Atom Superposition Research Articles

Evolution of point defects in pulsed-laser-melted Ge1-x Sn x probed by positron annihilation lifetime spectroscopy

Direct-band-gap Germanium-Tin alloys (Ge1-x Sn x ) with high carrier mobilities are promising materials for nano- and optoelectronics. The concentration of open volume defects in the alloy, such as Sn and Ge vacancies, influences the final device performance. In this article, we present an evaluation of the point defects in molecular-beam-epitaxy grown Ge1-x Sn x films treated by post-growth nanosecond-range pulsed laser melting (PLM). Doppler broadening – variable energy positron annihilation spectroscopy and variable energy positron annihilation lifetime spectroscopy are used to investigate the defect nanostructure in the Ge1-x Sn x films exposed to increasing laser energy density. The experimental results, supported with ATomic SUPerposition calculations, evidence that after PLM, the average size of the open volume defects increases, which represents a raise in concentration of vacancy agglomerations, but the overall defect density is reduced as a function of the PLM fluence. At the same time, the positron annihilation spectroscopy analysis provides information about dislocations and Ge vacancies decorated by Sn atoms. Moreover, it is shown that the PLM reduces the strain in the layer, while dislocations are responsible for trapping of Sn and formation of small Sn-rich-clusters.

Structural Analyses of Substrate-pH Activity Pairing Observed across Diverse Polysaccharide Lyases.

Anionic polysaccharides found in nature are functionally and structurally diverse, and so are the polysaccharide lyases (PLs) that catalyze their degradation. Atomic superposition of various PL folds according to their cleavable substrate structure confirms the occurrence of structural convergence at PL active sites. This suggests that various PL folds have emerged to cleave a particular class of anionic polysaccharide during the course of evolution. Whereas the structural and mechanistic similarity of PL active site has been highlighted in earlier studies, a detailed understanding regarding functional properties of this catalytic convergence remains an open question, especially the role of extrinsic factors such as pH in the context of substrate binding and catalysis. Our earlier structural and functional work on pH directed multisubstrate specificity of Smlt1473 inspired us to regroup PLs according to substrate type to analyze the pH dependence of their catalytic activity. Interestingly, we find that particular groups of substrates are cleaved in a particular pH range (acidic/neutral/basic) irrespective of PL fold, boosting the idea of functional convergence as well. On the basis of this observation, we set out to define structurally and computationally the key constituents of an active site among PL families. This study delineates the structural determinants of conserved "substrate-pH activity pairing" within and between PL families.

Time evolution of quantum correlations induced by atomic state superpositions

In this article, we study the time evolution of Gaussian quantum correlations induced by the superposition of atomic states. Photon-based quantum information and communication are powerful and suitable because the relevant physical mechanisms, the high combination rate of photons, and the sources of coherence can be understood and easily modeled. To this end, coupled photon pairs produced by coherent superposition of atomic states in an atomic laser and influences of spontaneous atomic decay due to vacuum field fluctuations have been considered. The dynamics of the quantum system leads to temporal quantum correlations such as quantum discord, quantum entanglement, and quantum steering, which are treated by the density operator approach. It was found that the generated photon pairs are completely in a separable state in the initial phase of the dynamical processes. The quantum coherences must be given sufficient time to generate quantum correlations that saturate after very short time scales. The strength of these quantum correlations has been improved by increasing the number of superposed atoms per unit of time. In particular, two-way quantum steering, which is a guarantee for the existence of quantum discord and quantum entanglement, can be achieved by increasing the atom injection rate from 10 kHz to 100 kHz when the probability of finding atoms in the excited state is 45%.

Effect of Classical and Quantum Superposition of Atomic States on Quantum Correlations

In this paper, we report the effect of classical and quantum superposition of atomic states on quantum correlations. Coupled photon pairs generated in a ladder quantum beat laser using coherent-induced classical field and atomic state coherent superposition are considered. Once the quantum coherence get sufficient time, it can generate quantum correlations that include quantum discord, quantum entanglement, and quantum steering, which quickly increase with time until they get their maximum strength. Their strength can be improved further by increasing the number of superposed atoms per unit time, selecting an appropriate amplitude of the classical fields, and managing the amount of temperatures and phase fluctuations. In particular, two-way quantum steering, which is a guarantee for the existence of quantum discord and quantum entanglement, can be achieved by increasing the rate of atomic injection from 2 kHz to 25 kHz even if the mean temperature of the heat bath is considered. The maximum achievable strength of quantum correlations is enhanced by increasing the rate of atomic injection and choosing an appropriate parameters of the coherent-induced classical field in the open quantum system which is treated by using the density operator approach.

