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

Jixing Zhang, Cheuk Kit Cheung, Michael Kübler et al.

Abstract Nitrogen-vacancy (NV) center ensembles in diamond are one of the most promising solid-state quantum platforms for various sensing applications. Achieving ultimate sensitivity requires simultaneously long spin dephasing times ( $${T}_{2}^{* }$$ T 2 * ) and high NV center concentrations. In this work, we propose a systematic measurement approach to quantify the electron spin dephasing in NV center ensembles and analyze the contributions of various sources to the dephasing time, including NV-NV interactions, strain and electric field distributions, 13C nuclear spins, and P1 electron spins. Our method is validated using a series of high-performance diamond samples, providing a comprehensive understanding of dephasing mechanisms and revealing correlations between NV concentration and different dephasing sources. Building on these insights, we outline strategies to further enhance the achievable sensitivity for DC magnetic field measurements.

Anthony J. Cressman, Rahul Sarpeshkar

Analog circuits have emerged as a valuable quantum emulation and simulation platform. Specifically, they have been experimentally shown to excel in emulating coherent state vector dynamics and motifs of quantum circuits, such as the quantum Fourier transform, tensor product superpositions, two-level systems such as Josephson junctions, and nuclear magnetic resonance state dynamics, all on a very large scale integration chip at room temperature (Cressman et al., 2022; Sarpeshkar, 2019a, 2019b, 2019c; Sarpeshkar, 2020). However, the ability to model simple state vectors is insufficient for modeling open quantum systems, i.e., systems with environmental noise. Noisy quantum systems are essential in practical implementations and applications that exploit noise. The density matrix formalism enables us to model such states, including finite reservoir state systems, and all states that can be represented as state vectors. To our knowledge, no one has yet demonstrated the mapping of a density matrix system to classical analog circuit components. We review the procedure for emulating the dynamics of a finite state vector with four essential analog circuit components and extend this procedure to emulate density matrix dynamics. We then simulate these systems as analog circuits in the presence of noise. This protocol opens up exciting possibilities for further research and development in noisy quantum emulation and simulation using analog circuits for arbitrarily large or small systems.

Kai Hebeler

Hui Wang, Yan-Jun Zhao, Xun-Wei Xu

We propose a theoretical scheme to realize the controllable non-Hermitian qubit–qubit coupling by adding a high-loss resonator in a tunable coupling superconducting quantum circuit. By changing the effective qubit–qubit coupling, the phase and amplitude of resonator–qubit interaction, and the qubits’ quantum states, we can continually tune the energy level attraction, the position of EP (exceptional point), and the non-reciprocity in the non-Hermitian superconducting circuit. The EPs and non-reciprocity can affect the quantum states’ evolutions and exchange efficiencies for two qubits in the non-Hermitian superconducting circuit. The controllable non-Hermitian and non-reciprocal interactions between two qubits provide new insights and methods for exploring the unconventional quantum effects in superconducting quantum circuits.

Adrian Valadkhani, Jonas B. Profe, Andreas Kreisel et al.

Abstract Scanning tunneling spectroscopy (STS) and scanning tunneling microscopy (STM) are perhaps the most promising ways to detect the superconducting gap size and structure in the canonical unconventional superconductor Sr2RuO4 directly. However, in many cases, researchers have reported being unable to detect the gap at all in STM conductance measurements. Recently, an investigation of this issue on various local topographic structures on a Sr-terminated surface found that superconducting spectra appeared only in the region of small nanoscale canyons, corresponding to the removal of one RuO surface layer. Here, we analyze the electronic structure of various possible surface structures using first principles methods, and argue that bulk conditions favorable for superconductivity can be achieved when removal of the RuO layer suppresses the RuO4 octahedral rotation locally. We further propose alternative terminations to the most frequently reported Sr termination where superconductivity surfaces should be observed.

