State preparation and block encoding are essential subroutines in quantum computing. The former provides basic encoding of quantum states, while the latter transforms classical data into a matrix representation within a quantum circuit. Some quantum advantages are built on the assumption that the block-encoding subroutine has been compiled in the quantum circuit, and this derives a problem of how to efficiently compile a block encoding. The resource tradeoffs of block encoding, such as circuit size, subnormalization factor, compilation complexity (both time and space), and robustness against errors, are central to its efficiency. In this work, the binary tree block-encoding (<monospace>BITBLE</monospace>) protocol is introduced, which optimizes these tradeoffs. For a classical matrix in <inline-formula><tex-math notation="LaTeX">$\mathbb {C}^{2^{n}\times 2^{n}}$</tex-math></inline-formula>, our approach reduces the compilation time to <inline-formula><tex-math notation="LaTeX">$\mathcal {O}(n2^{2n})$</tex-math></inline-formula> using <inline-formula><tex-math notation="LaTeX">$n$</tex-math></inline-formula> ancilla qubits, achieving superior resource tradeoffs compared to existing methods. Numerical experiments further reveal that the approach outlined in <monospace>BITBLE</monospace> enhances compilation efficiency, resource scalability, and robustness against single-qubit gate errors in various standard data encoding tasks. Moreover, all algorithms are available as open source.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Abstract Metallic strontium titanate (SrTiO3) is known to have both normal-state and superconducting properties that strongly vary over a wide range of charge carrier densities, but the complex interplay between lattice and electronic degrees of freedom has hindered the development of a clear qualitative description of the observed behavior. A major challenge is to understand how the charge carriers themselves evolve with doping and temperature, with possible polaronic effects and evidence of an effective mass that strongly increases with temperature. Here we use 47,49Ti nuclear magnetic resonance (NMR) to perform a comprehensive study of the electronic spin susceptibility in the metallic state of strontium titanate across the doping-temperature phase diagram. We find a temperature-dependent Knight shift that can be quantitatively understood within a nondegenerate Fermi gas model that fully takes into account the complex band structure of SrTiO3. Our data are consistent with a temperature-independent effective mass, and we show that the behavior of the spin susceptibility is universal in a wide range of temperatures and carrier concentrations. These results provide a microscopic foundation for the understanding of the properties of the unconventional low-density metallic state in strontium titanate and related materials.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
Abstract Shastry-Sutherland magnet is a typical frustrated spin system hosting rich phases. While the Heisenberg limit has been extensively studied, the role of spin-orbit coupling is not well explored. Motivated by newly discovered rare-earth Shastry-Sutherland magnets, we construct a generic effective-spin model that describes the interactions between Kramers doublet local moments on a Shastry-Sutherland lattice. Due to the strong spin-orbit coupling, the model takes the form of extended XYZ interactions on both intra- and inter-dimer bonds. We show that, in addition to the conventional “singlet” dimer phase, strong spin-orbit coupling can stabilize peculiar “triplet” dimer phases. These “triplet” dimer phases, though fully gapped, respond immediately to magnetic fields and evolve smoothly into the fully polarized phase. We present that the recently discovered Shastry-Sutherland magnet Yb2Be2GeO7 belongs to the “triplet” dimer phase, and discuss the implication of our results to a broad class of quantum magnets in general.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
The problem of electromagnetic wave propagation in a plasma cylinder with a cylindrical cavity along the axis is considered. In the axial direction, the tubular discharge under consideration is limited by conductive walls. The problem is reduced to a system of six differential equations for complex field amplitudes and, with the remainder, to a fourth-order differential equation with the Bessel operator and the square of this operator for the longitudinal complex amplitude of the electric field in the plasma. This equation (by derivation) assumes a homogeneous plasma (the components of the permittivity tensor do not depend on the radius). But there is another (more general) equation for inhomogeneous plasma that is suitable for its solution by the finite difference method. However, the transition to finite differences gives very cumbersome expressions, which force us to limit ourselves to an analytical solution of the problem with a tubular discharge only in the case of a homogeneous plasma.
Atomic physics. Constitution and properties of matter
Yueguang Zhou, George Kountouris, Yujing Wang
et al.