Transport of ultracold atoms in superpositions of S - and D -band states in a moving optical lattice

Ultracold atoms in a moving optical lattice with high controllability are a feasible platform to research the transport phenomenon. Here, we study the transport process of ultracold atoms at the $D$ band in a one-dimensional optical lattice and manipulate the transport of superposition states with different superposition weights of $S$-band and $D$-band atoms. In the experiment, we first load ultracold atoms into an optical lattice using the shortcut method and then accelerate the optical lattice by scanning the phase of lattice beams. The atomic transport at the $D$ band and $S$ band is demonstrated, respectively. The group velocity of atoms at the $D$ band is opposite to that at the $S$ band. By preparing superposition states with different superposition weights of the $D$-band and $S$-band atoms, we realize the manipulation of atomic group velocity from positive to negative, and observe the quantum interference between atoms at different bands. The influence of the lattice depth and acceleration on the transport process is also studied. Moreover, the multiorbital simulations are coincident with the experimental results. Our paper sheds light on the transport process of ultracold atoms at higher bands in optical lattices and provides a useful method to manipulate the transport of atomic superposition states.

Nanocutting mechanisms of Cu50Zr50 amorphous alloy: A molecular dynamics simulation

Amorphous structures can achieve high mechanical strength and toughness, excellent magnetic properties, anti-corrosion, and anti-friction properties, resulting in their wide applicability, thereby prompting research interest in the role of nanofabrication for amorphous alloys. In this study, the deformation behavior of amorphous alloy Cu50Zr50 during nano cutting was investigated via molecular dynamics simulations. By analyzing the variations of the displacement vector, shear strain, cutting force, and cutting temperature, the removal mechanism of the amorphous alloy material was studied in detail. The amorphous alloy was removed via extrusion during nano cutting. The shear transition zone was formed via the local atomic superposition to form a shear band, and the atoms recovered elastically to form a machined surface. The effects of the cutting depth, cutting speed, and tool angle on the deformation behavior of the material were investigated. The results indicate that the cutting force, cutting temperature, and friction coefficient are increased with an increasing in cutting depth. An appropriate increase in the clearance angle and decrease in the rake angle can reduce the cutting force and friction coefficient. Based on the evolution law of the surface, the plastic transformation of the cutting amorphous alloys was predicted. At the cutting speed of 100–200 m/s, the friction coefficient remained unchanged, which accelerated the formation of a plastic transition zone. For different machining angles, the largest cutting force and surface roughness were obtained at 45°, whereas the least values were obtained at 60°. Therefore, the different machining angle can reduce the cutting forces and improve the quality of the machined surface.

Axion-like dark matter detection using Stern–Gerlach interferometer

Quantum sensors based on the superposition of neutral atoms are promising for sensing the nature of dark matter (DM). In this study, we utilize the Stern–Gerlach (SG) interferometer configuration to seek a novel method for the detection of axion-like particles (ALPs). Using an SG interferometer, we create a spatial quantum superposition of neutral atoms such as ^{3}He and ^{87}Rb. It is shown that the interaction of ALPs with this superposition induces a relative phase between superposed quantum components. We use the quantum Boltzmann equation (QBE) to introduce a first-principles analysis that describes the temporal evolution of the sensing system. The QBE approach employs quantum field theory (QFT) to highlight the role of the quantum nature of the interactions with the quantum systems. The resulting exclusion area demonstrates that our scheme allows for the exclusion of a range of ALP mass in the range 10^{-10}le m_{a}le 10^{2},textrm{eV} and ALP-atom coupling constant in the range 10^{-13}le g_{ae}le 10^{0}.

