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

Martin Mootz, Yong-Xin Yao

We present an adaptive variational quantum algorithm to estimate the Berry phase accumulated by a nondegenerate ground state under cyclic, adiabatic evolution of a time-dependent Hamiltonian. Our method leverages cyclic adiabatic evolution of the Hamiltonian and employs adaptive variational quantum algorithms for state preparation and evolution, optimizing circuit efficiency while maintaining high accuracy. We benchmark our approach on dimerized Fermi–Hubbard chains with four sites, demonstrating precise Berry phase simulations in both noninteracting and interacting regimes. Our results show that circuit depths reach up to 106 layers for noninteracting systems and increase to 279 layers for interacting systems due to added complexity. In addition, we demonstrate the robustness of our scheme across a wide range of parameters governing adiabatic evolution and variational algorithms. These findings highlight the potential of adaptive variational quantum algorithms for advancing quantum simulations of topological materials and computing geometric phases in strongly correlated systems.

Lorenzo Cavicchi, Koen J. A. Reijnders, Mikhail I. Katsnelson et al.

Y. Xing, R. Namba, K. Imamura et al.

Abstract The layered honeycomb magnet α-RuCl3 has emerged as a promising candidate for realizing a Kitaev quantum spin liquid. Previous studies have reported oscillation-like anomalies in the longitudinal thermal conductivity and half-integer quantized thermal Hall conductivity above the antiferromagnetic critical field H c , generating significant interest. However, the origins of these phenomena remain contentious due to strong sample dependence. Here we re-examine the magnetothermal transport properties using recently available ultra-pure α-RuCl3 single crystals to further elucidate potential signatures of the spin liquid state. Our findings reveal that while anomalies in thermal conductivity above H c persist even in ultraclean crystals, their magnitude is significantly attenuated, contrary to the quantum oscillations hypothesis. This suggests that the anomalies are likely attributable to localized stacking faults inadvertently introduced during magnetothermal transport measurements. The thermal Hall conductivity exhibits a half-quantized plateau, albeit with a narrower width than previously reported. This width reduction can be understood through two distinct mechanisms: sample-dependent magnetic critical fields that influence the lower boundary of the plateau region, and the decoupling between chiral Majorana edge currents and phononic thermal transport that determines the upper boundary. These results indicate that structural imperfections exert a substantial influence on both the oscillation-like anomalies and quantization effects observed in magnetothermal transport measurements of α-RuCl3.

C. R. Das

Elijah Pelofske, Andreas Bartschi, Stephan Eidenbenz et al.

Quantum information cannot be perfectly cloned, but approximate copies of quantum information can be generated. Quantum telecloning combines approximate quantum cloning, more typically referred to as quantum cloning, and quantum teleportation. Quantum telecloning allows approximate copies of quantum information to be constructed by separate parties, using the classical results of a Bell measurement made on a prepared quantum telecloning state. Quantum telecloning can be implemented as a circuit on quantum computers using a classical coprocessor to compute classical feedforward instructions using if statements based on the results of a midcircuit Bell measurement in real time. We present universal symmetric optimal <inline-formula><tex-math notation="LaTeX">$1 \rightarrow M$</tex-math></inline-formula> telecloning circuits and experimentally demonstrate these quantum telecloning circuits for <inline-formula><tex-math notation="LaTeX">$M=2$</tex-math></inline-formula> up to <inline-formula><tex-math notation="LaTeX">$M=10$</tex-math></inline-formula>, natively executed with real-time classical control systems on IBM Quantum superconducting processors, known as dynamic circuits. We perform the cloning procedure on many different message states across the Bloch sphere, on seven IBM Quantum processors, optionally using the error suppression technique X&#x2013;X sequence digital dynamical decoupling. Two circuit optimizations are utilized: one that removes ancilla qubits for <inline-formula><tex-math notation="LaTeX">$M=2, 3$</tex-math></inline-formula>, and one that reduces the total number of gates in the circuit but still uses ancilla qubits. Parallel single-qubit tomography with maximum likelihood estimation density matrix reconstruction is used in order to compute the mixed-state density matrices of the clone qubits, and clone quality is measured using quantum fidelity. These results present one of the largest and most comprehensive noisy intermediate-scale quantum computer experimental analyses on (single qubit) quantum telecloning to date. The clone fidelity sharply decreases to 0.5 for <inline-formula><tex-math notation="LaTeX">$M &gt; 5$</tex-math></inline-formula>, but for <inline-formula><tex-math notation="LaTeX">$M=2$</tex-math></inline-formula>, we are able to achieve a mean clone fidelity of up to 0.79 using dynamical decoupling.

