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A simple phenomenological thermodynamic model is developed to describe the chemical bonding and unbonding in homonuclear diatomic systems. This model describes the entire phase diagram of dimer-forming systems and shows a transition from monomers to dimers, with monomers favored at both very low and very high pressures, as well as at high temperatures. In the context of hydrogen, the former region corresponds to hydrogen present in most interstellar gas clouds, while the latter is associated with the long sought-after fluid metallic phase. The model predicts a molecular to atomic fluid transition in dense deuterium, which is in agreement with recently reported experimental measurements. [ABSTRACT FROM AUTHOR]

We report an external-cavity mode-locked semiconductor laser that uses a Faraday atomic filter as a saturable absorber (SA), termed as the quantum mode-locked Faraday laser. The unique SA exhibits nonlinear transmission characteristics exclusively in the vicinity of the atomic quantum transition frequency, which narrows down the spectral bandwidth of the mode-locked pulses to the gigahertz level and results in a central wavelength of the mode-locked pulses corresponding to the 87Rb (F = 2) component of the D 2 quantum transition line. Simultaneously, influenced by the slow-light effect of rubidium-dispersive vapor in the SA configuration, the fundamental repetition rate of the mode locking can vary between 261 and 228 MHz. Pulse delay tests conducted outside the resonator provide conclusive evidence of a gigahertz-bandwidth slow light within the Faraday laser. The mode-locking technique presented here can be applied to pulsed light sources of other quantum transition lines by setting appropriate atomic filter parameters. In addition, this narrow-spectrum mode-locked laser, with a tunable repetition rate and a central wavelength corresponding to a quantum transition line, has potential applications in the fields of atomic precision spectroscopy and quantum precision metrology. [ABSTRACT FROM AUTHOR]

Quantum mechanics would not be quantum mechanics without the many technical terms which emerged a century ago but are still found in modern textbooks. The theory was mainly created by German-speaking physicists, which is reflected in German–English hybrid words such as "eigenvalue" and "eigenstate." While "eigenvalue" was a neologism—such as was "quantum mechanics" itself—other terms in the quantum lexicon were metaphors adopted from everyday language, e.g., "spin" and "tunneling." Conversely, a few of the specialized quantum terms were later reused in common language with new meanings. In today's parlance, to make a "quantum jump" has a meaning entirely different from the one in which the expression originated. This paper examines various linguistic aspects associated with the early development of quantum mechanics and its predecessor, the old quantum theory. For example, all physicists are familiar with the quantum concept of degeneracy. But the same term has also been employed to denote certain groups of people as "degenerate." Is there any historical connection between the two widely different connotations? Editor's note: Such a specialized field as quantum mechanics naturally uses many specialized terms. Words such as "spin," "degeneracy," and "quantum jump," have come out of a variety of contexts, and some have even taken on new meanings in the general public. This paper discusses the origins and linguistic history of quantum terminology. Readers will especially enjoy learning how certain words came to be the dominant, established, terms in the field. For example, why do we talk about "eigenvalues" today when we could be speaking of "proper values" or "eigenwerts?" [ABSTRACT FROM AUTHOR]

The probability PNEET of excitation in the plasma of nuclei of multiply charged ions due to transitions in their electronic shells is considered, when the energy difference between nuclear and electronic transitions ΔENEET becomes small due to the deformation of the electron shells of ions during their collisions. It is shown that such a resonance is possible only in a two-component plasma containing, along with multiply charged ions, singly charged ions. For ΔENEET up to ~100 eV, the occurrence of resonance can increase the probability PNEET by several orders of magnitude. It is noted that in plasma there is also the possibility of resonant conversion of the excitation of nuclei into the excitation of their electron shells. [ABSTRACT FROM AUTHOR]

The laser's frequency noise is crucial to the sensitivity of quantum sensors. Two commonly used methods to suppress the laser's frequency noise are locking the laser to an atomic transition by the lock-in technique or to an ultra-low thermal expansion (ULE) glass cavity by the PDH technique. The former cannot suppress rapidly changing frequency noise and hardly meets the needs; the latter has powerful performance but a heightened cost. The lack of high-performance and low-cost laser noise suppression methods dramatically limits the practical application of quantum sensors. This work demonstrates that, in many quantum sensing applications such as the Rydberg atomic superheterodyne receiver, by cascade locking the laser to both the atomic transition and a low-cost (LC) cavity, the same performance as locking to the ULE cavity can be achieved. This work is significant in promoting the practical application of quantum sensors. [ABSTRACT FROM AUTHOR]

Magnetic one-dimensional nanostructures show great potential in spintronics and can be used as basic building blocks for magnetic materials and devices with multiple functions. In this study, transition group atomic chains (V, Cr, Mn, Fe, Co, and Ni) are introduced into nonmagnetic MoS2 with a 4|8ud-type grain boundary. Based on first-principles calculations, the V atomic chains show good thermodynamic stability and can self-assemble along the grain boundary direction. The formation of V, Cr, Mn, and Ni atomic chains can induce magnetism into a 4|8ud-type MoS2 system through typical d-d and p-d interactions. This joint effect of transition metal doping and grain boundaries on the magnetism of monolayer MoS2 is of great significance for exploring the electromagnetic properties of monolayer MoS2 for the development of electronic devices. [ABSTRACT FROM AUTHOR]

Atomic‐level surface design of 2D materials, which benefits from their ultra‐high occupancy of surface atoms, has demonstrated significant potential for regulating electronic states. Despite efforts to explore heterojunctions on 2D surfaces, the stacking‐dominated surface electronic structures and their influences on dielectric polarization remain unclear. Herein, a confined growth strategy is proposed to accurately adjust the surface atom occupancy of MoS2 nanoflakes and thereby boost the polarization‐dominated microwave absorption (MA). By altering the stacking layer number from single layers to tens of layers of MoS2, the charge transfer from graphite substrate to MoS2 surface atoms, accompanied by the formation of local electric fields, reaches its highest intensity at two layers and then degrades dramatically with thicker MoS2 nanoflakes. The strengthened dielectric properties eventually enhance the MA performance, increasing the maximum absorption intensity (41.9 dB) by 346% and the effective absorption bandwidth (3 GHz) by 750%. These discoveries shed new light on the electronic modification of 2D materials and their electromagnetic functionalization. [ABSTRACT FROM AUTHOR]

