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

Haode Wang, Tongning Wu, Haoyu Jiang et al.

This study develops an optimized personalized microwave hyperthermia framework for glioblastoma treatment, integrating a 19-channel radiofrequency array of geometrically and electromagnetically co-optimized cosine-curved dipole antennas. We initiated the design by optimizing the conductor geometry (amplitude, wavelength, and phase offset) to reshape the current distribution. Concurrently, resonant coupling loops were incorporated to provide additional degrees of freedom for impedance tuning. This combined approach establishes a synergistic mechanism, thereby overcoming the limitations of ultra-high-frequency dipoles and achieving enhanced impedance matching at 2.45 GHz, which is demonstrated by an S11 value of −19.2 dB obtained through particle swarm optimization. The semidefinite relaxation (SDR) algorithm optimizes channel excitations under a 72-W total power constraint to maximize the tumor-specific absorption rate while minimizing exposure to healthy tissue. Multianatomical electromagnetic–thermal validation confirms a treatment planning time of 0.31 min, representing a 50% speed improvement over particle swarm optimization. This delivers a precise 41.69°C mean tumor temperature with superior targeting quantified by a specific absorption rate amplification factor (SAF) of 4.46 and a hotspot-to-target quotient (HTQ) of 0.81. Parametric analysis reveals depth-progressive SAF attenuation from 4.33 at superficial positions to 2.67 at 4 cm depth alongside improved large-tumor targeting achieving SAF 4.63 and HTQ 0.75 at 5 cm diameter. A pediatric model exhibits heightened electromagnetic sensitivity showing SAF 5.02 versus less than 5% variation in adult models, establishing a clinically translatable pathway for precision brain hyperthermia. This work is a computational study validated entirely through in silico simulations, without involving in vivo or clinical experiments.

Benedikt Baier, Ria Rosenauer, Vili Li et al.

Future communication systems are expected to integrate quantum networks to enable highly secure communication and enhance computational capabilities. In quantum networks, communication is accomplished by sharing entanglement between remote locations, which is the basis for most known quantum protocols. Entanglement is a correlation between qubits that is not reproducible with classical means. However, as entanglement is susceptible to noise limiting its range, quantum repeaters can enable entanglement over more considerable distances. Using the entanglement swapping protocol, quantum repeaters can be placed between remote locations to establish entanglement. This requires each repeater to first generate entanglement with its neighboring nodes, named entanglement generation. However, as the size of current quantum networks is limited, the development and evaluation of quantum networks and quantum protocols are based on simulations. To simulate quantum networks accurately, accurate and high-performance models of the entanglement generation process must be employed. This article proposes two new models for generating entanglement in simulations and develops quantum protocols for generating and purifying entanglement. The protocols are evaluated in thorough simulations under perfect and realistic conditions regarding delay and fidelity. Furthermore, the accuracy and runtime of the models are evaluated. The results show that the models are accurate, with delay primarily influenced by the source duration, while longer coherence times significantly enhance fidelity. The model runtimes are consistently shorter than the simulation runtimes across all protocols, averaging about 2% of the total simulation time.

Xiao-Wei Zhang, Kaijie Yang, Chong Wang et al.

Abstract We develop a twist-angle transferable continuum model for twisted transition metal dichalcogenide (tTMD) homobilayers, using tMoTe2 and tWSe2 as examples. All model parameters are extracted from density functional theory (DFT) calculations at a single twist angle (3.89°) and monolayer data. Our model captures both lattice relaxation effects and the long-range behavior of piezoelectric and ferroelectric potentials. Leveraging lattice relaxations obtained via machine learning force fields (MLFFs), the model can be efficiently transferred to other twist angles without requiring additional DFT calculations. It accurately reproduces the DFT band dispersions and quantum geometries across a wide range of twist angles. Furthermore, our model reveals that a second flat Chern band arises near 2° when the interlayer potential difference becomes comparable to the interlayer tunneling. This continuum model provides a clear understanding and starting point for engineering novel electronic phases in moiré TMDs through twist angles and lattice relaxations.

Niccolò Baldelli, Hannes Karlsson, Benedikt Kloss et al.

Abstract The phenomena of superconductivity and charge density waves are observed in close vicinity in many strongly correlated materials. Increasing evidence from experiments and numerical simulations suggests both phenomena can also occur in an intertwined manner, where the superconducting order parameter is coupled to the electronic density. Employing density matrix renormalization group simulations, we investigate the nature of such an intertwined state of matter stabilized in the phase diagram of the elementary $$t-{t}^{{\prime} }-U$$ t − t ′ − U Hubbard model in the strong coupling regime. Remarkably, the condensate of Cooper pairs is shown to be fragmented in the presence of a charge density wave where more than one pairing wave function is macroscopically occupied. Moreover, we provide conclusive evidence that the macroscopic wave functions of the superconducting fragments are well-described by soliton solutions of a Ginzburg-Landau equation in a periodic potential constituted by the charge density wave. In the presence of an orbital magnetic field, the order parameters are gauge invariant, and superconducting vortices are pinned between the stripes. This intertwined Ginzburg-Landau theory is proposed as an effective low-energy description of the stripe fragmented superconductor.