Jian-Rui Soh, Irián Sánchez-Ramírez, Xupeng Yang et al.

Abstract In the rapidly expanding field of topological materials there is growing interest in systems whose topological electronic band features can be induced or controlled by magnetism. Magnetic Weyl semimetals, which contain linear band crossings near the Fermi level, are of particular interest owing to their exotic charge and spin transport properties. Up to now, the majority of magnetic Weyl semimetals have been realized in ferro- or ferrimagnetically ordered compounds, but a disadvantage of these materials for practical use is their stray magnetic field which limits the minimum size of devices. Here we show that Weyl nodes can be induced by a helical spin configuration, in which the magnetization is fully compensated. Using a combination of neutron diffraction and resonant elastic x-ray scattering, we find that below T N = 14.5 K the Eu spins in EuCuAs develop a planar helical structure which induces two quadratic Weyl nodes with Chern numbers C = ±2 at the A point in the Brillouin zone.

Jean Bellissard

Bo Yang, Chenxiao Zhao, Bing Xia et al.

Abstract Introducing superconductivity into two-dimensional (2D) films with nontrivial topology has been intensively pursued as one of the feasible scenarios to realize 1D topological superconductor. Prevailing endeavors mostly exploit the external gating or proximity effect of a traditional superconductor, by which the critical temperatures ( T c $T_{\mathrm{c}}$ ) are limited to several Kelvin range. Here, we report on the discovery of interface-enhanced superconductivity in monolayer 1T′-MoTe2 film. A thermally driven phase transition from Mo6Te6 nanowires to 1T′-MoTe2 films, grown on SrTiO3(001) surface by the molecular beam epitaxial methods, is demonstrated. A combined study of scanning tunneling microscopy/spectroscopy, electrical transport and magnetization measurements indicates the T c $T_{\mathrm{c}}$ of MoTe2 film is around 30 K, two orders of magnitude larger than its 3D counterpart crystal. This study shows that interfacial engineering is an efficient way to tune monolayer 1T′-MoTe2 film into superconducting states, and thus may pave the way toward higher- T c $T_{\mathrm{c}}$ 1D intrinsic topological superconductivity.

Shang-Wei Lien, Ion Garate, Utkarsh Bajpai et al.

Abstract Nontrivial band topologies in semimetals lead to robust surface states that can contribute dominantly to the total conduction. This may result in reduced resistivity with decreasing feature size contrary to conventional metals, which may highly impact the semiconductor industry. Here we study the resistivity scaling of a representative topological semimetal CoSi using realistic band structures and Green’s function methods. We show that there exists a critical thickness d c dividing different scaling trends. Above d c , when the defect density is low such that surface conduction dominates, resistivity reduces with decreasing thickness; when the defect density is high such that bulk conduction dominates, resistivity increases as in conventional metals. Below d c where bulk states are depopulated, the persistent Fermi-arc remnant states give rise to decreasing resistivity down to the ultrathin limit, unlike topological insulators. The observed CoSi scaling can apply to broad classes of topological semimetals, providing guidelines for materials screening in back-end-of-line interconnect applications.