We theoretically propose a single-photon source design based on a circular Bragg grating microcavity incorporating two air triangles in a bowtie configuration. Our proposed design allows for extreme light confinement with a Purcell factor of approximately 166 with a bandwidth of ~9 nm for a triangle separation of 5 nm combined with a collection efficiency above 80 $\%$ . The Purcell factor is enhanced by a factor of 8 relative to the reference cavity thanks to the reduction of the mode volume. Furthermore, we demonstrate the critical role of the dipole emitter polarization orientation and spatial position in achieving optimal Purcell enhancement.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Abstract Atomic transport properties specifically the shear viscosity and the diffusion coefficient for Zn x Bi 1 − x liquid monotectic segregating alloys are theoretically investigated by using the Rice–Allnatt theory. The essential ingredient for the microscopic description of the metals and their alloys is the interionic interaction which in the present work is described by a widely used local pseudopotential. The temperature dependent behaviour of the above mentioned physical properties is also examined. The overall agreement of our calculated results with the available experimental data is found to be good for the full range of concentration. More interestingly, the temperature dependent results for the viscosity and the diffusion coefficient apparently exhibit a signature of liquid–liquid phase separation through a sudden bending in their concentration dependent profiles. Onset of this bending also provides information about the critical temperature and the critical concentration, and also provides a value for the critical exponent of liquid–liquid phase separation.
We report on the development and characterization of superconducting damascene tantalum nitride (TaN) nanowires, 100 nm–3 <italic>μ</italic>m wide, with TaN thicknesses varying from 5 to 35 nm, using 193-nm optical lithography and chemical mechanical planarization among other 300-mm wafer-scale processes. The TaN film composition chosen for nanowire fabrication was informed by a detailed study of unpatterned TaN films with varying nitrogen to tantalum ratios, formed by reactive sputtering. We also discuss the influence of encapsulation by copper and disordered atomic layer deposited TaN on the critical current of superconducting nanowires. Superconducting critical current density (measured at 12 mK) ranges from 0.12 to 0.85 MA/cm<sup>2</sup> depending on nanowire width and film thickness. The potential of ultrathin TaN nanowires at 300-mm scale is discussed in the context of applications such as on-chip integration for readout of superconducting qubits, in single-photon detection for quantum computing, as well as in large single-photon detecting focal plane arrays for cosmology in a broader range of wavelengths.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Solid-state deuterium NMR is well suited to the study of the conformational dynamics of DNA. Deuterium quadrupole echo spectra for a particular motional model can be calculated and matched to the experimental spectrum to extract information on the DNA dynamics; however, doing so can be very time-intensive. The two-axis motion used to model the dynamics of either 2″ or 5′/5″ furanose ring deuteron is particularly complex with up to ten independent variables that can be optimized. Here, we present a program which automates both the input script generation and searches the parameter space for the best fit using a simulated annealing algorithm. The parameter, χred2, provides a relative measure of goodness of fit. This method reduces the overall time to determine the best fit of a line shape to a few days, in most cases, when running on a low-power desktop PC. The automated fitting program presented here can be easily modified to generate input scripts for new models, incorporate a weighting factor to the χred2 calculation to emphasize key line shape features, or fit nonsymmetrized data. This adaptable program will make simulation of solid-state deuterium spectra accessible to a broader audience.
Medical physics. Medical radiology. Nuclear medicine, Atomic physics. Constitution and properties of matter
It is important for the design of a distributed quantum circuit (DQC) to minimize the communication cost in <italic>k</italic>-way balanced partitioning. In this article, given an original quantum circuit (QC), a partitioning number <italic>k</italic>, the maximum capacity δ inside each partition, and the maximum size tolerance γ between two partitions, a new <italic>k</italic>-way (δ, γ)-balanced partitioning problem can be formulated as a <italic>k</italic>-way partitioning problem under the capacity constraint δ and the size-tolerance constraint γ, and a fuzzy-based partitioning algorithm can be proposed to minimize the communication cost in <italic>k</italic>-way (δ, γ)-balanced partitioning for a DQC design. First, an edge-weighted connection graph can be constructed from the gates in a given QC. Furthermore, based on the estimation of the probabilistic connection strength between two vertices in the connection graph and the <italic>initial k-way</italic> partitioning result in the connection graph, the fuzzy memberships on <italic>k</italic> clusters can be generated in fuzzy <italic>k</italic>-means graph clustering. Finally, based on the fuzzy memberships on <italic>k</italic> clusters in the connection graph, the maximum capacity inside each partition, and the maximum size tolerance between two partitions, all the vertices in the connection graph can be assigned onto <italic>k</italic> partitions to minimize the communication cost in <italic>k</italic>-way (δ, γ)-balanced partitioning. Compared with Daei's recursive Kernighan–Lin-based algorithm in four-way balanced partitioning, the experimental results show that the proposed fuzzy-based partitioning algorithm with three size-tolerance constraints γ = 1, γ = 2, and γ = 3 can use 58.3%, 61.3%, and 64.5% of CPU time to reduce 16.1%, 21.2%, and 24.6% of the communication cost for the eight tested circuits on the average, respectively. Compared with the modified partitioning algorithm from Dadkhah's partitioning algorithm in three-way, four-way, or five-way balanced partitioning, the experimental results show that the proposed fuzzy-based partitioning algorithm with the size-tolerance constraint γ = 3 can use 35.0% of CPU time to reduce 11.1% of the communication cost for the eight tested circuits on the average, respectively.