We report an observation of the 6s5d1D2 – 5d2 1D2 forbidden transition in Ba atom by means of high-resolution atomic-beam laser spectroscopy. Stark shifts and splittings of this forbidden transition were measured for 136Ba and 138Ba using the Stark-induced interference method, increasing as the applied electric field increases. From measured spectra at various electric fields, scalar and tensor polarizabilities of the forbidden transition were obtained and found to be much larger than those of other levels. The forbidden transition with large electric polarizabilities, resulting from strong mixing between the two closely lying levels of 5d2 1D2 and 5d6p1D2, provides a good candidate for atomic parity non-conservation study. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDs) are considered promising candidates for the next generation of electronic building blocks in integrated circuits due to their superior performance in mitigating various challenges such as short channel effects. Optical lithography and electron beam lithography are commonly employed for fabricating electrical contacts and patterning TMDs to create electronic devices. The atomic layer structure of TMDs is highly susceptible to external conditions, making conventional lithography methods, which often leave undesirable polymer residues and involve high-energy electron radiation, not ideal for achieving high device performance. Shadow mask lithography has been used to define electrodes and etch patterns on these sensitive materials, thereby avoiding the need for photoresists and electron irradiation. In this study, we introduce a novel, cost-effective electrochemical method for manufacturing reusable and flexible shadow masks with ultrafine feature sizes. By combining electroplating techniques with the dry transfer method, we successfully produced metal masks with ultrafine features, which were then utilized to evaporate metal electrodes with micron feature sizes onto nanostructured substrates. These metal masks, with specifically designed patterns, were employed as etching masks to pattern monolayer MoS2 (a type of TMD) materials without the need for photoresists or solution processes. Moreover, the resulting metal mask-evaporated electrodes, with smooth edges, were integrated with atomic layer transition metal dichalcogenides through van der Waals interactions to create devices based on MoS2. [ABSTRACT FROM AUTHOR]

Evolution of nitrogen under shock compression up to 100 GPa is revisited via molecular dynamics simulations using a machine-learned interatomic potential. The model is shown to be capable of recovering the structure, dynamics, speciation, and kinetics in hot compressed liquid nitrogen predicted by first-principles molecular dynamics, as well as the measured principal shock Hugoniot and double shock experimental data, albeit without shock cooling. Our results indicate that a purely molecular dissociation description of nitrogen chemistry under shock compression provides an incomplete picture and that short oligomers form in non-negligible quantities. This suggests that classical models representing the shock dissociation of nitrogen as a transition to an atomic fluid need to be revised to include reversible polymerization effects. [ABSTRACT FROM AUTHOR]

Within the Rabi quantum model, it has been shown theoretically that a two-level atom ultrastrongly coupled to an electromagnetic field generates or absorbs photons. Photons can be generated if the field is initially in the vacuum state. Under certain initial states of the atom + field system, the absorption of photons is possible in the field mode in the ultrastrong atom–field coupling regime. If the atom is initially in the ground (unexcited) state and the field is in the vacuum state, photons can be generated under resonance condition ωa ≈ ωf or ξ ≡ ωa/ωf ≈ 1, where ωa and ωf are the atomic transition and field frequencies, respectively, in the ultrastrong coupling regime. At the negative detuning when ξ 1 or ωa ωf, Rabi oscillations of the average number of photons with are observed in the case of the ultrastrong coupling with the atom–field coupling constant ; in this case, the population of the excited atomic state is Pe(t) ≈ 0.5. At a large positive detuning when ξ 1, photons are not generated, i.e., , and the atom remains in the initial state, i.e., Pe(t) ≈ 0. The statistics of photons in the generation regime is nearly chaotic: the variance of photons is much larger than the level of the coherent field state (i.e., is super-Poisson). Field photons are absorbed without the excitation of the atom in the ultrastrong coupling regime in the case of the coherent initial state of the field for certain positive detuning values. In this case, the field becomes sub-Poisson. [ABSTRACT FROM AUTHOR]

We propose boson sampling from a system of coupled photons and Bose–Einstein condensed atoms placed inside a multi-mode cavity as a simulation process testing the quantum advantage of quantum systems over classical computers. Consider a two-level atomic transition far-detuned from photon frequency. An atom–photon scattering and interatomic collisions provide interactions that create quasiparticles and excite atoms and photons into squeezed entangled states, orthogonal to the atomic condensate and classical field driving the two-level transition, respectively. We find a joint probability distribution of atom and photon numbers within a quasi-equilibrium model via a hafnian of an extended covariance matrix. It shows a sampling statistics that is ♯P-hard for computing, even if only photon numbers are sampled. Merging cavity-QED and quantum-gas technologies into a hybrid boson sampling setup has the potential to overcome the limitations of separate, photon or atom, sampling schemes and reveal quantum advantage. [ABSTRACT FROM AUTHOR]

Magnetically induced (MI) transitions of 85Rb atoms, D2-lines 5S1/2 → 5P3/2, Fg = 3 → Fe = 1 with circular polarization σ–, the intensities of which are zero in a zero magnetic field, have been studied experimentally and theoretically. However, their intensities increase significantly in magnetic fields of 0.5–1 kG. The MI transition Fg = 3 → Fe = 1 was used for the first time at the probe radiation frequency to implement the process of electromagnetically induced transparency (EIT). The frequency of the coupling radiation was resonant with the Fg = 2 → Fe = 1 transition. The generated EIT resonance was located on the low-frequency tail of the spectrum. It was shown that EIT resonance was formed only when the probe and coupling radiations had the same circular polarization σ–. This was true for MI transitions Fe – Fg = ΔF = –2. [ABSTRACT FROM AUTHOR]

Zebrafish collective behaviour is widely used to assess their physical and mental state, serving as a valuable tool to assess the impact of ageing, disease genetics, and the effect of drugs. The essence of these macroscopic phenomena can be represented by active matter models, where the individuals are abstracted as interactive self-propelling agents. The behaviour of these agents depends on a set of parameters in a manner reminiscent of those between the constituents of physical systems. In a few cases, the system may be controlled at the level of the individual constituents such as the interactions between colloidal particles, or the enzymatic behaviour of de novo proteins. Usually, however, while the collective behaviour may be influenced by environmental factors, it typically cannot be changed at will. Here, we challenge this scenario in a biological context by genetically modifying zebrafish. We thus demonstrate the potential of genetic modification in the context of controlling the collective behaviour of biological active matter systems at the level of the constituents, rather than externally. In particular, we probe the effect of the lack of col11a2 gene in zebrafish, which causes the early onset of osteoarthritis. The resulting col11a2 -/- zebrafish exhibited compromised vertebral column properties, bent their body less while swimming, and took longer to change their orientations. Surprisingly, a group of 25 mutant fish exhibited more orderly collective motion than the wildtype. We show that the collective behaviour of wildtype and col11a2 -/- zebrafish are captured with a simple active matter model, in which the mutant fish are modelled by self–propelling agents with a higher orientational noise on average. In this way, we demonstrate the possibility of tuning a biological system, changing the state space it occupies when interpreted with a simple active matter model. Author summary: Collective behaviour emerges across a very wide range of systems which span lengthscales of many orders of magnitude. Examples include phase transitions in atomic and molecular materials, and colloidal dispersions, and self-propelled particles. Recently universal behaviour has been found connecting these physical systems to motile cells and groups of animals, such as the murmuration in Starlings. The swimming of a group of Zebrafish can be described with surprising accuracy by self-propelled particles which follow very simple mathematical rules. This model exhibits an ordering transition in which all individuals travel in the same direction. Here we study the effect of genetic modification of their spines on the swimming of the Zebrafish. We find that the genetically modified fish take a longer time to make turns, and have a continuous range of swim speeds, while wild type fish turn tightly and tend to swim either slowly or quickly. Surprisingly, the mutant fish are also described by the very same model of self-propelled particles but under a slight change of parameter. This work shows that genetic modification can tune the dynamical behaviour of a biological system and this can be captured accurately with a very simple physical model. [ABSTRACT FROM AUTHOR]

