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

Nilesh Sharma, Shashank Kumar Ranu, Prabha Mandayam et al.

Measurement-device-independent quantum key distribution (MDI-QKD) enhances security by removing vulnerabilities associated with detector side channels. Real-world implementations ofMDI-QKD face practical challenges, such as channel asymmetry and physical imperfections, which degrade the visibility of Hong&#x2013;Ou&#x2013;Mandel interference, an essential factor in determining the secure key rate. In this work, we evaluate the performance of differential phase encoded (DPE) MDI-QKD under realistic, asymmetric conditions. We analyze the effects of polarization and pulsewidth mismatches caused by channel asymmetry and identify tolerable limits for secure key generation. We introduce a plug-and-play DPE-MDI-QKD architecture that mitigates polarization fluctuations using Faraday mirrors and also compensates for pulsewidth mismatches. Furthermore, we propose an improved sifting scheme that raises the sifting efficiency from <inline-formula><tex-math notation="LaTeX">$\frac{4}{9}$</tex-math></inline-formula> to <inline-formula><tex-math notation="LaTeX">$\frac{2}{3}$</tex-math></inline-formula>, improving the secure key generation rates by 50&#x0025; and making it especially suitable for plug-and-play systems. These results offer practical insights into enhancing the robustness and efficiency of DPE-MDI-QKD, enabling more secure quantum communication over imperfect and asymmetric quantum channels.

Andrew Cupo, Shuanglong Liu, Silas Hoffman et al.

We theoretically study Floquet engineering of magnetic molecules via a time-periodic magnetic field that couples to the emergent total electronic spin of the metal center. By focusing on the low-lying energy levels using an S = 1 spin Hamiltonian containing the zero-field and Zeeman terms, we demonstrate their continuous tunability under the Floquet field. Remarkably, under the action of linearly polarized Floquet controls, the energy levels of a clock transition qubit retain their stability against variations in an external static magnetic field. This property is closely linked to having a net-zero total Zeeman shift, which results from both static and effective dynamical contributions. Furthermore, using second-order Van Vleck degenerate perturbation theory, we derived an effective Hamiltonian analytically, which explicitly shows the dependence of the renormalized zero-field tensor on the driving field. Based on our theoretical predictions, experimentalists will be able to dynamically tune qubit energy gaps to values that are useful in their specific laboratory settings, while retaining the spin decoherence suppressing effect of maintaining a clock transition.

Hsin-Yeh Wu, Marc Besançon, Jia-Wern Chen et al.

A dual-operation mode SNSPD is proposed. In the conventional Geiger mode, the sensor operates at temperatures well below the critical temperature TC, working as an event counter without sensitivity to the number of photons that impinge on the sensor. In the calorimetric mode, the detector is operated at temperatures just below TC and displays calorimetric sensitivity in the range of 15–250 absorbed photon energy equivalent for a photon beam with a wavelength of 515 nm. In this energy-sensitive mode, photon absorption causes Joule heating of the SNSPD that becomes partially resistive without the presence of latching. Depending on the application, by tuning the sample temperature and bias current using the same readout system, the SNSPD can readily switch between the two modes. In the calorimetric mode, SNSPD recovery times shorter than those in the Geiger mode are observed, reaching values as low as 560 ps. Dual-mode SNSPDs, in addition to providing solutions in applications in spectroscopy and calorimetry, where precise timing and energy resolution are required, may also offer significant advancements in high-speed photon-number-resolving detection through their flexible hybrid architecture, driving innovation in optical quantum computing and quantum-source characterization.

H. G. Ahmad, D. Massarotti, F. Tafuri et al.

Yanik Herrmann, Julia M Brevoord, Julius Fischer et al.

Micrometer-scale thin diamond devices are key components for various quantum sensing and networking experiments, including the integration of color centers into optical microcavities. In this work, we introduce a laser-cutting method for patterning microdevices from millimeter-sized diamond membranes. The method can be used to fabricate devices with micrometer thicknesses and edge lengths of typically 10–100  µ m. We compare this method with an established nanofabrication process based on electron-beam lithography, a two-step transfer pattern utilizing a silicon nitride hard mask material, and reactive ion etching. Microdevices fabricated using both methods are bonded to a cavity Bragg mirror and characterized using scanning cavity microscopy. We record two-dimensional cavity finesse maps over the devices, revealing insights about the variation in diamond thickness, surface quality, and strain. The scans demonstrate that devices fabricated by laser-cutting exhibit similar properties to devices obtained by the conventional method. Finally, we show that the devices host optically coherent Tin- and Nitrogen-Vacancy centers suitable for applications in quantum networking.

