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

Limin Yan, Jiaqing Gao, Zihan Zhang et al.

Abstract Ising superconductors, known for their exceptionally high in-plane upper critical magnetic field ( $${{{\rm{\mu }}}_{0}H}_{{\rm{c}}2}^{\parallel }$$ μ 0 H c 2 ∥ ) beyond the Pauli limit, have so far been explored mainly in two-dimensional limit systems and molecularly intercalated bulk materials based on transition metal dichalcogenides. By exploiting the high pressure approach, we simultaneously optimize the superconducting transition temperature ( $${T}_{{\rm{c}}}$$ T c ) and $${{{\rm{\mu }}}_{0}H}_{{\rm{c}}2}^{\parallel }$$ μ 0 H c 2 ∥ in a bulk 4Hb-TaS2 Ising superconductor. The pressure-optimized Ising superconductivity of 4Hb-TaS2 exhibits drastically enhanced $${{{\rm{\mu }}}_{0}H}_{{\rm{c}}2}^{\parallel }$$ μ 0 H c 2 ∥ that is comparable to the performance of three-layer TaS2, while also with a record-high $${T}_{{\rm{c}}}$$ T c surpassing all the TaS2-based systems reported so far. Combined in-situ high-pressure X-ray diffraction, Hall-effect measurements, and theoretical calculations, we reveal that the dome-shaped $${T}_{{\rm{c}}}(P)$$ T c ( P ) behavior of 4Hb-TaS2 arises from competition between superconductivity in the H-layers and charge density wave (CDW) orders in the T and H layers. Simultaneously, the dome-like response of $${{{\rm{\mu }}}_{0}H}_{{\rm{c}}2}^{\parallel }$$ μ 0 H c 2 ∥ on pressure is governed by synergistic effects of interlayer coupling and spin-orbital coupling. These central findings provide a practical route to achieving record-high functionalities of Ising superconductivity with superior application potentials.

Boaz Lubotzky, Hamza Abudayyeh, Niko Nikolay et al.

Efficient readout of nitrogen-vacancy (NV) centers in diamonds is crucial for various quantum information technologies. However, achieving high-fidelity, single-shot readout at room temperature remains challenging due to limited photon collection efficiency (CE) and background noise. In this work, we enhance the readout efficiency of NV centers by integrating them into hybrid metal–dielectric bullseye nanoantennas using ultra-precise deterministic positioning. This approach enables highly directional emission while minimizing optical losses, resulting in a measured CE of ∼80% at a numerical aperture (NA) as low as 0.5 and approaching unity for NA > 0.8. This marks a substantial improvement over previous realizations using nanodiamonds, by combining hybrid nanoantennas with precise positioning. Our results mark a substantial advancement toward efficient single-shot readout of NV centers by significantly improving readout fidelity and efficiency in a simple on-chip configuration.

J. Montes, F. Borondo, Gabriel G. Carlo

Noisy intermediate-scale quantum processors have produced a quantum computation revolution in recent times. However, to make further advances, new strategies to overcome the error rate growth are needed. One possible way out is dividing these devices into many cores. On the other hand, the majorization criterion efficiently classifies quantum circuits in terms of their complexity, which can be directly related to their ability of performing non-classically simulatable computations. In this paper, we use this criterion to study the complexity behavior of a paradigmatic universal family of random circuits distributed into several cores with different architectures. We find that the optimal complexity is reached with few interconnects, giving further hope to actual implementations in available devices at present. A universal behavior is found irrespective of the architecture and (approximately) the core size. We also analyze the complexity properties when scaling processors up by means of adding cores of the same size. We provide a conjecture to explain the results.

Tyler Hecht, Griffin S. Hampton, Ryan Neff et al.

