Hasil untuk "Atomic physics. Constitution and properties of matter"

Ya-Jun Wang, Jun Zhang, Dong-Sheng Ding

Non-Hermitian physics exhibits unique physical properties beyond those of traditional Hermitian systems, such as symmetry breaking, the emergence of exceptional points, topological phase transitions, and more. These phenomena have been extensively studied across various platforms, including quantum optics, cold atom systems, superconducting circuits, and condensed matter physics. Rydberg atoms, with their long-range interactions and flexible controllability, provide a promising platform for the experimental realization of non-Hermitian physics. This review primarily summarizes the key experimental and theoretical achievements in the field of non-Hermitian physics within Rydberg atomic systems in recent years. It outlines the fundamental construction of non-Hermitian Hamiltonians, reveals the effective dissipation mechanisms induced by Rydberg atomic interactions, and discusses their impact on spectral properties and symmetry breaking. These studies not only deepen the understanding of quantum phase transitions in non-Hermitian many-body systems but also highlight the unique value of Rydberg atomic platforms in realizing and controlling topological states.

Bacui Li, Tansu Alpcan, Chandra Thapa et al.

By leveraging the principles of quantum mechanics, quantum machine learning (QML) opens doors to novel approaches in machine learning (ML) and offers potential speedup. However, ML models are well documented to be vulnerable to malicious manipulations, and this susceptibility extends to the models of QML. This situation necessitates a thorough understanding of QML's resilience against adversarial attacks, particularly in an era where quantum computing capabilities are expanding. In this regard, this article examines model-independent bounds on adversarial performance for QML. To the best of our knowledge, we introduce the first computation of an approximate lower bound for adversarial error when evaluating model resilience against sophisticated quantum-based adversarial attacks. Experimental results are compared to the computed bound, demonstrating the potential of QML models to achieve high robustness. In the best case, the experimental error is only 10% above the estimated bound, offering evidence of the inherent robustness of quantum models. This work not only advances our theoretical understanding of quantum model resilience but also provides a precise reference bound for the future development of robust QML algorithms.

Bin Shen, Efrain Insuasti Pazmino, Ramesh Dhakal et al.

Abstract We use magnetization measurements under pressure along with ab initio and cluster many-body calculations to investigate magnetism of the Kitaev candidate Li2RhO3. Hydrostatic compression leads to a decrease in the magnitude of the nearest-neighbor ferromagnetic Kitaev coupling K 1 and the corresponding increase in the off-diagonal anisotropy Γ1, whereas the experimental Curie-Weiss temperature changes from negative to positive with the slope of +40 K/GPa. On the other hand, spin freezing persists up to at least 3.46 GPa with the almost constant freezing temperature of 5 K that does not follow the large changes in the exchange couplings and indicates the likely extrinsic origin of spin freezing. Magnetic frustration in Li2RhO3 is mainly related to the interplay between ferromagnetic K 1 and antiferromagnetic Γ1, along with the weakness of the third-neighbor coupling J 3 that would otherwise stabilize zigzag order. The small J 3 distinguishes Li2RhO3 from other Kitaev candidates.

Jiaming Wang, Kirill Petrovnin, J. Pertti Hakonen et al.

Single-photon detectors are essential for implementing optical quantum technologies, such as quantum key distribution, and for enhancing optical imaging systems such as lidar, while also playing a crucial role in studying the statistical properties of light. In this work, we show how the underlying photon statistics can be revealed by using a threshold detector, implemented as a Josephson parametric amplifier operating near a first-order phase transition. We describe the detection protocol, which utilizes a series of pumping pulses followed by the observation of activated switching events. The acquired data are analyzed using two binomial tests, and the results are compared to a theoretical model that takes into account the photon statistics of the microwave field, with additional validation provided by computer simulations. We show that these tests provide conclusive evidence for the Poissonian statistics in the case of a coherent state, in agreement with the experimental data. In addition, this method enables us to distinguish between different statistics of the incoming probe field. Our approach is broadly applicable to standard non-photon-number-resolving detectors, offering a practical pathway to characterize photon statistics in quantum microwave and optical systems.

