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

Vikesh Siddhu, Avhishek Chatterjee, Krishna Jagannanthan et al.

Quantum queue-channels arise naturally in the context of buffering in quantum networks, wherein the noise suffered by the quantum states depends on the time spent waiting in the buffer. Mandayam (2020) derived a simple upper bound on the classical capacity of an additive queue-channel and showed it to be achievable for the erasure and depolarizing channels. In this article, we characterize the classical capacity for the class of unital qubit queue-channels and show that a simple product (nonentangled) decoding strategy is capacity achieving. As an intermediate step, we present a simpler derivation of an explicit capacity-achieving product decoding strategy for any independent identically distributed unital qubit channel, which may be of interest. As an important special case, we also derive the capacity and optimal decoding strategies for a symmetric generalized amplitude damping queue-channel. Our results provide useful insights toward designing practical quantum communication networks and highlight the need to explicitly model the impact of buffering.

Abir Mukherjee, Kajal Sharma, Kamlesh Bhatt et al.

In this work, we report the wafer scale growth of high-quality, ultra-thin (3L) MoTe2 quantum wells using molecular beam epitaxy on a HfO2/WSe2 heterostructure. The structural and morphological quality of the 2H-MoTe2 was confirmed via in situ reflection high energy electron diffraction pattern and its oscillations, XPS, and AFM spectroscopy. The underlying WSe2, grown by chemical vapor deposition, retains its crystallinity and integrity throughout the growth process, as verified by HR-TEM, XRD, and XPS measurements. Cryogenic transport measurements reveal a distinct resonant tunneling peak in the vertical device structure comprising n-WSe2/HfO2/MoTe2/HfO2/Au. Complementary quantum transport modeling based on the non-equilibrium Green’s function formalism further elucidates the role of quantum well width above the excitonic Bohr radius (∼0.7 nm) in tuning the resonant tunneling behavior along with fundamental insights due to phonon-induced decoherence, a key limiting factor in 2D-quantum materials and devices. Therefore, the present work may provide the route for the fabrication of 2D-MoTe2-based quantum devices with further development in high frequency devices, terahertz-emitters, and future quantum processing operations at ultra-low temperatures.

Zeng-Zhao Li, Chi-Hang Lam, Cho-Tung Yip et al.

We present a new approach for investigating the Markovian to non-Markovian transition in quantum aggregates strongly coupled to a vibrational bath through the analysis of linear absorption spectra. Utilizing hierarchical algebraic equations in the frequency domain, we elucidate how these spectra can effectively reveal transitions between Markovian and non-Markovian regimes, driven by the complex interplay of dissipation, aggregate–bath coupling, and intra-aggregate dipole–dipole interactions. Our results demonstrate that reduced dissipation induces spectral peak splitting, signaling the emergence of bath-induced non-Markovian effects. The spectral peak splitting can also be driven by enhanced dipole–dipole interactions, although the underlying mechanism differs from that of dissipation-induced splitting. In addition, with an increase in aggregate–bath coupling strength, initially symmetric or asymmetric peaks with varying spectral amplitudes may merge under weak dipole–dipole interactions, whereas strong dipole–dipole interactions are more likely to cause peak splitting. Moreover, we find that spectral features serve as highly sensitive indicators for distinguishing the geometric structures of aggregates while also unveiling the critical role that geometry plays in shaping non-Markovian behavior. This study not only deepens our understanding of the Markovian to non-Markovian transition but also provides a robust framework for optimizing and controlling quantum systems.

S. M. Thomas, C. S. Kengle, W. Simeth et al.

Abstract Materials in the family RV6Sn6 (R = rare earth) provide a unique platform to investigate the interplay between local moments from R layers and nonmagnetic vanadium kagome layers. Yet, the investigation of actinide members remains scarce. Here we report the synthesis of UV6Sn6 single crystals through the self-flux technique. Physical property measurements reveal two uranium-driven antiferromagnetic transitions at T N1 = 29 K and T N2 = 24 K, a complex field-temperature phase diagram, and unusual negative domain-wall magnetoresistance. Specific heat and angle-resolved photoemission spectroscopy measurements show a moderate f-electron enhancement to the density of states at the Fermi level (E F ), whereas our band structure calculations place the vanadium flat bands 0.25 eV above E F . These findings point to a materials opportunity to expand the uranium 166 family with the goal of enhancing correlations by tuning 5f and 3d flat bands to E F .

Shang-Shun Zhang, Gábor B. Halász, Cristian D. Batista

Abstract Identifying experimental probes capable of diagnosing extreme quantum behavior is widely regarded as one of the foremost challenges in modern condensed matter physics. Here, we propose a novel approach for detecting chiral Kitaev spin-liquid states through measurements of the local dynamical spin structure factor on the boundary using scanning tunneling microscopy (STM). We specifically focus on unpaired (“dangling”) Majorana fermions, which naturally emerge along boundaries of Kitaev spin liquids, and can serve as indicators of chiral boundary modes under broad conditions, thereby offering a clear signature of these exotic quantum states.