Qing Zhou, Songfeng Lu

We propose a Quantum inspired Hash Function using controlled alternate quantum walks with Memory on cycles (QHFM), where the <inline-formula><tex-math notation="LaTeX">$j$</tex-math></inline-formula>th message bit decides whether to run quantum walk with one-step memory or to run quantum walk with two-step memory at the <inline-formula><tex-math notation="LaTeX">$j$</tex-math></inline-formula>th time step, and the hash value is calculated from the resulting probability distribution of the walker. Numerical simulation shows that the proposed hash function has near-ideal statistical performance and is at least on a par with the state-of-the-art hash functions based on quantum walks in terms of sensitivity of hash value to message, diffusion and confusion properties, uniform distribution property, and collision resistance property; and theoretical analysis indicates that the time and space complexity of the new scheme are not greater than those of its peers. The good performance of QHFM suggests that quantum walks that differ not only in coin operators but also in memory lengths can be combined to build good hash functions, which, in turn, enriches the construction of controlled alternate quantum walks.

Khaled A. Helal Kelany, Nikitas Dimopoulos, Clemens P. J. Adolphs et al.

The focus of this work is to explore the use of quantum annealing solvers for the problem of phase unwrapping of synthetic aperture radar (SAR) images. Although solutions to this problem exist based on network programming, these techniques do not scale well to larger sized images. Our approach involves formulating the problem as a quadratic unconstrained binary optimization (QUBO) problem, which can be solved on a quantum annealer. Given that present embodiments of quantum annealers remain limited in the number of qubits they possess, we decompose the problem into a set of subproblems that can be solved individually. These individual solutions are close to optimal up to an integer constant, with one constant per subimage. In a second phase, these integer constants are determined as a solution to yet another QUBO problem. This basic idea is extended to several passes, where each pass results in an image which is subsequently decomposed to yet another set of subproblems until the resulting image can be accommodated by the annealer at hand. Additionally, we explore improvements to the method by decomposing the original image into overlapping subimages and ignoring the results on the overlapped (marginal) pixels. We test our approach with a variety of software-based QUBO solvers and on a variety of images, both synthetic and real. Additionally, we experiment using D-wave systems&#x2019; quantum annealer, the D-wave 2000Q_6 and developed an embedding method which, for our problem, yielded improved results. Our method resulted in high quality solutions, comparable to state-of-the-art phase-unwrapping solvers.

V. I. Tretyak

Nuclear decays with simultaneous emission of two alpha particles are energetically possible for a number of nuclides. Prospects of searching for such kind of decay for nuclides present in the natural isotopic composition of elements are discussed here. The first experimental limit on half-life for 2α decay is set for 209Bi as T1/2 > 2.9·1020 y at 90 % C.L., using the data of work [P. de Marcillac et al. Nature 422 (2003) 876]. Theoretical T1/2 estimations for the process are also given. Using these values, which are on the level of 1033 y or more, one can conclude that the prospects of experimental observation of 2α decay are very pessimistic.

Daisuke Saida, Yuki Yamanashi, Mutsuo Hidaka et al.

Experimental demonstrations of quantum annealing with &#x201C;native&#x201D; implementation of Boolean logic Hamiltonians are reported. As a superconducting integrated circuit, a problem Hamiltonian whose set of ground states is consistent with a given truth table is implemented for quantum annealing with no redundant qubits. As examples of the truth table, <sc>nand</sc> and <sc>nor</sc> are successfully fabricated as an identical circuit. Similarly, a native implementation of a multiplier comprising six superconducting flux qubits is also demonstrated. These native implementations of Hamiltonians consistent with Boolean logic provide an efficient and scalable way of applying annealing computation to so-called circuit satisfiability problems that aim to find a set of inputs consistent with a given output over any Boolean logic functions, especially those like factorization through a multiplier Hamiltonian. A proof-of-concept demonstration of a hybrid computing architecture for domain-specific quantum computing is described.

A. Kreisel, C. A. Marques, L. C. Rhodes et al.

Abstract The single-layered ruthenate Sr2RuO4 is one of the most enigmatic unconventional superconductors. While for many years it was thought to be the best candidate for a chiral p-wave superconducting ground state, desirable for topological quantum computations, recent experiments suggest a singlet state, ruling out the original p-wave scenario. The superconductivity as well as the properties of the multi-layered compounds of the ruthenate perovskites are strongly influenced by a van Hove singularity in proximity of the Fermi energy. Tiny structural distortions move the van Hove singularity across the Fermi energy with dramatic consequences for the physical properties. Here, we determine the electronic structure of the van Hove singularity in the surface layer of Sr2RuO4 by quasi-particle interference imaging. We trace its dispersion and demonstrate from a model calculation accounting for the full vacuum overlap of the wave functions that its detection is facilitated through the octahedral rotations in the surface layer.