Quantum metrology by one-minute interrogation of a coherent atomic spatial superposition

Quantum metrology by one-minute interrogation of a coherent atomic spatial superposition

Conformational Variation in Enzyme Catalysis: A Structural Study on Catalytic Residues

Conformational variation in catalytic residues can be captured as alternative snapshots in enzyme crystal structures. Addressing the question of whether active site flexibility is an intrinsic and essential property of enzymes for catalysis, we present a comprehensive study on the 3D variation of active sites of 925 enzyme families, using explicit catalytic residue annotations from the Mechanism and Catalytic Site Atlas and structural data from the Protein Data Bank. Through weighted pairwise superposition of the functional atoms of active sites, we captured structural variability at single-residue level and examined the geometrical changes as ligands bind or as mutations occur. We demonstrate that catalytic centres of enzymes can be inherently rigid or flexible to various degrees according to the function they perform, and structural variability most often involves a subset of the catalytic residues, usually those not directly involved in the formation or cleavage of bonds. Moreover, data suggest that 2/3 of active sites are flexible, and in half of those, flexibility is only observed in the side chain. The goal of this work is to characterise our current knowledge of the extent of flexibility at the heart of catalysis and ultimately place our findings in the context of the evolution of catalysis as enzymes evolve new functions and bind different substrates.

Electrometry of a single resonator mode at a Rydberg-atom–superconducting-circuit interface

The electric-field distribution in a single mode of a $\ensuremath{\lambda}/4$ superconducting coplanar waveguide (CPW) microwave resonator has been probed using beams of helium Rydberg atoms. In the experiments the atoms were prepared in the $1\mathrm{s}55\mathrm{s}{\phantom{\rule{0.16em}{0ex}}}^{3}{\mathrm{S}}_{1}$ Rydberg level by laser photoexcitation. They then traveled over the CPW resonator that was fabricated on a NbN superconducting chip operated at 3.8 K. The resonator was driven at its third-harmonic frequency, near resonant with the two-photon $1\mathrm{s}55\mathrm{s}{\phantom{\rule{0.16em}{0ex}}}^{3}{\mathrm{S}}_{1}\ensuremath{\rightarrow}1\mathrm{s}56\mathrm{s}{\phantom{\rule{0.16em}{0ex}}}^{3}{\mathrm{S}}_{1}$ transition at ${\ensuremath{\omega}}_{55\mathrm{s},\phantom{\rule{0.16em}{0ex}}56\mathrm{s}}/2=2\ensuremath{\pi}\phantom{\rule{0.16em}{0ex}}\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0.16em}{0ex}}19.556\phantom{\rule{0.16em}{0ex}}499$ GHz. The coherence times of the atom--resonator-field interaction were determined at selected locations above the resonator by time-domain measurements of Rabi oscillations and found to be up to $0.8\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{s}$ for Rabi frequencies of $\ensuremath{\sim}2\ensuremath{\pi}\phantom{\rule{0.16em}{0ex}}\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0.16em}{0ex}}3$ MHz. The coherence times of the atomic superposition states, generated following the interaction of the atoms with the microwave field in the resonator, were inferred from high-resolution cavity-enhanced Ramsey spectra to be $\ensuremath{\sim}2.5\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{s}$. These Ramsey spectra also allowed the measurement of residual uncanceled dc electric fields of $26.6\ifmmode\pm\else\textpm\fi{}0.6$ mV/cm at the position of the atoms $\ensuremath{\sim}300\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$ above the surface of the superconducting chip. These results represent an essential step toward applications of hybrid systems, comprising Rydberg atoms coherently coupled to superconducting microwave circuits, in quantum optics and quantum information processing.

Atomic Spacetime Model Based on Atomic AString Functions

A novel model of spacetime and fields atomization based on Atomic Series over finite Atomic AString Functions is offered. Formulated Atomization Theorems allow representing polynomials, analytic functions, and solutions of field equations including General Relativity via superposition of solitonic atoms which can be associated with flexible spacetime quantum, metriants, or elementary distortions. Spacetime is conceptualized as a lattice of flexible Atomic Solitons adjusting locations to reproduce different metrics and other physical fields. It may offer the variants of unified field theory based on Atomic Solitons where, like in string theory, fields become interconnected having a common mathematical ancestor.

