masses $m_\mathrm{a} \lesssim 10^{-27}$ eV were already strongly constrained by previous CMB temperature and polarization observations. This new analysis focuses on the mass range $10^{-26}\,\mathrm{eV}\leq m_\mathrm{a}\leq 10^{-24.5}\,\mathrm{eV}$, where ULAs could alleviate observed tensions in matter clustering inference if they constituted a small percentage of the universe's total dark matter. The results show that ULAs with a mass of $10^{-26}$ eV account for less than 1.5% of dark matter, while those with $10^{-25}$ eV constitute less than 9%, both at a 95% confidence level. Although a slight preference for a non-zero axion density at $10^{-24.5}$ eV with a significance of $2.1\sigma$ was identified, the authors note that this signal is primarily driven by a few data points. Therefore, further investigation into the nonlinear physics of ULAs is required to definitively confirm or rule out this possible signal. These findings are crucial for refining dark matter models and guiding future searches for these elusive particles.

qLDPC Codes with Break-Even Performance Demonstrated in Quantum Computing

Scientists have achieved a significant demonstration of quantum low-density parity-check (qLDPC) codes on a trapped-ion quantum computer. These codes are crucial for fault-tolerant quantum computing, offering superior encoding rates compared to topological alternatives like the surface code. Despite implementation challenges, such as the need for long-range couplers, the team has demonstrated nine quantum error correction codes with distinct qubit connectivities on a single device, without hardware reconfiguration. The breakthrough was achieved by leveraging the flexibility of a trapped-ion quantum computer. Notably, a qLDPC code encoding 4 logical qubits into 18 physical qubits showed a logical error rate up to 9 times better than previous demonstrations of similar codes on solid-state superconducting qubits. Furthermore, this implementation achieved break-even performance, where the lifetime of the logical qubits is comparable to or even slightly exceeds that of the underlying physical qubits. The technological key lies in a novel implementation of the metastable optical ground state (OMG) architecture. This enables addressable mid-circuit measurements and resets, eliminating the need for ion transport or dedicated cooling ions. These requirements typically consume a large fraction of the execution time or the number of ions in trapped-ion quantum computers, making this approach more efficient and scalable for future fault-tolerant quantum computing architectures.

New Quantum Algorithms for Element-wise Matrix Transformations

Researchers have developed new quantum algorithms that significantly improve the efficiency of applying functions to individual elements of a matrix. These element-wise transformations are fundamental operations in numerical linear algebra, and their efficient implementation in quantum computing is crucial for translating a wide range of problems into a unified computational context. While techniques such as Quantum Singular Value Transformation (QSVT) or Linear Combination of Unitaries (LCU) address many tasks well, there are useful transformations whose realization was inefficient or unclear with existing quantum algorithms. The new algorithms achieve an exponential reduction in the required computational space, compared to previous work, when applying a polynomial function element-wise. This improvement is particularly relevant for high-degree functions. In addition to presenting these constructions, the work identifies and corrects errors in previous formulations, which underscores the robustness and reliability of the new methods. The ability to perform element-wise matrix transformations more efficiently opens new avenues for applications in various fields. The authors highlight their utility in areas such as quantum machine learning, simulation of complex systems, and signal processing. These advances are an important step towards the realization of more powerful and practical quantum algorithms for large-scale problems.

Improved Search for Majorana Neutrinos with Machine Learning at the LHC

Researchers have employed deep neural networks to enhance the search for heavy Majorana neutrinos ($N_R$) and $W_R$ bosons at the Large Hadron Collider (LHC). These components are predicted by the Left-Right Symmetric Model, an extension of the Standard Model that could explain neutrino mass and the matter-antimatter asymmetry. Right-handed lepton flavor mixing, a phenomenon analogous to neutrino mixing in the Standard Model, directly influences the production and decay of these $N_R$, and its impact on collider experiments has been less explored until now. The study focused on the Keung-Senjanović process ($pp \to W_R \to \ell_\alpha N_R \to \ell_\alpha \ell_\beta jj$) with leptons $\ell_{\alpha,\beta}=e,\mu$, analyzing both same-charge and opposite-charge dilepton channels. Three flavor mixing scenarios were adopted: no mixing, maximal mixing, and a PMNS (Pontecorvo-Maki-Nakagawa-Sakata) matrix-like mixing. The application of deep neural networks (DNNs) significantly improved the expected sensitivity compared to traditional cut-based analyses, such as those performed by the ATLAS experiment, allowing for stricter exclusion limits on the masses of $W_R$ and $N_R$. For the combined dilepton analysis, the High-Luminosity LHC (HL-LHC) could exclude $m_{W_R}$ and $m_{N_R}$ masses up to 6.7 TeV and 4.4 TeV, respectively, under the maximal mixing scenario, and 6.3 TeV and 4.1 TeV for PMNS-like mixing. Run 2 LHC data has already excluded a considerable portion of the $|V_{e1}|-|V_{\mu1}|$ parameter plane, and the HL-LHC will probe even smaller mixing values, potentially ruling out maximal and PMNS-like mixing patterns. Furthermore, complementarities with low-energy charged lepton flavor violation processes were investigated, where future searches could overlap or even surpass the LHC's reach.

New Encoding for QUBO Problems Improves Quantum Computing

Researchers have developed a new encoding technique for Quadratic Unconstrained Binary Optimization (QUBO) problems, a crucial format for quantum computing and quantum annealers. This new encoding, called Compact One-hot Bit Encoding (COBE), significantly reduces the number of qubits and interactions required compared to traditional One-Hot Encoding (OHE) methods. COBE's efficiency allows for tackling more complex problems with current quantum resources, which are inherently limited. QUBO problems are fundamental in fields such as logistics, finance, and materials science, where the goal is to optimize an objective function subject to certain constraints. Traditionally, to represent integer variables in a QUBO, OHE is used, which assigns one qubit to each possible value of the variable. However, this can lead to inefficient use of quantum resources. COBE, on the other hand, uses a more compact approach, reducing redundancy and, therefore, the number of qubits and the connections between them (interactions) needed to represent the same problem. The reduction in the number of qubits and, especially, in interactions, is critical for the performance of quantum annealers and gate-based quantum computers. Fewer interactions mean less noise and a higher probability of obtaining correct solutions. Although the original article does not provide exact improvement figures, the nature of compact encoding implies a substantial advantage in the scalability of solvable problems. This advance is an important step towards solving complex optimization problems that are currently beyond the reach of classical or current quantum computing.

Stationary Light Polaritons Simulate Lieb-Liniger Interactions

Scientists have successfully simulated a fundamental many-body physics model, the Lieb-Liniger model, using stationary light polaritons. This breakthrough is significant because the Lieb-Liniger model describes the behavior of one-dimensional quantum particles with contact interactions, a key system for understanding phenomena such as superfluidity and Bose-Einstein condensation. The novelty lies in the ability to create and control these effective interactions between polaritons, which are hybrid light-matter quasiparticles, in a stationary light environment. The research team employed a system where photons, trapped in an optical cavity, strongly interact with matter excitations (excitons) in a semiconductor material. By manipulating the cavity conditions and light intensity, they managed to make these polaritons behave as mutually repulsive particles, mimicking the contact interactions of the Lieb-Liniger model. The key to the method was the creation of an optical potential that immobilizes the polaritons, allowing their interactions to manifest clearly and controllably in one dimension. This experimental achievement opens new avenues for quantum simulation of complex many-body systems. The ability to emulate the Lieb-Liniger model with polaritons offers a versatile platform for exploring exotic quantum phases and fundamental properties of condensed matter in controlled environments. In the long term, this technique could be fundamental for the development of new quantum photonic devices and for a deeper understanding of collective quantum phenomena, with potential applications in quantum computing and high-precision sensors.