In this paper, we contrast frequentist and Bayesian approaches to parameter estimation for a magnetic resonance (MR) relaxometry signal model which takes the form of a two-dimensional biexponential decay. The signal consists of two terms, each parameterized by an amplitude and a transverse and longitudinal relaxation time constant. There are two user-selected parameters, defining the two-dimensional character of the signal; these are an inversion time TI and a set of echo times, TE. Of particular interest is the fact that for two values of TI, which we call the null points, the signal becomes a monoexponential function in TE. Extracting the two parameters—the amplitude and decay constant—from the signal observed at or near a null point is particularly ill-posed since the monoexponential signal is highly overparameterized by the four parameter biexponential models. We seek to estimate these null points, which directly provide values for the longitudinal relaxation time constants, using both frequentist and Bayesian techniques. The frequentist approach uses nonlinear least squares (NLLS), and the Bayesian approach uses the Metropolis–Hastings algorithm. In addition to point estimates, both methods generate point clouds of parameter estimates representing uncertainties. Due to the symmetry of the biexponential model, these point clouds consist of two clusters. The variance of a single cluster and the separation between the two clusters, both of which capture the size of the point clouds, may be used as metrics for ill-posedness. Increasing point cloud size, indicating an undesired greater flexibility in parameter choice, illustrates a greater degree of ill-posedness. We find that both the frequentist and Bayesian approaches can estimate the null points using the extrema of these metrics and yield qualitatively similar and consistent results.

Johannes Figueiredo, Marten Richter, Mirco Troue et al.

Abstract Heterostructures made from 2D transition-metal dichalcogenides are known as ideal platforms to explore excitonic phenomena ranging from correlated moiré excitons to degenerate interlayer exciton ensembles. So far, it is assumed that the atomic reconstruction appearing in some of the heterostructures gives rise to a dominating localization of the exciton states. We demonstrate that the center-of-mass wavefunction of the excitonic states in reconstructed MoSe2/WSe2 heterostructures can extend well beyond the moiré periodicity of the investigated heterostructures. The results are based on real-space calculations yielding a lateral potential map for interlayer excitons within the strain-relaxed heterostructures with weak random disorder, as expected for realistic samples, and the corresponding real-space center-of-mass excitonic wavefunctions. We combine the theoretical results with cryogenic photoluminescence experiments, which support the computed level structure and relaxation characteristics of the interlayer excitons.

Rian Koots, Grace Ding, Jesús Pérez-Ríos

The recombination of halogen atoms has been a research topic in chemical physics for over a century. All theoretical descriptions of atom recombination depend on a two-step assumption, where two colliding atoms first form an unstable complex before a third colliding body either relaxes or reacts with it to yield a diatomic molecule. These mechanisms have served well in describing some of the dynamics of atom recombination, but have not yet provided a full theoretical understanding. In this work, we consider the role of the direct three-body recombination mechanism in halogen recombination reactions X + X + M $\rightarrow$ X$_2$ + M, where X is a halogen atom, and M is a rare gas atom. Our results agree well with experimental bromide and iodine recombination measurements, demonstrating that direct three-body recombination is essential in halogen recombination reactions.

Ren Zhang, Hui Zhai

Abstract In a quantum many-body system, autocorrelation functions can determine linear responses nearby equilibrium and quantum dynamics far from equilibrium. In this letter, we bring out the connection between the operator complexity and the autocorrelation function. In particular, we focus on a particular kind of operator complexity called the Krylov complexity. We find that a set of Lanczos coefficients { b n } $\{b_{n}\}$ computed for determining the Krylov complexity can reveal the universal behaviors of autocorrelations, which are otherwise impossible. When the time axis is scaled by b 1 $b_{1}$ , different autocorrelation functions obey a universal function form at short time. We further propose a characteristic parameter deduced from { b n } $\{b_{n}\}$ that can largely determine the behavior of autocorrelations at the intermediate time. This parameter can also largely determine whether the autocorrelation function oscillates or monotonically decays in time. We present numerical evidences and physical intuitions to support these universal hypotheses of autocorrelations. We emphasize that these universal behaviors are held across different operators and different physical systems.

