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

Chukwudubem Umeano, Oleksandr Kyriienko

We introduce a quantum data embedding protocol based on the preparation of a ground state of a parameterized Hamiltonian. We analyze the corresponding quantum feature map, recasting it as an adiabatic state preparation procedure with Trotterized evolution. We compare the properties of underlying quantum models with ubiquitous Fourier-type quantum models and show that ground state embeddings can be described effectively by a spectrum with a degree that grows rapidly with the number of qubits, corresponding to a large model capacity. We observe that the spectrum contains massive frequency degeneracies and the weighting coefficients for the modes are highly structured, thus limiting model expressivity. Our results provide a step toward understanding models based on quantum data and contribute to fundamental knowledge needed for building efficient quantum machine learning (QML) protocols. As non-trivial embeddings are crucial for designing QML protocols that cannot be simulated classically, our findings guide the search for high-capacity quantum models that can largely outperform classical models.

Purin Pongpanich, Tanasanee Phienthrakul

This study presents an investigation of the dual-discriminator hybrid quantum generative adversarial network (DDHQ-GAN), a framework designed to enhance the performance of conventional generative adversarial networks (GANs) through the incorporation of a hybrid quantum discriminator. The proposed DDHQ-GAN architecture comprises three primary components: a generator and two discriminators. The research evaluates the efficacy of the DDHQ-GAN in comparison with existing GAN variants, employing the Fréchet inception distance (FID) as a quantitative metric to assess image generation quality. The study further examines the interplay between the structural configurations of parameterized quantum circuits, classical neural network architectures, and model hyperparameters, using the Modified National Institute of Standards and Technology (MNIST) dataset as the experimental benchmark. Empirical results demonstrate that the DDHQ-GAN achieves superior performance, reflected by lower FID scores, while incurring only a marginal increase in the number of parameters and quantum computational resources.

I. S. Sushchev

We propose a novel point-to-point quantum key distribution protocol based on the states from a great circle of the Bloch sphere that maintains the simplicity of the widely used BB84 protocol while offering enhanced resilience against fake-state attacks. Our approach leverages an infinite set of bases, reducing the probability of successful eavesdropping through basis-matching strategies. We derive the security of the protocol against collective attacks, provide an estimation of secret key length, and outline its resistance to common fake-state attack techniques, such as detector blinding. We also use entropic uncertainty relations to set the lower bound on Eve’s conditional entropy. Furthermore, we explore the realistic eavesdropping scenario considering finite-precision state preparation and discuss potential implementation strategies for our protocol considering finite resources and noise affection.

Kyryl Shtefiienko, Cole Phillips, Shirin Mozaffari et al.

This study investigates the electronic structure of the vanadium-based kagome metal YV6Sn6 using magnetoresistance (MR) and torque magnetometry. The MR exhibits a nearly linear, non-saturating behavior, increasing by up to 55% at 35 T but shows no evidence of Shubnikov–de Haas oscillations. In contrast, the torque signal, measured up to 41.5 T, reveals clear de Haas–van Alphen (dHvA) oscillations over a wide frequency range, from a low frequency of Fα ∼20 T to high frequencies between 8 and 10 kT. Angular and temperature-dependent dHvA measurements were performed to probe the Fermi surface parameters of YV6Sn6. The dHvA frequencies display weak angular dependence, and the effective mass, determined by fitting the temperature-dependent data to the Lifshitz–Kosevich formula, is 0.097 mo, where mo represents the free electron mass. To complement the experimental findings, we computed the electronic band structure and Fermi surface using density functional theory. The calculations reveal several notable features, including multiple Dirac points near the Fermi level, flatbands, and Van Hove singularities. Two bands cross the Fermi level, contributing to the Fermi surface, with theoretical frequencies matching well with the observed dHvA frequencies. These combined experimental and theoretical insights enhance our understanding of the electronic structure of YV6Sn6 and provide a valuable framework for studying other vanadium- and titanium-based kagome materials.

