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

Lijun Yan, Xinlin Mi, Yongzhang Shi et al.

Abstract Long-range tunable strongly coupled photon-magnon systems are crucial for large-scale hybrid networks enabling coherent information processing. Here, we experimentally fabricate a photon-magnon system with a saturable gain, achieving long-range strong coupling in the linear regime for the first time, aside from the nonlinear regime. By modulating the propagation phase of traveling waves mediating photons and magnons, we achieve flexible switching between coherent coupling and dissipative coupling. Theoretically, we construct a Hamiltonian model comprising a van der Pol oscillator and a harmonic oscillator, from which we derive the dynamical equations of the cavity magnonic system and numerically simulate the time evolution of photon and magnon modes amplitudes under the long-range strong coupling. The results reveal energy exchange in the linear regime and mode synchronization in the nonlinear regime. Our work integrates experimental results and theoretical models, establishing a foundation for cross-platform information exchange and controllable coupling in hybrid systems.

Niccolò Sellati, Jacopo Fiore, Stefano Paolo Villani et al.

Abstract Hybrid lattice-light modes, known as phonon polaritons, represent the backbone of advanced protocols based on THz pumping of infrared modes. Here we provide a theoretical framework able to capture the different roles played by phonon polaritons in experimental protocols based either on Raman-like pump and probe schemes, typical of four-wave mixing processes, or on THz pump-visible probe three-wave mixing protocols. By using a many-body description of the nonlinear optical kernel, along with a perturbative solution of nonlinear Maxwell’s equations, we discuss the limitations of all-optical four-wave mixing protocols and we highlight the advantages of exploiting broadband THz pumps to enlarge the phase space of the phonon polariton dispersion at low momenta accessible in a single experiment. Besides providing a quantitative description of existing and future experiments, our results offer a general framework for the theoretical modeling of the hybridization between light and lattice degrees of freedom in time-resolved experiments.

Daniel Jost, Eder G. Lomeli, Woo Jin Kim et al.

Abstract The layered cobaltate CaCoO 2 exhibits a unique herringbone-like structure. Serving as a potential prototype for a new class of complex lattice patterns, we study the properties of CaCoO 2 using X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). Our results reveal a significant inter-plane hybridization between the Ca 4s- and Co 3d- orbitals, leading to an inversion of the textbook orbital occupation of a square planar geometry. Further, our RIXS data reveal a strong low energy mode, with anomalous intensity modulations as a function of momentum transfer close to a quasi-static response. These findings indicate that the newly discovered herringbone structure exhibited in CaCoO 2 may serve as a promising laboratory for the design of materials having strong electronic, orbital and lattice correlations.

Sanjiang Li, Xiangzhen Zhou, Yuan Feng

Current superconducting quantum devices impose strict connectivity constraints on quantum circuit execution, necessitating circuit transformation before executing quantum circuits on physical hardware. Numerous quantum circuit transformation (QCT) algorithms have been proposed. To enable faithful evaluation of state-of-the-art QCT algorithms, this article introduces qubit mapping benchmark with known near-optimality (QKNOB), a novel benchmark construction method for QCT. <monospace>QKNOB</monospace> circuits have built-in transformations with near-optimal (close to the theoretical optimum) <sc>swap</sc> count and depth overhead. <monospace>QKNOB</monospace> provides general and unbiased evaluation of QCT algorithms. Using <monospace>QKNOB</monospace>, we demonstrate that <monospace>SABRE</monospace>, the default Qiskit compiler, consistently achieves the best performance on the 53-qubit IBM Q Rochester and Google Sycamore devices for both <sc>swap</sc> count and depth objectives. Our results also reveal significant performance gaps relative to the near-optimal transformation costs of <monospace>QKNOB</monospace>. Our construction algorithm and benchmarks are open-source.

Nhat A. Nghiem, Trung V. Phan

We explore the physical quantum properties of atoms in fractal spaces, both as a theoretical generalization of normal integer-dimensional Euclidean spaces and as an experimentally realizable setting. We identify the threshold of fractality at which Ehrenfest atomic instability emerges, where the Schrödinger equation describing the wave-function of a single electron orbiting around an atom becomes scale-free, and discuss the potential of observing this phenomena in laboratory settings. We then study the Rydberg states of stable atoms using the Wentzel-Kramers-Brillouin approximation, along with a proposed extension for the Langer modification, in general fractal dimensionalities. We show that fractal space atoms near instability explode in size even at low-number excited state, making them highly suitable to induce strong entanglements and foster long-range many-body interactions. We argue that atomic physics in fractal spaces -- ``fractatomic physics'' -- is a rich research avenue deserving of further theoretical and experimental investigations.

