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

Daniele Lizzio Bosco, Beatrice Portelli, Giuseppe Serra

Image processing is one of the most promising applications for quantum machine learning. Quanvolutional neural networks with nontrainable parameters are the preferred solution to run on current and near future quantum devices. The typical input preprocessing pipeline for quanvolutional layers comprises of four steps: optional input binary quantization, encoding classical data into quantum states, processing the data to obtain the final quantum states, and decoding quantum states back to classical outputs. In this article, we propose two ways to enhance the efficiency of quanvolutional models. First, we propose a flexible data quantization approach with memoization, applicable to any encoding method. This allows us to increase the number of quantization levels to retain more information or lower them to reduce the amount of circuit executions. Second, we introduce a new integrated encoding strategy, which combines the encoding and processing steps in a single circuit. This method allows great flexibility on several architectural parameters (e.g., number of qubits, filter size, and circuit depth) making them adjustable to quantum hardware requirements. We compare our proposed integrated model with a classical convolutional neural network and the well-known rotational encoding method, on two different classification tasks. The results demonstrate that our proposed model encoding exhibits a comparable or superior performance to the other models while requiring fewer quantum resources.

V. A. Babenko, V. M. Pavlovych, I. A. Khomych et al.

We have analyzed the activities conducted at the WWR-M nuclear research reactor of the Institute for Nuclear Research, NAS of Ukraine, over the past five years, with a focus on nuclear safety and ongoing research efforts. In 2019-2022, preparatory work was carried out for the irradiation of surveillance specimens of nuclear power reactor vessel metals in the vertical channels of the WWR-M reactor, commissioned by National Nuclear Energy Generating Company (NNEC) "Energoatom". To support this effort, vertical channels for sample irradiation were designed and manufactured, and computational analyses were performed to determine the optimal core configuration, the optimal placement of channels within the core, neutron flux distributions, and the required irradiation time. The research presented here is based on computational modeling using the MCNP-4C code, with calculations performed to evaluate neutron fluxes, reactivity parameters, and nuclear safety margins. For each configuration, critical nuclear safety parameters were determined, including the reactivity margin, the control rod worth, the reactivity of the irradiated channels, and that of each fuel assembly. The analysis confirmed the feasibility of the proposed configuration and provided essential insights into optimizing neutron flux distributions and reactivity control. In early 2022, all reactor operations were halted, and the fuel was removed from the core and transferred to storage facilities. As a result, the need arose to improve the nuclear safety justification for the spent nuclear fuel storage facility, taking into account the actual arrangement of fuel assemblies. The present work examines reactor safety considerations and explores approaches to improving the justification of spent fuel storage. It also presents the results of a series of such calculations that were initiated and remain ongoing. Overall, our research contributes to current efforts in nuclear safety assessment and provides a foundation for future investigations in this field.

Lars Meschede, Daniel D. A. Clarke, Ortwin Hess

The unprecedented pace of evolution in nanoscale architectures for cavity quantum electrodynamics (cQED) has posed crucial challenges for theory, where the quantum dynamics arising from the non-perturbative dressing of matter by cavity electric and magnetic fields as well as the fundamentally non-Hermitian character of the system are to be treated without significant approximation. The lossy electromagnetic resonances of photonic, plasmonic, or magnonic nanostructures are described as quasinormal modes (QNMs), whose properties and interactions with quantum emitters and spin qubits are central to the understanding of dissipative nano-optics and magnetodielectric cQED. Despite recent advancements toward a fully quantum framework for QNMs, a general and universally accepted approach to QNM quantization for arbitrary linear media remains elusive. In this work, we introduce a unified theoretical framework, based on macroscopic QED and complex coordinate transformations, which achieves QNM quantization for a wide class of spatially inhomogeneous, dissipative and dispersive, linear, magnetodielectric resonators. The complex coordinate transformations equivalently convert the radiative losses into non-radiative material dissipation, and via a suitable transformation that reflects all the losses of the resonator, we define creation and annihilation operators that allow the construction of modal Fock states for the joint excitations of field-dressed matter. By directly addressing the intricacies of modal loss in a fully quantum theory of magnetodielectric cQED, our approach enables the exploration of modern, quantum nano-optical experiments utilizing dielectric, plasmonic, magnetic, or hybrid cQED architectures and paves the way toward a rigorous assessment of room-temperature, quantum nanophotonic technologies without recourse to ad hoc quantization schemes.