Carlotta Ciancico, Iacopo Torre, Bernat Terrés et al.

Two-dimensional crystals and their heterostructures unlock access to a class of photonic devices, bringing nanophotonics from the nanometer scale down to the atomic level where quantum effects are relevant. Single-photon emitters are central in quantum photonics as quantum markers linked to their electrostatic, thermal, magnetic, or dielectric environment. This aspect is exciting in two-dimensional (2D) crystals and their heterostructures, where the environment can be abruptly modified through vertical stacking or lateral structuring, such as moiré or nano-patterned gates. To further develop 2D-based quantum photonic devices, there is a need for quantum markers that are capable of integration into various device geometries and that can be read out individually, non-destructively, and without additional electrodes. Here, we show how to optically detect charge carrier accumulation using sub-GHz linewidth SPEs coupled to a graphene device. We employ the single molecule Stark effect, sensitive to the electric fields generated by charge puddles, such as those at the graphene edge. The same approach enables dynamic sensing of electronic noise, and we demonstrate the optical readout of low-frequency white noise in a biased graphene device. The approach described here can be further exploited to explore charge dynamics in 2D heterostructures using quantum emitter markers.

Benjamin Gys, Lander Burgelman, Kristiaan De Greve et al.

The development of future full-scale quantum computers (QCs) not only comprises the design of good quality qubits, but also entails the design of classical complementary metal–oxide semiconductor (CMOS) control circuitry and optimized operation protocols. The construction and implementation of quantum error correction (QEC) protocols, necessary for correcting the errors that inevitably occur in the physical qubit layer, form a crucial step in this design process. The steadily rising numbers of qubits in a single system make the development of small-scale quantum architectures that are able to execute such protocols a pressing challenge. Similar to classical systems, optimized simulation tools can greatly improve the efficiency of the design process. We propose an automated simulation framework for the development of qubit microarchitectures, in which the effects of design choices in the physical qubit layer on the performance of QEC protocols can be evaluated, whereas the focus in the current state-of-the-art design tools only lies on the simulation of the individual quantum gates. The hybrid Hamiltonian framework introduces the innovative combination of a hybrid nature that allows to incorporate several levels throughout the QC stack, with optimized embedded solvers. This provides the level of detail required for an in-depth analysis of the QEC protocol's stability.

Arman Rashidi, William Huynh, Binghao Guo et al.

Abstract The superconducting quantum interference (SQI) patterns of Josephson junctions fabricated from hybrid structures that interface an s-wave superconductor with a topological insulator can be used to detect signatures of novel quasiparticle states. Here, we compare calculated and experimental SQI patterns obtained from hybrid junctions fabricated on cadmium arsenide, a two-dimensional topological insulator. The calculations account for the effects of Abrikosov (anti-) vortices in the superconducting contacts. They describe the experimentally observed deviations of the SQI from an ideal Fraunhofer pattern, including anomalous phase shifts, node lifting, even/odd modulations of the lobes, irregular lobe spacing, and an asymmetry in the positive/negative magnetic field. We also show that under a current bias, these vortices enter the electrodes even if there is no intentionally applied external magnetic field. The results show that Abrikosov vortices in the electrodes of the junctions can explain many of the observed anomalies in the SQI patterns of topological insulator Josephson junctions.

Hai-Yang Ma, Jin-Feng Jia

Abstract Altermagnetism emerges as the third fundamental collinear magnetism recently. Associating nontrivial topology and quantum orders to this newly established magnetism is an important physical topic and may lead to interesting physics such as unusual quantum spin Hall effect with time-reversal-symmetry breaking, topological superconductivity and spin-valley locking. Here, we first generalize the spinless Haldane model from the usual honeycomb lattice to the otherwise simpler square lattice. We then restore the doublet spin degree of freedom, the resulted spinful model resembles the Kane-Mele model and is able to describe the unprecedented physics which intertwine C $\mathcal{C}$ -paired spin-valley locking, Dirac physics, nontrivial band topology and altermagnetism. Our works shed lights on future studies and applications in spintronics and valleytronics for altermagnetic materials, the lattice theories developed in this article may also find their broad applications to optical lattice with ultra cold atoms, photonic lattice, etc. other than the usual electronic systems.

Bagas Prabowo, Jurgen Dijkema, Xiao Xue et al.