Regulation of Cr3+ doping on the defect characteristics and magnetic order in the CuFe1-xCrxO2 ceramics

ABSTRACT The defect characteristic and magnetic properties of CuFe1-x Cr x O2 (x = 0.0–0.4) compounds have been investigated in detail. The results demonstrate that Cr3+ ions enter into the CuFeO2 lattice sites and induce local lattice contraction but do not change the valance state of Cu+ and Fe3+ ions. We calculate the positron annihilation lifetime in the bulk and vacancy defect trapping states by the atomic superposition method in 3 × 3 × 1 CuFeO2 super-cell. Combined with theoretical calculation results, the positron annihilation results indicate that the positrons are mainly annihilated in vacancy clusters in CuFe1-x Cr x O2. The substitution of Cr3+ for Fe3+ ions decreases the open volume and increases the concentration of vacancy defects but does not change the integral defect surroundings at annihilation sites. Magnetization measurements manifest that doping with Cr3+ reduces the antiferromagnetic transition temperature and promotes the formation of short-range magnetic correlation. Meanwhile, the enhanced short-range magnetic correlation in Cr3+-doped CuFeO2 is more readily driven by thermal activation energy and a faster dynamic behavior can be seen in time windows.

Transcoherent States: Optical States for Maximal Generation of Atomic Coherence

Quantum technologies are built on the power of coherent superposition. Atomic coherence is typically generated from optical coherence, most often via Rabi oscillations. However, canonical coherent states of light create imperfect resources; a fully-quantized description of "$\tfrac{\pi}{2}$ pulses" shows that the atomic superpositions generated remain entangled with the light. We show that there are quantum states of light that generate coherent atomic states perfectly, with no residual atom-field entanglement. These states can be found for arbitrarily short times and approach slightly-number-squeezed $\tfrac{\pi}{2}$ pulses in the limit of large intensities; similar ideal states can be found for any $(2k+1)\tfrac{\pi}{2}$ pulses, requiring more number squeezing with increasing $k$. Moreover, these states can be repeatedly used as "quantum catalysts" to successfully generate coherent atomic states with high probability. From this perspective we have identified states that are "more coherent" than coherent states.

Asymmetries in ionization of atomic superposition states by ultrashort laser pulses

Progress in ultrafast science allows for probing quantum superposition states with ultrashort laser pulses in the new regime where several linear and nonlinear ionization pathways compete. Interferences of pathways can be observed in the photoelectron angular distribution and in the past they have been analyzed for atoms and molecules in a single quantum state via anisotropy and asymmetry parameters. Those conventional parameters, however, do not provide comprehensive tools for probing superposition states in the emerging research area of bright and ultrashort light sources, such as free-electron lasers and high-order harmonic generation. We propose a new set of generalized asymmetry parameters which are sensitive to interference effects in the photoionization and the interplay of competing pathways as the laser pulse duration is shortened and the laser intensity is increased. The relevance of the parameters is demonstrated using results of state-of-the-art numerical solutions of the time-dependent Schrödinger equation for ionization of helium atom and neon atom.

Quantized Constant-Q Gabor Atoms for Sparse Binary Representations of Cyber-Physical Signatures.

Increased data acquisition by uncalibrated, heterogeneous digital sensor systems such as smartphones present new challenges. Binary metrics are proposed for the quantification of cyber-physical signal characteristics and features, and a standardized constant-Q variation of the Gabor atom is developed for use with wavelet transforms. Two different continuous wavelet transform (CWT) reconstruction formulas are presented and tested under different signal to noise ratio (SNR) conditions. A sparse superposition of Nth order Gabor atoms worked well against a synthetic blast transient using the wavelet entropy and an entropy-like parametrization of the SNR as the CWT coefficient-weighting functions. The proposed methods should be well suited for sparse feature extraction and dictionary-based machine learning across multiple sensor modalities.

Quantum reversibility in cooperative interaction of the atom system with bi-modal cavity field in Raman conversion

The restoration of the initial state in the Raman interaction of the two atoms with the quantified pump and Stokes (anti-Stokes) cavity modes is analytically obtained. For this the su (2) symmetry representation of the bimodal field and a system of two atoms in scattering interaction is proposed for the simplification of the problem. Using the proprieties of the generators su (2) algebra the exact non-stationary solution of the system of two atoms in interaction with the bimodal field is found, taking into consideration the initial disentangled state between the atomic and field superposition. It is demonstrated that after this collapse and revivals of the inversion of flying atoms in the processes of absorption and emission of the photons from Stokes and pump modes the system atoms and field becomes entangled. The conditions of the restoration of the initial state of the atom-field system were established as a function of the flying time through the resonator possible. A set of discrete flying time intervals for the restoration of the initial disentangled state was found.