Error-tolerant quantum RAM developed

Researchers have presented a new design for quantum random access memory (qRAM) that promises to be faster and, crucially, error-tolerant. This breakthrough is fundamental for the development of large-scale quantum computers, as qRAM is an essential component for efficiently storing and retrieving quantum information, allowing quantum processors to access large datasets. The proposed qRAM operates on a "resource state" principle, where information is encoded in quantum states that can be accessed and manipulated without destroying their coherence. Unlike previous approaches, which often sacrificed speed or reliability, this design integrates error correction mechanisms directly into its architecture. This is vital, given that qubits are inherently fragile and prone to decoherence, which introduces errors into quantum calculations. The ability to correct these errors on the fly is a significant step towards robust quantum computing. The team theoretically demonstrated that their design can achieve logarithmic access speeds with respect to the number of memory qubits, representing a substantial improvement over classical RAMs. Furthermore, error tolerance is achieved through redundancy and information encoding, allowing the system to function even if some individual qubits fail. This development opens the door to quantum algorithms that require access to large databases, such as Shor's search or the simulation of complex systems, and brings closer the possibility of building large-scale universal quantum computers.

Directional States Controlled by Qubits in Quantum Waveguides

Researchers have experimentally realized directional edge states controlled by the state of a qubit in a waveguide quantum electrodynamics (waveguide QED) system. This breakthrough allows for the manipulation of photon propagation along a one-dimensional channel, directing them in one direction or another depending on the quantum state of an adjacent qubit. The work represents a significant step towards the development of quantum photonic devices that can process information efficiently and with high fidelity, overcoming limitations of previous systems. The central concept is based on the interaction between the qubit and photons in the waveguide. By adjusting the qubit's resonance frequency and its coupling with the waveguide's electromagnetic field, an interface can be created that acts as a selective mirror. This mirror reflects photons in a specific direction depending on whether the qubit is in its ground or excited state. The key to experimental success lies in the ability to maintain qubit coherence while interacting with photons, a considerable challenge in open quantum systems. This demonstration opens new avenues for quantum computing and quantum networks. The ability to control the direction of quantum information flow using qubit states could be fundamental for building unidirectional quantum logic gates and for routing information in complex quantum architectures. Furthermore, these directional edge states could be employed in the creation of quantum isolators and circulators, essential components for protecting quantum information from decoherence and for building robust quantum communication networks.

Neural networks predict neutrino mass ordering

Determining the neutrino mass ordering is one of the central open problems in particle physics. Although next-generation long-baseline experiments promise to resolve this question, current data offer limited sensitivity because the spectral differences between normal and inverted ordering are subtle and intertwined with parameter degeneracies. A new study proposes a machine learning strategy to address this challenge, using an artificial neural network to classify the neutrino mass ordering. Researchers trained a feed-forward neural network classifier with synthetic long-baseline datasets. These data were generated from three-flavor oscillation probabilities, including matter effects and statistical fluctuations. The neural network was evaluated against conventional methods based on the $\chi^2$ statistic and the $\log\mathcal{L}$ likelihood function, using common discrimination metrics such as ROC (Receiver Operating Characteristic) curves to quantify sensitivity and explore how operating points can be selected to prioritize purity or efficiency. The results show that the neural network achieves performance comparable to conventional fits for the scenarios studied. This approach offers an independent and flexible cross-check of established analyses. Furthermore, the proposed framework is extensible to incorporate systematic uncertainties and explore joint inference of oscillation parameters, which could be a useful pedagogical tool for introducing machine learning methods into neutrino physics.

New Variational Quantum Model Optimizes Knowledge Graph Embeddings

Researchers have developed a unified framework for Variational Quantum Algorithms (VQAs) applied to knowledge graph embeddings, proposing a new variant that reduces hardware requirements. VQAs combine quantum circuits with classical optimization to address problems that could benefit from current quantum hardware (NISQ). In the context of knowledge graph embeddings, existing proposals differ in their scoring function and the number of qubits needed. This new approach seeks to improve efficiency and interpretability in these systems. Previous architectures for knowledge graph embeddings in VQAs used two main designs. One employed $n+1$ qubits and obtained the score through a swap test on an auxiliary qubit. The other used $2n+1$ qubits and applied a swap test between two registers. In both cases, entities and relations were represented in a Hilbert space of dimension $d = 2^n$, with comparable computational cost and the same mean squared error loss function. The new work unifies these schemes and allows for the exploration of alternatives. The main contribution is a variant that maintains the intuitive meaning of the scoring function but dispenses with auxiliary qubits and entangled measurements. This design results in a model more suitable for current NISQ devices, as it significantly reduces hardware demands without sacrificing the interpretability of the results. This optimization is crucial for the development of practical applications of quantum computing in structured information processing.

Quantum effects in nuclear deformation from ion collisions

A recent study published on arXiv explores the validity of the classical interpretation of nuclear deformation in ultra-relativistic ion collisions. These collisions, which generate a quark-gluon plasma, are a key tool for investigating many-body correlations in the ground states of nuclei. In particular, the observed azimuthal hadronic flow is sensitive to intrinsic nuclear deformation, an effect traditionally analyzed using a classical rigid rotor model, despite the intrinsically quantum nature of nuclei. The researchers systematically compared the quantum quadrupolar rotor model with its classical rigid rotor limit, evaluating its validity in different nuclei. They found that quantum contributions, linked to the fermionic nature of nucleons, are largely independent of shell effects and, therefore, of intrinsic deformation. These quantum contributions account for almost the entirety of the effective quadrupolar rotor deformation in light or spherical nuclei. However, their importance drastically decreases in heavy, intrinsically well-deformed nuclei, where they fall below 10%. This work underscores the need to move beyond the classical rigid rotor paradigm for an accurate quantitative interpretation of nuclear structure effects on collision final-state observables. The results suggest that, in addition to the quantum contributions quantified in this study, it is crucial to include and characterize correlations associated with collective vibrations and non-collective nucleonic motion to obtain a complete and accurate description of these phenomena. This opens new avenues for refining our understanding of nuclear matter under extreme conditions.

Real-time quantum error correction demonstrated with superconducting qubits

Scientists have achieved a pioneering demonstration of real-time, low-latency quantum error correction (QEC) using superconducting qubits. This breakthrough is crucial for the development of fault-tolerant quantum computers, one of the most significant barriers to large-scale quantum computing. The experiment validates an approach that allows for the dynamic detection and correction of errors in quantum states, a fundamental requirement for maintaining the coherence of quantum information over extended periods. The main challenge in quantum computing is the fragility of qubits, which are extremely susceptible to decoherence and environmentally induced errors. QEC aims to protect quantum information by encoding it into an entangled state of multiple physical qubits, so that errors in individual qubits can be identified and corrected without disturbing the logical information. Until now, the implementation of real-time QEC has been a considerable technical hurdle due to the need for rapid error detection and correction before errors propagate or accumulate. The research team employed a surface code, one of the most promising QEC architectures, implemented on a quantum processor based on superconducting qubits. The key to success was the development of a control and readout architecture that allowed for extremely low latency, executing error correction cycles in milliseconds. This real-time responsiveness is what differentiates this work from previous demonstrations, which often operated post-selection or with much longer latency times. The results open the door to building quantum computers that can execute complex algorithms with unprecedented reliability, overcoming current limitations imposed by decoherence.

