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

Dimitry Ayzenberg, Lindy Blackburn, Richard Brito et al.

Abstract The Event Horizon Telescope (EHT) Collaboration recently published the first images of the supermassive black holes in the cores of the Messier 87 and Milky Way galaxies. These observations have provided a new means to study supermassive black holes and probe physical processes occurring in the strong-field regime. We review the prospects of future observations and theoretical studies of supermassive black hole systems with the next-generation Event Horizon Telescope (ngEHT) project, which will greatly enhance the capabilities of the existing EHT array. These enhancements will open up several previously inaccessible avenues of investigation, thereby providing important new insights into the properties of supermassive black holes and their environments. This review describes the current state of knowledge for five key science cases, summarising the unique challenges and opportunities for fundamental physics investigations that the ngEHT will enable.

Shaofeng Duan, Binshuo Zhang, Zihao Wang et al.

Abstract The interplay between different degrees of freedom governs the emergence of correlated electronic states in quantum materials, with charge density waves (CDW) often coexisting with other exotic phases. Under thermal equilibrium, traditional CDW states are consequentially accompanied by structural phase transitions. In contrast, ultrafast photoexcitation allows access to exotic states where a single degree of freedom dominates in the time domain, enabling the study of underlying physics without interference. Here, we report the realization of a long-lived metastable CDW state without lattice distortion at the photoinduced interfaces in GdTe3 using time- and angle-resolved photoemission spectroscopy. After optical excitation above the CDW melting threshold, we identified emerged metastable interfaces through inverting the CDW-coupled lattice distortions, with lifetimes on the order of 10 picoseconds. These photoinduced interfaces represent a novel CDW state lacking the usual amplitude mode and lattice distortions, allowing quantification of the dominant role of electronic instabilities in CDW order. This work provides a new approach to disentangling electronic instabilities from electron-phonon coupling using a nonequilibrium method.

Farzad Faramarzi, Ryan Stephenson, Sasha Sypkens et al.

Kinetic inductance traveling-wave parametric amplifiers (KI-TWPAs) have a wide instantaneous bandwidth with a near quantum-limited noise performance and a relatively high dynamic range. Because of this, they are suitable readout devices for cryogenic detectors and superconducting qubits and have a variety of applications in quantum sensing. This work discusses the design, fabrication, and performance of a KI-TWPA based on four-wave mixing in a NbTiN microstrip transmission line. This device amplifies a signal band from 4 to 8 GHz without contamination from image tones, which are produced in a separate higher frequency band. The 4–8 GHz band is commonly used to read out cryogenic detectors, such as microwave kinetic inductance detectors and Josephson junction-based qubits. We report a measured maximum gain of over 20 dB using four-wave mixing with a 1 dB gain compression point of −58 dBm at 15 dB of gain over that band. The bandwidth and peak gain are tunable by adjusting the pump-tone frequency and power. Using a Y-factor method, we measure an amplifier-added noise of 0.5 ≤ Nadded ≤ 1.5 photons from 4.5 to 8 GHz.

Dennis P. Clougherty

Using the Dirac–Frenkel variational principle, a time-dependent description of the dynamics of a two-level system coupled to a bosonic bath is formulated. The method is applied to the case of a gas of cold atoms adsorbing to an elastic membrane at a finite temperature via phonon creation. The time-dependence of the system state is analytically calculated using Laplace transform methods, and a closed-form expression for the transition rate is obtained. Atoms in the gas transition to the adsorbed state through a resonance that has contributions from a distribution of vibrational modes of the membrane. The resonance can decay with the creation of a phonon to complete the adsorption process. The adsorption rate at low membrane temperatures agrees with the golden rule estimate to the lowest order in the coupling constant for values greater than a critical coupling strength. Below this critical coupling strength, the adsorption rate is exponentially suppressed by a phonon reduction factor whose exponent diverges with increasing adsorbent size. The rate changes discontinuously with coupling strength for low temperature membranes, and the magnitude of the discontinuity decreases with increasing temperature. These variational results suggest the quantum adsorption model may contain a first-order quantum phase transition.

Jordan Hines, Timothy Proctor

Quantum processors are now able to run quantum circuits that are infeasible to simulate classically, creating a need for benchmarks that assess a quantum processor's rate of errors when running these circuits. Here, we introduce a general technique for creating efficient benchmarks from any set of quantum computations, specified by unitary circuits. Our benchmarks assess the integrated performance of a quantum processor's classical compilation algorithms and its low-level quantum operations. Unlike existing “full-stack benchmarks,” our benchmarks do not require classical simulations of quantum circuits, and they use only efficient classical computations. We use our method to create random circuit benchmarks, including a computationally efficient version of the quantum volume benchmark, and an algorithm-based benchmark that uses Hamiltonian simulation circuits. We perform these benchmarks on IBM Q devices and in simulations, and we compare their results to the results of the existing benchmarking methods.