Adam Olejniczak, Yury Rakovich, Victor Krivenkov

The Nobel Prizes in Physics (2022) and Chemistry (2023) heralded the recognition of quantum information science and the synthesis of quantum dots (QDs), respectively. This acknowledgment has propelled colloidal QDs and perovskite nanocrystals to the forefront of quantum technologies. Their distinct emission properties, facilitating the efficient generation of both single photons and photon pairs, render them particularly captivating. Moreover, their adaptability to diverse structures, ranging from traditional electronics to nanopatterned frameworks, underscores their pivotal role in shaping quantum technologies. Despite notable strides in synthesis, certain properties require refinement for enhanced applicability in quantum information, encompassing emission brightness, stability, single-photon indistinguishability, and entanglement fidelity of photon pairs. Here we offer an overview of recent achievements in plasmon-exciton quantum emitters (QEs) based on luminescent semiconductor nanocrystals. Emphasizing the utilization of the light-matter coupling phenomenon, we explore how this interaction enables the manipulation of quantum properties without altering the chemical structure of the emitters. This approach addresses critical aspects for quantum information applications, offering precise control over emission rate, intensity, and energy. The development of these hybrid systems represents a significant stride forward, demonstrating their potential to overcome existing challenges and advance the integration of QEs into cutting-edge quantum technology applications.

G Landry, C Bradac

Single photon emitters are core building blocks of quantum technologies, with established and emerging applications ranging from quantum computing and communication to metrology and sensing. Regardless of their nature, quantum emitters universally display fluorescence intermittency or photoblinking: interaction with the environment can cause the emitters to undergo quantum jumps between on and off states that correlate with higher and lower photoemission events, respectively. Understanding and quantifying the mechanism and dynamics of photoblinking is important for both fundamental and practical reasons. However, the analysis of blinking time traces is often afflicted by data scarcity. Blinking emitters can photo-bleach and cease to fluoresce over time scales that are too short for their photodynamics to be captured by traditional statistical methods. Here, we demonstrate two approaches based on machine learning that directly address this problem. We present a multi-feature regression algorithm and a genetic algorithm that allow for the extraction of blinking on/off switching rates with ⩾85% accuracy, and with ⩾10× less data and ⩾20× higher precision than traditional methods based on statistical inference. Our algorithms effectively extend the range of surveyable blinking systems and trapping dynamics to those that would otherwise be considered too short-lived to be investigated. They are therefore a powerful tool to help gain a better understanding of the physical mechanism of photoblinking, with practical benefits for applications based on quantum emitters that rely on either mitigating or harnessing the phenomenon.

V. V. Ilkovych

A VVER-1000 reactor model using the Monte Carlo Serpent 2 code for core power distribution calculation is presented. The core and zones located near to the core were modeled in detail, without simplification. The assembly power distribution and axial power profiles were calculated for fresh core of the X2 VVER-1000 benchmark, namely the core of the KhNPP2 first loading for the hot zero power. The results were compared with the data obtained by specialists from Helmholtz-Zentrum Dresden-Rossendorf.

Pauline Yzombard, Simon Thomas, Lucile Julien et al.

We study the 1S-3S two-photon transition of hydrogen in a thermal atomic beam, using a homemade cw laser source at 205 nm. The experimental method is described, leading in 2017 to the measurement of the 1S-3S transition frequency in hydrogen atom with a relative uncertainty of $9 \times 10^{-13}$. This result contributes to the "proton puzzle" resolution but is in disagreement with the ones of some others experiments. We have recently improved our setup with the aim of carrying out the same measurement in deuterium. With the improved detection system, we have observed a broadened fluorescence signal, superimposed on the narrow signal studied so far, and due to the stray accumulation of atoms in the vacuum chamber. The possible resulting systematic effect is discussed.

Nick P. Proukakis

The emergence of macroscopic coherence in a many-body quantum system is a ubiquitous phenomenon across different physical systems and scales. This Chapter reviews key concepts characterizing such systems (correlation functions, condensation, quasi-condensation) and applies them to the study of emerging non-equilibrium features in the dynamical path towards such a highly-coherent state: particular emphasis is placed on emerging universal features in the dynamics of conservative and open quantum systems, their equilibrium or non-equilibrium nature, and the extent that these can be observed in current experiments with quantum gases. Characteristic examples include symmetry-breaking in the Kibble-Zurek mechanism, coarsening and phase-ordering kinetics, and universal spatiotemporal scalings around non-thermal fixed points and in the context of the Kardar- Parisi-Zhang equation; the Chapter concludes with a brief review of the potential relevance of some of these concepts in modelling the large-scale distribution of dark matter in the universe.

Christoph Wuttke, Federico Caglieris, Steffen Sykora et al.