Yu. V. Khomutinin, O. V. Kosarchuk, S. V. Polischuk

methodology for mapping the density of 137Cs contamination of agricultural land is proposed and tested. The methodology is based on data on gamma-dose rate measurements, gamma-logging results, and direct determination of 137Cs in soil samples, which were obtained by different organizations in different years. It allows to generalize all available information on 137Cs contamination of the lands and significantly improves the representativeness of estimates of the spatial distribution of the radionuclides at the mapping.

Mohammad Ali Javidian, Vaneet Aggarwal, Zubin Jacob

This article proposes circular hidden quantum Markov models (c-HQMMs), which can be applied for modeling temporal data. We show that c-HQMMs are equivalent to a tensor network (more precisely, circular local purified state) model. This equivalence enables us to provide an efficient learning model for c-HQMMs. The proposed learning approach is evaluated on six real datasets and demonstrates the advantage of c-HQMMs as compared to HQMMs and HMMs.

Md Nurul Huda, Shawulienu Kezilebieke, Teemu Ojanen et al.

Vimal Kumar Jain

B. G. Struzhko

Original article: Yaderna Fizyka ta Energetyka (Nucl. Phys. At. Energy) 22(1) (2021) 111.

Christopher Orthodoxou, Amelle Zaïr, George H. Booth

Abstract With a combination of numerical methods, including quantum Monte Carlo, exact diagonalization, and a simplified dynamical mean-field model, we consider the attosecond charge dynamics of electrons induced by strong-field laser pulses in two-dimensional Mott insulators. The necessity to go beyond single-particle approaches in these strongly correlated systems has made the simulation of two-dimensional extended materials challenging, and we contrast their resulting high-harmonic emission with more widely studied one-dimensional analogues. As well as considering the photo-induced breakdown of the Mott insulating state and magnetic order, we also resolve the time and ultra-high-frequency domains of emission, which are used to characterize both the photo-transition, and the sub-cycle structure of the electron dynamics. This extends simulation capabilities and understanding of the photo-melting of these Mott insulators in two dimensions, at the frontier of attosecond non-equilibrium science of correlated materials.

Institute for Nuclear Research

Brief biography and scientific achievements of Volodymyr Andriyovych Plujko in relation with his 70-th anniversary.

Thomas Krauss, Joey McCollum, Chapman Pendery et al.

This article addresses the question of implementing a maximum flow algorithm on directed graphs in a formulation suitable for a quantum annealing computer. Three distinct approaches are presented. In all three cases, the flow problem is formulated as a quadratic unconstrained binary optimization (QUBO) problem amenable to quantum annealing. The first implementation augments a graph with integral edge capacities into a multigraph with unit-capacity edges and encodes the fundamental objective and constraints of the maximum flow problem using a number of qubits equal to the total capacity of the graph $\sum _i{c_i}$. The second implementation, which encodes flows through edges using a binary representation, reduces the required number of qubits to $\mathcal {O}(|E| \log C_{\max })$, where $|E|$ and $C_{\max }$ denote the number of edges and maximum edge capacity of the graph, respectively. The third implementation adapts the dual minimum cut formulation and encodes the problem instance using $|V|$ qubits, where $|V|$ is the number of vertices in the graph. Scaling factors for penalty terms and coupling matrix construction times are made explicit in this article.

V. A. Plujko, S. Goriely, O. M. Gorbachenko et al.

Closed-form models for photon strength functions for the description of photoabsorption cross section in the energy range 5 - 30 MeV for even-even nuclei are tested. The experimental database was prepared with systematic uncertainty less than 10 % from the EXFOR data. The uncertainties are estimated using the calculations of the photo cross sections within TALYS 1.6 code. The theoretical models are compared with experimental photoabsorption cross section data. The minimum of the least-square deviation and the root-mean-square deviation factor are used as a criteria comparison of the theoretical calculations with experimental data. It is shown that the simple modified Lorentzian model is the best approach for simulation of the photoabsorption cross section at the gamma-ray energies below ~ 30 MeV.

Petr Opletal, Jan Prokleška, Jaroslav Valenta et al.