Jiahao Chen, Elyana Crowder, Lian Xiang et al.

The non-Markovian dynamics of an open quantum system can be rigorously derived using the Feynman–Vernon influence functional approach. Although this formalism is exact, practical numerical implementations often require compromises. The time-convolutionless (TCL) master equation offers an exact framework, yet its application typically relies on a perturbative expansion of both the time forward and time backward state propagators. Due to the significant computational effort involved—and the scarcity of analytical solutions for most open quantum systems—the fourth-order perturbative TCL generator (TCL4) has only been benchmarked on a limited range of systems and parameter spaces. Recent advancements, however, have made the computation of TCL4 faster and more accessible. In this paper, we benchmark the TCL4 master equation against numerically exact methods for the biased spin-boson model. We focus on the regime near critical bath coupling where perturbative master equations are expected to become inaccurate. Our findings reveal that the TCL4 approach is most reliable at low temperatures and more efficient than the numerical exact methods. This study aims to delineate the conditions under which the TCL4 perturbative master equation enhances the accuracy of the TCL2.

Alberto Tarable, Rudi Paolo Paganelli, Elisabetta Storelli et al.

This article introduces generalized quantum-assisted digital signature (GQaDS), an improved version of a recently proposed scheme whose information-theoretic security is inherited by adopting quantum key distribution keys for digital signature purposes. Its security against forging is computed considering a trial-and-error approach taken by the malicious forger, and GQaDS parameters are optimized via an analytical approach balancing between forgery and repudiation probabilities. The hash functions of the previous implementation are replaced with Carter–Wegman message authentication codes, strengthening the scheme security and reducing the signature length. For particular scenarios where the second verifier has a safe reputation, a simplified version of GQaDS, namely deterministic GQaDS, can further reduce the required signature length, keeping the desired security strength.

João C. Getelina, Prachi Sharma, Thomas Iadecola et al.

Finding ground state energies on current quantum processing units (QPUs) using algorithms such as the variational quantum eigensolver (VQE) continues to pose challenges. Hardware noise severely affects both the expressivity and trainability of parameterized quantum circuits, limiting them to shallow depths in practice. Here, we demonstrate that both issues can be addressed by synergistically integrating VQE with a quantum subspace expansion, allowing for an optimal balance between quantum and classical computing capabilities and costs. We perform a systematic benchmark analysis of the iterative quantum-assisted eigensolver in the presence of hardware noise. We determine ground state energies of 1D and 2D mixed-field Ising spin models on noisy simulators and the IBM QPUs ibmq_quito (5 qubits) and ibmq_guadalupe (16 qubits). To maximize accuracy, we propose a suitable criterion to select the subspace basis vectors according to the trace of the noisy overlap matrix. Finally, we show how to systematically approach the exact solution by performing controlled quantum error mitigation based on probabilistic error reduction on the noisy backend fake_guadalupe.

Aleksandr Melkozerov, Ashot Avanesov, Ivan Dyakonov et al.

Bell state measurements (BSMs) play a significant role in quantum information and quantum computing, in particular in fusion-based quantum computing (FBQC). The FBQC model is a framework for universal quantum computing, provided that we are able to perform entangling measurements, called fusions, on qubits within small entangled resource states. Here, we analyze the usage of different linear-optical BSM circuits as fusions in the FBQC schemes and numerically evaluate hardware requirements for fault-tolerance in this framework. We examine and compare the performance of several BSM circuits with varying additional resources and estimate the requirements on losses for every component of the linear-optical realization of fusions under which errors in fusion networks caused by these losses can be corrected. Our results show that fault-tolerant quantum computing in the FBQC model is possible with currently achievable levels of optical losses in an integrated photonic implementation, provided that we can create and detect single photons of the resource states with a total marginal efficiency higher than 0.973.

David Winderl, Nicola Franco, Jeanette Miriam Lorenz

Variational quantum optimization algorithms, such as the variational quantum eigensolver (VQE) or the quantum approximate optimization algorithm (QAOA), are among the most studied quantum algorithms. In our work, we evaluate and improve an algorithm based on the VQE, which uses exponentially fewer qubits compared to the QAOA. We highlight the numerical instabilities generated by encoding the problem into the variational ansatz and propose a classical optimization procedure to find the ground state of the ansatz in fewer iterations with a better or similar objective. In addition, we propose a method to embed the linear interpolation of the MaxCut problem on a quantum device. Furthermore, we compare classical optimizers for this variational ansatz on quadratic unconstrained binary optimization and graph partitioning problems.