Marta Gladysiewicz, M. S. Wartak

This study examines the effect of substrate orientation on the optical properties of InGaAsN(P) quantum wells using an eight-band k · p Hamiltonian extended to account for strain effects in arbitrary orientations. Numerical simulations were performed for key substrate orientations, including (001), (110), (111), and (112), with particular focus on the impact of strain-induced piezoelectric fields on band alignment and wavefunction localization. The results reveal substantial differences in the band structure, wavefunctions, absorption coefficients, and material gain across the studied orientations. The (111) orientation exhibits the strongest piezoelectric fields, leading to enhanced confinement and the formation of additional bound states in the conduction band. Band structure analysis indicates significant strain-induced variations in the bandgap and energy levels, particularly in non-(001) orientations. In addition, the absorption coefficient strongly depends on the substrate orientation. The (111) and (001) orientations exhibit the highest absorption coefficient values, making them strong candidates for solar cell applications. Other orientations may be more suitable for laser applications due to their high material gain values.

Yuxin Jiang, Jihua Zhang, Jinyong Ma et al.

Current nonlinear metasurface photon-pair sources face limitations in angular emission range and uniformity due to optical resonance dispersion, potentially hindering their application in quantum imaging, which demands broad-angle emission for a wide field of view and high resolution. Here, we propose a broad-angle photon-pair source using flatband engineering. We demonstrate that tailored partially etched patterns in a lithium niobate metasurface can facilitate a flatband across a wide transverse wavevector range (±0.2 rad/μm) around a 1573 nm wavelength. The flatband metasurface supports enhanced photon-pair generation at a simulated rate of 539 Hz/mW within a cone of 3° apex angle relative to the pump propagation, which is an order of magnitude broader than previously reported metasurfaces. This general approach is also scalable to other wavelengths, opening new possibilities for compact entangled photon-pair sources in quantum imaging.

Tatsuhiko Shirai, Nozomu Togawa

In this article, we propose a postprocessing variationally scheduled quantum algorithm (pVSQA) for solving constrained combinatorial optimization problems (COPs). COPs are typically transformed into ground-state search problems of the Ising model on a quantum annealer or gate-based quantum device. Variational methods are used to find an optimal schedule function that leads to high-quality solutions in a short amount of time. Postprocessing techniques convert the output solutions of the quantum devices to satisfy the constraints of the COPs. The pVSQA combines the variational methods and the postprocessing technique. We obtain a sufficient condition for constrained COPs to apply the pVSQA based on a greedy postprocessing algorithm. We apply the proposed method to two constrained NP-hard COPs: the graph partitioning problem and the quadratic knapsack problem. The pVSQA on a simulator shows that a small number of variational parameters is sufficient to achieve a (near-) optimal performance within a predetermined operation time. Then, building upon the simulator results, we implement the pVSQA on a quantum annealer and a gate-based quantum device. The experimental results demonstrate the effectiveness of our proposed method.

M. D. Bondarkov, V. О. Zheltonozhsky, D. E. Myznikov et al.

A spectroscopic method has been developed based on measuring of beta-spectra, which takes into account the physico-chemical state of the investigated objects and the instability of electronic systems in field conditions. This method allows for the investigation of the 90Sr and 137Cs concentration in various objects with a change in the 137Cs/90Sr ratio from 1 to 100 with an error of better than 20 %. A methodology has been developed that takes into account the change in the density of the inanimate objects and is based on shifting of the peak position of the conversion electrons from the 137Cs decay. The verification of the methodology compared to radiochemical measurements of 90Sr in soil samples showed complete agreement within 10 - 15 %, with a change of the activity in the samples by four orders of magnitude.