Air pollution in the interior of our homes is caused by diverse chemical, physical, and biological entities. This review comprehensively explores the current understanding of sources and health impacts of gaseous and particulate pollutants. Trend analysis of indoor air research worldwide revealed a quantum jump of 2.8 times in the number of publications during the last ten years. Indoor air pollutants are innumerable, but only a few are widely prevalent in most households. The qualitative complexity of pollutants translates to different health problems, including respiratory diseases, cardiovascular conditions, cancer, and deaths. There exist wide-scale disparities in the negative impacts among different economic strata, genders, and age groups; children and elderly populations are more vulnerable. In developing countries, pollutants primarily arise from traditional sources, whereas in developed countries, pollutants from non-conventional sources are comparatively significant. Only a few countries have indoor air regulations, policies, monitoring plans and effective enforcement. [ABSTRACT FROM AUTHOR]

For a three-level system monitored by an ancilla, we show that the quantum Zeno effect can be employed to control quantum jump for error correction. Further, we show that we can realize cNOT gate, and effect dense coding and teleportation using a three-level system with an ancilla. We believe that this work paves the way to generalize the control of a qudit. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the energy spectra, wave functions and the B (E 2) transition rates for 9 8 – 1 1 2 Ru atomic nuclei, using the conformable fractional Bohr Hamiltonian model. For the β -part of the potential, the newly proposed Yukawa plus modified exponential potential is considered and the harmonic oscillator potential in γ -part, with γ fixed around π 6 . By using the conformable fractional Nikiforov–Uvarov method, energy spectra and wave functions are obtained analytically. The sensitivity of the potential parameters and the spectra with respect to the fractional order parameter is investigated. The normalized fractional energies and fractional electric quadrupole transition rates are compared with the available experimental predictions and those from existing theoretical studies. Comparisons are made at different values of the fractional derivative order. The results are presented across a broader range of values of α , providing a systematic analysis of how variations in this parameter influence the energy spectra, wave functions, and B (E 2) transition rates in Ru nuclei. Overall, the comparison of our results with experimental data shows the good accuracy of our model, especially when the fractional parameter goes to lower values. It can be concluded that the order of fractional derivative plays a crucial role in refining theoretical predictions of electric quadrupole transition rates, especially for transitions involving higher multipolarities. [ABSTRACT FROM AUTHOR]

In this paper, the unconventional light‐matter interactions between giant atoms and structured baths (i.e., lattices) are studied with either Hermitian or non‐Hermitian next‐nearest‐neighbor coupling terms. Essentially different dynamics of the atoms and the propagating field in the Hermitian and non‐Hermitian cases is revealed, which can be further engineered by tuning parameters such as the atomic transition frequency and the (synthetic) magnetic field associated to the coupling terms. The next‐nearest‐neighbor couplings play an important role in controlling the emission direction and the field distribution in the lattice, thus providing opportunities for tailoring exotic dipole–dipole interactions. The results in this paper have potential applications in, e.g., engineering unconventional quantum networks and simulating quantum many‐body systems. [ABSTRACT FROM AUTHOR]

The Pauli exclusion principle (PEP), a cornerstone of quantum mechanics and whole science, states that in a system, two fermions can not simultaneously occupy the same quantum state. Several experimental tests have been performed to place increasingly stringent bounds on the validity of PEP. Among these, the series of VIP experiments, performed at the Gran Sasso Underground National Laboratory of INFN, is searching for PEP-violating atomic X-ray transitions in copper. In this paper, the upgraded VIP-3 setup is described, designed to extend these investigations to higher-Z elements such as zirconium, silver, palladium, and tin. We detail the enhanced design of this setup, including the implementation of cutting-edge, 1 mm thick, silicon drift detectors, which significantly improve the measurement sensitivity at higher energies. Additionally, we present calculations of expected PEP-violating energy shifts in the characteristic lines of these elements, performed using the multi-configurational Dirac–Fock method from first principles. The VIP-3 realization will contribute to ongoing research into PEP violation for different elements, offering new insights and directions for future studies. [ABSTRACT FROM AUTHOR]

Understanding fast pedestal dynamics and turbulent transport in the edge and scrape-off layer (SOL) plasma of spherical tokamaks is crucial for the design and operation of future fusion reactors. The alkali beam emission spectroscopy diagnostic technique offers a means to measure the absolute electron density radial profile and fluctuation amplitude in these regions. In this study, we demonstrate that injecting a sodium neutral beam radially into the plasma and analyzing the light emission from its 3p–3s atomic transition using near-orthogonal viewing angles allows for accurate measurement of the electron density profile and fluctuations in the National Spherical Torus Experiment (NSTX) Upgrade spherical tokamak. Our findings indicate a peak signal-to-noise ratio of 118 in the pedestal and 12 in the SOL under typical NSTX plasma conditions. The spatial resolution for the electron density profile is estimated to be between 2 and 8 mm, while for fluctuation measurements, it ranges from 12 to 15 mm. [ABSTRACT FROM AUTHOR]

A generalization of the stars system through the interaction between two three-level atoms in the Ξ-type and two systems of N two-level non-interacting atoms in the aftermath of the nonlinear coupling functions are investigated. The wave function of the system is obtained in the resonance case. With different forms of the nonlinearity functions, the atomic population is studied which display the phenomenon of collapses and revivals besides transition of the atomic initial state to a superposition state by gaining (or losing) energy depending on the initial atomic state. Also we consider the correlation function where the choice of the nonlinearity function can produce non-classical effects. [ABSTRACT FROM AUTHOR]

A generalized kinetic model of atomic level populations in an optically dense plasma excited by laser pulses of arbitrary duration is formulated and studied. This model is based on a nonstationary expression for the probability of excitation of an atomic transition and takes into account the effects of laser pulse penetration into an optically dense medium. A universal formula for the excitation probability as a function of time and propagation length is derived and applied to the case of a Lorentzian spectral profile of an atomic transition excited by a laser pulse with a Gaussian envelope. The features of nonstationary excitation probabilities are presented for different optical depths of the plasma, laser pulse durations, and carrier frequencies. The formulas derived here will be useful for the description of atomic populations excited by laser pulses under realistic conditions of dense plasmas. [ABSTRACT FROM AUTHOR]