Ilora Maity, Junaid ur Rehman, Symeon Chatzinotas

Quantum key distribution (QKD) provides a secure method to exchange encrypted information between two parties in a quantum communication infrastructure (QCI). The primary challenge in deploying a QCI is the cost of using optical fibers and trusted repeater nodes (TRNs). Practical systems combine quantum and classical channels on the same fiber to reduce the cost of fibers dedicated to QKD. In such a system with quantum-classical coexistence, the optimal distribution of QKD requests with minimal deployment cost and power usage on the multiplexed links is challenging due to the diverse key rate demands of the requests, number of classical and quantum channels, guard band spacing between classical and quantum channels, and secret key rate of the quantum channels that decreases with distance. To address these challenges, in this work, we propose a Steiner tree-based approach for constructing a QCI that connects all quantum nodes with minimum TRNs. In addition, we propose a genetic algorithm-based solution to optimally distribute the end-to-end QKD requests over the QCI. We also determine feasible optical bypass routes to reduce the overall energy consumption in the network further. The proposed approach reduces the QCI deployment cost by 19.42% compared to the benchmark MST-Baseline. Also, on average, TAQNet with optical bypass achieves 4.69 kbit per Joule more energy efficiency compared to the nonbypass approach.

О. M. Pugach, V. L. Diemokhin, V. N. Bukanov et al.

A detailed description of the dosimetric experiment to determine the characteristics of the neutron field at the locations of surveillance specimens at Rivne NPP Unit No. 3 is presented. Through the complex analysis of the experimental data, the presence of general regularities in the behavior of neutron spectrum characteristics, such as the spectral index, at these locations was identified. A comparison of the calculated and experimental data was carried out, demonstrating that the MCSS code package is suitable for determining the irradiation conditions of surveillance specimens, particularly when developing an upgraded program.

Zichang He, Bo Peng, Yuri Alexeev et al.

Given their potential to demonstrate near-term quantum advantage, variational quantum algorithms (VQAs) have been extensively studied. Although numerous techniques have been developed for VQA parameter optimization, it remains a significant challenge. A practical issue is that quantum noise is highly unstable and thus it is likely to shift in real time. This presents a critical problem as an optimized VQA ansatz may not perform effectively under a different noise environment. For the first time, we explore how to optimize VQA parameters to be robust against unknown shifted noise. We model the noise level as a random variable with an unknown probability density function (PDF), and we assume that the PDF may shift within an uncertainty set. This assumption guides us to formulate a distributionally robust optimization problem, with the goal of finding parameters that maintain effectiveness under shifted noise. We utilize a distributionally robust Bayesian optimization solver for our proposed formulation. This provides numerical evidence in both the quantum approximate optimization algorithm and the variational quantum eigensolver with hardware-efficient ansatz, indicating that we can identify parameters that perform more robustly under shifted noise. We regard this work as the first step toward improving the reliability of VQAs influenced by shifted noise from the parameter optimization perspective.

I. I. Fishchuk

The amorphous material films are resistant to high-energy irradiation. Therefore, devices built using the properties of these materials can work in conditions of increased radiation much longer than devices using the properties of crystals. An important characteristic of these materials is their degree of disorder. To determine this characteristic, a model of random fluctuations of the local edge of the conduction band is considered for the theoretical study of magnetoconductivity in amorphous oxide semiconductors. The effective medium approximation is used. An approach to determining the amount of energy disorder based on experimental measurement of changes in longitudinal and transverse electrical conductivity in a magnetic field is proposed.

Younes Javanmard, Ugne Liaubaite, Tobias J. Osborne et al.

The Variational Quantum Eigensolver (VQE) algorithm, as applied to finding the ground state of a Hamiltonian, is particularly well-suited for deployment on noisy intermediate-scale quantum (NISQ) devices. Here, we utilize the VQE algorithm with a quantum circuit ansatz inspired by the Density Matrix Renormalization Group (DMRG) algorithm. To ameliorate the impact of realistic noise on the performance of the method, we employ zero-noise extrapolation. We find that, with realistic error rates, our DMRG–VQE hybrid algorithm delivers good results for strongly correlated systems. We illustrate our approach with the Heisenberg model on a Kagome lattice patch and demonstrate that DMRG–VQE hybrid methods can locate and faithfully represent the physics of the ground state of such systems. Moreover, the parameterized ansatz circuit used in this work is low depth and requires a reasonably small number of parameters, so it is efficient for NISQ devices.

James Fitzjohn, Adrian Winckles, George Wilson et al.