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Abstract Interplay of magnetism and electronic band topology in unconventional magnets enables the creation and fine control of novel electronic phenomena. In this work, we use scanning tunneling microscopy and spectroscopy to study thin films of a prototypical kagome magnet Fe3Sn2. Our experiments reveal an unusually large number of densely-spaced spectroscopic features straddling the Fermi level. These are consistent with signatures of low-energy Weyl fermions and associated topological Fermi arc surface states predicted by theory. By measuring their response as a function of magnetic field, we discover a pronounced evolution in energy tied to the magnetization direction. Electron scattering and interference imaging further demonstrates the tunable nature of a subset of related electronic states. Our experiments provide a direct visualization of how in-situ spin reorientation drives changes in the electronic density of states of the Weyl fermion band structure. Combined with previous reports of massive Dirac fermions, flat bands, and electronic nematicity, our work establishes Fe3Sn2 as an interesting platform that harbors an extraordinarily wide array of topological and correlated electron phenomena.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
Timothee Goubault de Brugiere, Marc Baboulin, Benoit Valiron
et al.
In quantum computing the decoherence time of the qubits determines the computation time available, and this time is very limited when using current hardware. In this article, we minimize the execution time (the depth) for a class of circuits referred to as linear reversible circuits, which has many applications in quantum computing (e.g., stabilizer circuits, “CNOT+T” circuits, etc.). We propose a practical formulation of a divide-and-conquer algorithm that produces quantum circuits that are twice as shallow as those produced by existing algorithms. We improve the theoretical upper bound of the depth in the worst case for some range of qubits. We also propose greedy algorithms based on cost minimization to find more optimal circuits for small or simple operators. Overall, we manage to consistently reduce the total depth of a class of reversible functions, with up to 92% savings in an ancilla-free case and up to 99% when ancillary qubits are available.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
The advent of noisy intermediate-scale quantum (NISQ) devices provide crucial promise for the development of quantum algorithms. Variational quantum algorithms have emerged as one of the best hopes to utilize NISQ devices. Among these is the famous variational quantum eigensolver (VQE), where one trains a parameterized and fixed quantum circuit (or an ansatz) to accomplish the task. However, VQE also suffers from some serious challenges, which are training difficulty and accuracy reduction due to deep quantum circuit and hardware noise. Motivated by these issues, we propose a runtime and resource-efficient scheme, Monto Carlo tree (MCT) search-based quantum circuit architecture optimization, where the ansatz is built in the variable form. Our approach first models the search space with a MCT and regards it as a supernet, where we make use of layers dependence to reduce the size of the search space. Second, a two-stage scheme is proposed for the search space training, where weight sharing and warm-up strategies are employed to avoid huge computation cost. Training results are stored in nodes of the MCT for future decisions, and hierarchical node selection is presented to obtain an optimal ansatz. As a proof of principle, we carry out a series of numerical experiments for condensed matter and quantum chemistry in a quantum simulator with and without noise. Consequently, our scheme can be efficient to mitigate trainability and accuracy issues by minimizing the ansatz depth and the number of entanglement gates.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
The results of experimental determination of the forms of uranium and radionuclides 90Sr, 137Cs, 154Eu, 238Pu, 239+240Pu, 241Am, and 244Cm in the bottom sediments of the premises 001/3 of the "Shelter" object are presented. By the sequential extraction procedure, the following amounts are determined: water-soluble, exchange, carbonate, and acid-soluble forms of uranium, fission products (90Sr, 137Cs, 154Eu), and transuranium elements (238Pu, 239+240Pu, 241Am, 244Cm) in the bottom sediments in the premises 001/3 on a mark of -2.60 m of auxiliary systems of the reactor compartment of the "Shelter" object. The concentration of uranium in the bottom sediments of room 001/3 is 3.1 ± 0.5 g/kg. Specific activity of 90Sr, 137Cs in the bottom sediments is within the range of 6·108 - 1·109 Bq/kg, and 239+240Pu and 241Am within the range of 6·105 - 8·106 Bq/kg. Radionuclides 90Sr, 137Cs, 154Eu, 238Pu, 239+240Pu, 241Am, 244Сm in the bottom sediments are in different chemical forms that will define their different potential mobility. Uranium and 137Cs in the bottom sediments of premises 001/3 mainly are in exchange forms. The amount of water-soluble forms of uranium and cesium is 1.5 - 3 %. The basic amount of 90Sr, more than 60 %, is carbonate soluble in a weak acid at рН 4.8. More than 65 % of 238Pu and 239+240Pu in the bottom sediments are in acid-soluble forms. The mobility of 154Eu, 241Am and 244Cm in the bottom sediments is much higher than that of plutonium; at pH 4.8 more than 40 % of 241Am go to soluble state. The ratio between the activities of 137Cs/90Sr, 90Sr/239+240Pu, 241Am/239+240Pu, and 244Cm/239+240Pu in the bottom sediments considerably differ from the analogical relations of radionuclides in a fuel containing materials of the "Shelter" object.