Shahrooz Pouryousef, Hassan Shapourian, Alireza Shabani et al.

Existing classical optical network infrastructure cannot be immediately used for quantum network applications due to photon loss. The first step toward enabling quantum networks is the integration of quantum repeaters into optical networks. However, the expenses and intrinsic noise inherent in quantum hardware underscore the need for an efficient deployment strategy that optimizes the placement of quantum repeaters and memories. In this article, we present a comprehensive framework for network planning, aiming to efficiently distribute quantum repeaters across existing infrastructure, with the objective of maximizing quantum network utility within an entanglement distribution network. We apply our framework to several cases including a preliminary illustration of a dumbbell network topology and real-world cases of the SURFnet and ESnet. We explore the effect of quantum memory multiplexing within quantum repeaters, as well as the influence of memory coherence time on quantum network utility. We further examine the effects of different fairness assumptions on network planning, uncovering their impacts on real-time network performance.

Nitin Kumar, Ye-Shun Lan, Iksu Jang et al.

Abstract Atomic-scale spin entity in a two-dimensional topological insulator lays the foundation to manufacture magnetic topological materials with single atomic thickness. Here, we have successfully fabricated Fe monomer, dimer and trimer doped in the monolayer stanene/Cu(111) through a low-temperature growth and systematically investigated Kondo effect by combining scanning tunneling microscopy/spectroscopy (STM/STS) with density functional theory (DFT) and numerical renormalization group (NRG) method. Given high spatial and energy resolution, tunneling conductance (dI/dU) spectra have resolved zero-bias Kondo resonance and resultant magnetic-field-dependent Zeeman splitting, yielding an effective spin S eff = 3/2 with an easy-plane magnetic anisotropy on the self-assembled Fe atomic dopants. Reduced Kondo temperature along with attenuated Kondo intensity from Fe monomer to trimer have been further identified as a manifestation of Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between Sn-separated Fe atoms. Such magnetic Fe atom assembly in turn constitutes important cornerstones for tailoring topological band structures and developing magnetic phase transition in the single-atom-layer stanene.

Christoph Becher, Weibo Gao, Swastik Kar et al.

Quantum technologies are poised to move the foundational principles of quantum physics to the forefront of applications. This roadmap identifies some of the key challenges and provides insights on material innovations underlying a range of exciting quantum technology frontiers. Over the past decades, hardware platforms enabling different quantum technologies have reached varying levels of maturity. This has allowed for first proof-of-principle demonstrations of quantum supremacy, for example quantum computers surpassing their classical counterparts, quantum communication with reliable security guaranteed by laws of quantum mechanics, and quantum sensors uniting the advantages of high sensitivity, high spatial resolution, and small footprints. In all cases, however, advancing these technologies to the next level of applications in relevant environments requires further development and innovations in the underlying materials. From a wealth of hardware platforms, we select representative and promising material systems in currently investigated quantum technologies. These include both the inherent quantum bit systems and materials playing supportive or enabling roles, and cover trapped ions, neutral atom arrays, rare earth ion systems, donors in silicon, color centers and defects in wide-band gap materials, two-dimensional materials and superconducting materials for single-photon detectors. Advancing these materials frontiers will require innovations from a diverse community of scientific expertise, and hence this roadmap will be of interest to a broad spectrum of disciplines.

Yu. P. Hrynevych, L. I. Makovetska, A. I. Lуpska et al.