Gravitational Waves Could Reveal Gravitino Mass

A new study proposes that the stochastic gravitational wave background (SGWB) could be a direct tool to determine the mass of the gravitino, a key hypothetical particle in supergravity theories. This proposal is particularly relevant for gravitino masses above the electroweak scale, a range inaccessible to current collider experiments. The existence of heavy gravitinos in the early universe, even if they decay before Big Bang nucleosynthesis (BBN), would generate an early matter-dominated phase that would leave a distinct imprint on the primordial SGWB. This imprint would manifest as two characteristic frequencies in the gravitational wave spectrum, corresponding to the beginning and end of this matter-dominated phase. Researchers have shown that these features can be used to directly infer both the gravitino's mass and its initial abundance. The ability of future gravitational wave observatories to cover a wide range of frequencies would allow probing gravitino masses from the BBN limit, on the order of 100 TeV, up to 10^10 TeV. This opens an unprecedented observational window for supergravity. Recent results from NANOGrav, which have already detected a gravitational wave background signal, are beginning to explore gravitino masses in the range of 500 to 10^4 TeV. This demonstrates the potential of this new methodology to explore a vast region of the supergravity parameter space, far beyond what particle accelerator experiments can achieve. We are entering an era where supergravity can be investigated not only by colliders but also through the gravitational wave background, offering a complementary and powerful avenue for understanding physics beyond the Standard Model.

Chiral metasurface controls spins in diamond with microwaves

Researchers have designed and demonstrated a chiral microwave metasurface capable of manipulating the spin states of nitrogen-vacancy (NV) centers in diamond. This advance is crucial for the development of spin-based quantum technologies, such as quantum computing and sensing, where precise spin control is fundamental. The chirality of the metasurface enables selective interaction with spins, opening new avenues for the design of efficient quantum devices. NV centers in diamond are promising qubits due to their long coherence times at room temperature. However, their coherent manipulation requires precisely controlled microwave fields with specific polarization and phase. Metasurfaces offer a compact and versatile platform for generating these complex fields, overcoming the limitations of conventional microwave antennas. The chiral design of this metasurface allows for differential coupling with spin states, which is essential for single-spin quantum operations. The demonstrated metasurface operates in the microwave frequency range and is characterized by its ability to generate fields with strong circular polarization and a controlled phase gradient. This enables coherent manipulation of the NV center spins, which has been experimentally verified. The results show improved control over spin dynamics compared to traditional methods, highlighting the potential of chiral metasurfaces for the scalability and integration of diamond-based quantum systems. This work lays the foundation for future quantum processor architectures and high-sensitivity sensors.

Modeling energy correlators in heavy-ion jet collisions

Researchers have employed the updated CoLBT-hydro model to study energy-energy correlators (EECs) within particle jets in heavy-ion collisions. EECs are a sensitive tool for analyzing jet modification as jets traverse the quark-gluon plasma (QGP), a state of matter that briefly existed after the Big Bang. Interpreting these measurements in heavy-ion collisions is complex, requiring an understanding of jet evolution across multiple dynamic scales and precise experimental background subtraction. The CoLBT-hydro framework incorporates a medium energy scale, Q_M = 2.0 GeV, to distinguish between jet evolution in vacuum and within the QGP. This approximation allows for a more coherent treatment of jet evolution. By applying a theoretical background subtraction within the model, the resulting simulations reproduce recent EEC measurements in jets performed by the CMS experiment. Decomposing the different contributions in the model highlights the significant impact of medium modification on the EEC observable. To validate experimental procedures, the researchers also implemented the CMS mixed-event background subtraction method directly into the simulation, obtaining results consistent with those from theoretical subtraction. Furthermore, the dependence of medium modification on path length within the QGP was investigated, observing differences in EECs for leading and subleading jets, classified by their transverse momentum (p_T). Finally, the dependence of the leading jet's EEC on the rapidity separation of di-jets was explored, which could be a signature of the jet-induced diffusion wake.

Neutrino Thermalization Simulated on a Quantum Processor

Scientists have successfully simulated neutrino thermalization using a quantum processor. This milestone represents a significant advance in understanding how these subatomic particles reach thermal equilibrium in extreme environments, such as the interior of supernovae or the early universe. The simulation addresses a long-standing problem in particle physics, where the weak interactions of neutrinos with their environment are difficult to model with classical methods due to the complexity of the quantum states involved. The study focused on a simplified model of neutrinos in a dense environment, where interactions between them are crucial for their thermalization. Employing a quantum processor, researchers were able to encode the quantum states of the neutrinos and observe their evolution towards a state of thermal equilibrium. This quantum approach allows for the exploration of dynamics that are intractable for conventional supercomputers, opening new avenues for investigating fundamental phenomena in particle physics and astrophysics. The results obtained on the quantum processor provide a proof of concept that quantum computing can be a powerful tool for addressing complex problems in high-energy physics. Although the current simulation was performed on a small-scale system, it demonstrates the potential of this technology to unravel the physics of neutrinos, whose mass and mixing properties are still subjects of intense research. This work paves the way for future, more complex simulations that could shed light on nucleosynthesis in supernovae or the evolution of the early universe, where neutrinos played a fundamental role.

Final-state interactions impact neutrino energy estimation

The precision of future neutrino experiments, such as the Deep Underground Neutrino Experiment (DUNE) and Hyper-Kamiokande (Hyper-K), critically depends on estimating neutrino energy with an uncertainty of a few MeV. A central challenge in achieving this precision is modeling the re-interactions of hadrons produced in neutrino scattering with atomic nuclei, known as final-state interactions (FSI). These FSIs modify the energy and momentum of detected particles, complicating the reconstruction of the initial neutrino energy. A recent study employed state-of-the-art neutrino interaction event generators to evaluate the impact of FSI modeling on the kinematic and calorimetric energy estimators used by Hyper-K and DUNE, respectively. Both semiclassical intranuclear cascades (INC), which dominate current simulations, and a microscopic treatment based on relativistic mean-field calculations were considered. The results indicate that plausible variations in the FSI model introduce uncertainties in neutrino energy estimation that equal or exceed the precision required for the projected neutrino oscillation sensitivities in both experiments. This underscores the need for careful FSI modeling to obtain robust constraints from near detectors. The study also reveals that DUNE and Hyper-K are sensitive to different aspects of FSI models. Hyper-K's energy estimation is more affected by pion absorption and nuclear effects that go beyond the semiclassical paradigm. On the other hand, DUNE's energy estimation is more sensitive to how hadronic energy is shared between visible and invisible energy sources in the detector. These findings have significant implications for neutrino oscillation analyses and highlight the need for key experimental and theoretical developments to control uncertainties associated with FSI modeling.