Marzio Vallero, Emanuele Dri, Edoardo Giusto et al.

Quanvolutional neural networks (QNNs) have been successful in image classification, exploiting inherent quantum capabilities to improve performance of traditional convolution. Unfortunately, the qubit&#x0027;s reliability can be a significant issue for QNNs inference, since its logical state can be altered by both intrinsic noise and by the interaction with natural radiation. In this article, we aim at investigating the propagation of logical-shift errors (i.e., the unexpected modification of the qubit state) in QNNs. We propose a bottom&#x2013;up evaluation reporting data from 13&#x2009;322&#x2009;547&#x2009;200 logical-shift injections. We characterize the error propagation in the quantum circuit implementing a single convolution and then in various designs of the same QNN, varying the dataset and the network depth. We track the logical-shift error propagation through the qubits, channels, and subgrids, identifying the faults that are more likely to cause misclassifications. We found that up to 10&#x0025; of the injections in the quanvolutional layer cause misclassification and even logical-shifts of small magnitude can be sufficient to disturb the network functionality. Our detailed analysis shows that corruptions in the qubits&#x0027; state that alter their probability amplitude are more critical than the ones altering their phase, that some object classes are more likely than others to be corrupted, that the criticality of subgrids depends on the dataset, and that the control qubits, once corrupted, are more likely to modify the QNN output than the target qubits.

Kieran Hymas, Alessandro Soncini, Kuduva R. Vignesh et al.

Abstract Molecular toroidal states have come to the forefront as candidates for next-generation quantum information devices owing to their bistability and protection from weak, short-range magnetic interactions. The protection offered by these non-magnetic vortex spin states proves to be a double-edged sword as inferring their existence in a molecular system has yet to be achieved through experimental means alone. Here, we investigate the anomalous, sickle-shaped, single-crystal magnetisation profile arising in μ-SQUID measurements of a novel CrDy3 molecule. Theoretical modelling supported by ab initio calculations demonstrates that the weak field CrDy3 spin dynamics is resultant from quantum superposition of the CrIII spin states determined by three competing interactions: (i) the alignment of the CrIII magnetic moment to the external magnetic field, (ii) the zero-field splitting of the CrIII ground quartet, and (iii) coupling to the remnant magnetisation of the toroidal ground state in the Dy3 triangle. If zero-field splitting of the central transition metal ion is quenched, it operates as a quantum spin sensor, which can be exploited to experimentally discriminate between ferrotoroidic and antiferrotoroidic ground states in MDy6 double triangle complexes through electron paramagnetic resonance experiments and single-crystal magnetisation measurements with a restricted field sweeping domain.

V. I. Skalozubov, O. A Dorozh, Yu. O. Komarov et al.

An original thermal-hydraulic method for optimizing the thermal resistance of thermal conductivity of fuel rod matrix upgrades has been developed to achieve the maximum burnup depth of nuclear fuel while ensuring safety conditions in operating and emergency modes of nuclear power plants. Based on the developed method, the boundaries of the optimization area for upgrades of the thermal resistance of the fuel rod matrix thermal conductivity are determined in accordance with the accepted optimization criteria and safety conditions. It is established that when optimizing upgrades to the thermal resistance of nuclear fuel, it is necessary to take into account both normal operating conditions and emergency conditions with impaired heat removal from the reactor core. It is established that the optimal values of thermal resistance of nuclear fuel thermal conductivity depend on the design and technical parameters of reactor installations, composition, and condition of nuclear fuel, accident management systems, and other factors.

Lebing Chen, Xiaokun Teng, Ding Hu et al.

Abstract We use elastic and inelastic neutron scattering (INS) to study the antiferromagnetic (AF) phase transitions and spin excitations in the two-dimensional (2D) zig-zag antiferromagnet FePSe3. By determining the magnetic order parameter across the AF phase transition, we conclude that the AF phase transition in FePSe3 is first-order in nature. In addition, our INS measurements reveal that the spin waves in the AF ordered state have a large easy-axis magnetic anisotropy gap, consistent with an Ising Hamiltonian, and possible biquadratic magnetic exchange interactions. On warming across T N, we find that dispersive spin excitations associated with three-fold rotational symmetric AF fluctuations change into FM spin fluctuations above T N. These results suggest that the first-order AF phase transition in FePSe3 may arise from the competition between C 3 symmetric AF and C 1 symmetric FM spin fluctuations around T N, in place of a conventional second-order AF phase transition.

Mathieu Toubeix, Eric Guthmuller, Adrian Evans et al.