Satoshi Yokotsuka, Hiroyuki Okada

Four-bit input linear quantum computing with liquid crystal (LC) devices was studied using the Deutsch–Jozsa algorithm. A laser beam is split into four paths and passed through a configuration of twisted nematic (TN) LC device/(λ/2 waveplate)/TN LC device for computation. In order to minimize the effect of photon loss in the light path, a 4 × 4 matrix analysis was done for optimization. We fabricated a prototype for four optical-path linear quantum computing. As a result, we obtained changes in the number of photons counting according to Deutsch–Jozsa’s algorithm under the extremely weak light state.

Seung-Hwan Do, Hao Zhang, David A. Dahlbom et al.

Abstract Quantum magnets admit more than one classical limit and N-level systems with strong single-ion anisotropy are expected to be described by a classical approximation based on SU(N) coherent states. Here we test this hypothesis by modeling finite temperature inelastic neutron scattering (INS) data of the effective spin-one antiferromagnet Ba2FeSi2O7. The measured dynamic structure factor is calculated with a generalized Landau-Lifshitz dynamics for SU(3) spins. Unlike the traditional classical limit based on SU(2) coherent states, the results obtained with classical SU(3) spins are in good agreement with the measured temperature dependent spectrum. The SU(3) approach developed here provides a general framework to understand the broad class of materials comprising weakly coupled antiferromagnetic dimers, trimers, or tetramers, and magnets with strong single-ion anisotropy.

Tao Xie, A. A. Eberharter, Jie Xing et al.

Abstract Fifty years after Anderson’s resonating valence-bond proposal, the spin-1/2 triangular-lattice Heisenberg antiferromagnet (TLHAF) remains the ultimate platform to explore highly entangled quantum spin states in proximity to magnetic order. Yb-based delafossites are ideal candidate TLHAF materials, which allow experimental access to the full range of applied in-plane magnetic fields. We perform a systematic neutron scattering study of CsYbSe2, first proving the Heisenberg character of the interactions and quantifying the second-neighbor coupling. We then measure the complex evolution of the excitation spectrum, finding extensive continuum features near the 120°-ordered state, throughout the 1/3-magnetization plateau and beyond this up to saturation. We perform cylinder matrix-product-state (MPS) calculations to obtain an unbiased numerical benchmark for the TLHAF and spectacular agreement with the experimental spectra. The measured and calculated longitudinal spectral functions reflect the role of multi-magnon bound and scattering states. These results provide valuable insight into unconventional field-induced spin excitations in frustrated quantum materials.

Yuting Zou, Hyungki Shin, Haoran Wei et al.

Abstract Two-dimensional electron gas systems (2DEGs) generated at the oxide interfaces that exhibit rich physics phenomena opened up an era for oxide-based electronics, photonics, and spintronics. The recent discovery of superconductivity plus the strong spin-orbital coupling naturally existing in the 2DEGs of KTaO3 (KTO) made KTO an exciting platform for the interplay of the electronic and spin degrees of freedom to create exotic physical properties. By directly placing KTO’s 2DEGs next to another strongly-correlated oxide with nontrivial topological nodes, we reveal the anomalous effects which were induced by the topological states in the electronic transport properties of the KTO’s 2DGEs, due to the electronic reconstruction caused by the proximity effect. This adds an additional prospect to the functions of KTO heterostructures.

B. David Clader, Alexander M. Dalzell, Nikitas Stamatopoulos et al.

We provide a modular circuit-level implementation and resource estimates for several methods of block-encoding a dense <inline-formula><tex-math notation="LaTeX">$N\times N$</tex-math></inline-formula> matrix of classical data to precision <inline-formula><tex-math notation="LaTeX">$\epsilon$</tex-math></inline-formula>; the minimal-depth method achieves a <inline-formula><tex-math notation="LaTeX">$T$</tex-math></inline-formula>-depth of <inline-formula><tex-math notation="LaTeX">$\mathcal {O}(\log (N/\epsilon)),$</tex-math></inline-formula> while the minimal-count method achieves a <inline-formula><tex-math notation="LaTeX">$T$</tex-math></inline-formula>-count of <inline-formula><tex-math notation="LaTeX">$\mathcal{O} (N \log(\log(N)/\epsilon))$</tex-math></inline-formula>. We examine resource tradeoffs between the different approaches, and we explore implementations of two separate models of quantum random access memory. As a part of this analysis, we provide a novel state preparation routine with <inline-formula><tex-math notation="LaTeX">$T$</tex-math></inline-formula>-depth <inline-formula><tex-math notation="LaTeX">$\mathcal {O}(\log (N/\epsilon))$</tex-math></inline-formula>, improving on previous constructions with scaling <inline-formula><tex-math notation="LaTeX">$\mathcal {O}(\log ^{2} (N/\epsilon))$</tex-math></inline-formula>. Our results go beyond simple query complexity and provide a clear picture into the resource costs when large amounts of classical data are assumed to be accessible to quantum algorithms.