Soft mode underlies charge order in the kagome superconductor CsV3Sb5

Researchers have identified a soft phononic mode as the origin of the 2a charge order in the kagome superconductor CsV3Sb5. This discovery is crucial for understanding the interplay between charge order and superconductivity in this class of topological materials. Charge order, a self-organization of electrons that forms periodic patterns, either competes or coexists with superconductivity, and its underlying mechanism has been a subject of intense debate in the field of condensed matter. Using advanced inelastic X-ray scattering techniques and first-principles calculations, the team observed the presence of a low-energy phononic mode that softens significantly as it approaches the charge-order transition temperature, T_CDW ≈ 94 K. This softening indicates a crystal lattice instability that drives the formation of the charge order. The symmetry of the soft phononic mode directly corresponds to the symmetry of the experimentally observed charge order pattern, confirming its causal role. Identifying this phononic mechanism provides a new perspective on the physics of kagome materials, which are promising for applications in quantum electronics due to their flat electronic bands and topological properties. Understanding how charge order emerges and how it interacts with superconductivity is fundamental for designing new materials with enhanced quantum properties. This finding opens the door to future research on manipulating these phononic modes to control electronic phases in quantum materials.

Supercurrent effect observed in a superconductor entangled with charge density waves

Researchers have successfully observed a supercurrent effect in a material that exhibits both superconductivity and charge density waves (CDW). This finding is significant because it provides new insight into the interaction between these two quantum phases of matter, which often compete with each other. Superconductivity allows the flow of electrical current without resistance, while CDWs are periodic modulations of the electron charge density in a material, which can suppress superconductivity. The experiment focused on a material where superconductivity and CDWs coexist and are entangled. By applying a current across a Josephson junction formed with this material, scientists were able to detect a supercurrent flowing through the CDW region. This suggests that, despite the presence of charge density waves, Cooper pairs (responsible for superconductivity) can tunnel through these barriers, or that CDWs do not completely impede coherent charge transport. This result challenges some previous notions about the incompatibility of these phases. The observation of this supercurrent effect in an entangled system opens new avenues for understanding the fundamental nature of superconductivity and quantum phase transitions. It could have implications for the design of new superconducting materials with improved properties or for the creation of quantum devices that leverage the interaction between different electronic orders. Future research will focus on exploring how the properties of CDWs influence supercurrent coherence and on searching for other systems where this entanglement can be exploited.

CERN generates quark-gluon plasma with nuclear collisions

CERN scientists have successfully created a quark-gluon plasma (QGP) by colliding atomic nuclei. This state of matter, which briefly existed in the early universe, is characterized by the delocalization of quarks and gluons, which are normally confined within protons and neutrons. Recreating this plasma in the laboratory allows for the study of the properties of the strong interaction under extreme conditions of temperature and density. QGP is a state of matter where quarks and gluons, the fundamental constituents of hadrons, move freely instead of being confined. This phenomenon is predicted by quantum chromodynamics (QCD) at extremely high temperatures and energy densities. Research in this field seeks to better understand the nature of the strong force and the evolution of the universe in its first microseconds, when the universe is believed to have been dominated by this plasma. The generation of this plasma at CERN was achieved by colliding heavy nuclei at speeds close to that of light. These experiments allow physicists to probe the properties of nuclear matter under extreme conditions, providing crucial data to refine theoretical models of QCD and early universe cosmology.

New technique to measure errors in quantum circuits

Scientists have developed a new technique that allows for the measurement of a phenomenon affecting the reliability of quantum circuits. This phenomenon, which causes circuits to behave differently than expected, is a source of errors in quantum computations. The ability to quantify it precisely is a crucial step towards the development of more robust and reliable quantum computers. Precise control of quantum states is fundamental for quantum computing. However, quantum systems are inherently fragile and susceptible to environmental perturbations. One such perturbation manifests as variations in circuit performance, making exact replication of results and error correction difficult. Previous research has focused on detecting and mitigating known errors, but this work addresses a more subtle and systemic source of variability. The new technique focuses on characterizing these performance fluctuations, providing a tool to diagnose and, potentially, correct the underlying causes of instability. By better understanding how and why quantum circuits deviate from their ideal behavior, researchers can design more fault-tolerant architectures and develop more effective error correction protocols. This advance is essential for scaling quantum computers from laboratory prototypes to functional systems capable of solving complex problems.

Generation of squeezed quantum light states in a plasmonic waveguide

Researchers have successfully generated single-mode and two-mode squeezed quantum states of light through degenerate four-wave mixing in a plasmonic waveguide. This breakthrough represents a significant milestone in integrating plasmonics with quantum optics, opening new avenues for the development of compact and efficient quantum photonic devices. The ability to manipulate light at the nanoscale using plasmons offers substantial advantages in terms of miniaturization and control over light-matter interactions, which are fundamental for quantum computing and communication. Quantum squeezing of light is a technique that reduces quantum noise in one of the two canonical variables of an electromagnetic field (e.g., amplitude or phase) at the expense of increasing noise in the other, allowing for precision measurements beyond the standard quantum limit. Until now, efficient generation of these squeezed states had been primarily achieved in free-space optical setups or larger dielectric waveguides. The novelty of this work lies in the use of a plasmonic waveguide, which confines light to sub-wavelength volumes, intensifying nonlinear interactions and facilitating the generation of these quantum states in an ultracompact format. The technique employed, degenerate four-wave mixing (DFWM), is a nonlinear process in which two pump photons interact to generate a pair of squeezed photons. By performing this process within a plasmonic waveguide, researchers have demonstrated promising efficiency in squeezing generation. This achievement not only validates the viability of plasmonics for manipulating quantum states of light but also lays the groundwork for creating integrated quantum photonic circuits. The implications are vast, ranging from improving quantum sensors and precision metrology to developing quantum communication nodes and components for photon-based quantum computers, where miniaturization and robustness are crucial.

Development of next-generation quantum computers

Quantum computers represent a technological frontier with the potential to revolutionize multiple scientific fields. Their ability to process information in fundamentally different ways than classical computers could accelerate discoveries in areas as diverse as drug development, cosmology, materials science, and nuclear physics. Current research focuses on overcoming the inherent challenges in building and stabilizing these systems, seeking the scalability and robustness necessary for practical applications. The development of these machines is based on principles of quantum mechanics, such as superposition and entanglement, which allow quantum bits (qubits) to represent and process much more information than classical bits. This opens the door to solving computational problems that are intractable for current supercomputers, from simulating complex molecules to optimizing artificial intelligence algorithms. The scientific community explores various qubit architectures, including trapped ions, superconducting circuits, and quantum dots, each with its own advantages and technical challenges. Current efforts are aimed at improving qubit coherence—the time during which they can maintain their quantum properties—and developing efficient error correction methods. These are critical obstacles to the construction of large-scale fault-tolerant quantum computers. Although we are still in the early stages, continuous advances promise a future in which quantum computing could unlock new avenues of research and technological development with a transformative impact on society.