The effect of total single X-ray irradiation (1.5 Gy) on the course of free radical processes (FRP) in the blood and liver of red fistula (Myodes glareolus) and yellow-throated mouse (Apodemus flavicollis) was studied. It is shown that physicochemical regulation of FRP in the blood of murine rodents under total X-ray irradiation (1.5 Gy) in the early stages is carried out mainly due to catalase and reduced glutathione (GSH). This is evidenced by the stoichiometry of the CL reaction and symbat changes in the prooxidant-antioxidant ratio (PAR) and basic kinetic parameters of the CL reaction (Imax, Ifin) and antibat changes to PAR - catalase and GSH.

Shingo Kaneta-Takada, Yuki K. Wakabayashi, Yoshiharu Krockenberger et al.

Abstract High-mobility two-dimensional carriers originating from surface Fermi arcs in magnetic Weyl semimetals are highly desired for accessing exotic quantum transport phenomena and for topological electronics applications. Here, we demonstrate high-mobility two-dimensional carriers that show quantum oscillations in magnetic Weyl semimetal SrRuO3 epitaxial films by systematic angle-dependent, high-magnetic field magnetotransport experiments. The exceptionally high-quality SrRuO3 films were grown by state-of-the-art oxide thin film growth technologies driven by machine-learning algorithm. The quantum oscillations for the 10-nm SrRuO3 film show a high quantum mobility of 3.5 × 103 cm2/Vs, a light cyclotron mass, and two-dimensional angular dependence, which possibly come from the surface Fermi arcs. The linear thickness dependence of the phase shift of the quantum oscillations provides evidence for the non-trivial nature of the quantum oscillations mediated by the surface Fermi arcs. In addition, at low temperatures and under magnetic fields of up to 52 T, the quantum limit of SrRuO3 manifests the chiral anomaly of the Weyl nodes. Emergence of the hitherto hidden two-dimensional Weyl states in a ferromagnetic oxide paves the way to explore quantum transport phenomena for topological oxide electronics.

Institute for Nuclear Research

Brief biography and scientific achievements of Vitaliy Yuriyovych Denysov in relation with his 60-th anniversary.

Gia Dvali, Marco Michel, Sebastian Zell

Abstract We discuss a class of quantum theories which exhibit a sharply increased memory storage capacity due to emergent gapless degrees of freedom. Their realization, both theoretical and experimental, is of great interest. On the one hand, such systems are motivated from a quantum information point of view. On the other hand, they can provide a framework for simulating systems with enhanced capacity of pattern storage, such as black holes and neural networks. In this paper, we develop an analytic method that enables us to find critical states with increased storage capabilities in a generic system of cold bosons with weak attractive interactions. The enhancement of memory capacity arises when the occupation number N of certain modes reaches a critical level. Such modes, via negative energy couplings, assist others in becoming effectively gapless. This leads to degenerate microstates labeled by the occupation numbers of the nearly-gapless modes. In the limit of large N, they become exactly gapless and their decoherence time diverges. In this way, a system becomes an ideal storer of quantum information. We demonstrate our method on a prototype model of N attractive cold bosons contained in a one-dimensional box with Dirichlet boundary conditions. Although we limit ourselves to a truncated system, we observe a rich structure of quantum phases with a critical point of enhanced memory capacity.

Mohamed Bencheikh, Abdelmajid Maghnouj, Jaouad Tajmouati et al.

For safety and radioprotection reasons in radiotherapy treatment, the exit dose is evaluated with irradiation field size and photon beam energy. The objective of this study is to introduce an empirical law for predicting the delivered dose at the other side of patient while radiotherapy treatment of cancer. In this study, the exit dose is the delivered dose out of the phantom on beam central axis. The measurements of percentage depth dose were done as a function of irradiation field size with an uncertainty of 2 % as recommended by IAEA protocols for two photon beam energies 6 and 18 MV. For high radioprotection quality inside radiotherapy department, an empirical law is elaborated with a reliability of 97 %. Thereafter, it consists a basic law that should be used theoretically to know the delivered dose variation with field size at the exit dose point for knowing the behavior of dose outside of radiotherapy treatment region. The medical physicists and physicians should take this law in radiotherapy treatment of the cancer.