One of the major obstacles to the adoption of quantum computing is the requirement to define quantum circuits at the quantum gate level. Many programmers are familiar with high-level or low-level programming languages but not quantum gates nor the low-level quantum logic required to derive useful results from quantum computers. The steep learning curve involved when progressing from quantum gates to complex simulations such as Shor's algorithm has proven too much for many developers. The purpose of this article and the software presented within addresses this challenge by providing a Software Development Kit (SDK), translation layer, emulator, and a framework of techniques for executing Intel 8080/Z80 assembler on a quantum computer, i.e., all salient points of CPU execution, logic, arithmetic, and bitwise manipulation will be executed on the quantum computer using quantum circuits. This provides a novel means of displaying the equivalency and interoperability of quantum and classical computers. Developers and researchers can use the SDK to write code in Intel 8080/Z80 assembler which is executed locally via traditional emulation and remotely on a quantum computer in parallel. The emulator features side-by-side code execution with visibility of the running quantum circuit and reusable/overridable methods. This enables programmers to learn, reuse, and contrast techniques for performing any traditional CPU-based technique/instruction on a quantum computer, e.g., a programmer may know how to multiply and perform checks on a classical CPU but is not able to perform the same tasks in a quantum implementation, and this SDK allows the programmer to pick and choose the methods they would like to use to fulfil their requirements. The SDK makes use of open-source software, specifically Python and Qiskit for the emulation, translation, API calls, and execution of user-supplied code or binaries.

Stephen DiAdamo, Corey O'Meara, Giorgio Cortiana et al.

In this work, we aim to solve a practical use-case of unsupervised clustering that has applications in predictive maintenance in the energy operations sector using quantum computers. Using only cloud access to quantum computers, we complete thorough performance analysis of what some current quantum computing systems are capable of for practical applications involving nontrivial mid-to-high-dimensional datasets. We first benchmark how well distance estimation can be performed using two different metrics based on the swap-test, using angle and amplitude data embedding. Next, for the clustering performance analysis, we generate sets of synthetic data with varying cluster variance and compare simulation to physical hardware results using the two metrics. From the results of this performance analysis, we propose a general, competitive, and parallelized version of quantum <inline-formula><tex-math notation="LaTeX">$k$</tex-math></inline-formula>-means clustering to avoid some pitfalls discovered due to noisy hardware and apply the approach to a real energy grid clustering scenario. Using real-world German electricity grid data, we show that the new approach improves the balanced accuracy of the standard quantum <inline-formula><tex-math notation="LaTeX">$k$</tex-math></inline-formula>-means clustering by 67.8&#x0025; with respect to the labeling of the classical algorithm.

A. Yu. Danyk, O. O. Sudakov

A mathematical model for the determination of X-ray scattering kernels’ shapes based on incomplete simulation or measurement data was introduced and tested using a mathematical phantom. The model is originally intended for low-dose X-ray imaging without anti-scatter grids. The proposed model fits different kinds of symmetrical and asymmetrical scattering kernels in different tissues well enough for practical applications. Kernels asymmetry is mostly caused by irradiation of the object near the boundaries of different tissues. The model describes a variety of asymmetrical kernels by proposed “sectoral” members. Application of the proposed model in scattering compensation procedure reduces resulting error up to 50 % for “wide” scattering kernels.

Jia Yu, Congcong Le, Zhiwei Li et al.

Abstract Materials with exceptional magnetism and superconductivity usually conceive emergent physical phenomena. Here, we investigate the physical properties of the (Eu,La)FeAs2 system with double magnetic sublattices. The parent EuFeAs2 shows anisotropy-associated magnetic behaviors, such as Eu-related moment canting and exchange bias. Through La doping, the magnetic anisotropy is enhanced with ferromagnetism of Eu2+ realized in the overdoped region, and a special exchange bias of the superposed ferromagnetic/superconducting loop revealed in Eu0.8La0.2FeAs2. Meanwhile, the Fe-related antiferromagnetism shows unusual robustness against La doping. Theoretical calculation and 57Fe Mössbauer spectroscopy investigation reveal a doping-tunable dual itinerant/localized nature of the Fe-related antiferromagnetism. The coexistence of the Eu-related ferromagnetism, Fe-related robust antiferromagnetism, and superconductivity is further revealed in Eu0.8La0.2FeAs2, providing a platform for further exploration of potential applications and emergent physics. Finally, an electronic phase diagram is established for (Eu,La)FeAs2 with the whole superconducting dome adjacent to the Fe-related antiferromagnetic phase, which is of benefit for seeking underlying clues to high-temperature superconductivity.