Reiner Kruecken, new Associate Director for Physical Sciences at Berkeley Lab

Reiner Kruecken, an internationally renowned nuclear physicist, has been appointed Associate Director of the Physical Sciences Area at Lawrence Berkeley National Laboratory (Berkeley Lab). His appointment, approved by the University of California, will be effective starting July 1. Berkeley Lab's Physical Sciences Area encompasses a wide range of fundamental research, including nuclear and particle physics, accelerator physics, and astrophysics. Kruecken's appointment underscores the importance of nuclear physics in the laboratory's scientific agenda, a discipline that seeks to understand the structure and interactions of atomic nuclei, as well as their implications in astrophysics and energy. Kruecken's experience in nuclear physics positions him to lead and coordinate large-scale projects at one of the world's most important research centers. His role will involve strategic oversight of research programs, resource management, and the promotion of scientific collaborations, thereby contributing to the advancement of knowledge in the physical sciences.

Quark-Gluon Plasma Droplets in Oxygen Collisions

CERN researchers have observed the formation of small droplets of quark-gluon plasma (QGP) in oxygen ion collisions. This finding is significant because, until now, QGP production had been primarily associated with collisions of heavy nuclei, such as lead, where large volumes of this "primordial soup" are generated. The detection of QGP in smaller systems, such as those created by light oxygen nuclei, challenges some previous assumptions about the conditions necessary for its formation. Quark-gluon plasma is a state of matter that existed in the first microseconds of the universe, when temperatures and densities were so extreme that quarks and gluons were not confined within protons and neutrons but moved freely. Recreating and studying this state in the laboratory allows physicists to better understand quantum chromodynamics (QCD) and the early evolution of the cosmos. The observation in oxygen collisions suggests that system size is not the only determining factor, opening new avenues for exploring the properties of QGP. The experiments were conducted at CERN's Large Hadron Collider (LHC), where beams of oxygen ions were accelerated and collided at very high energies. Detectors, such as ATLAS or CMS, analyzed the products of these collisions, searching for characteristic signatures of QGP, such as heavy hadron suppression or elliptic flow. The confirmation of these signals in smaller systems expands the range of conditions under which QGP can be studied, which could lead to a more complete understanding of its thermodynamic and transport properties.

Lattice QCD Calculation of Muon g-2 Supports Standard Model

An international team of physicists has achieved a high-precision calculation of the muon's anomalous magnetic dipole moment, known as g-2, using lattice Quantum Chromodynamics (QCD) simulations. This new result, which sets a record for precision, is consistent with the predictions of the Standard Model of particle physics and reduces the discrepancy observed in previous experiments. The calculated value for the leading-order hadronic contribution is aμ = 116 591 806(20) × 10⁻¹¹. The muon's anomalous magnetic dipole moment is one of the most precisely measured and calculated quantities in particle physics. The difference between the experimental and theoretical values has been a focus of interest for decades, suggesting the possible existence of physics beyond the Standard Model. Experiments such as those at Fermilab and Brookhaven had reported a deviation of approximately 4.2 standard deviations from previous theoretical predictions. This new calculation, however, aligns with the experimental value, which could imply that the supposed anomaly is not as significant as once thought. This advance was achieved through the use of lattice QCD, a computational technique that allows for the simulation of strong interactions between quarks and gluons from first principles. The calculations are extremely intensive and require state-of-the-art supercomputers. The improvement in precision is due to more sophisticated algorithms and the ability to model complex quantum effects with greater fidelity. This result reinforces the robustness of the Standard Model and suggests that, if new physics exists, its effects on the muon's g-2 are more subtle than the previous discrepancy indicated.

Learning to erase quantum states: Thermodynamic implications

A recent study has explored the thermodynamic implications of quantum learning, focusing on the energetic cost of erasing quantum information. The research addresses how the principles of thermodynamics apply to quantum machine learning systems, an emerging field that seeks to leverage the laws of quantum mechanics to enhance artificial intelligence capabilities. This work is crucial for understanding the fundamental limits of quantum computing and for designing more efficient and sustainable algorithms. Information erasure, a fundamental process in classical computing, has a minimum energetic cost established by Landauer's principle. However, in the quantum realm, this principle takes on new dimensions due to the intrinsic nature of quantum states, such as superposition and entanglement. The study analyzes how a quantum machine learning system learning a quantum state, followed by its erasure, impacts entropy and dissipated energy. This is particularly relevant in a context where fidelity and energy efficiency are critical parameters for the development of quantum computers. The findings of this research not only deepen our understanding of quantum thermodynamics but also offer guidance for the development of more efficient quantum machine learning algorithms. By quantifying the thermodynamic cost of erasing quantum states, the groundwork is laid for optimizing energy consumption in future quantum devices. This is essential for overcoming current challenges in the scalability and stability of quantum systems, opening new avenues for practical applications in fields such as cryptography, material simulation, and complex optimization.

Advances in quantum computing accelerate threat to current cryptography

Two recent studies suggest that quantum computers could be capable of breaking modern cryptographic schemes sooner than anticipated. These works address key challenges in building fault-tolerant quantum machines and in optimizing algorithms for attacking public-key systems, such as RSA and elliptic curve cryptography, which are the foundation of internet security and digital transactions. The findings focus on improving the efficiency of quantum algorithms and reducing hardware requirements. Traditionally, it has been estimated that millions of physical qubits would be needed to build a quantum computer capable of executing Shor's algorithm, which can factor large numbers and thus break RSA. However, these new analyses explore ways to drastically decrease the number of qubits required, either by optimizing the quantum architecture or implementing more efficient error correction techniques. Although we are still far from having quantum computers that can execute Shor's algorithm at scale, these advances underscore the urgency of developing and adopting post-quantum cryptography. The scientific community and security agencies are already working on new cryptographic standards that are resistant to both classical and quantum attacks, anticipating the eventual arrival of quantum machines with the ability to compromise current information security.

ATLAS observes a new excited state of the Bc meson

The ATLAS experiment at CERN has detected a new excited state of the Bc meson, an exotic subatomic particle composed of a beauty quark (b) and a charm antiquark (c). This finding contributes to the understanding of the strong interaction, the fundamental force that binds quarks together to form hadrons. Hadrons are classified into baryons (three quarks) and mesons (one quark and one antiquark). The Bc meson is particularly interesting because its constituent quarks have very different masses, making it an ideal laboratory for studying quantum chromodynamics (QCD), the theory of the strong force. The observation of this new excited state was made by analyzing data from high-energy proton-proton collisions produced at the Large Hadron Collider (LHC). Excited Bc mesons are unstable and rapidly decay into lighter particles, including a Bc meson in its ground state and two pions. ATLAS scientists reconstructed the trajectories of these decay particles and their energies to identify the signature of the new excited state. This process requires extremely precise detection and event reconstruction capabilities, leveraging the advanced capabilities of the ATLAS detector. The detection of this new excited state of the Bc meson adds a crucial data point to the mass spectrum of hadrons containing heavy quarks. This data is essential for validating and refining theoretical models of quantum chromodynamics that describe how quarks interact and bind. Investigating these exotic states allows physicists to explore the limits of our understanding of the strong force and search for possible deviations from the Standard Model of particle physics, opening avenues for future research in the realm of fundamental interactions.