Quantum phase transitions: Tuned in metallic ferromagnets Clean ferromagnetic systems are predicted to exhibit quantum phase transitions (QPTs) rather than critical points. QPTs happen at zero temperature due to quantum fluctuations between the phases, and can be triggered by non-thermal perturbations such as hydrostatic pressure, chemical composition or magnetic fields. Jan Prokleška at Czesh Charles University and colleagues from Czech Republic and Germany demonstrate that it is possible to tune the QPT of the metallic ferromagnet UCo1-xRuxAl by pressure or weak Ru doping. The experimental study of QPTs in metallic ferromagnets is typically hindered by the extreme conditions required to drive the system into the transition, or by the presence of additional phases such as superconductivity. Instead, UCo1-xRuxAl allows to get access to the QPT at easily accessible experimental conditions, opening the possibility of studying in detail quantum critical phenomena.

Daiki Sakabe, Zheng Liu, Kazutomo Suenaga et al.

Condensed Matter Physics: Charge density wave occurs in the two dimensional limit Charge density wave (CDW), a wave-like charge modulation, occurs in tri-, bi- and mono-layer crystals. A team led by Satoshi Tanda at Hokkaido University and collaborators at AIST in Japan observed CDWs in mono-, bi-, and tri-layer 1T-TaS2 crystal without a substrate using a low voltage scanning transmission electron microscope. The CDW in a mono-layer sample does not exhibit a topological phase with vortex type point defects, which had been previously anticipated from a two-dimensional model. Instead, new topological CDW phases with intra-layer line defects are observed in mono-layer and bi-layer samples, suggesting a significant role of strong electron-phonon interaction in thinned samples. (In tri-layer, commensurate CDW phase without defects was observed.) These results shed a light to understand the stripe type structures in high temperature superconductors and call for new understandings in a pure material to the two dimensional limit. (141 words)

V. V. Kanivets, S. I. Kireev, G. V. Laptev et al.

Results of long-term observations on 137Cs and 90Sr concentration in water mass of the ChNPP Cooling Pond are presented. Drastic transformation of the intrinsic trend in changes with time of averaged radionuclides con-tent in water is clearly demonstrated alongside with the spatial heterogeneity of radioactive contamination of water body. The cycling character of seasonal changes of 137Cs activity concentration in water is being linked to hydrochemical, temperature and oxygen regimes of the Cooling Pond.

A. I. Ali, A. Hassen

The electric and magnetic properties of layered perovskites have been investigated systematically over the doping range . It was found that both Sr1.5Y0.5CoO4and Sr1.4Y0.6CoO4undergo ferromagnetic (FM) transition around 145 K and 120 K, respectively. On the other hand, Sr1.3Y0.7CoO4and Sr1.2Y0.8CoO4compounds showed paramagnetic behavior over a wide range of temperatures. In addition, spin-glass transition () was observed at 10 K for Sr1.3Y0.7CoO4. All investigated samples are semiconducting-like within the temperature range of 10–300 K. The temperature dependence of the electrical resistivity, , was described by two-dimensional variable range hopping (2D-VRH) model at 50 K < ≤ 300 K. Comparison with other layered perovskites was discussed in this work.

L. I. Grygorieva, K. V. Grygoriev

The results of retrospective definition of the radiation load to the population of south Ukraine the under abnormal condition Chernobyl release of radionuclide, executed from data of aerophare, spectrometry and dosimetric researches on territory Nikolaev, Odessa, Kirovograd areas and Autonomous Republic of Crimea, conducted by the Nikolaev research laboratory “Larani” in 1986 and in subsequent years are presented in the article.

Yu. O. Ivanov, S. E. Levchuk, S. I. Kireev et al.

Some results on long-term dynamics of migration movability of ChNPP release radionuclides in soils of abandoned areas have been analyzed and summarized. Role of physical-chemical forms of fallout as well as landscape-geochemical characteristics of the territory has been estimated. Dynamics of 90Sr migration in soils of fuel tracks of ChNPP fallout is in the main difference in comparison with 137Cs.