In semiconductor spin quantum bits (qubits), the radio-frequency (RF) gate-based readout is a promising solution for future large-scale integration, as it allows for a fast, frequency-multiplexed readout architecture, enabling multiple qubits to be read out simultaneously. This article introduces a theoretical framework to evaluate the effect of various parameters, such as the readout probe power, readout chain's noise performance, and integration time on the intrinsic readout signal-to-noise ratio, and thus readout fidelity of RF gate-based readout systems. By analyzing the underlying physics of spin qubits during readout, this work proposes a qubit readout model that takes into account the qubit's quantum mechanical properties, providing a way to evaluate the tradeoffs among the aforementioned parameters. The validity of the proposed model is evaluated by comparing the simulation and experimental results. The proposed analytical approach, the developed model, and the experimental results enable designers to optimize the entire readout chain effectively, thus leading to a faster, lower power readout system with integrated cryogenic electronics.

Mohadeseh Azari, Paul Polakos, Kaushik P. Seshadreesan

The Gottesman–Kitaev–Preskill (GKP) code, being information theoretically near optimal for quantum communication over Gaussian thermal-loss optical channels, is likely to be the encoding of choice for advanced quantum networks of the future. Quantum repeaters based on GKP-encoded light have been shown to support high end-to-end entanglement rates across large distances despite realistic finite squeezing in GKP code preparation and homodyne detection inefficiencies. Here, we introduce a quantum switch for GKP qubit-based quantum networks. Its architecture involves multiplexed GKP qubit-based entanglement link generation with clients and their all-photonic storage, enabled by GKP qubit graph state resources. The switch uses a multiclient generalization of a recently introduced entanglement-ranking-based link matching heuristic for bipartite entanglement distribution between clients via entanglement swapping. Since generating the GKP qubit graph state resource is hardware intensive, given a total resource budget and an arbitrary layout of clients, we address the question of their optimal allocation to the different client–pair connections served by the switch such that the switch's sum throughput is maximized while also being fair in terms of the individual entanglement rates. We illustrate our results for an exemplary data center network, where the data center is a client of a switch, and all of its other clients aim to connect to the data center alone—a scenario that also captures the general case of a gateway router connecting a local area network to a global network. Together with compatible quantum repeaters, our quantum switch provides a way to realize quantum networks of arbitrary topology.

Desheng Wu, Jianlin Luo

Abstract We reported herein the single crystal growth and the comprehensive study of basic physical properties including electronic transport, magnetic, specific heat of topological insulator candidate LaP. Single crystal LaP of rock salt type structure was synthesized by Sn flux method. Under low temperature and high magnetic field of T = 2 $T= 2$  K and B = 9 $B= 9$ T, large positive magnetoresistance (LMR) of 500% was discovered. The Hall effect measurements show that the conduction carriers are dominated by holes among the temperature range from 300 K to 2 K, the carrier concentration n h = 4.94 × 10 19 $n_{h} =4.94\times 10^{19}$ cm−3 and n e = 5.02 × 10 16 $n_{e} =5.02\times 10^{16}$ cm−3 and the mobility of LaP reached as high as μ h = 1.57 × 10 4 $\mu _{h}=1.57\times 10^{4}$ cm2 V−1 S−1 and μ e = 1.55 × 10 3 $\mu _{e} = 1.55\times 10^{3}$ cm2 V−1 S−1 obtained at 2 K, which can be explained by multiband model physics like other topological quantum material systems with large MR. LaP shows diamagnetism over a wide temperature range from 2 K to 300 K without any magnetic phase transition by susceptibility measurements. No evidence of phase transitions from 2 K to 300 K was observed in the specific heat measurement. The electronic specific heat coefficient is obtained 0.538 m J mol−1 K−2 for LaP single crystal, which responds to a small electron density state near the Fermi level. Our results would be helpful in renewing interest in studying emergent phenomena arisen from topological semimetals. LaP offers a platform for understanding the interactions between large magnetoresistance, high mobility and topological band structure.

Cheng-Jie Wang, Pengfei Wang, Yan Zhou et al.

Abstract Various properties and potential technological applications of magnetic skyrmions have stimulated a flourishing interest in topological spin textures. Among them, biskyrmions with a rare topological charge of two are observed but their existence is still under debate. In this work, we present the formation of biskyrmion bubbles mediated by emergent monopoles via micromagnetic simulations. We find that biskyrmion bubbles and trivial bubbles share a unified three-dimensional structure, in which the relative position of an intrinsic emergent monopole-antimonopole pair dominates the two-dimensional topological property at the middle plane of magnetic uniaxial films. Biskyrmion bubbles can be transformed from trivial bubbles by the motion of emergent monopoles in confined geometry, paving the way for developing devices. These results highlight the three-dimensional aspect of skyrmion-related nanostructures and the versatile roles of emergent monopoles in topological spin textures.