Abstract The role of nematic fluctuations for unconventional superconductivity has been the subject of intense discussions for many years. In iron-based superconductors, the most established probe for electronic-nematic fluctuations, i.e. the elastoresistivity seems to imply that superconductivity is reinforced by electronic-nematic fluctuations, since the elastoresistivity amplitude peaks at or close to optimal T c . However, on the over-doped side of the superconducting dome, the diminishing elastoresistivity suggests a negligible importance in the mechanism of superconductivity. Here we introduce the Nernst coefficient as a genuine probe for electronic nematic fluctuations, and we show that the amplitude of the Nernst coefficient tracks the superconducting dome of two prototype families of iron-based superconductors, namely Rh-doped BaFe2As2 and Co-doped LaFeAsO. Our data thus provide fresh evidence that in these systems, nematic fluctuations foster the superconductivity throughout the phase diagram.

Joaquin Chung, Ely M. Eastman, Gregory S. Kanter et al.

The Illinois Express Quantum Network (IEQNET) is a program to realize metropolitan-scale quantum networking over deployed optical fiber using currently available technology. IEQNET consists of multiple sites that are geographically dispersed in the Chicago metropolitan area. Each site has one or more quantum nodes (Q-Nodes) representing the communication parties in a quantum network. Q-Nodes generate or measure quantum signals such as entangled photons and communicate the measurement results via standard classical signals and conventional networking processes. The entangled photons in IEQNET nodes are generated at multiple wavelengths and are selectively distributed to the desired users via transparent optical switches. Here, we describe the network architecture of IEQNET, including the Internet-inspired layered hierarchy that leverages software-defined networking (SDN) technology to perform traditional wavelength routing and assignment between the Q-Nodes. Specifically, SDN decouples the control and data planes, with the control plane being entirely implemented in the classical domain. We also discuss the IEQNET processes that address issues associated with synchronization, calibration, network monitoring, and scheduling. An important goal of IEQNET is to demonstrate the extent to which the control plane classical signals can copropagate with the data plane quantum signals in the same fiber lines (quantum-classical signal “coexistence”). This goal is furthered by the use of tunable narrowband optical filtering at the receivers and, at least in some cases, a wide wavelength separation between the quantum and classical channels. We envision IEQNET to aid in developing robust and practical quantum networks by demonstrating metropolitan-scale quantum communication tasks such as entanglement distribution and quantum-state teleportation.

Roberto Vittorio Roell, Arif Warsi Laskar, Franz Richard Huybrechts et al.

Quantum Hall physics is at the heart of research on both matter and artificial systems, such as cold atomic gases, with non-trivial topological order. We report on the observation of a chiral edge current by transferring atomic wavepackets simultaneously to opposite edges of a synthetic Hall system realized in the two-dimensional state space formed by one spatial and one synthetic dimension encoded in the J=6 electronic spin of erbium atoms. To characterize the system, the Hall drift of the employed atomic Bose-Einstein condensate in the lowest Landau-like level is determined. The topological properties are verified by determining the local Chern marker, and upon performing low-lying excitations both cyclotron and skipping orbits are observed in the bulk and edges respectively. Future prospects include studies of novel topological phases in cold atom systems.

Junde Li, Rasit O. Topaloglu, Swaroop Ghosh

Existing drug discovery pipelines take 5&#x2013;10 years and cost billions of dollars. Computational approaches aim to sample from regions of the whole molecular and solid-state compounds called chemical space, which could be on the order of <inline-formula><tex-math notation="LaTeX">$10^{60}$</tex-math></inline-formula>. Deep generative models can model the underlying probability distribution of both the physical structures and property of drugs and relate them nonlinearly. By exploiting patterns in massive datasets, these models can distill salient features that characterize the molecules. Generative adversarial networks (GANs) discover drug candidates by generating molecular structures that obey chemical and physical properties and show affinity toward binding with the receptor for a target disease. However, classical GANs cannot explore certain regions of the chemical space and suffer from training instabilities. The practical utility of such models is limited due to the vast size of the search space, characterized by millions of parameters. A full quantum GAN may require more than 90 qubits even to generate small molecules with up to nine heavy atoms. The proposed quantum GAN with a hybrid generator (QGAN-HG) model is composed of a hybrid quantum generator that supports various number of qubits and quantum circuit layers, and a classical discriminator. The QGAN-HG with less than 20&#x0025; of the original parameters can learn molecular distributions as efficiently as its classical counterpart. Another extended version of the proposed QGAN-HG, which utilizes multiple quantum subcircuits, considerably accelerates our standard QGAN-HG training process and avoids the potential gradient vanishing issue of deep neural networks.