Bao-Jun Cai, Bao-An Li, Yu-Gang Ma

Nucleon short-range correlations (SRCs) and their high-momentum tails (HMTs) encode key short-range dynamics in nuclei and dense matter. This review provides a concise overview of SRC features relevant to the Equation of State (EOS) of isospin-asymmetric nuclear matter. We summarize empirical and theoretical properties of the single-nucleon momentum distribution $n(k)$, emphasizing the role of the neutron--proton tensor force, the dominance of correlated np pairs, and the enhancement of minority-species HMTs. Links to nucleon effective E-masses, quasi-deuteron components, and orbital entanglement are briefly noted. We examine how SRC-induced HMTs modify kinetic and potential contributions to the EOS in both non-relativistic and relativistic frameworks, including the softening of the kinetic symmetry energy and departures from the isospin parabolic approximation of asymmetric nuclear EOS. Sensitivity to high-momentum components and generalizations to arbitrary dimensions are also highlighted. Implications for heavy-ion reactions are summarized, including effects on particle yields, collective flows, deeply sub-threshold particle production and hard photon emission, driven by modified initial nucleon momentum distributions and abundant high relative-momentum np pairs during the reaction. Finally, we outline SRC-HMT consequences for neutron-star matter, covering proton fractions, tidal deformabilities, $Z$-factors, cooling, and the core--crust transition, as well as possible connections to dark-matter interactions in dense environments.

B. Rohila, N. Kaur

High spin states of 140Sm have been populated using the 116Cd (28Si, 4n) 140Sm heavy ion fusion evaporation reaction. The previously reported level scheme has been considerably modified and extended. Spin and parity assignments have been made using the DCO and IPDCO methods. Multi-quasiparticle configurations have been assigned to various ΔI = 1 and ΔI = 2 bands based on systematic. A band structure similar to 140Sm has been found in 136Ce. So, the alignments in both the nuclei are compared for various band structures having similar band head spin. This helps in assigning the configuration to various band structures. Level structures have been discussed in the framework of the tilted axis cranking model. Lifetimes of states have been measured using the DSAM method.

Min She, Jiangshan Tang, Keyu Xia

A high-sensitivity gyroscope is vital for both investigation of the fundamental physics and monitoring of the subtle variation of Earth’s behaviors. However, it is a challenge to realize a portable gyroscope with sensitivity approaching a small fraction of the Earth’s rotation rate. Here, we theoretically propose a method for implementing a table-top gyroscope with remarkably high sensitivity based on photon drag in a rotating dielectric object. By inserting an Er3+-doped glass rod in a Fabry–Pérot optical cavity with only 20 cm length, we theoretically show that the giant group refractive index and the narrowing cavity linewidth due to slow light can essentially increase the nonreciprocal phase shift due to the photon drag to achieve a rotation sensitivity of 26 frad/s/Hz. This work paves the way to accurately detect tiny variations of the Earth’s rotation rate and orientation and even can test the geodetic and frame-dragging effects predicted by the general relativity with small-volume equipment.

Subhasis Samanta, Fabrizio Cossu, Heung-Sik Kim

Abstract Co-based honeycomb magnets have been actively studied recently for the potential realization of emergent quantum magnetism therein such as the Kitaev spin liquid. Here we employ density functional and dynamical mean-field theory methods to examine a family of the Kitaev magnet candidates BaCo2(XO4)2 (X = P, As, Sb), where the compound with X = Sb being not synthesized yet. Our study confirms the formation of Mott insulating phase and the J eff = 1/2 spin moments at Co2+ sites despite the presence of a sizable amount of trigonal crystal field in all three compounds. The pnictogen substitution from phosphorus to antimony significantly changes the in-plane lattice parameters and direct overlap integral between the neighboring Co ions, leading to the suppression of the Heisenberg interaction. More interestingly, the marginal antiferromagnetic nearest-neighbor Kitaev term changes sign into a ferromagnetic one and becomes sizable at the X = Sb limit. Our study suggests that the pnictogen substitution can be a viable route to continuously tune magnetic exchange interactions and to promote magnetic frustration for the realization of potential spin liquid phases in BaCo2(XO4)2.

Diego Blas, John Carlton, Christopher McCabe

Atom interferometers offer exceptional sensitivity to ultra-light dark matter (ULDM) by precisely measuring effects on atomic systems. Previous studies have demonstrated their capability to detect scalar and vector ULDM candidates, yet their potential for probing spin-2 ULDM remains unexplored. In this work, we address this gap by investigating the sensitivity of atom interferometers to spin-2 ULDM across several frameworks for massive gravity, including the Lorentz-invariant Fierz-Pauli case and two distinct Lorentz-violating scenarios. We show that coherent oscillations of the spin-2 ULDM field induce measurable phase shifts in atom interferometers through three coupling mechanisms: scalar interactions that modify atomic energy levels, and vector and tensor effects that alter the propagation of both atoms and light. We demonstrate that these multifaceted interactions enable atom interferometers to probe a range of ULDM properties and mass scales that are inaccessible to laser interferometric gravitational wave detectors. Our results establish the potential of atom interferometers to open a new experimental frontier for spin-2 dark matter detection.