Paulo C. C. Freire, Norbert Wex

Abstract The discovery of the first pulsar in a binary star system, the Hulse–Taylor pulsar, 50 years ago opened up an entirely new field of experimental gravity. For the first time it was possible to investigate strong-field and radiative aspects of the gravitational interaction. Continued observations of the Hulse–Taylor pulsar eventually led, among other confirmations of the predictions of general relativity (GR), to the first evidence for the reality of gravitational waves. In the meantime, many more radio pulsars have been discovered that are suitable for testing GR and its alternatives. One particularly remarkable binary system is the Double Pulsar, which has far surpassed the Hulse–Taylor pulsar in several respects. In addition, binary pulsar-white dwarf systems have been shown to be particularly suitable for testing alternative gravitational theories, as they often predict strong dipolar gravitational radiation for such asymmetric systems. A rather unique pulsar laboratory is the pulsar in a hierarchical stellar triple, that led to by far the most precise confirmation of the strong-field version of the universality of free fall. Using radio pulsars, it could be shown that additional aspects of the Strong Equivalence Principle apply to the dynamics of strongly self-gravitating bodies, like the local position and local Lorentz invariance of the gravitational interaction. So far, GR has passed all pulsar tests with flying colours, while at the same time many alternative gravity theories have either been strongly constrained or even falsified. New telescopes, instrumentation, timing and search algorithms promise a significant improvement of the existing tests and the discovery of (qualitatively) new, more relativistic binary systems.

Ioannis Krikidis

In this article, we study the problem of digital pre/postcoding design in multiple-input multiple-output (MIMO) systems with 1-b resolution per complex dimension. The optimal solution that maximizes the received signal-to-noise ratio relies on an NP-hard combinatorial problem that requires exhaustive searching with exponential complexity. By using the principles of alternating optimization and quantum annealing (QA), an iterative QA-based algorithm is proposed that achieves near-optimal performance with polynomial complexity. The algorithm is associated with a rigorous mathematical framework that casts the pre/postcoding vector design to appropriate real-valued quadratic unconstrained binary optimization (QUBO) problems. Experimental results in a state-of-the-art D-WAVE QA device validate the efficiency of the proposed algorithm. To further improve the efficiency of the D-WAVE quantum device, a new preprocessing technique, which preserves the quadratic QUBO matrix from the detrimental effects of the Hamiltonian noise through nonlinear companding, is proposed. The proposed preprocessing technique significantly improves the quality of the D-WAVE solutions as well as the occurrence probability of the optimal solution.

Fysol Ibna Abbas, G M Bhuiyan

Abstract Atomic transport properties specifically the shear viscosity and the diffusion coefficient for Zn x Bi 1 − x liquid monotectic segregating alloys are theoretically investigated by using the Rice–Allnatt theory. The essential ingredient for the microscopic description of the metals and their alloys is the interionic interaction which in the present work is described by a widely used local pseudopotential. The temperature dependent behaviour of the above mentioned physical properties is also examined. The overall agreement of our calculated results with the available experimental data is found to be good for the full range of concentration. More interestingly, the temperature dependent results for the viscosity and the diffusion coefficient apparently exhibit a signature of liquid–liquid phase separation through a sudden bending in their concentration dependent profiles. Onset of this bending also provides information about the critical temperature and the critical concentration, and also provides a value for the critical exponent of liquid–liquid phase separation.