The measurement problem of quantum mechanics concerns the question as to under which circumstances coherent wave evolution becomes disrupted to produce eigenstates of observables, instead of evolving superpositions of eigenstates. The problem already needs to be addressed within wave mechanics, before second quantization, because low-energy interactions can be dominated by particle-preserving potential interactions. We discuss a scattering array of harmonic oscillators, which can detect particles penetrating the array through interaction with a short-range potential. Evolution of the wave function of scattered particles, combined with Heisenberg's assertion that quantum jumps persist in wave mechanics, indicates that the wave function will collapse around single oscillator sites if the scattering is inelastic, while it will not collapse around single sites for elastic scattering. The Born rule for position observation is then equivalent to the statement that the wave function for inelastic scattering amounts to an epistemic superposition of possible scattering states, in the sense that it describes a sum of probability amplitudes for inelastic scattering off different scattering centers, whereas, at most, one inelastic scattering event can happen at any moment in time. Within this epistemic interpretation of the wave function, the actual underlying inelastic scattering event corresponds to a quantum jump, whereas the continuously evolving wave function only describes the continuous evolution of probability amplitudes for scattering off different sites. Quantum jumps then yield definite position observations, as defined by the spatial resolution of the oscillator array. [ABSTRACT FROM AUTHOR]

Exceptional points are the branch-point singularities of non-Hermitian Hamiltonians and have rich consequences in open-system dynamics. While the exceptional points and their critical phenomena are widely studied in the non-Hermitian settings without quantum jumps, they also emerge in open quantum systems depicted by the Lindblad master equations, wherein they are identified as the degeneracies in the Liouvillian eigenspectrum. These Liouvillian exceptional points often have distinct properties compared to their counterparts in non-Hermitian Hamiltonians, leading to fundamental modifications of the steady states or the steady-state-approaching dynamics. Since the Liouvillian exceptional points widely exist in quantum systems such as the atomic vapors, superconducting qubits, and ultracold ions and atoms, they have received increasing amount of attention of late. Here, we present a brief review on an important aspect of the dynamic consequence of Liouvillian exceptional points, namely the chiral state transfer induced by the parametric encircling the Liouvillian exceptional points. Our review focuses on the theoretical description and experimental observation of the phenomena in atomic systems that are experimentally accessible. We also discuss the ongoing effort to unveil the collective dynamic phenomena close to the Liouvillian exceptional points, as a consequence of the many-body effects therein. Formally, these phenomena are the quantum-many-body counterparts to those in classical open systems with nonlinearity, but hold intriguing new potentials for quantum applications. [ABSTRACT FROM AUTHOR]

Exceptional points are the branch-point singularities of non-Hermitian Hamiltonians and have rich consequences in open-system dynamics. While the exceptional points and their critical phenomena are widely studied in the non-Hermitian settings without quantum jumps, they also emerge in open quantum systems depicted by the Lindblad master equations, wherein they are identified as the degeneracies in the Liouvillian eigenspectrum. These Liouvillian exceptional points often have distinct properties compared to their counterparts in non-Hermitian Hamiltonians, leading to fundamental modifications of the steady states or the steady-state-approaching dynamics. Since the Liouvillian exceptional points widely exist in quantum systems such as the atomic vapors, superconducting qubits, and ultracold ions and atoms, they have received increasing amount of attention of late. Here, we present a brief review on an important aspect of the dynamic consequence of Liouvillian exceptional points, namely the chiral state transfer induced by the parametric encircling the Liouvillian exceptional points. Our review focuses on the theoretical description and experimental observation of the phenomena in atomic systems that are experimentally accessible. We also discuss the ongoing effort to unveil the collective dynamic phenomena close to the Liouvillian exceptional points, as a consequence of the many-body effects therein. Formally, these phenomena are the quantum-many-body counterparts to those in classical open systems with nonlinearity, but hold intriguing new potentials for quantum applications. [ABSTRACT FROM AUTHOR]

In this study, we have conducted a thorough investigation into the influence of the atomic radius of transition metals on the structural, electronic, and optical properties of nanolaminated borides MAlB (M = Cr , Mo, W) using first principles calculation. The validity and dependability of our calculation parameters are confirmed and compared with other available data sets. The calculated elastic constants reveal stronger resistance to deformation along the c direction as compared to the a- and b-directions. The mechanical properties of these borides increased in tandem with the atomic radius of transition metal. The chemical bonding within the borides is a mix of metallic and covalent bonds. Interestingly, there is a decrease in the boride metallicity concurrent with an increase in the atomic radius of the transition metal. Optical property analysis shows promise for these borides as absorbent materials. Furthermore, there is a correlation between the increase in the atomic nucleus of the transition metal and the increase in the maximum absorption coefficient. [ABSTRACT FROM AUTHOR]

Herein we report the catalytic ethanol decomposition over cobalt catalyst synthesized using conventional solution combustion synthesis (SCS). The reaction pathway proposed in-situ DRIFT analysis shows that the decomposition reaction proceeds through the formation of surface ethoxy intermediates that transformed into acetates and aldehydes which further decompose to releases CH 4 , H 2 and CO 2 with some deposition of carbon on the catalyst surface. The catalytic reaction shows 100 % ethanol conversion at 420 °C, with high selectivity of H 2 in the output. The structural transformation of the catalyst and deposited carbon was analyzed using high-resolution transmission electron microscope (HRTEM). Presence of small Co nanoparticles (size <30 nm) surrounded with graphene and larger metal nanoparticles trapped inside MWCNTs was visible during a stability run over 50 h that motivates in proposing the reaction mechanism of the fluctuating metal nanoparticle along with carbon on the catalyst surface. Moreover, this work opens up the possibility of synthesizing highly dispersed Co nanoparticles in an efficient way without any complex experimental procedures and equipment that can further be used as effective catalysts in many industrial reactions. • Catalytic reaction shows 100 % ethanol conversion at 420 °C on cobalt catalyst. • Transformation on particle and carbon structure during stability run is seen. • Co nanoparticles between 10 and 30 nm with graphene layer were observed. • Metal nanoparticles trapped inside MWCNTs after 50 h of ethanol conversion. • Proposed mechanism describes the metal nanoparticle fluctuation with carbon structure. [ABSTRACT FROM AUTHOR]