As scaling becomes a key issue for large-scale quantum computing, hardware control systems will become increasingly costly in resources. This article presents a compact direct digital synthesis architecture for signal generation adapted for spin qubits that is scalable in terms of waveform accuracy and the number of synchronized channels. The architecture can produce programmable combinations of ramps, frequency combs, and arbitrary waveform generation (AWG) at 5 GS/s, with a worst-case digital feedback latency of 76.8 ns. The field-programmable gate array (FPGA)-based system is highly configurable and takes advantage of bitstream switching to achieve the high flexibility required for scalable calibration. The architecture also provides GHz rate, multiplexed, in-phase and quadrature component, single-side band modulation for scalable reflectometry. This architecture has been validated in hardware on a Xilinx ZCU111 FPGA demonstrating the mixing of complex signals and the quality of the frequency comb generation for multiplexed control and measurement. The key benefits of this design are the increase of controllability of ramps at the digital-to-analog converter (DAC) frequency and the reduction in memory requirements by several orders of magnitude compared with existing AWG-based architectures. The hardware for a single channel is very compact, 2&#x0025; of ZCU111 logic resources for one DAC lane in the default configuration, leaving significant circuit resources for integrated feedback, calibration, and quantum error correction.

Jorge Yago Malo, Luca Lepori, Laura Gentini et al.

Physics is living an era of unprecedented cross-fertilization among the different areas of science. In this perspective review, we discuss the manifold impact that ultracold-atom quantum technologies can have in fundamental and applied science through platforms for quantum simulation, computation, metrology and sensing. We illustrate how the engineering of table-top experiments with atom technologies is engendering applications to understand problems in condensed matter and fundamental physics, cosmology and astrophysics, foundational aspects of quantum mechanics, quantum chemistry and the emerging field of quantum biology. We take the perspective of two main approaches, i.e. creating quantum analogues and building quantum simulators, highlighting that independently of the ultimate goal of a universal quantum computer to be met, the remarkable transformative effects of these achievements remain unchanged. We convey three main messages. First, atomic quantum technologies have enabled a new way in which quantum technologies are used for fundamental science, even beyond the advancement of knowledge, which is characterised by truly cross-disciplinary research, extended interplay between theoretical and experimental thinking, and intersectoral approach. Second, quantum many-body physics is taking the center stage in frontier's science. Third, quantum science progress will have capillary impact on society. Thus, the adoption of a responsible research and innovation approach to quantum technologies is mandatory, to accompany citizens in building awareness and future scaffolding. Following on all these reflections, this perspective review is aimed at scientists active or interested in interdisciplinary research, providing the reader with an overview of the current status of these wide fields of research where ultracold-atomic platforms play a vital role in their description and simulation.

Byungkyun Kang, Corey Melnick, Patrick Semon et al.

Abstract The recent and exciting discovery of superconductivity in the hole-doped infinite-layer nickelate Nd1−δ Sr δ NiO2 draws strong attention to correlated quantum materials. From a theoretical view point, this class of unconventional superconducting materials provides an opportunity to unveil a physics hidden in correlated quantum materials. Here we study the temperature and doping dependence of the local spectrum as well as the charge, spin and orbital susceptibilities from first principles. By using ab initio LQSGW+DMFT methodology, we show that onsite Hund’s coupling in Ni-d orbitals gives rise to multiple signatures of Hund’s metallic phase in Ni-e g orbitals. The proposed picture of the nickelates as an e g (two orbital) Hund’s metal differs from the picture of the Fe-based superconductors as a five orbital Hund’s metal as well as the picture of the cuprates as doped charge transfer insulators. Our finding uncover a new class of the Hund’s metals and has potential implications for the broad range of correlated two orbital systems away from half-filling.

Naoto Tsuji

Quantum systems driven by a time-periodic field are a platform of condensed matter physics where effective (quasi)stationary states, termed "Floquet states", can emerge with external-field-dressed quasiparticles during driving. They appear, for example, as a prethermal intermediate state in isolated driven quantum systems or as a nonequilibrium steady state in driven open quantum systems coupled to environment. Floquet states may have various intriguing physical properties, some of which can be drastically different from those of the original undriven systems in equilibrium. In this article, we review fundamental aspects of Floquet states, and discuss recent topics and applications of Floquet states in condensed matter physics.

Koichi Miyamoto, Kenji Kubo

Following the recent great advance of quantum computing technology, there are growing interests in its applications to industries, including finance. In this article, we focus on derivative pricing based on solving the Black&#x2013;Scholes partial differential equation by the finite-difference method (FDM), which is a suitable approach for some types of derivatives but suffers from the <italic>curse of dimensionality</italic>, that is, exponential growth of complexity in the case of multiple underlying assets. We propose a quantum algorithm for FDM-based pricing of multi-asset derivative with exponential speedup with respect to dimensionality compared with classical algorithms. The proposed algorithm utilizes the quantum algorithm for solving differential equations, which is based on quantum linear system algorithms. Addressing the specific issue in derivative pricing, that is, extracting the derivative price for the present underlying asset prices from the output state of the quantum algorithm, we present the whole of the calculation process and estimate its complexity. We believe that the proposed method opens the new possibility of accurate and high-speed derivative pricing by quantum computers.