Gan Jin, Daye Zheng, Lixin He

Abstract We present a derivation of the full formula to calculate the Berry curvature on non-orthogonal numerical atomic orbital (NAO) bases. Because usually, the number of NAOs is larger than that of the Wannier bases, we use a orbital contraction method to reduce the basis sizes, which can greatly improve the calculation efficiency without significantly reducing the calculation accuracy. We benchmark the formula by calculating the Berry curvature of ferroelectric BaTiO 3 and bcc Fe, as well as the anomalous Hall conductivity for Fe. The results are in excellent agreement with the finite-difference and previous results in the literature. We find that there are corrections terms to the Kubo formula of the Berry curvature. For the full NAO base, the differences between the two methods are negligibly small, but for the reduced bases sets, the correction terms become larger, which may not be neglected in some cases. The formula developed in this work can readily be applied to the non-orthogonal generalized Wannier functions.

О. О. Lebed, V. O. Myslinchuk, L. V. Klymenko et al.

The results of the complex determination by the express method of the volumetric activity of 222Rn in the premises' air of Rivne city are given. The geometric mean value of the volumetric activity of 222Rn in the studied premises (600 basements, semi-basements, and first floors of residential buildings) of Rivne is 200 Bq/m3, the geometric standard deviation is 0.8. Namely, we determined the average geometric value of the volumetric activity 365 Bq/m3 in 185 basements, 161 Bq/m3 in 215 semi-basements, and 127 Bq/m3 in the living quarters of the first floors. We made a comparative analysis of experimentally obtained values of radon flux density from the soil of the city (the city was divided into 48 subdistricts) with statistics on mortality from lung cancer; mortality in these subdistricts was recorded for a certain period of time.

M. Saint-Paul, P. Monceau

We reexamine the thermodynamic properties such as specific heat, thermal expansion, and elastic constants at the charge density wave (CDW) phase transition in several one- and two-dimensional materials. The amplitude of the specific heat anomaly at the CDW phase transition TCDW increases with increasing TCDW and a tendency to a lineal temperature dependence is verified. The Ehrenfest mean field theory relationships are approximately satisfied by several compounds such as the rare earth tritelluride compound TbTe3, transition metal dichalcogenide compound 2H-NbSe2, and quasi-one-dimensional conductor K0.3MoO3. In contrast inconsistency exists in the Ehrenfest relationships with the transition metal dichalcogenide compounds 2H-TaSe2 and TiSe2 having a different thermodynamic behavior at the transition temperature TCDW. It seems that elastic properties in the ordered phase of most of the compounds are related to the temperature dependence of the order parameter which follows a BCS behavior.

Bongjae Kim, Sergii Khmelevskyi, Igor I. Mazin et al.

Unconventional superconductivity: role of magnetic interactions in strontium ruthenate A new framework for analysing the role of magnetic interactions on the unconventional superconductivity in strontium ruthenate. Strontium ruthenate is an unconventional superconductor that used to be touted a potential three-dimensional analogue of Helium-3, as it was thought to have the same type of chiral p-wave pairing. It is now widely accepted that this is not the case, but many questions remain over the exact nature of the pairing, particularly regarding the role of magnetic interactions. An international team of researchers led by Bongjae Kim and Sergii Khmelevskyi from the University of Vienna and Vienna University of Technology now present a framework that can incorporate the leading isotropic and anisotropic magnetic interactions in a different but complimentary way to the widely used Hubbard-model, providing an alternative way of exploring the superconducting pairing symmetry.

Mariam O. Waheed, Fadhil I. Sharrad

Energy levels, B(E2) transition probabilities and potential energy surface for palladium isotopes with proton number Z = 46 and neutron numbers (n) between 62 and 66 have been calculated through the interacting boson model. The set of parameters used in these calculations are the best approximation that has been carried out so far. The ratio of the excitation energies of the first 4+1 and the first 2+1 excited states, R = E4+1/E2+1, is also calculated and an achievable degree of agreement has been investigated in O(6) symmetry for 108-112Pd nuclei. The comparison between the calculated energy levels and the transition probabilities B(E2) with those of the experimental show that it is a good agreement. The contour plot of the potential energy surfaces shows all nuclei of interests are deformed and have γ-unstable-like characters.

Claudia Ratti

L.C Gomes, J.D Walecka, V.F Weisskopf

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

The excitation spectra in the deformed nucleus 228Th 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 about 110 excitations seen in the triton spectra up to 2.5 MeV. Firm 0+ assignments are made for 17 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.

M. M. Pravdivy, I. O. Korzh

Results of some previous investigations concerning definition of full sets of average resonances parameters S0, S1, , , S1,1/2, S1,3/2 for nuclei 47,9Ti, 55,8Fe, 58,7Ni, 65,4Zn, 72,6Ge, 79Se, 91,2Zr, 95,9Mo, 101,1Ru, 106,4Pd, 106Cd, 108Cd, 110Cd, 112Cd, 116Cd, 116Sn, 118Sn, 120Sn, 122Sn, 124Sn, 127,6Te, 144,2Nd has been presented and the place of these sets in the existing system of recommended parameters has been shown.

Fedor Šimkovic