Qing-Ge Mu, Feng-Ren Fan, Horst Borrmann et al.

Abstract Weyl semimetals (WSMs) hosting Weyl points (WPs) with different chiralities attract great interest as an object to study chirality-related physical properties, topological phase transitions, and topological superconductivity. Quantum oscillation measurements and theoretical calculations imply that the type-II WPs in NbIrTe4 are robust against the shift of chemical potential making it a good material for pressure studies on topological properties. Here we report the results of electrical transport property measurements and Raman spectroscopy studies under pressures up to 65.5 GPa accompanied by theoretical electronic structure calculations. Hall resistivity data reveal an electronic transition indicated by a change of the charge carrier from multiband character to hole-type at ~12 GPa, in agreement with the calculated Fermi surface. An onset of superconducting transition is observed at pressures above 39 GPa, with critical temperature increasing as pressure increases. Moreover, theoretical calculations indicate that WPs persist up to highly reduced unit cell volume (−17%), manifesting that NbIrTe4 is a candidate of topological superconductor.

Asher Davidson, George Petrov, Daniel Gordon et al.

Ultrafast laser heating of electrons on a metal surface breaks the pressure equilibrium within the material, thus initiating ablation. The stasis of a room-temperature metal results from a balance between repulsive and attractive binding pressures. We calculate this with a choice of Equation of State (EOS), whose applicability in the Warm-Dense-Matter regime is varied. Hydrodynamic modeling of surface ablation in this regime involves calculation of electrostatic and thermal forces implied by the EOS, and therefore the physics outlining the evolution of the net inter-atomic binding (negative pressure) during rapid heating is of interest. In particular, we discuss the Thomas-Fermi-Dirac-Weizsacker model, and Averaged Atom Model, and their binding pressure as compared to the more commonly used models. A fully nonlinear hydrodynamic code with a pressure-sourced electrostatic field solver is then implemented to simulate the ablation process, and the ablation depths are compared with known measurements with good agreement. Results also show that re-condensation of a previously melted layer significantly reduces the overall ablated depth of copper for laser fluence between 10-30J/cm^2, further explaining a well-known trend observed in experiments in this regime. A transition from electrostatic to pressure-driven ablation is observed with laser fluence increasing.

Adam J. Sirois, Manuel Castellanos-Beltran, Anna E. Fox et al.

Quantum computers with thousands or millions of qubits will require a scalable solution for qubit control and readout electronics. Colocating these electronics at millikelvin temperatures has been proposed and demonstrated, but there exist significant challenges with power dissipation, reproducibility, fidelity, and scalability. In this article, we experimentally demonstrate the use of a Josephson arbitrary waveform synthesizer (JAWS) to generate control signals at 4 K and perform spectroscopy of two components of a typical superconducting quantum information system: a linear resonator and a (nonlinear) transmon qubit. By locating the JAWS chip at 4 K and a qubit at 0.1 K, the direct path for quasi-particle poisoning from the JAWS chip to the qubit is broken. We demonstrate the stable, self-calibrated, and reproducible output signal of the JAWS when operated in its quantum locking range, a feature that allows these synthesizers to be replicated and scaled in the cryostat, all with identical on-chip, quantized, outputs. This is a proof-of-concept demonstration to generate signals at 4 K using driven superconducting electronics to control qubits at lower temperatures.

S. Ya. Goroshchenko, A. V. Nesterov, V. A. Nesterov

We consider the question of calculations of the interaction energy of two uniformly charged spheroids. Three cases are realized in the software: the interaction of a uniformly charged spheroid with a point charge; interaction of two coaxial spheroids; and the general case of mutual position of spheroids. The presented programs are initially oriented for nuclear calculations. However, by a change of numerical coefficients, they can be used in the calculations of the interaction energy in any cases of spheroidal objects with the uniformly distributed charge or mass.