Jack D Briscoe, Fraser D Logue, Danielle Pizzey et al.

Cascading light through two thermal vapour cells has been shown to improve the performance of atomic filters that aim to maximise peak transmission over a minimised bandpass window. In this paper, we explore the atomic physics responsible for the operation of the second cell, which is situated in a transverse (Voigt) magnetic field and opens a narrow transmission window in an optically thick atomic vapour. By assuming transitions with Gaussian line shapes and magnetic fields sufficiently large to access the hyperfine Paschen-Back regime, the window is modelled by resolving the two transitions closest to line centre. We discuss the validity of this model and perform an experiment which demonstrates the evolution of a naturally abundant Rb transmission window as a function of magnetic field. The model results in a significant reduction in two-cell parameter space, which we use to find theoretical optimised cascaded line centre filters for Na, K, Rb and Cs across both D lines. With the exception of Cs, these all have a better figure of merit than comparable single cell filters in literature. Most noteworthy is a Rb-D2 filter which outputs >92% of light through a single peak at line centre, with maximum transmission 0.71 and a width of 330 MHz at half maximum.

Markus Sebastian Feser, Ingrid Krumphals

To date, there is a lack of research on learning environments for pre-service physics teachers that allow them to learn and practise diagnosing students' conceptions that are (currently) not covered in physics education textbooks (e.g. students' conceptions about viscosity). In this study, we developed and piloted such a learning environment, which was implemented and piloted twice in a seminar for pre-service physics teachers. As coping with a diagnostic process is particularly demanding for pre-service physics teachers, our accompanying research aims to identify learning barriers within our developed learning environment. The results indicate that the participants experience the learning environment with varying degrees of difficulty. One main difficulty for pre-service physics teachers seems to be in interconnecting their content knowledge with their pedagogical content knowledge in the diagnostic process.

D. J. Buettner, P. D. Morley

We challenge the traditional wisdom that cosmological (big bang relic) neutrinos can only be hot Dark Matter. We provide a critical review of the concepts, derivations and arguments in foundational books and recent publications that led respected researchers to proclaim that "[Dark Matter] cannot be neutrinos". We then provide the physics resulting in relic neutrino's significant power loss from the interaction of its anomalous magnetic moment with a high-intensity primordial magnetic fields, resulting in subsequent condensation into Condensed Neutrino Objects (CNOs). Finally, the experimental degenerate mass bounds that would rule out condensed cosmological neutrinos as the Dark Matter (unless there is new physics that would require a modification to the CNO Equation of State) are provided. We conclude with a discussion on new directions for research.

Jin Chen, Jian Chen, Xin Li et al.

Abstract HgCdTe avalanche photodiodes promise various fascinating applications due to the outstanding capability of detecting weak signals or even single photon. However, the underlying transport mechanisms of diverse dark current components are still unresolved at high reverse bias, thus limiting the development of high-performance devices. Here, we establish an accurate model to demonstrate the competitive mechanism between band-to-band and avalanche dark currents in positive-intrinsic-negative structures. Based on the high consistency between the simulated and measured results, we find that both components jointly dominate overall dark current but with a larger avalanche current. This breaks the conventional cognition that band-to-band dark current contributes the majority. With the guidance, we reconstruct an optimized device and achieve gain 1876 (6153) and dark current 10−10 (10−9) A at bias −10 (−10.5) V, respectively. Comparisons of dark current and gain with reported single-element devices further confirm the outstanding performance of our device.

Li Wan

Abstract We study excitations of atomic vibrations in the reciprocal space for amorphous solids. There are two kinds of excitations we obtained, collective excitation and local excitation. The collective excitation is the collective vibration of atoms in the amorphous solids while the local excitation is stimulated locally by a single atom vibrating in the solids. We introduce a continuous wave vector for the study and transform the equations of atomic vibrations from the real space to the reciprocal space. We take the amorphous silicon as an example and calculate the structures of the excitations in the reciprocal space. Results show that an excitation is a wave packet composed of a collection of plane waves. We also find a periodical structure in the reciprocal space for the collective excitation with longitudinal vibrations, which is originated from the local order of the structure in the real space of the amorphous solid. For the local excitation, the wave vector is complex. The imaginary part of the wave vector is inversed to evaluate the decaying length of the local excitation. It is found that the decaying length is larger for the local excitation with a higher vibration frequency.

Nicola Manini