S. Yu. Mezhevych, A. T. Rudchik, K. Rusek et al.

New experimental data for differential cross-sections of the 14C(11B, 12C)13B reaction obtained recently at the energy Еlab(11B) = 45 MeV for the ground states of 13B and 12C were analyzed within the coupled reaction channels (CRC) method that included the 11B + 14C elastic scattering channel as well as channels for one- and two-step transfers of nucleons in the coupling scheme. The necessary 11B + 14C Woods - Saxon (WS) optical potential parameters for the entrance reaction channel were obtained from 11B elastic scattering in the previous work, while those for 12C + 13B interaction were deduced from fitting the CRC calculations to the 14C(11B, 12C)13B reaction data. Needed spectroscopic amplitudes of transferred nucleons and clusters were calculated within the translational-invariant shell model. The data are well described by the direct transfer of a proton while contributions from two-step transfers were found to be negligible. The deduced 13B + 12C WS optical potential parameters are compared with those of the 10,11,12B + 12C nuclei interactions. The effect of isotopic differences in these interactions was observed.

Hiroko Yokota, Takeshi Hayashida, Dan Kitahara et al.

Abstract The spontaneous symmetry breakdown of matter is one of the most important concepts in materials physics and leads to a phase transition into an ordered phase and domain formation in its consequence. The so-called ‘ferroaxial order’ characterized by a rotational structural distortion with an axial vector symmetry has gained growing interest as a new class of ordered state. However, the observation of ferroaxial domain states, that is, clockwise and counterclockwise rotational states, is not straightforward and has been little investigated. Here, we propose that the circular intensity difference in second harmonic generation (CID-SHG) offers an experimental technique to investigate ferroaxial order and its domain states through the transition process of higher-order multipoles such as magnetic-dipole and electric-quadrupole. By using CID-SHG microscopy, we successfully visualize three-dimensional images of ferroaxial domain structures in NiTiO3. Our results indicate that CID-SHG is a sensitive probe of ferroaxial order and opens possibilities for the use of ferroaxial materials in nonlinear optical manipulations.

Sudipta Moshat, Dirtha Sanyal

Simon Martiel, Thomas Ayral, Cyril Allouche

Existing protocols for benchmarking current quantum coprocessors fail to meet the usual standards for assessing the performance of high-performance-computing platforms. After a synthetic review of these protocols&#x2014;whether at the gate, circuit, or application level&#x2014;we introduce a new benchmark, dubbed Atos Q-score, which is application-centric, hardware-agnostic, and scalable to quantum advantage processor sizes and beyond. The Q-score measures the maximum number of qubits that can be used <italic>effectively</italic> to solve the MaxCut combinatorial optimization problem with the quantum approximate optimization algorithm. We give a robust definition of the notion of effective performance by introducing an improved approximation ratio based on the scaling of random and optimal algorithms. We illustrate the behavior of Q-score using perfect and noisy simulations of quantum processors. Finally, we provide an open-source implementation of Q-score that makes it easy to compute the Q-score of any quantum hardware.

Sebastian de Bone, Runsheng Ouyang, Kenneth Goodenough et al.

The distribution of high-quality Greenberger-Horne-Zeilinger (GHZ) states is at the heart of many quantum communication tasks, ranging from extending the baseline of telescopes to secret sharing. They also play an important role in error-correction architectures for distributed quantum computation, where Bell pairs can be leveraged to create an entangled network of quantum computers. We investigate the creation and distillation of GHZ states out of nonperfect Bell pairs over quantum networks. In particular, we introduce a heuristic dynamic programming algorithm to optimize over a large class of protocols that create and purify GHZ states. All protocols considered use a common framework based on measurements of nonlocal stabilizer operators of the target state (i.e., the GHZ state), where each nonlocal measurement consumes another (nonperfect) entangled state as a resource. The new protocols outperform previous proposals for scenarios without decoherence and local gate noise. Furthermore, the algorithms can be applied for finding protocols for any number of parties and any number of entangled pairs involved.

R Besson, L Thuinet, M-A Louchez

Abstract We performed atomic-scale ab initio calculations to investigate the stacking fault (SF) properties of the metastable ζ -Zr 2 H zirconium hydride. The effect of H near the SF was found to entail the existence of negative SF energies, showing that the ζ compound is probably unstable with respect to shearing in the basal plane. The effect of temperature on SFs was investigated by means of free energy calculations in the quasiharmonic approximation. This evidenced unexpectedly large temperature effects, confirming the main conclusions drawn at 0 K, in particular the ζ mechanical instability. The complex behaviour of H atoms during the shear process suggested ζ -hcp  →  Zr 2 H -fcc as a plausible shear path leading to an fcc compound with same composition as ζ . Finally, as shown by an analysis based on microelasticity, this Zr 2 H -fcc intermediate compound may be relevant for better interpreting the currently intricate issue of hydride habit planes in zirconium.