Context. A quantum model of a cold dark matter galactic halo is developed. The model requires specifying the mass and radius of the halo as well as its density profile. The structure of the halo resulting from the theory is predicted and its physical properties are determined. Verification of these theoretical predictions by observations is proposed and discussed. Aims. The model is constructed by analytically solving the governing equation and using its time-independent solutions to determine the internal structure of a galactic halo with an Navarro–Frenk–White cold dark matter density profile. Methods. The governing equation that is the basis of the developed theory is derived from the irreducible representations of the extended Galilean group. The method of finding the solutions is analytical, even though an Navarro–Frenk–White density profile is used in the calculations. Results. The theory predicts a halo with a core composed of free dark matter particles that move randomly with frequent collisions. It also predicts an envelope in which the particles are confined to their orbits, which are quantized. Except in the close vicinity of the core, the population of the orbits remains fixed, and physical reasons for the nonexistence of quantum jumps between these orbits are presented. Conclusions. A quantum model of a galactic cold dark matter halo with a given Navarro–Frenk–White density profile is constructed. It predicts a quantum structure of the halo that is significantly different than any previously known dark matter model. The quantum model naturally accounts for dark matter being collisionless, and it predicts that dark matter can only emit radiation of one fixed frequency. The values of this frequency are computed for dark matter particles of different masses. A potential observational verification of the theory is also discussed. [ABSTRACT FROM AUTHOR]

The titanium dioxide (TiO2) semiconductor's wide band gap property restricts its application in a variety of fields. To ensure cost-effectiveness and time efficiency, researchers emphasized material modeling and theoretical analysis. This study employs a Density Functional Theory approach to investigate how the presence of transition metal elements (TME) like rhodium (Rh) and rhenium (Re) affects the optoelectronic properties of TiO2. The study was carried out using the VASP software package and the plane-wave pseudopotential technique. The formation energy, electronic band structure, and optical properties of TiO2 were affected by the addition of both Rh and Re as doping materials. The outcomes of the band structure and total density of states (TDOS), point out notable alterations in the energy gap (Eg) of TiO2. The plot of the band structure illustrates that the introduction of Re leads to a more substantial reduction in the TiO2 band gap compared to Rh. The introduction of numerous sub-states into the band gap causes the valence band to approach the conduction band at the Gamma point. The band gap reduction caused by the addition of Rh and Re TME is confirmed by the relocation of the TDOS to lower energies in the doped TiO2 structure. Furthermore, significant changes in the partial density of states of TiO2 upon Re doping have been observed at the bottom of the conduction band, highlighting the effectiveness of Re doping in modifying the electronic band structure of TiO2. The outcomes of band structure and TDOS proved that TME with high atomic mass is certain to decrease TiO2's band gap to the range required for usage as a photocatalytic material. Rh and Re doping in TiO2 alter their optical properties, making them suitable for optoelectronic devices. [ABSTRACT FROM AUTHOR]

In quantum science and technology applications such as optical clocks, ultrastable laser sources can address extremely narrow atomic transitions without introducing noise to the system. The required level of stability and precision has historically only been achieved under controlled laboratory conditions. Novel commercial solutions combined with new approaches are now meeting the high demands for field applications of emergent quantum technologies. [ABSTRACT FROM AUTHOR]

The present work expands previous studies on the kinetics of the n-C3H7I unimolecular decomposition and the thermodynamic properties of n-C3H7I and i-C3H7I molecules, by providing combined experimental and theoretical data on the rate constant for reaction of n-C3H7I + Ar ⇌ n-C3H7 + I + Ar, as well as thermodynamic data for iodopropane isomers, calculated based on the density functional theory. The n-C3H7I dissociation rate constant has been precisely determined in shock-tube experiments by applying atomic resonance absorption spectrometry (ARAS) at the resonance transition wavelength of atomic iodine (183.0 nm) in a temperature range from 830 to 1230 K at a pressure of 3–4 bar. The resulting expression is presented in the Arrhenius form: k1st = 1.17 × 1013exp(−191.4 kJ mol−1/RT) (s−1). Theoretical RRKM/ME calculation of the temperature- and pressure-dependent rate constant and channel branching ratio have been based on quantum chemical calculations and were performed over a wide range of thermodynamic conditions (T = 300–2000 K, p = 10−4 to 102 bar). Additionally, the thermochemistry of the reactions of n-C3H7I dissociation and isomerization has been calculated on B3LYP/cc-pVTZ-PP level of theory. Thermodynamic data, which are provided in NASA polynomial format, are in a better agreement with the available experimental data and previous theoretical estimates. [ABSTRACT FROM AUTHOR]

Molecular spin qubits have demonstrated immense potential in quantum information science research due to the addressability of electron spins using microwave frequencies, and the scalability and tunability of molecular systems. Exemplary in this regard is the holmium polyoxometalate, [Na9Ho(W5O18)2]·35H2O (HoW10), which features an accessible atomic clock transition at 9.4 GHz; however, the coherence time of this molecule is limited by spin-phonon coupling driven decoherence processes. To limit these decoherence pathways, materials need to be designed to reduce energy overlap between spin and phonon states, and this necessitates developing a better understanding on how structural modifications impact the vibrational landscape for classes of complexes. Herein we conducted a full investigation into the fundamental structural and vibrational properties of the lanthanide Lindqvist polyoxometalate series, [Na9Ln(W5O18)2]·xH2O (Ln = La(III)–Lu(III), except Pm(III)) (LnW10), to assess how structural changes effect vibrational characteristics and to elucidate pathways to improve the coherence properties of HoW10. Single crystal X-ray diffraction results revealed four distinct structural polymorphs in complexes 1–14 wherein first coordination spheres were identical, and differences manifested as changes in lattice packing. Interestingly, the subtle changes in packing exhibited by the four polymorphs were found to impact distortions away from ideal D4d symmetry for each of the LnW10 complexes. Raman and far-infrared (FIR) spectra of complexes 1–14 were collected to identify vibrational modes present in low energy regions and peak fitting assignments were made according to literature precedents. Qualitative and Partial least squares (PLS) analysis show correlations between complex structural parameters with the low energy Raman and FIR vibrational modes of interest. Overall, this investigation shows that the second coordination sphere plays an integral role in modulation of the structural and vibrational characteristics of LnW10 complexes, which makes it a viable route for tuning spin and vibrational manifolds of species within this series. [ABSTRACT FROM AUTHOR]

Today's most precise timekeeping is based on optical atomic clocks. However, those could potentially be outperformed by a nuclear clock, based on a nuclear transition instead of an atomic shell transition. Such a nuclear clock promises intriguing applications in applied as well as fundamental physics, ranging from geodesy and seismology to the investigation of possible time variations of fundamental constants and the search for dark matter. Only one nuclear state is known so far that could drive a nuclear clock: the "Thorium Isomer" 229 m Th, i.e., the isomeric first excited state of 229 Th, representing the lowest nuclear excitation so far reported in the landscape of nuclear isotopes. Indirectly conjectured to exist already in 1976, decades of experimental efforts were dedicated to unambiguously identify this elusive nuclear state and to characterize its properties. However, for 40 years, these efforts remained inconclusive. The turning point was marked by the first direct detection of 229 m Th via its internal conversion decay branch in 2016. Since then, remarkable progress could be achieved in characterizing the properties and decay parameters. The half-life of the neutral isomer was determined, the hyperfine structure was measured via collinear laser spectroscopy, providing information on nuclear moments and the nuclear charge radius and also the excitation energy of the isomer could be directly determined with different techniques. In a recent experiment at CERN's ISOLDE facility, the long-sought radiative decay of the Thorium isomer could be observed for the first time via implantation of (β -decaying) 229 Ac into a vacuum-ultraviolet (VUV) transparent crystal and subsequent fluorescence detection in a VUV spectrometer. Thus, the excitation energy of 229 m Th could be determined with unprecedented precision to 8.338(24) eV, corresponding to a wavelength of 148.71(42) nm. These achievements, together with ongoing laser developments for the required VUV wavelength, open the door toward a laser-driven control of the isomeric transition and thus to the development of an ultra-precise nuclear frequency standard. [ABSTRACT FROM AUTHOR]