M. V. Pugach, V. M. Dobishuk, V. O. Kyva et al.

A system for quality assessment of micropixel detectors is presented. The system includes a laser scanning microprobe and a setup for studying the response of micro detectors to minimum ionizing particles. The results of the validation of the developed system indicate its suitability for assessing the quality of the latest monolithic active pixel sensors (MAPS), promising elements of large-area tracking systems for future high-energy physics experiments. Comparison of MAPS with the double-sided microstrip detectors of the CBM experiment (FAIR, Darmstadt) indicates the feasibility of the upgrade of its Silicon Tracking System using MAPS.

Ka Ho Wong, Mark R. Hirsbrunner, Jacopo Gliozzi et al.

Abstract Quantum engineering of topological superconductors and of the ensuing Majorana zero modes might hold the key for realizing topological quantum computing and topology-based devices. Magnet-superconductor hybrid (MSH) systems have proven to be experimentally versatile platforms for the creation of topological superconductivity by custom-designing the complex structure of their magnetic layer. Here, we demonstrate that higher order topological superconductivity (HOTSC) can be realized in two-dimensional MSH systems by using stacked magnetic structures. We show that the sensitivity of the HOTSC to the particular magnetic stacking opens an intriguing ability to tune the system between trivial and topological phases using atomic manipulation techniques. We propose that the realization of HOTSC in MSH systems, and in particular the existence of the characteristic Majorana corner modes, allows for the implementation of a measurement-based protocols for topological quantum computing.

Sreekar Voleti, Koushik Pradhan, Subhro Bhattacharjee et al.

Abstract Quantum materials with non-Kramers doublets are a fascinating venue to realize multipolar hidden orders. Impurity probes which break point group symmetries, such as implanted muons or substitutional impurities, split the non-Kramers degeneracy and exhibit a Janus-faced influence in such systems: they can destroy the very order they seek to probe. Here, we explore this duality in cubic osmate double perovskites which are candidates for exotic d-orbital octupolar order competing with quadrupolar states. Using ab initio computations, Landau theory, and Monte Carlo simulations, we show that Janus impurities induce local strain fields, nucleating quadrupolar puddles and suppressing the octupolar T c . At the same time, strains mix the non-Kramers doublet with an excited magnetic triplet, creating parasitic dipole moments which directly expose the hidden octupolar order parameter. Our work unravels this Janus duality in recent impurity nuclear magnetic resonance (NMR) experiments, with important implications for uncovering hidden order in diverse multipolar materials.

Dylan G Stone, Carlo Bradac

In recent years, machine and quantum learning have gained considerable momentum sustained by growth in computational power and data availability and have shown exceptional aptness for solving recognition- and classification-type problems, as well as problems that require complex, strategic planning. In this work, we discuss and analyze the role machine and quantum learning are playing in the development of diamond-based quantum technologies. This matters as diamond and its optically addressable spin defects are becoming prime hardware candidates for solid state-based applications in quantum information, computing and metrology. Through a selected number of demonstrations, we show that machine and quantum learning are leading to both practical and fundamental improvements in measurement speed and accuracy. This is crucial for quantum applications, especially for those where coherence time and signal-to-noise ratio are scarce resources. We summarize some of the most prominent machine and quantum learning approaches that have been conducive to the presented advances and discuss their potential, as well as their limits, for proposed and future quantum applications.

D. F. Liu, E. K. Liu, Q. N. Xu et al.

Abstract The spin–orbit coupling (SOC) lifts the band degeneracy that plays a vital role in the search for different topological states, such as topological insulators (TIs) and topological semimetals (TSMs). In TSMs, the SOC can partially gap a degenerate nodal line, leading to the formation of Dirac/Weyl semimetals (DSMs/WSMs). However, such SOC-induced gap structure along the nodal line in TSMs has not yet been systematically investigated experimentally. Here, we report a direct observation of such gap structure in a magnetic WSM Co3Sn2S2 using high-resolution angle-resolved photoemission spectroscopy. Our results not only reveal the existence and importance of the strong SOC effect in the formation of the WSM phase in Co3Sn2S2, but also provide insights for the understanding of its exotic physical properties.

Chen He, Jiazhen Li, Weiqi Liu et al.

In this article, we propose a low-complexity quantum principal component analysis (qPCA) algorithm. Similar to the state-of-the-art qPCA, it achieves dimension reduction by extracting principal components of the data matrix, rather than all components of the data matrix, to quantum registers, so that the samples of measurement required can be reduced considerably. Both our qPCA and Lin&#x2019;s qPCA are based on quantum singular-value thresholding (QSVT). The key of Lin&#x2019;s qPCA is to combine QSVT, and modified QSVT is to obtain the superposition of the principal components. The key of our algorithm, however, is to modify QSVT by replacing the rotation-controlled operation of QSVT with the controlled-<sc>not</sc> operation to obtain the superposition of the principal components. As a result, this small trick makes the circuit much simpler. Particularly, the proposed qPCA requires three phase estimations, while the state-of-the-art qPCA requires five phase estimations. Since the runtime of qPCA mainly comes from phase estimations, the proposed qPCA achieves a runtime of roughly 3/5 of that of the state of the art. We simulate the proposed qPCA on the IBM quantum computing platform, and the simulation result verifies that the proposed qPCA yields the expected quantum state.