Daniel Volya, Prabhat Mishra

Quantum computers present a compelling platform for the study of open quantum systems, namely, the nonunitary dynamics of a system. Here, we investigate and report digital simulations of Markovian nonunitary dynamics that converge to a unique steady state. The steady state is programmed as a desired target state, yielding semblance to a quantum state preparation protocol. By delegating ancilla qubits and system qubits, the system state is driven to the target state by repeatedly performing the following steps: 1) executing a designated system–ancilla entangling circuit; 2) measuring the ancilla qubits; and 3) reinitializing ancilla qubits to known states through active reset. While the ancilla qubits are measured and reinitialized to known states, the system qubits undergo a nonunitary evolution and are steered from arbitrary initial states to desired target states. We show results of the method by preparing arbitrary qubit states and qutrit (three-level) states on contemporary quantum computers. We also demonstrate that the state convergence can be accelerated by utilizing the readouts of the ancilla qubits to guide the protocol in a nonblind manner. Our work serves as a nontrivial example that incorporates and characterizes essential operations, such as qubit reuse (qubit reset), entangling circuits, and measurement. These operations are not only vital for near-term noisy intermediate-scale quantum applications but are also crucial for realizing future error-correcting codes.

Yiwen Huang, Yuanhua Li, Zhantong Qi et al.

Abstract Exploiting the fantastic features of quantum mechanics, a hyperentangled quantum network encoded in multiple degree of freedoms (DOF), e.g., polarization and orbital angular momentum DOFs, can encode more qubits per transmitted photon and offers a promising platform for many dramatic applications. Here, we demonstrate such a hyperentangled multiuser network with a fully connected network architecture by using dense wavelength division multiplexing and entanglement transfer technique. Three hyperentangled states in polarization and time-energy DOFs are multiplexed to three single mode fibers to form the fully connected network architecture. Then, three interferometric quantum gates are utilized for transferring quantum entanglement from time-energy to orbital angular momentum DOF. The experimental results reveal a high quality of the hyperentanglement of the constructed network with the entangled state fidelity of higher than 96%. Our approach can provide a novel way to construct a large-scale hyperentangled network that can support various kinds of quantum tasks like superdense coding and teleportation.

O. A. Vasylkevych, V. I. Slisenko

The problem considered in this work relates to the physics of liquids. Rather, to the physics of dynamic processes in liquids. The method of quasielastic scattering of slow neutrons was used to study the dynamics of molecules of the water-ethanol system as a function of concentration at a temperature of 8 °C and as a function of temperature at a concentration of X = 0.04 molar particles (mol. particl.). The overall coefficient of self-diffusion of molecules D, its single-particle Ds-p and collective Dcoll components, as well as the time of settled life of a molecule in a vibrational state t, are determined. The region of small concentrations was studied in detail, where in the vicinity of concentrations X = 0.04 mol. particl. and X = 0.2 mol. particl. two minima are found in the coefficients D and Ds-p. Time t at these concentrations increases significantly. This indicates a significant decrease in the intensity of the activation mechanism of molecular diffusion at these concentrations, which is quite possibly caused by the binding of water and ethanol molecules into complexes (clusters). Similarly, a deep minimum was found in the D and Ds-p coefficients near the temperature of 4 °С. Time t at this temperature also increases. That is, at a temperature of 4 °C, the intensity of the activation mechanism of the diffusion of solution molecules decreases. Therefore, at a concentration of X = 0.04 mol. particl. and at a temperature of 4°C, a special point exists in the water-ethanol system. However, its position does not coincide with the data on scattering light.

Shuai Li, C. M. Wang, Z. Z. Du et al.

Abstract The classical and quantum Hall effects are important subjects in condensed matter physics. The emergent 3D quantum Hall effects and nonlinear Hall effect have attracted considerable interest recently, with the former elevating the quantum Hall effect to a higher dimension and the latter extending the Hall effect to higher-order responses. In this perspective, we briefly introduce these two new members of the Hall family and discuss the open questions and future research directions.

Chandra Sekhar Mukherjee, Subhamoy Maitra, Vineet Gaurav et al.

Exact requirement of controlled NOT (CNOT) and single-qubit gates to implement a quantum algorithm in a given architecture is one of the central problems in this computational paradigm. In this article, we take a tutorial approach in explaining the preparation of Dicke states (|D_kⁿ〉) using concise realizations of partially defined unitary transformations. We show how to efficiently implement the state-of-the-art deterministic Dicke state preparation circuits and in turn optimize them in terms of CNOT and single-qubit gate counts. We explain theoretical ideas in reducing the gate counts and observe how these improvements are reflected in actual implementation of the circuits. To emphasize the advantages, we describe the circuit for preparing |D₂⁴〉 on the “ibmqx2” machine of the IBM quantum experience (QX) service. Our approach shows that the error induced due to noise in the system is lesser in comparison to the existing works. We conclude by describing the CNOT map of the generic |D_kⁿ〉 preparation circuit and analyze different ways of distributing the CNOT gates in the circuit and its effect on the induced error in the Noisy Intermediate Scale Quantum environment.