Atomic physics. Constitution and properties of matter
Changes of the 137Cs and 40K content during a year in the plants of forest ecosystems were investigated on the territory of the "Paryshev" sampling area (the Chornobyl NPP exclusion zone). One- and two-year-old needles and branches of P. sylvestris were used as objects of study. Samples were se-lected at intervals of 1 time every two weeks during 2014 and 2015. As a result of the research, it was found that the magnitude of the specific activity of 137Cs and 40K in the needles and branches of P. sylvestris is not constant, but leaped during the year. It has been suggested that fluctuations in the concentrations of activity of these radionuclides in the studied organs of P. sylvestris are associated with their circulation in the chain "soil - fungus-symbiotroph - plant". The correlation coefficients R within 0.5 - 0.68 indicate the existence of direct and moderate relationship between fluctuations in the concentration of 40K and 137Cs activity in the needles and branches of P. sylvestris throughout the year. Probably, the mechanisms of absorption and escape of these radionuclides in P. sylvestris are similar. The content of 40K in the researched organs is higher than the content of 137Cs. It can be connected to the ability of the mycorrhiza to hold radiocaesium (to be a barrier) and to the selective accumulation of potassium by the plant.
Atomic physics. Constitution and properties of matter
Paper is devoted to the development of the mathematical model and analysis of the problem of corium melt interaction with low-temperature melting blocks in the passive protection systems against severe accidents at the NPP, which is of high importance for substantiation of the nuclear power safety, for building and successful op-erating of passive protection systems. In the third-generation reactors passive protection systems against severe accidents at the NPP are mandatory, therefore this paper is of importance for the nuclear power safety. A few configurations for the cooling blocks’ distribution have been considered and an analysis of the blocks’ melting and corium’s cooling in the pool under reactor vessel have been done, which can serve more effective for further improvement of the safety current systems and for the development of new ones. The ways for solution of the problems and the methods for their successful elaboration were discussed. The developed mathematical models and the analysis performed in the paper might be helpful for the design of passive protection systems of the cori-um melt retention inside the containment after corium melt eruption from the broken reactor vessel.
Atomic physics. Constitution and properties of matter
Condensed matter: Creating black holes in materials A material that mimics the behavior of a black hole is developed by researchers in China and Singapore. Yugui Yao from the Beijing Institute of Technology and colleagues show that mechanical strain in a material known as Dirac semimetal can imitate the warping of space–time predicted by general relativity. Simulations of the Universe predict a wide range of counter-intuitive phenomenon. But many of these are beyond state-of-the-art technology to detect. Instead, scientists can engineer materials that are governed by equations similar to those that define astrophysical phenomena. Yao et al. investigate Dirac semimetals whose electronic bandstructure gives rise to massless quasiparticles that resemble relativistic particles. They show that altering the uniaxial strain enables control over these quasiparticles so that they emulate the behavior associated with black and white holes, event horizons and gravitational lensing.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
In the laboratory experiments the parameters of radiological effectiveness of countermeasures such as sanding, adding of ferrocyanides and ferrocyanides-bentonite sorbent into the peat-bog soils of Rokytne district of Rivne region, which are characterized by an abnormally high transfer of 137Cs from soil to plants were estimated. The applied countermeasure efficiencies are presented during 26 months of the vegetation period.
Atomic physics. Constitution and properties of matter
A semi-classical approximation is applied to the calculations of single-particle and statistical level densities in excited nuclei. Landau's conception of quasi-particles with the nucleon effective mass m* < m is used. The approach provides the correct description of the continuum contribution to the level density for realistic finite-depth potentials. It is shown that the continuum states does not affect significantly the thermodynamic calculations for sufficiently small temperatures T ≤ 1 MeV but reduce strongly the results for the excitation energy at high temperatures. By use of standard Woods - Saxon potential and nucleon effective mass m* = 0.7m the A-dependency of the statistical level density parameter K was evaluated in a good qualitative agreement with experimental data.
Atomic physics. Constitution and properties of matter