S. N. Fedotkin

Corrections to the wave functions of atomic electrons in hydrogen-like atom are calculated by using the Thomas - Fermi potential in the framework of perturbation theory. In this approach the interaction of electrons in atom is approximately taken into account. Corrections to wave functions are important for describing various processes involving electrons in multielectronic atoms. Cross sections of the photoelectric effect on the L-shell of the atom are calculated in the proposed approach with impurity for the admixture of K-shell states.

X. Leng, J. Pereiro, J. Strle et al.

Electrolyte gating: Hydrogenation mechanism in WO3 The mechanism leading to large carrier density changes and even concomitant electronic phase transitions with electrolyte gating is under debate. An international team led by Ivan Božović at USA’s Brookhaven National Laboratory and Yale University report a series of experiments based on WO3 films, which is found to exhibit an insultator-to-metal transition under gating, with both ionic liquids and polymer electrolytes. The experimental results allow to rule out some mechanisms—such as charge accumulation near the interface or oxygen vacancy formation—previously suggested in other material systems. Instead, the authors propose that the primary effect of electrolyte gating in WO3 is hydrogen intercalation. Hydrogenation leads to the formation of a dense polaronic gas that explains the conductive ground state. The doping mechanism behind electrolyte gating seems to be material dependent.

І. P. Drozd, Yu. S. Oliynyk, O. A. Sova

Scientific analysis of the theoretical basis of the methodology for estimating the radioecological capacity of the territories in the zone of the influence of the operating facilities of nuclear fuel cycle in Ukraine was carried out. Existing concept of the environmental security under the technogenic impact to the environment was considered. The methods of the estimation of the radioecological capacity of the territory near existing and new potential enterprises in the context of human security was proposed.

V. P. Krasnov, T. V. Kurbet, Z. M. Shelest et al.

137Cs distribution in sod-podzol forest soil of Ukrainian Polissia in different types of forest condition is studied. Rates of specific and total radionuclide’s activity in the layers of forest floor and in the mineral part of soil are analyzed. According to the qualitative study of 137Cs distribution in the soil of pine plantation the forest floor is considered to be the geochemical barrier for the migration of radionuclides into soil. The highest total radionuclide activity in humus-eluvial horizont is observed.

John Stachel

This is a historical-critical study of the hole argument, concentrating on the interface between historical, philosophical and physical issues. Although it includes a review of its history, its primary aim is a discussion of the contemporary implications of the hole argument for physical theories based on dynamical, background-independent space-time structures. The historical review includes Einstein’s formulations of the hole argument, Kretschmann’s critique, as well as Hilbert’s reformulation and Darmois’ formulation of the general-relativistic Cauchy problem. The 1970s saw a revival of interest in the hole argument, growing out of attempts to answer the question: Why did three years elapse between Einstein’s adoption of the metric tensor to represent the gravitational field and his adoption of the Einstein field equations? The main part presents some modern mathematical versions of the hole argument, including both coordinate-dependent and coordinate-independent definitions of covariance and general covariance; and the fiber bundle formulation of both natural and gauge natural theories. By abstraction from continuity and differentiability, these formulations can be extended from differentiable manifolds to any set; and the concepts of permutability and general permutability applied to theories based on relations between the elements of a set, such as elementary particle theories. We are closing with an overview of current discussions of philosophical and physical implications of the hole argument.

A. V. Mikhailov, Yu. N. Pavlenko, V. L. Shablov et al.

The modified final-state interaction theory taking into consideration the Coulomb interaction between two-fragment nuclear resonance decay products and accompanying reaction products is developed including the case of near-threshold resonances. The branching ratio change is also studied for the near-threshold resonance 7Li*(Ex = 7.45 MeV), which is formed in the reaction 7Li(α, α)7Li* at Eα = 27.2 MeV.