Clare Burrage, Jeremy Sakstein

Abstract Theories of modified gravity, where light scalars with non-trivial self-interactions and non-minimal couplings to matter—chameleon and symmetron theories—dynamically suppress deviations from general relativity in the solar system. On other scales, the environmental nature of the screening means that such scalars may be relevant. The highly-nonlinear nature of screening mechanisms means that they evade classical fifth-force searches, and there has been an intense effort towards designing new and novel tests to probe them, both in the laboratory and using astrophysical objects, and by reinterpreting existing datasets. The results of these searches are often presented using different parametrizations, which can make it difficult to compare constraints coming from different probes. The purpose of this review is to summarize the present state-of-the-art searches for screened scalars coupled to matter, and to translate the current bounds into a single parametrization to survey the state of the models. Presently, commonly studied chameleon models are well-constrained but less commonly studied models have large regions of parameter space that are still viable. Symmetron models are constrained well by astrophysical and laboratory tests, but there is a desert separating the two scales where the model is unconstrained. The coupling of chameleons to photons is tightly constrained but the symmetron coupling has yet to be explored. We also summarize the current bounds on f(R) models that exhibit the chameleon mechanism (Hu and Sawicki models). The simplest of these are well constrained by astrophysical probes, but there are currently few reported bounds for theories with higher powers of R. The review ends by discussing the future prospects for constraining screened modified gravity models further using upcoming and planned experiments.

Qingyu Lei, Maryam Golalikhani, Bruce A. Davidson et al.

Applied physics: New technique for oxide interfaces Recent advances in synthesizing and engineering oxide interfaces and heterostructures have provided a powerful strategy for creating new artificial structures exhibiting phenomena not possible in other materials form. Now Professor Xiaoxing Xi at Temple University from the US collaborates with researchers from the US, Italy and China showing a success in constructing oxides with well controlled stoichiometry and atomic layer precision. The central method—atomic layer-by-layer laser molecular beam epitaxy (ALL-Laser MBE)—is built upon the combined strengths of molecular beam epitaxy and pulsed laser deposition. It allows not only the growth of thin films of a Ruddlesden-Popper phase La5Ni4O13, but LaAlO3/SrTiO3 interfaces. Remarkably, no oxygen vacancies are detected in the oxide interfaces because of the high oxygen pressures during the growth and the carrier density of the two-dimensional electron gas agrees with the electronic reconstruction mechanism.

A. I. Levon, G. Graw, R. Hertenberger et al.

The excitation spectra in the deformed nucleus 232U have been studied by means of the (p, t) reaction, using the Q3D spectrograph facility at the Munich Tandem accelerator. The angular distributions of tritons were measured for 162 excitations seen in the triton spectra up to 3.25 MeV. 0+ assignments are made for 13 excited states by comparison of experimental angular distributions with the calculated ones using the CHUCK3 code. Assignments up to spin 6+are made for other states.

М. F. Mitrokhovich

Correlation study of the "shake-off" electron (as accompanying particle) with positron (as a main particle) has been performed for 152Eu decay with installation to measure double, triple, fourth γ-quanta coincidences with β±-particles, electrons and with low energy electrons, including eo-electrons of the secondary electron emission. Correlation ϒ = (4π/P)dp/dΩ of "shake-off" electron with positron was measured regarding correlation of "shake-off" electron with β--particle on the basis of the measurements of γ, γβ, γ(еo+β)-, γβеo- and γβγ511-, γβγ511еo-spectra. It was established that accompanying "shake-off" electron is strongly correlated forward with the main particle (β±-particle) and correlation of ϒ motion with positron is 1.6 times greater than correlation motion with β--particle and is equal to 5.2(20) at the measurement in 152Eu decay. Possible qualitative mechanism of strong correlation motion of the accompanying particle with the main particle in β-decay processes and internal conversion, caused by current components of the direct interaction of particles, is discussed.

O. E. Valkov, O. V. Dubinin, O. K. Zaichenko

Method of measuring of the beam parameters at the entrance of the ion-optical tract of the cyclotron U-240 stable isotope separator is described.

V. F. Razbudey

Ideology of simulation of neutron experiments using Monte Carlo method for optimization of experimental conditions and analysis of measurement results is set out. Potentialities are shown and recommendations are worked out relative to use of simulation both on the stage of planning experiment and while correcting the results of measuring for ill-wresting factors.