Pranav Gokhale, Olivia Angiuli, Yongshan Ding et al.

Variational quantum eigensolver (VQE) is a promising algorithm for near-term quantum machines. It can be used to estimate the ground state energy of a molecule by performing separate measurements of O(N⁴) terms. This quartic scaling appears to be a significant obstacle to practical applications. However, we note that it empirically reduces to O(N³) when we partition the terms into linear-sized commuting families that can be measured simultaneously. We confirm these empirical observations by studying the MIN-COMMUTING-PARTITION problem at the level of the fermionic Hamiltonian and its encoding into qubits. Moreover, we provide a fast, precomputable procedure for creating linearly sized commuting partitions by solving a round-robin scheduling problem via flow networks. In addition, we demonstrate how to construct the quantum circuits necessary for simultaneous measurement, and we discuss the statistical implication of simultaneous measurement. Our results are experimentally validated by a ground state estimation of deuteron with low shot budget on a 20-qubit IBM machine.

J. R. Hortensius, D. Afanasiev, A. Sasani et al.

Abstract Strain engineering has been extended recently to the picosecond timescales, driving ultrafast metal–insulator phase transitions and the propagation of ultrasonic demagnetization fronts. However, the nonlinear lattice dynamics underpinning interfacial optoelectronic phase switching have not yet been addressed. Here we perform time-resolved all-optical pump-probe experiments to study ultrafast lattice dynamics initiated by impulsive light excitation tuned in resonance with a polar lattice vibration in LaAlO3 single crystals, one of the most widely utilized substrates for oxide electronics. We show that ionic Raman scattering drives coherent rotations of the oxygen octahedra around a high-symmetry crystal axis. By means of DFT calculations we identify the underlying nonlinear phonon–phonon coupling channel. Resonant lattice excitation is also shown to generate longitudinal and transverse acoustic wave packets, enabled by anisotropic optically induced strain. Importantly, shear strain wave packets are found to be generated with high efficiency at the phonon resonance, opening exciting perspectives for ultrafast material control.

Dalal Naji Hameed, Ali Khalaf Hasan

In this work, nuclear shell model was applied using modified surface delta-interaction to calculate, in particle-hole state, the energy levels of isobar nuclei 40Sc and 40K. Particles are in the model space (1f7/2) while the holes are found in the model space (1d3/2, 1s1/2, 1d5/2). The total angular momentum and parity are identified for possible particles and holes in nuclei above. Thus, we have used a theoretical study to find relationship between energy levels and the semi-classical coupling angle θ1,2 at different orbitals within particle-hole configuration. We notice the energy levels seem to follow two universal functions which depend on the semi-classical coupling angles θ1,2. We found the theoretical data agree to the experimental data.

А. P. Voiter, M. I. Doronin, A. M. Kovalev et al.

The architecture, operating principles, software and design of eight-channel spectrometric ADC with programmable logic for multiparameter measurement systems for research of nuclear reactions is considered.

L. V. Mikhailov, A. I. Ustinov, L. G. Makarenko et al.

Investigations allowing obtaining of 82Sr isotope upon irradiation of target RbCl by internal proton beam in the cyclotron U-240 were performed. The facility, providing long exposure of the target RbCl upon internal proton beam with the intensity of 150 mA and with energy not less than 70 MeV, was constructed.

O. V. Kosarchuk, M. M. Lazarev, O. M. Kadygrib

Averaged assessments of radiological effectiveness dynamics of mineral fertilizers of long-term application at the late phase of ChNPP accident have been carried out on the base of 3-5-years experiments. The influence of mineral fertilizers, used in different doses for agricultural plants, has been shown for intensity of 137Cs accumu-lation by plants on various soil-climatic conditions of radioactively contaminated territory of the Ukraine.