An Atomic Sensor for Direct Detection of Weak Microwave Signals

This paper demonstrates direct detection of weak signals at microwave frequencies based on parametric frequency conversion. The atomic medium is optically pumped by a resonant light field and prepared in a coherent atomic superposition by a weak microwave field. The coherent atomic superposition causes a parametric modulation of the polarization of a probe light field at the microwave field frequency. An upper limit magnetic field component sensitivity of 1.2(1.0) pT/Hz1/2, corresponding to 3.7(3.1)- $\mu $ V/cm/Hz1/2 electric field component sensitivity, is achieved at ~6.835 GHz with a 33-mm3 vapor cell.

Valley splitting in the van der Waals heterostructure WSe2/CrI3 : The role of atom superposition

A recent experiment shows that the ${K}^{\ensuremath{'}}K$ valley degeneracy can be lifted in monolayer ${\mathrm{WSe}}_{2}$ deposited on a layered ferromagnetic substrate of ${\mathrm{CrI}}_{3}$. In this work, we take a van der Waals heterostructure ${\mathrm{WSe}}_{2}/{\mathrm{CrI}}_{3}$ to model the monolayer ${\mathrm{WSe}}_{2}$ on the ${\mathrm{CrI}}_{3}$ substrate and investigate the effects underpinning the ${K}^{\ensuremath{'}}K$ valley splitting based on first-principles calculations. We demonstrate that the interfacial atom superposition plays an important role and a W-Cr superposition is essential for a relatively large valley splitting. The results indicate inevitable sample-to-sample variations in the ${K}^{\ensuremath{'}}K$ valley splitting in the ${\mathrm{WSe}}_{2}/{\mathrm{CrI}}_{3}$. Furthermore, we show that the ${K}^{\ensuremath{'}}K$ valley splitting can be tuned in the trilayer ${\mathrm{CrI}}_{3}/{\mathrm{WSe}}_{2}/{\mathrm{CrI}}_{3}$ from nearly zero to more than two times of that in the bilayer ${\mathrm{WSe}}_{2}/{\mathrm{CrI}}_{3}$ by manipulating the layer alignment.

Quantum tunneling of composite object coupled with quantized radiation field

We study quantum tunneling of a composite object, which has a dipole or quadrupole moment coupled with quantized (photon or gravitational) radiation field, through a potential barrier. The dipole or quadrupole moment is represented by an oscillator in the relative coordinate of two constituent particles of the object. The center of mass degrees of freedom of the object is not directly coupled with the radiation field. However, we show that, for the object with the oscillator in the excited state, dissipation caused by the radiation field can suppress its quantum tunneling rate in the center of mass degrees of freedom. In addition, when the initial energy of its center of mass motion is similar to that of the excited state of the oscillator, a spatial superposition state of the object prepared by the barrier can decohere due to the radiation field. The main purpose of this article is to investigate how two different interplays (i) among the center of mass, the relative coordinate degrees of freedom and the potential barrier, and (ii) between the relative coordinate degrees of freedom and the radiation field, can affect the quantum tunneling and the creation of the spatial superposition state of the object. Our toy model can give insight into tests of quantum tunneling and quantum superposition of atoms or molecules with its dipole or quadrupole moment coupled with the radiation field.

Evolución de correlaciones cuánticas de dos qubits en una cavidad con disipación bifotónica

En este trabajo se estudia la evolución de correlaciones cuánticas en un modelo Tavis-Cummings que consta de dos qubits y un único modo cuantizado del campo electromagnético. Se consideran procesos de emisión/absorción de un sólo fotón y de dos fotones correlacionados, para cada uno de los qubits. El modelo se estudia teniendo en cuenta disipaciones unifotónicas y bifotónicas, a través de una cavidad que interactúa con un reservorio térmico. La solución numérica de una ecuación maestra Lindblad nos permite realizar una descripción de la evolución de las correlaciones cuánticas, entrelazamiento cuántico y discordia cuántica, en función del tiempo para un estado atómico tipo superposición. Se muestra que los diferentes resultados de las correlaciones cuánticas, presentan comportamientos cualitativamente diferentes en su evolución.