Virtually noiseless due to the scarcity of spinful nuclei in the lattice, simple oxides hold promise as hosts of solid-state spin qubits. However, no suitable spin defect has yet been found in these systems. Using high-throughput first-principles calculations, we predict spin defects in calcium oxide with electronic properties remarkably similar to those of the NV center in diamond. These defects are charged complexes where a dopant atom — Sb, Bi, or I — occupies the volume vacated by adjacent cation and anion vacancies. The predicted zero phonon line shows that the Bi complex emits in the telecommunication range, and the computed many-body energy levels suggest a viable optical cycle required for qubit initialization. Notably, the high-spin nucleus of each dopant strongly couples to the electron spin, leading to many controllable quantum levels and the emergence of atomic clock-like transitions that are well protected from environmental noise. Specifically, the Hanh-echo coherence time increases beyond seconds at the clock-like transition in the defect with 209Bi. Our results pave the way to designing quantum states with long coherence times in simple oxides, making them attractive platforms for quantum technologies. Recently, long spin coherence times have been predicted for spin defects in simple oxides. Here, by using high-throughput first-principles calculations, the authors identify promising spin defects in CaO, with electronic properties similar to those of NV centers but with longer coherence times. [ABSTRACT FROM AUTHOR]

A driven‐dissipative system is considered, consisting of an atomic Bose‐Einstein condensates loaded into a 2D Hubbard lattice and coupled to a single mode of an optical cavity. Due to the interplay between strong, repulsive atomic interaction and the atom‐cavity coupling, the system exhibits several phases of atoms and photons including the atomic superfluid (SF) and supersolid (SS). The dynamical behavior of the system, where dissipation is included by means of Lindblad master equation formalism. Due to the discontinuous nature of the Dicke transition for strong atomic repulsion, extended co‐existence region of different phases are found. The resulting switching dynamics are investigated, particularly between the coexisting SF and SS phases, which eventually becomes damped by the dissipation. [ABSTRACT FROM AUTHOR]

Quantum-clock interferometry has been suggested as a quantum probe to test the universality of free fall and the universality of gravitational redshift. In typical experimental schemes, it seems advantageous to employ Doppler-free E1–M1 transitions which have so far been investigated in quantum gases at rest. Here, we consider the fully quantized atomic degrees of freedom and study the interplay of the quantum center-of-mass (COM)—that can become delocalized—together with the internal clock transitions. In particular, we derive a model for finite-time E1–M1 transitions with atomic intern–extern coupling and arbitrary position-dependent laser intensities. We further provide generalizations to the ideal expressions for perturbed recoilless clock pulses. Finally, we show, at the example of a Gaussian laser beam, that the proposed quantum-clock interferometers are stable against perturbations from varying optical fields for a sufficiently small quantum delocalization of the atomic COM. [ABSTRACT FROM AUTHOR]

Increasing the utilization efficiency of platinum is critical for advancing proton exchange-membrane fuel cells (PEMFCs). Despite extensive research on catalysts for the cathodic oxygen reduction reaction (ORR), developing highly active and durable Pt-based catalysts that can suppress surface dealloying in corrosive acid conditions remains challenging. Herein, we report a facile synthesis of bimetallic ultrathin PtM (M = Mo, W, and Cr) nanowires (NWs) composed of group VI B transition metal atomic sites anchored on the surface. These NWs possess uniform sizes and well-controlled atomic arrangements. Compared to PtW and PtCr catalysts, the PtMo0.05 NWs exhibit the highest half-wave potential of 0.935 V and a mass activity of 1.43 A·mgPt−1. Remarkably, they demonstrate a remarkable 23.8-fold enhancement in mass activity compared to commercial Pt/C for ORR, surpassing previously reported Pt-based catalysts. Additionally, the PtMo NWs cathode in membrane electrode assembly tests achieves a remarkable peak power density of 1.443 W·cm−2 (H2-O2 conditions at 80 °C), which is 1.09 times that of commercial Pt/C. The ligand effect in the bimetallic surface not only facilitates strong coupling between Mo (4d) and Pt (5d) atomic orbitals to hinder atom leaching but also modulates the d-states of active site, significantly optimizing the adsorption of key oxygen (⋆O and ⋆OH) species and accelerating the rate-determining step in ORR pathways. [ABSTRACT FROM AUTHOR]

Modeling the non-equilibrium dissipative dynamics of strongly interacting quantized degrees of freedom is a fundamental problem in several branches of physics and chemistry. We implement a quantum state trajectory scheme for solving Lindblad quantum master equations that describe coherent and dissipative processes for a set of strongly coupled quantized oscillators. The scheme involves a sequence of stochastic quantum jumps with transition probabilities determined by the system state and the system-reservoir dynamics. Between consecutive jumps, the wave function is propagated in a coordinate space using the multi-configuration time-dependent Hartree method. We compare this hybrid propagation methodology with exact Liouville space solutions for physical systems of interest in cavity quantum electrodynamics, demonstrating accurate results for experimentally relevant observables using a tractable number of quantum trajectories. We show the potential for solving the dissipative dynamics of finite size arrays of strongly interacting quantized oscillators with high excitation densities, a scenario that is challenging for conventional density matrix propagators due to the large dimensionality of the underlying Hilbert space. [ABSTRACT FROM AUTHOR]

We present a means of studying rare reactive pathways in open quantum systems using transition path theory and ensembles of quantum jump trajectories. This approach allows for the elucidation of reactive paths for dissipative, nonadiabatic dynamics when the system is embedded in a Markovian environment. We detail the dominant pathways and rates of thermally activated processes and the relaxation pathways and photoyields following vertical excitation in a minimal model of a conical intersection. We find that the geometry of the conical intersection affects the electronic character of the transition state as defined through a generalization of a committor function for a thermal barrier crossing event. Similarly, the geometry changes the mechanism of relaxation following a vertical excitation. Relaxation in models resulting from small diabatic coupling proceeds through pathways dominated by pure dephasing, while those with large diabatic coupling proceed through pathways limited by dissipation. The perspective introduced here for the nonadiabatic dynamics of open quantum systems generalizes classical notions of reactive paths to fundamentally quantum mechanical processes. [ABSTRACT FROM AUTHOR]