R. M. Vernydub, O. I. Kyrylenko, O. V. Konoreva et al.

The optical characteristics of the GaAs1-хPх output LEDs and LEDs irradiated with electrons with Е = 2 MeV, Ф = 1015 ÷ 1016 cm-2 were studied. The width of the band gap of the GaAs1-хPх (х = 0.45) solid solution was estimated. Its growth is caused by the heating of carriers by the field of the p-n junction. The damage coefficients of the lifetime of minority charge carriers for irradiated GaAsP LEDs have been calculated and the consequences of exposure to radiation on the operational parameter Т1, which determines the thermal stability of the diodes, have been analyzed.

Francesco Vissani

This writeup is a review of current hot topics on solar neutrinos. It is based on a talk at the conference “Neutrinos: the quest for a new physics scale”, held at the CERN on March 2017, where the Organizers entrusted me with a discussion of the provocative question “whether solar neutrino physics is over”. Rather than providing a straight (negative) answer, in view of an audience consisting mostly of colleagues working in theoretical particle physics, I deemed it more useful providing a description of what is the current activity of the physicists working in solar neutrinos, leaving the listener free of forming his/her own opinion apropos.

P. Belli, R. Bernabei, F. Cappella et al.

Experiment to search for double β decay of 96Ru and 104Ru is in progress in the underground Gran Sasso National Laboratories of the INFN (Italy) with the help of ultra-low background high purity (HP) Ge γ spectrometry. After 2162 h of data taking with 473 g ruthenium sample in low-background set-ups with HP Ge detectors, new improved limits on 2β processes in 96Ru and 104Ru have been established on the level of 1018–1019 yr.

A. T. Rudchik, Yu. O. Shyrma, O. A. Ponkratenko

The moment of inertia for collective rotation is derived analytically for the harmonic-oscillator Hamiltonian within the cranking model for any rotation frequency and at finite temperature. Semiclassical shell-structure moments of the inertia are obtained in terms of the free-energy shell corrections through the rigid-body inertia of the statistically equilibrium rotation of a heated Fermi system by using the periodic-orbit theory. Their analytical structure in terms of the equatorial and 3-dimensional periodic orbits for the axially-symmetric harmonic-oscillator potential is in perfect agreement with quantum results for critical deformations and temperatures.

O. F. Nemets, Yu. N. Pavlenko, V. L. Shablov et al.

Measurements of differential cross-sections of α-particle inelastic scattering by 7 Li nuclei and 7 Li(α, α6 Li)n, 7 Li(α, αα)t reactions have been performed at the energy Eα = 27,2 MeV. Probability of 7 Li*(7,45 MeV) decay into 6 Li + n channel has been determined from the ratio of cross-sections measured in kinematically complete and incomplete experiments. The large discrepancy of this value (P = 0,49 ± 0,06) and of those obtained at the study of 7 Li*(7,45 MeV) decay in binary reactions can be explained by the influence of Coulomb field of accompanied αparticle on the decay of near-threshold resonances in three-particle reactions.

Yu. A. Maklyuk, S. P. Gaschak, A. M. Maksimenko et al.

Comparative analysis of published data concerning dose burdens in Chernobyl’s wild small mammals are given, as well as own assessment for the conditions of year 2005. According to the calculations total values of absorbed doses and structure of contributions from various sources depend on features concrete animal species and ecological characteristics of sites. In 2005 the contribution of incorporated radionuclides (90Sr, 137Cs) averaged 55 % of absorbed dose, external beta-irradiation – 21 %, external gamma-irradiation – 23%. On some areas of the Chernobyl zone even in 19 years after the accident small mammals are getting dose burdens up to 1 - 50 mGy/day.

V. K. Tartakovsky, A. V. Fursayev

The reduced probability of the magnetic dipole transition in the 12С nucleus and the corresponding angular distribution of inelastically scattered electrons under excitation of the 1+ nuclear level with the energy of 15,1 MeV have been calculated with due regard for meson exchange currents. An agreement with experimental data is achieved under the condition that the many-particle shell model with intermediate coupling is used.