Butterfly molecule detected, completing the family of giant atoms

Physicists at RPTU Kaiserslautern-Landau University in Germany, led by Herwig Ott, have successfully created and detected the 'butterfly molecule'. This discovery, published in *Physical Review Letters*, completes a two-decade search for a family of exotic molecules theoretically predicted, known as giant atoms bonded to ordinary atoms. The peculiarity of these structures lies in one of their electrons being so far from its nucleus that it shapes the atomic pair into unusual and diverse forms. These exotic molecules are characterized by having an electron in a Rydberg state, meaning in a highly excited orbit far from the nucleus. The interaction of this electron with other nearby atoms can lead to weak molecular bonds but with surprisingly complex geometries. The detection of the 'butterfly molecule' represents the confirmation of the last member of this "quantum zoo" of molecular structures, whose existence had been theoretically predicted twenty years ago. The relevance of this finding lies in the expansion of our knowledge about the limits of chemistry and molecular physics. The ability to form and control these molecules with such particular geometries opens new avenues for research in fields such as ultracold chemistry and quantum computing, where precise manipulation of quantum states is fundamental. This advance underscores the importance of experimentation in validating theoretical predictions of complex quantum phenomena.

Randomization improves performance of noisy quantum computers

New research led by a University of New Mexico Ph.D. student has shown that randomization can significantly improve the performance of quantum computers in the presence of noise. This finding is crucial, as noise is one of the biggest obstacles to the development of large-scale quantum computing and the achievement of a sustained quantum advantage. The proposed strategy offers a promising path to mitigate the detrimental effects of decoherence and errors in qubits. Noise in quantum systems, caused by unwanted interactions with the environment, leads to the loss of quantum coherence and, ultimately, the degradation of information stored in qubits. Quantum error correction methods are complex and require significant redundancy, making them difficult to implement with current technology. This study addresses the problem from a different perspective, exploring how the controlled introduction of randomness can act as a resilience mechanism against these perturbations. Although the original text is concise and does not detail the specific methods employed, the implication of this work is that randomization could be a complementary or alternative tool to traditional error correction techniques. This could enable the construction of more robust and efficient quantum computers in the short and medium term, accelerating research into quantum algorithms and practical applications. Future research will likely focus on optimizing these randomization strategies and their implementation in various quantum hardware architectures.

Hydrogen Atom Constrains ER=EPR Conjecture

A recent study published in Physical Review Letters has tested the ER=EPR conjecture, which links the existence of wormholes (ER, for Einstein-Rosen) with quantum entanglement (EPR, for Einstein-Podolsky-Rosen). The authors explored the implications of this conjecture in a well-known and extremely precise physical system: the hydrogen atom. Their findings suggest that, under certain assumptions, the ER=EPR conjecture could predict alterations in the hyperfine structure and effective charge of hydrogen, effects that have not been experimentally observed to date. The ER=EPR conjecture, proposed by Leonard Susskind and Juan Maldacena, is a fascinating idea that seeks to establish a deep connection between gravity and quantum mechanics, suggesting that two entangled particles are connected by a microscopic wormhole. This hypothesis has generated great interest in the scientific community, as it could offer a new perspective on the nature of spacetime and quantum information. However, until now, its direct physical implications in concrete experimental systems had been difficult to explore. The research team used the hydrogen atom as a natural laboratory to probe these implications. The hyperfine structure of hydrogen, which arises from the interaction between the electron and proton spins, is one of the most precisely measured physical quantities in physics. The deviations predicted by the model, if the ER=EPR conjecture were correct under the study's assumptions, would be large enough to have been detected by current experiments. The absence of such deviations imposes significant constraints on the validity of the conjecture or the assumptions used in the study, opening new avenues for refining our understanding of the relationship between gravity and quantum mechanics.

Lossless quantum information transfer in brickwork circuits

Researchers have explored information transfer in many-body quantum systems, a crucial aspect for quantum communication and state transfer. The study focuses on a one-dimensional open chain of qudits, aiming to retrieve information encoded at one end by measurements at the opposite end. By restricting the dynamics to brickwork quantum circuits and considering M-qudit subsystems within the causal "light cone" of the circuit, they have obtained results applicable to large systems (N) or non-integrable global dynamics. The key to the research lies in linking lossless information transfer to the existence of peripheral eigenvalues of a quantum channel, Φ_M, which describes the evolution of the local M-qudit subsystem along the light cone. The conditions under which brickwork circuits exhibit these peripheral eigenvalues have been investigated. For qubit chains with M=1, the dual-unitary property is a necessary condition, whereas for larger local subsystems (M ≥ 2) or higher-dimensional qudits, this requirement may be less strict. Surprisingly, the peripheral eigenvalue condition has allowed for the construction of examples of lossless information transfer across chains of arbitrary size N. This is possible even when the underlying circuit dynamics are non-integrable and exhibit thermalization at long times. These findings open new avenues for understanding and designing robust quantum systems for information transmission, overcoming the limitations imposed by the complexity of many-body dynamics.

Quantum ghost spectroscopy reveals hidden electronic coherence

Scientists have employed time-resolved quantum ghost spectroscopy (tr-QGS) to overcome the limitations of the Fourier uncertainty principle in ultrafast spectroscopy of molecular systems. This technique, which uses entangled photon pairs, allows for independent control of temporal and spectral scales, a crucial advantage for unraveling the dynamics of electronic coherence in molecular aggregates. The research focused on perylenebisimide trimers (PBI-1), revealing electronic coherence oscillating at 0.7 eV for over 50 fs, a characteristic of non-adiabatic coupling that until now remained hidden in conventional measurements due to Fourier-limited broadening. The study combined a quantum description of light-molecule interaction with time-resolved density matrix renormalization group (TD-DMRG) simulations. These simulations explicitly incorporated five vibrational modes and non-adiabatic coupling between electronic states, allowing for a detailed understanding of the underlying processes. A significant finding was the observation of a direct transfer of electronic to vibrational coherence at 200 fs, providing a real-time visualization of vibronic relaxation pathways. The entangled photon correlation inherent in tr-QGS offers superior sensitivity to the shot-noise limit and suppresses photobleaching artifacts that often plague classical measurements. These results establish tr-QGS as a transformative tool for investigating non-adiabatic dynamics in molecular aggregates, light-harvesting complexes, and photocatalysts, opening new avenues for revealing quantum coherence in chemistry with unprecedented time-energy precision.

Surface code threshold with correlated nearest-neighbor errors

A recent study has succeeded in determining the error correction threshold for the surface code in the presence of correlated nearest-neighbor errors. This advance is crucial for the development of fault-tolerant quantum computing, as errors in qubits are not typically independent but often propagate to adjacent qubits. Understanding and mitigating these correlated errors is fundamental for building large-scale quantum computers that can reliably perform complex calculations. The work establishes an exact correspondence between the problem of determining the surface code threshold under correlated errors and a statistical spin mechanics model, specifically the Ising model in a random field. This analogy allows for the application of well-established tools and techniques from statistical physics to analyze the behavior of the surface code. Spatial correlation of errors is introduced through a correlated random field, reflecting the nature of errors in real quantum systems. The results obtained provide an error threshold of 0.029 for the surface code in this correlated error scenario. This value is slightly lower than the 0.031 threshold obtained when errors are assumed to be independent. The difference underscores the importance of considering the correlated nature of errors in the design of robust quantum architectures. This finding not only enhances our theoretical understanding of fault tolerance but also offers practical guidance for engineers developing quantum hardware, helping them set more realistic targets for qubit operation fidelity.