Diatoms are a group of marine algae that are responsible for a significant part of global oxygen production. Adapted to life in an aqueous environment dominated by the blue–green light, their major light-harvesting antennae—fucoxanthin–chlorophyll protein complexes (FCPs)—exhibit different pigment compositions than of plants. Despite extensive experimental studies, until recently the theoretical description of excitation energy dynamics in these complexes was limited by the lack of high-resolution structural data. In this work, we use the recently resolved crystallographic information of the FCP complex from Phaeodactylum tricornutum diatom [Wang et al., Science 363, 6427 (2019)] and quantum chemistry-based calculations to evaluate the chlorophyll transition dipole moments, atomic transition charges from electrostatic potential, and the inter-chlorophyll couplings in this complex. The obtained structure-based excitonic couplings form the foundation for any modeling of stationary or time-resolved spectroscopic data. We also calculate the inter-pigment Förster energy transfer rates and identify two quickly equilibrating chlorophyll clusters. [ABSTRACT FROM AUTHOR]

Dynamic interactions between the myosin motor head on thick filaments and the actin molecular track on thin filaments drive the myosin-crossbridge cycle that powers muscle contraction. The process is initiated by Ca2+ and the opening of troponin--tropomyosin--blocked myosin-binding sites on actin. The ensuing recruitment of myosin heads and their transformation from pre-powerstroke to post-powerstroke conformation on actin produce the force required for contraction. Cryo-EM-based atomic models confirm that during this process, tropomyosin occupies three different average positions on actin. Tropomyosin pivoting on actin away from a TnI-imposed myosin-blocking position accounts for part of the Ca2+ activation observed. However, the structure of tropomyosin on thin filaments that follows pre-powerstroke myosin binding and its translocation during myosin's pre-powerstroke to post-powerstroke transition remains unresolved. Here, we approach this transition computationally in silico. We used the myosin helix-loop-helix motif as an anchor to dock models of pre- powerstroke cardiac myosin to the cleft between neighboring actin subunits along cardiac thin filaments.We then performed targeted molecular dynamics simulations of the transition between pre- and post-powerstroke conformations on actin in the presence of cardiac troponin--tropomyosin. These simulations show Arg 369 and Glu 370 on the tip of myosin Loop-4 encountering identically charged residues on tropomyosin. The charge repulsion between residues causes tropomyosin translocation across actin, thus accounting for the final regulatory step in the activation of the thin filament, and, in turn, facilitating myosin movement along the filament. We suggest that during muscle activity, myosin-induced tropomyosin movement is likely to result in unencumbered myosin head interactions on actin at low-energy cost. [ABSTRACT FROM AUTHOR]

Chalcogenide-based nonvolatile phase change materials (PCMs) have a long history of usage, from bulk disk memory to all-optic neuromorphic computing circuits. Being able to perform uniform phase transitions over a subwavelength scale makes PCMs particularly suitable for photonic applications. For switching between nonvolatile states, the conventional chalcogenide phase change materials are brought to a melting temperature to break the covalent bonds. The cooling rate determines the final state. Reversible polymorphic layered materials provide an alternative atomic transition mechanism for low-energy electronic (small domain size) and photonic nonvolatile memories (which require a large effective tuning area). The small energy barrier of breaking van der Waals force facilitates low energy, fast-reset, and melting-free phase transitions, which reduces the chance of element segregation-associated device failure. The search for such material families starts with polymorphic In2Se3, which has two layered structures that are topologically similar and stable at room temperature. In this perspective, we first review the history of different memory schemes, compare the thermal dynamics of phase transitions in amorphous-crystalline and In2Se3, detail the device implementations for all-optical memory, and discuss the challenges and opportunities associated with polymorphic memory. [ABSTRACT FROM AUTHOR]

Myosin motors use the energy of ATP to produce force and directed movement on actin by a swing of the lever arm. ATP is hydrolysed during the off-actin re-priming transition termed recovery stroke. To provide an understanding of chemo-mechanical transduction by myosin, it is critical to determine how the reverse swing of the lever arm and ATP hydrolysis are coupled. Previous studies concluded that the recovery stroke of myosin II is initiated by closure of the Switch II loop in the nucleotide-binding site. Recently, we proposed that the recovery stroke of myosin VI starts with the spontaneous re-priming of the converter domain to a putative pre-transition state (PTS) intermediate that precedes Switch II closing and ATPase activation. Here, we investigate the transition from the pre-recovery, post-rigor (PR) state to PTS in myosin VI using geometric free energy simulations and the string method. First, our calculations rediscover the PTS state agnostically and show that it is accessible from PR via a low free energy transition path. Second, separate path calculations using the string method illuminate the mechanism of the PR to PTS transition with atomic resolution. In this mechanism, the initiating event is a large movement of the converter/lever-arm region that triggers rearrangements in the Relay-SH1 region and the formation of the kink in the Relay helix with no coupling to the active site. Analysis of the free-energy barriers along the path suggests that the converter-initiated mechanism is much faster than the one initiated by Switch II closure, which supports the biological relevance of PTS as a major on-pathway intermediate of the recovery stroke in myosin VI. Our analysis suggests that lever-arm re-priming and ATP hydrolysis are only weakly coupled, so that the myosin recovery stroke is initiated by thermal fluctuations and stabilised by nucleotide consumption via a ratchet-like mechanism. Author summary: Myosin is an ATP-powered motor protein that is crucial for cellular functions like muscle contraction, cell division, and the transport of molecular cargos. Understanding how myosin transforms chemical energy from ATP hydrolysis into mechanical work is a central open question in structural bioenergetics, which could guide the design of next-generation synthetic nanomachines. In myosin, ATP hydrolysis is coupled to the re-priming of the lever-arm during the recovery stroke transition. Using advanced molecular dynamics simulations, we described the sequence of events and the energetics at an early stage of the recovery stroke of myosin VI with an unprecedented level of detail. The results support a mechanism in which the re-priming of the mechanical amplifier region of the protein is almost entirely driven by thermal fluctuations and stabilized by ATP hydrolysis. This weakly-coupled mechanism suggests that myosin can "rectify" thermal fluctuations to work efficiently in an isothermal environment dominated by stochastic fluctuations like the cell. [ABSTRACT FROM AUTHOR]