Sebastian Philipp Neumann, Siddarth Koduru Joshi, Matthias Fink et al.

Abstract Satellites are the most efficient way to achieve global scale quantum communication (Q.Com) because unavoidable losses restrict fiber based Q.Com to a few hundred kilometers. We demonstrate the feasibility of establishing a Q.Com uplink with a 3U CubeSat, measuring only 10 × 10 × 34 cm3, using commercial off-the-shelf components, the majority of which have space heritage. We demonstrate how to leverage the latest advancements in nano-satellite body-pointing to show that our 4 kg CubeSat can generate a quantum-secure key, which has so far only been shown by a much larger 600 kg satellite mission. A comprehensive link budget and simulation was performed to calculate the secure key rates. We discuss design choices and trade-offs to maximize the key rate while minimizing the cost and development needed. Our detailed design and feasibility study can be readily used as a template for global scale Q.Com.

Daniel KL Oi, Alex Ling, Giuseppe Vallone et al.

Abstract Quantum communication is a prime space technology application and offers near-term possibilities for long-distance quantum key distribution (QKD) and experimental tests of quantum entanglement. However, there exists considerable developmental risks and subsequent costs and time required to raise the technological readiness level of terrestrial quantum technologies and to adapt them for space operations. The small-space revolution is a promising route by which synergistic advances in miniaturization of both satellite systems and quantum technologies can be combined to leap-frog conventional space systems development. Here, we outline a recent proposal to perform orbit-to-ground transmission of entanglement and QKD using a CubeSat platform deployed from the International Space Station (ISS). This ambitious mission exploits advances in nanosatellite attitude determination and control systems (ADCS), miniaturised target acquisition and tracking sensors, compact and robust sources of single and entangled photons, and high-speed classical communications systems, all to be incorporated within a 10 kg 6 litre mass-volume envelope. The CubeSat Quantum Communications Mission (CQuCoM) would be a pathfinder for advanced nanosatellite payloads and operations, and would establish the basis for a constellation of low-Earth orbit trusted-nodes for QKD service provision.

Sabine Hossenfelder

We review the question of whether the fundamental laws of nature limit our ability to probe arbitrarily short distances. First, we examine what insights can be gained from thought experiments for probes of shortest distances, and summarize what can be learned from different approaches to a theory of quantum gravity. Then we discuss some models that have been developed to implement a minimal length scale in quantum mechanics and quantum field theory. These models have entered the literature as the generalized uncertainty principle or the modified dispersion relation, and have allowed the study of the effects of a minimal length scale in quantum mechanics, quantum electrodynamics, thermodynamics, black-hole physics and cosmology. Finally, we touch upon the question of ways to circumvent the manifestation of a minimal length scale in short-distance physics.

O. L. Zarubin

Dynamic of the artificial radionuclides content of in water of the cooling-pond of ChNPP was studied starting from 1978 till 2004. The total content of radionuclides was founded within the limits of 0,005 - 0,05 Bq/l in the period of 1978 - 1984. After the accident in 1986 the total content of radionuclides in water amounted to 3,7 ⋅ 105 Bq/l. The main contribution in radionuclides’ pollution of water introduces 137Cs and 90Sr from the end of 1986. Their content is sharply decreased till 1990 - 1992, and then the decrease occurs more smoothly. Seasonal dynamic of the content of 137Cs is revealed. In by autumn its quantity in water is increased. The abnormal low relation 90Sr/137Cs in water of cooling-pond on comparison with other reservoirs 30-km Zone is registered during 1987 - 2004. The content of radionuclides in water of the cooling-pond of ChNPP in 2004 approximately in 100 times exceeds the levels of content before the accident.

Winicour Jeffrey

I review the development of numerical evolution codes for general relativity based upon the characteristic initial value problem. Progress is traced from the early stage of 1D feasibility studies to current 3D codes that simulate binary black holes. A prime application of characteristic evolution is Cauchy-characteristic matching, which is also reviewed.