Wenliang Zhang, Cliò Efthimia Agrapidis, Yi Tseng et al.

Abstract The nature of the spin excitations in superconducting cuprates is a key question toward a unified understanding of the cuprate physics from long-range antiferromagnetism to superconductivity. The intense spin excitations up to the over-doped regime revealed by resonant inelastic X-ray scattering bring new insights as well as questions like how to understand their persistence or their relation to the collective excitations in ordered magnets (magnons). Here, we study the evolution of the spin excitations upon hole-doping the superconducting cuprate Bi2Sr2CaCu2O8+δ by disentangling the spin from the charge excitations in the experimental cross section. We compare our experimental results against density matrix renormalization group calculations for a t-J-like model on a square lattice. Our results unambiguously confirm the persistence of the spin excitations, which are closely connected to the persistence of short-range magnetic correlations up to high doping. This suggests that the spin excitations in hole-doped cuprates are related to magnons—albeit short-ranged.

Thiago R. F. Peixoto, Hendrik Bentmann, Philipp Rüßmann et al.

A Correction to this paper has been published: https://doi.org/10.1038/s41535-021-00314-9

O. P. Artykulnyi, M. M. Avdeev, Ye. M. Kosiachkin et al.

A polymer brush system of a neutral polymer poly (ethylene glycol) with a molecular weight of Mw = 20 kDa on silicon substrates in an aqueous medium was studied by the specular neutron reflectometry. Structural changes in the density profile of a polymer brush caused by the interaction of polymer chains with micelles of the anionic surfactant dodecylbenzenesulfonate acid were observed. The effect is shown to be related to the formation of molecular polymer-micelle associates in the bulk of the solution, which was previously studied by small-angle neutron scattering in a wide range of surfactant concentrations at various molecular weights of the polymer. The density of the dry polymer layer on the silicon substrate was additionally characterized by X-ray reflectometry and scanning atomic force microscopy.

L. I. Grygorieva, А. O. Aleksieieva, O. V. Makarova

Based on the results of radioecological studies in the aquatic ecosystem of the South-Ukrainian Nuclear Power Plant region (SUNPP), the tritium content in technological reservoirs (cooling pond, biological pond of the cleaning station, splash pool) and adjacent surface and groundwater bodies were analyzed. It is shown that the average annual volumetric activity of tritium in the water of technological reservoirs of the SUNPP during 2014 - 2018 is kept at the level of 110 - 160 Bq/l, with a tendency to increase with an average annual rate of 12 - 13 Bq/l, which correlates with a decrease in the volume of blowdown water discharge from the cooling pond (about 8698 thousand m3 per yr). Higher levels of volumetric activity of tritium were registered in the water of technical wells - leakage markers in the technical system, which, moreover, are fed from the pools of cooling towers and spray units. The tritium content in the bioponds of the sewage system of the SUNPP decreased from more than 1000 Bq/l in the early 1990s to 100 - 130 Bq/l in 2017 - 2018, which led to a decrease in its level in the Trikratsky reservoir and should affect lowering its level in groundwater sources, which are located below the natural runoff. Taking into account the physicochemical properties of tritium and the conclusions of well-known scientists about the extremely rapid accumulation of tritium in the environment, the necessity of hydroecological monitoring of the tritium content in surface water bodies is substantiated, the water of which is used for irrigation of agricultural crops and which are hydrodynamically connected with the technological water bodies of the SUNPP, as well as sources of drinking water located downstream of the natural runoff from the technological reservoirs of the nuclear power plant.

Wei Wang, Lijun Wu, Junjie Li et al.

Abstract Identifying and understanding the mechanisms behind strong phonon–phonon scattering in condensed matter systems is critical to maximizing the efficiency of thermoelectric devices. To date, the leading method to address this has been to meticulously survey the full phonon dispersion of the material in order to isolate modes with anomalously large linewidth and temperature-dependence. Here we combine quantitative MeV ultrafast electron diffraction (UED) analysis with Monte Carlo based dynamic diffraction simulation and first-principles calculations to directly unveil the soft, anharmonic lattice distortions of model thermoelectric material SnSe. A small single-crystal sample is photoexcited with ultrafast optical pulses and the soft, anharmonic lattice distortions are isolated using MeV-UED as those associated with long relaxation time and large displacements. We reveal that these modes have interlayer shear strain character, induced mainly by c-axis atomic displacements, resulting in domain formation in the transient state. These findings provide an innovative approach to identify mechanisms for ultralow and anisotropic thermal conductivity and a promising route to optimizing thermoelectric devices.