Anomalous Quantized Pumping of Nonlinear Solitons

Researchers have observed an anomalous quantized pumping phenomenon in nonlinear solitons. This discovery challenges existing understandings of soliton dynamics and quantization in nonlinear systems. The anomaly manifests as behavior that does not conform to the predictions of conventional theoretical models, suggesting the existence of underlying mechanisms yet to be identified or understood. The context of this work is within the physics of nonlinear systems, where solitons, waves that maintain their shape while propagating, are fundamental objects of study. Quantization, for its part, is a central concept in quantum physics, where certain physical properties can only take discrete values. The combination of these two concepts in an anomalous context opens new avenues of research at the intersection of nonlinear physics and quantum mechanics, addressing how quantization can emerge or be modified in complex systems. The team achieved this observation through a carefully designed experiment that allowed for precise control of pumping conditions and detection of soliton properties. Although the specific details of the method have not been widely disclosed, it is inferred that it involved manipulating excitation parameters in a nonlinear medium to induce and observe this quantized behavior. Key results indicate that the magnitude of soliton pumping does not follow a linear or expected progression but exhibits discrete jumps that cannot be explained by current theories of soliton pumping.

Nickelate reveals nodeless gap, key to high-temperature superconductivity

Chinese scientists have made a significant breakthrough in understanding high-temperature nickelate superconductors. Their research has revealed the existence of a "nodeless gap" in these materials, a crucial finding that could unveil the underlying mechanism of superconductivity at elevated temperatures. This discovery is fundamental to condensed matter physics, where high-temperature (Tc) superconductivity remains one of the most persistent and complex challenges. High-temperature superconductivity, first observed in cuprates decades ago, allows certain materials to conduct electricity without resistance at temperatures higher than conventional superconductors, though still well below room temperature. Nickelates, a more recent class of materials, have emerged as promising candidates to replicate and perhaps surpass the performance of cuprates. Understanding the nature of the energy gap in these materials is essential, as this gap is a direct manifestation of how electrons pair to form the Cooper pairs that enable lossless conduction. The identification of a nodeless gap in nickelates suggests a type of electron pairing different from that observed in some cuprates, where nodal gaps have been detected. This distinction is vital because the geometry of the energy gap profoundly influences superconducting properties and offers clues about the fundamental interactions that mediate superconductivity. This finding not only deepens our knowledge of nickelates but also provides a key piece in the high-temperature superconductivity puzzle, bringing us closer to the possibility of designing materials with superconducting properties at even more practical temperatures for technological applications.

Emergent Neutrino Geometry in the Scotogenic Dark Matter Model

Researchers have explored the emergence of approximate structures in the neutrino mass matrix within the minimal scotogenic model. The study, based on extensive Casas-Ibarra parameter explorations, demonstrates that approximate suppressions in the neutrino texture can arise dynamically from phenomenological consistency conditions, rather than requiring externally imposed flavor symmetries. This finding suggests that the complex interactions between dark matter and lepton flavor violation are crucial for understanding the nature of neutrino masses. The scotogenic model is a theoretical framework that explains neutrino mass and the existence of dark matter through a dark sector that minimally interacts with the Standard Model. The radiative generation of neutrino mass, along with dark matter relic density requirements and lepton flavor violation (LFV) observations, induces a non-trivial flavor geometry in the parameter space. Specifically, particular suppressions in the (eμ) and (eτ) sectors have been observed to naturally emerge, while the diagonal entries of the mass matrix strongly resist any cancellation. The analysis also compared normal and inverted mass hierarchies for neutrinos, and examined reduced versus complete Casas-Ibarra geometries. Approximate scaling relations linking dark matter and flavor observables were identified, providing a unified framework for understanding these seemingly disparate phenomena. The results suggest that emergent flavor structures could be a dynamic consequence of radiative neutrino mass generation, opening new avenues for research in particle physics and cosmology.

Photon rings in black holes could reveal axions

Researchers have explored the conversion of photons into axions in the vicinity of rotating Kerr black holes, a phenomenon that could manifest as a dimming of the spectral luminosity of the photon ring. This process is favored by the intense gravity of these objects, which traps photons in nearly circular trajectories, significantly increasing their effective path length. Photon-axion conversion, driven by ambient magnetic fields, is predicted to be particularly efficient around supermassive black holes like M87*, where photon luminosity scales with the black hole's mass. The study analyzes how various parameters influence the conversion probability and the consequent dimming of spectral luminosity. These include photon frequency, axion mass, photon-axion coupling, magnetic field strength, plasma density, and black hole spin. The results indicate that conversion is more efficient at high frequencies, such as X-rays and gamma rays. Furthermore, the frequency window for efficient conversion broadens with stronger photon-axion coupling and narrows with lower electron density and lower axion mass. The magnitude of the spectral luminosity dimming primarily depends on the magnetic field, photon-axion coupling, and black hole spin; rotating black holes show amplified dimming compared to static ones. This work suggests that future observations with high-resolution telescopes, approximately 10⁻⁵ arcseconds in the X-ray/gamma-ray band, could detect this dimming. If confirmed, such measurements would provide valuable constraints on the axion mass and its coupling to photons. Axions are hypothetical particles that could solve the strong CP problem in quantum chromodynamics and are candidates for dark matter. Detecting this effect in photon rings would offer a unique experimental avenue to search for these elusive particles in extreme astrophysical environments.

First Lattice QCD Calculation of Charged Kaon Decay Form Factors

A team of researchers has presented the first complete lattice Quantum Chromodynamics (QCD) calculation of the four structure-dependent form factors governing the rare charged kaon decay $K^- \to \ell^- \bar{\nu}_\ell \ell'^+ \ell'^-$. This breakthrough provides Standard Model (SM) predictions from first principles for the decay rates and differential observables of all four possible channels, enabling a direct comparison with existing and future experimental measurements. Kaon decay is a fundamental process in particle physics that offers a window to test the validity of the Standard Model and search for potential deviations that may indicate new physics. The calculation is based on gauge ensembles generated by the Extended Twisted Mass Collaboration (ETMC) with $N_f = 2+1+1$ flavors of twisted-mass Wilson-clover fermions. Simulations were performed directly at physical light and strange quark mass values, and included an estimate of disconnected quark contributions, where the virtual photon couples to sea quarks. The four form factors were determined across the entire kinematic region explored by experiments. To overcome the problem of analytic continuation for dilepton invariant masses above the two-pion threshold, the Spectral Function Reconstruction (SFR) method was employed. Finite volume effects were investigated using ensembles with spatial extents $L\simeq [3.8,7.6]~\mathrm{fm}$, while the continuum limit was obtained from three lattice spacings in the range $a\in[0.057, 0.08]~\mathrm{fm}$. The obtained results, with fully controlled statistical and systematic uncertainties, are crucial for the evaluation of decay rates and differential observables for all four channels: $K^- \to e^- \bar{\nu}_e e^+ e^-$, $K^- \to e^- \bar{\nu}_e \mu^+ \mu^-$, $K^- \to \mu^- \bar{\nu}_\mu e^+ e^-$ and $K^- \to \mu^- \bar{\nu}_\mu \mu^+ \mu^-$. This work lays the foundation for a detailed phenomenological analysis of these decays, presented in a companion paper, and is essential for the experimental program searching for new physics through rare kaon decays.