Dissipation in mechanics, optics, acoustics, and electronic circuits is nowadays recognized to be not always detrimental but can be exploited to achieve non-Hermitian topological phases or properties with functionalities for potential device applications, ranging from sensors with unprecedented sensitivity, energy funneling, wave isolators, non-reciprocal signal amplification, to dissipation induced phase transition. As elementary excitations of ordered magnetic moments that exist in various magnetic materials, magnons are the information carriers in magnonic devices with low-energy consumption for reprogrammable logic, non-reciprocal communication, and non-volatile memory functionalities. Non-Hermitian topological magnonics deals with the engineering of dissipation and/or gain for non-Hermitian topological phases or properties in magnets that are not achievable in the conventional Hermitian scenario, with associated functionalities cross-fertilized with their electronic, acoustic, optic, and mechanic counterparts, such as giant enhancement of magnonic frequency combs, magnon amplification, (quantum) sensing of the magnetic field with unprecedented sensitivity, magnon accumulation, and perfect absorption of microwaves. In this review article, we address the unified approach in constructing magnonic non-Hermitian Hamiltonian, introduce the basic non-Hermitian topological physics, and provide a comprehensive overview of the recent theoretical and experimental progress towards achieving distinct non-Hermitian topological phases or properties in magnonic devices, including exceptional points, exceptional nodal phases, non-Hermitian magnonic SSH model, and non-Hermitian skin effect. We emphasize the non-Hermitian Hamiltonian approach based on the Lindbladian or self-energy of the magnonic subsystem but address the physics beyond it as well, such as the crucial quantum jump effect in the quantum regime and non-Markovian dynamics. We provide a perspective for future opportunities and challenges before concluding this article. [ABSTRACT FROM AUTHOR]

Binary neutron star mergers are the first confirmed site of element nucleosynthesis by the rapid neutron-capture process (r -process). The kilonova AT2017gfo is the only electromagnetic counterpart of a neutron star merger spectroscopically observed. We analyse the entire spectral sequence of AT2017gfo (from merger to +10.4 d) and identify seven emission-like features. We confirm that the prominent 1.08  |$\mu{\text{m}}$| feature can be explained by the Sr  ii near-infrared triplet evolving from a P-Cygni profile through to pure emission. We calculate the expected strength of the [Sr  ii ] doublet and show that its absence requires highly clumped ejecta. Near-infrared features at 1.58 and 2.07  |$\mu {\text{m}}$| emerge after three days and become more prominent as the spectra evolve. We model these as optically thick P-Cygni profiles and alternatively as pure emission features (with FWHM ≃ 35 600 ± 6600 km s−1) and favour the latter interpretation. The profile of the strong 2.07  |$\mu {\text{m}}$| emission feature is best reproduced with two lines, centred at 2.059 and 2.135  |$\mu {\text{m}}$|⁠. We search for candidate ions for all prominent features in the spectra. Strong, permitted transitions of La  iii , Ce  iii , Gd  iii , Ra  ii , and Ac  i are plausible candidates for the emission features. If any of these features are produced by intrinsically weak, forbidden transitions, we highlight candidate ions spanning the three r -process peaks. The second r -process peak elements Te and I have plausible matches to multiple features. We highlight the need for more detailed and quantitative atomic line transition data. [ABSTRACT FROM AUTHOR]

We present a microwave mediated two-dimensional (2D) atom localization scheme involving Rydberg states. The localization of Rydberg atoms is realized in terms of the absorption of the optical probe field that connects the ground state with a four-level diamond-like closed-loop formed by two pump fields (producing mutually orthogonal standing-waves) and two microwave fields (which are running waves)-driven atomic transitions. It is observed that the probe laser is absorbed by the cold atoms in 2D plane which forms parallel line, wave-like line, elliptical- and lattice-like patterns. These patterns signify atom localization in 2D space. We have explored the influence of probe detuning, microwave field strength ratios and relative phase between them, van der Waals and dipole–dipole interactions between the atoms in the Rydberg states on the atom localization. The pump strength-to-microwave strength ratios corresponding to the two atomic transition branches, configuring the diamond-like closed-loop is found to affect the localization pattern for different relative phases. Interestingly, the strength ratios of the pump and microwave fields follow a balancing condition when discrete lattice-like patterns appear. This balancing condition is similar to the Wheatstone bridge balance condition for the electrical circuit. Besides, a possible application of this five-level system as a phase-diffraction cross-grating is presented by examining the variation of first-order diffraction intensity w.r.t. the probe detuning and the two microwave field strength ratios. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the dynamic effect of a reservoir computer (RC) on its performance. Modified Kuramoto's coupled oscillators are used to model the RC, and synchronization, Lyapunov spectrum (and dimension), Shannon entropy, and the upper bound of the Kolmogorov–Sinai entropy are employed to characterize the dynamics of the RC. The performance of the RC is analyzed by reproducing the distribution of random, Gaussian, and quantum jumps series (shelved states) since a replica of the time evolution of a completely random series is not possible to generate. We demonstrate that hyperchaotic motion, moderate Shannon entropy, and a higher degree of synchronization of Kuramoto's oscillators lead to the best performance of the RC. Therefore, an appropriate balance of irregularity and order in the oscillator's dynamics leads to better performances. [ABSTRACT FROM AUTHOR]

Understanding the complex behavior of quantum systems, particularly quantum jumping phenomena, is crucial for advancing quantum technologies. This study presents a novel approach that leverages Markov chain modeling to simulate the dynamics of quantum jumping, incorporating random initial state probabilities. The proposed model generates a transition matrix representing the probabilities of transitioning between different quantum states. These transition probabilities are then used to simulate the evolution of the quantum system over discrete time steps. Random initial state probabilities are also generated to capture the inherent uncertainty in the system's initial conditions. Through rigorous simulation, the Markov chain model tracks the probabilities of the quantum system occupying different states over time. The resulting dynamics offer valuable insights into the behavior of quantum jumping phenomena under random initial conditions. Analysis of convergence properties, steady-state behavior, and sensitivity to initial conditions provides further understanding of the underlying dynamics. This research contributes to the broader understanding of quantum phenomena and has practical implications for quantum computing, communication, and sensing. By incorporating random initial state probabilities into the Markov chain model, we gain a more comprehensive understanding of quantum jumping dynamics, paving the way for advancements in quantum technology. [ABSTRACT FROM AUTHOR]

The functionality of atomic quantum emitters is intrinsically linked to their host lattice coordination. Structural distortions that spontaneously break the lattice symmetry strongly impact their optical emission properties and spin-photon interface. Here we report on the direct imaging of charge state-dependent symmetry breaking of two prototypical atomic quantum emitters in mono- and bilayer MoS2 by scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). By changing the built-in substrate chemical potential, different charge states of sulfur vacancies (VacS) and substitutional rhenium dopants (ReMo) can be stabilized. Vac S − 1 as well as Re Mo 0 and Re Mo − 1 exhibit local lattice distortions and symmetry-broken defect orbitals attributed to a Jahn-Teller effect (JTE) and pseudo-JTE, respectively. By mapping the electronic and geometric structure of single point defects, we disentangle the effects of spatial averaging, charge multistability, configurational dynamics, and external perturbations that often mask the presence of local symmetry breaking. The microscopic structure of quantum defects in 2D materials is crucial to understand their optical properties and spin-photon interface. Here, the authors report the direct imaging of charge state-dependent symmetry breaking of sulfur vacancies and rhenium dopants in 2D MoS2, showing evidence of a Jahn-Teller effect. [ABSTRACT FROM AUTHOR]