S. Shlomo, A. I. Sanzhur

We provide a short review of the current status of the nuclear energy density functional (EDF) and the theoretical results obtained for properties of nuclei and nuclear matter. We will first describe a method for determining the parameters of the EDF, associated with the Skyrme type effective interaction, by carrying out a Hartree - Fock (HF)-based fit to the extensive set of data of ground-state properties and constraints. Next, we will describe the fully self-consistent HF-based random-phase-approximation (RPA) theory for calculating the strength functions S(E) and centroid energies ECEN of giant resonances and the folding model (FM) distorted wave Вorn approximation (DWBA) to calculate the excitation cross-section of giant resonances by α scattering. Then we will provide results for: (i) the Skyrme parameters of the KDE0v1 EDF; (ii) consequences of violation of self-consistency in HF-based RPA; (iii) FM-DWBA calculation of excitation cross-section; (iv) values of the ECEN of isoscalar and isovector giant resonances of multipolarities L = 0 – 3 for a wide range of spherical nuclei, using 33 EDFs associated with the standard form of the Skyrme type interactions, commonly employed in the literature; and (v) the sensitivities ECEN of the giant resonances to bulk properties of nuclear matter (NM). We also determine constraints on NM properties, such as the incompressibility coefficient and effective mass, by comparing with experimental data on ECEN of giant resonances.

Alexandre Jaoui, Gabriel Seyfarth, Carl Willem Rischau et al.

Abstract Lightly doped III–V semiconductor InAs is a dilute metal, which can be pushed beyond its extreme quantum limit upon the application of a modest magnetic field. In this regime, a Mott-Anderson metal–insulator transition, triggered by the magnetic field, leads to a depletion of carrier concentration by more than one order of magnitude. Here, we show that this transition is accompanied by a 200-fold enhancement of the Seebeck coefficient, which becomes as large as 11.3 mV K−1 $$\approx 130\frac{{k}_{B}}{e}$$ ≈ 130 k B e at T = 8 K and B = 29 T. We find that the magnitude of this signal depends on sample dimensions and conclude that it is caused by phonon drag, resulting from a large difference between the scattering time of phonons (which are almost ballistic) and electrons (which are almost localized in the insulating state). Our results reveal a path to distinguish between possible sources of large thermoelectric response in other low-density systems pushed beyond the quantum limit.

Alejandro Perez

This article reviews the present status of the spin-foam approach to the quantization of gravity. Special attention is payed to the pedagogical presentation of the recently-introduced new models for four-dimensional quantum gravity. The models are motivated by a suitable implementation of the path integral quantization of the Plebanski formulation of gravity on a simplicial regularization. The article also includes a self contained treatment of 2+1 gravity. The simple nature of the latter provides the basis and a perspective for the analysis of both conceptual and technical issues that remain open in four dimensions.

A. T. Rudchik, Yu. M. Stepanenko, A. A. Rudchik et al.

Angular distributions of the 7Li(18O, 17N)8Be reaction were measured for the transitions to the ground states of 8Be and 17N and excited states of 17N at the energy Elab(18O) = 114 MeV. The data were analyzed with coupled-reaction-channels method for one- and two-step transfers of nucleons and clusters. In the analysis, the 7Li + 18O potential de-duced in the analysis of the elastic 7Li + 18O-scattering data as well as shell-model spectroscopic amplitudes of trans-ferred nucleons and clusters were used. Parameters of the 8Be + 17N potential were deduced using the reaction data. Contributions of different one- and two-step transfers in the 7Li(18O, 17N)8Be reaction cross-section was studied.

A. I. Levon, G. Graw, Y. Eisermann et al.

Experimental data for the excited states in the deformed nucleus 230Th studied in the (p, t) reaction are analyzed. Sequences of the states are selected which can be treated as rotational bands and as multiplets of excitations. Experimental data are compared with the interacting boson model (IBM) and the quasiparticle-phonon model (QPM) calculations.

V. O. Kashparov, Yu. O. Bondar, V. I. Yoschenko

Dose rates to the Scots pine’ (Pinus sylvestris L.) apical meristem at three experimental sites were calculated. The morphological and cytogenetic changes of the trees were estimated, and the dependences of these changes on the dose rates to the apical meristem were formulated.

A. A. Rudchik, A. T. Rudchik, K. W. Kemper et al.

Data of the 7 Li + 16O elastic and inelastic scattering at Ec.m. = 6.26 - 34.78 MeV were analyzed within the optical model (OM) and coupled-reaction-channels method. The elastic and inelastic scattering as well as the reorientation of 7 Li were included in the coupled-channels-scheme. The contributions of the 7 Li reorientation to the elastic scattering data was estimated. The energy dependence of the 7 Li + 16O OM parameters was deduced. The dispersion relation between the real and imaginary parts of the OM potential was taken into account.