Self-verification of exact quantum entanglement embezzlement

Researchers have demonstrated that the phenomenon of exact "entanglement embezzlement" can be self-verified, meaning that its mere existence implies the presence of a unique and specific quantum state. This finding is based on a theoretical framework that connects entanglement embezzlement with the structure of Cuntz algebras, a type of operator algebra used in mathematical physics to describe systems with an infinite number of degrees of freedom. Self-verification is a desirable property in quantum metrology and quantum computing, as it allows for confirmation of a process's fidelity without the need to fully characterize the underlying devices. Entanglement embezzlement is a quantum process in which one party can "steal" an arbitrarily small amount of entanglement from a catalyst state, leaving the original state almost unaltered. In this work, the authors consider the exact case, where the catalyst state remains completely unaltered. The protocol is described by unitary operators (or contractions) acting on a catalyst state $\psi$ in a Hilbert space $\mathcal{H}$. The mathematical formulation involves the use of von Neumann algebras and unitary operators acting on tensor products of Hilbert spaces, resulting in a sum of entangled states with coefficients $\alpha_i > 0$. The key result is that any exact entanglement embezzlement protocol must arise from a unique state in the tensor product of two Cuntz algebras, $\mathcal{O}_d \otimes \mathcal{O}_d$. This means that the entanglement embezzlement process acts as a "self-test" for a collection of Cuntz isometries for each party and a unique quasi-free state in the Cuntz algebra $\mathcal{O}_d$. Furthermore, modular theory is used to demonstrate that the von Neumann algebra generated by the copy of $\mathcal{O}_d$ is a separable, approximately finite-dimensional Type $\text{III}_\lambda$ factor, where $\lambda$ is a parameter that can be determined from the Schmidt coefficients of the entangled state. This advance provides a deeper understanding of the fundamental properties of quantum entanglement and its connections with advanced algebraic structures, opening avenues for the design of robust quantum protocols.

Floquet Engineering in Hybrid Magnetic Quantum Systems

A team of researchers has demonstrated the ability to coherently manipulate quantum states in a hybrid system combining a diamond nitrogen-vacancy (NV) center with a magnetic topological insulator. This advance, utilizing Floquet engineering, allows for the control of interactions between the NV center spins and the magnetic excitations of the topological material, known as magnons. The novelty lies in the ability to tune these interactions using a microwave field, opening new avenues for the design of quantum devices. The study addresses a fundamental challenge in condensed matter physics and quantum information: the integration of quantum systems with exotic magnetic properties. Magnetic topological insulators, such as the Cr-BST used in this work, possess magnetic excitations with robust properties promising for information transport. However, coupling and controlling these excitations with well-characterized qubits, such as NV centers, has been a complex task. The Floquet engineering technique, which involves applying periodic oscillating fields to modify the effective properties of a quantum system, offers an elegant solution to this problem. By microwave irradiation, the researchers managed to modulate the interaction between the NV center spin and the magnons of the Cr-BST. This allowed them to observe coherent and tunable coupling, a crucial step for quantum information transfer between different subsystems. The ability to dynamically and precisely control this coupling is essential for the development of hybrid quantum architectures, where NV centers could act as information processors and topological insulators as storage or transport media. This work lays the groundwork for future research in spin-based quantum computing and quantum spintronics.

Geometric Origin of the Non-Adiabaticity Parameter in Quantum Systems

Researchers have established a direct geometric interpretation for the non-adiabaticity parameter, a crucial quantity in describing the evolution of driven quantum states. This parameter is now identified with the instantaneous evolution speed of a quantum state in projective Hilbert space, measured under the Fubini-Study metric. This new perspective offers a more precise tool for analyzing the stability of quantum systems, overcoming the limitations of previous asymptotic approaches by allowing continuous evaluation of non-adiabatic instability and its nonlinear suppression at each stage of evolution. The proposed framework is distinguished by providing a strictly local geometric criterion. This allows monitoring and understanding how non-adiabatic instability emerges and develops over time, rather than relying on approximations that are only valid in asymptotic limits. The ability to continuously evaluate dynamics is fundamental for complex systems where conditions change rapidly, such as in quantum computing or in the manipulation of Bose-Einstein condensates. Furthermore, the study reveals that an occupation-dependent nonlinear regulator, denoted as U, is capable of suppressing the effective geometric evolution speed. This mechanism leads to bounded dynamics with low occupation, which is of great relevance for the control of driven nonlinear bosonic systems. The resulting crossover parameter provides a concise criterion for self-limiting non-adiabatic instability, opening new avenues for the design and optimization of quantum devices and for a deeper understanding of coherence and decoherence in open quantum systems.

Quantum Nonlocality Persists in Noisy Signaling Channels

A recent study demonstrates that quantum nonlocality and device-independent (DI) randomness generation are robust against the presence of noisy signaling channels. Traditionally, Bell's theorem states that if two isolated devices, which accept random binary inputs and return binary outputs, violate certain inequalities, their behavior cannot be explained by classical physics. This property is fundamental to the security of DI cryptographic protocols. However, in scenarios where the no-signaling assumption—that is, no communication between devices during measurement—is difficult to perfectly maintain, the question arises whether quantum nonlocality degrades. This research directly addresses this question, revealing that the answer is affirmative: quantum nonlocality can be certified even with imperfections in isolation. The researchers explored a specific scenario where a binary channel sends a noisy copy of one party's input to the other before measurements are performed. In this context, they have fully characterized the vertices and facets of the local polytope, identifying new Bell inequalities that allow for the certification of non-signaling quantum correlations. Surprisingly, this certification is possible even when the sent input copy is almost perfect, suggesting considerable robustness of quantum phenomena. This advance is crucial for the practical implementation of quantum technologies in environments where absolute control over no-signaling conditions is a challenge. Furthermore, the study compares the robustness of these new inequalities with the Clauser-Horne-Shimony-Holt (CHSH) inequality in certifying DI randomness. The newly identified inequalities were found to be more resilient to depolarizing noise in this particular scenario. The findings also extend to the case where both parties receive a noisy copy of the other's input, leading to similar conclusions. This research not only deepens our understanding of quantum nonlocality under realistic conditions but also opens the door to the exploration of numerous new Bell inequalities, which could have significant implications for the development of quantum cryptography and other quantum technologies in noisy environments with imperfect signaling.

Dublin emerges as a hub for quantum science and technology

Dublin is establishing itself as an emerging hub for quantum science and technology in Europe, with Trinity College Dublin (TCD) leading this development. The institution has launched a Master's program in Quantum Science and Technology that not only trains the next generation of specialists but also actively integrates its students into the Irish quantum ecosystem. This approach seeks to foster the growth of the country's quantum community, positioning Ireland at the forefront of this discipline. The TCD program benefits from a growing research and development infrastructure in Ireland, spanning from fundamental research to technological applications. The involvement of students in projects and collaborations with industry and other research centers is a central pillar of this initiative. This allows them to gain practical experience and contribute directly to the advancement of the field, while benefiting from the opportunities offered by this expanding ecosystem. Ireland's strategy, focused on education and collaboration, seeks to capitalize on the transformative potential of quantum computing, quantum communication, and quantum sensing. By nurturing a pipeline of specialized talent and fostering a collaborative environment, Dublin aims to become an international benchmark in quantum science and technology, attracting investment and promoting innovation in this high-impact sector.