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

Alessandro Mameli, Giannis Thalassinos, Marco Capelli et al.

Fluorescent nanodiamonds (FNDs) containing negatively charged nitrogen-vacancy (NV ^− ) centers are vital for many emerging quantum sensing applications from magnetometry to intracellular sensing in biology. However, developing a scalable fabrication method for FNDs hosting color centers with consistent bulk-like photoluminescence (PL) and spin coherence properties remains a highly desired but unrealized goal. Here, we investigate optimized ball milling of single-crystal diamonds produced via chemical vapor deposition (CVD) and containing 2 ppm of substitutional nitrogen and 0.3 ppm of NV ^− to achieve this goal. The NV charge state, PL lifetime, and spin properties of bulk CVD diamond samples are directly compared to milled CVD FNDs and commercial high-pressure high-temperature (HPHT) FNDs. We find that on average, the relative contribution of the NV ^− charge state to the total NV PL is lower and the NV PL lifetime is longer in CVD FNDs compared to HPHT FNDs, both likely due to the lower N _s ^0 concentration in CVD FNDs. The CVD bulk and CVD FNDs on average show similar average T _1 spin relaxation times of 3.2 ± 0.7 ms and 4.7 ± 1.6 ms, respectively, compared to 0.17 ± 0.01 ms for commercial HPHT FNDs. Our results demonstrate that ball milling of CVD diamonds enables the large-scale fabrication of NV ensembles in FNDs with bulk-like T _1 spin relaxation properties.

Navinder Singh

The famous Two-Temperature Model (TTM) used extensively in the investigations of energy relaxation in photo excited systems originated in the seminal work of Kaganov et al. [Sov. J. Exp. Theor. Phys. 4, 173 (1957)]. The idea that with an ultrashort laser pulse a temporal (transient) state of electrons in a metal can be created, in which electrons after absorbing energy from the laser pulse heat up and their temperature becomes substantially greater than that of lattice, was originated in the work of Anisimov et al. [Sov. J. Exp. Theor. Phys. 39, 375 (1974)]. The heated electron sub-system (hot electrons) loses its energy to phonon sub-system via electron–phonon scattering, and thermodynamic equilibrium re-establishes over a time scale of a few picoseconds in metals. This field saw great developments in the 1980s and 1990s with the advent of femtosecond pump–probe spectroscopy. From 2000 onward, focus shifted from non-equilibrium phenomena in simple metals to those in more complex systems including strongly correlated systems such as high Tc cuprate superconductors. P. B. Allen, Phys. Rev. Lett. 59, 1460 (1987), revisits the calculations of KLT and rewrites the electron–phonon heat transfer coefficient α in terms of a very important parameter in the theory of superconductivity (λ⟨ω2⟩). This has far reaching consequences; λ, a very crucial dimensionless electron–phonon coupling parameter for a given superconducting material, can be estimated by doing pump–probe experiments on it. By mid 1990s, it became clear that TTM is violated and is not a sufficient model to discuss non-equilibrium relaxation. Year 2000 onward, field saw the development of models that go beyond the original TTM. Very recently, the field has entered into the attosecond domain. In this article, the author attempts a concise account of the development of the TTM and, in addition, a recent possible revival of it in the attosecond domain.

Jan Ole Ernst, Jan Snoeijs, Mitchell Peaks et al.

Radio frequency pulses are preponderant for the control of quantum bits and the execution of operations in quantum computers. The ability to fine-tune key pulse parameters, such as time-dependent amplitude, phase, and frequency, is essential to achieve maximal gate fidelity and mitigate errors. As systems increase in scale, a larger proportion of the control electronic processing will move closer to the qubits, to enhance integration and minimize latency in operations requiring fast feedback. This will constrain the space available in the memory of the control electronics to load time-resolved pulse parameters at high sampling rates. Cubic spline interpolation is a powerful and commonly used technique that divides the pulse into segments of cubic polynomials. We show an optimized implementation of this strategy, using a two-stage curve-fitting process and additional symmetry operations to load a high-sampling pulse output on an field-programmable gate array. This results in a favorable accuracy-versus-memory-footprint tradeoff. By simulating single-qubit population transfer and atom transport on a neutral-atom device, we show that high fidelities can be achieved with low memory requirements. This is instrumental for scaling up the number of qubits and gate operations in environments where memory is a limited resource.

Alexey E. Rastegin

Protocols of quantum information science often realize in terms of specially selected states. In particular, such states are used to perform measurements at the final stage of a protocol. This study aims to explore measurements assigned to a mutually unbiased-equiangular tight frame. The utilized method deals with Kirkwood–Dirac quasiprobabilities, which are increasingly used in contemporary research. These quasiprobabilities constitute a matrix that can be linked to unravelings of certain quantum channels. Using states of the given frame to build principal Kraus operators leads to quasiprobabilities that represent the measured state. The structure of a mutually unbiased-equiangular tight frame allows one to characterize entropies associated with a particular unraveling. To do this, we estimate some of the Schatten and Ky Fan norms of the matrix consisted of quasiprobabilities. New uncertainty relations in terms of Rényi and Tsallis entropies follow from the obtained inequalities. A utility of the presented inequalities is exemplified with mutually unbiased bases of a qubit and equiangular tight frames of a ququart.

Zejian Ren, Xu Yan, Kai Wen et al.

Optical tweezers have become an essential tool for dynamically manipulating objects, ranging from microspheres or biological molecules to neutral atoms. In this study, we demonstrate the creation of tweezer arrays using a generative neural network, which allows the trapping of neutral atoms with tunable atom arrays. We have successfully loaded cold strontium atoms into various optical tweezer patterns generated using a spatial light modulator (SLM) integrated with generative models. Our approach shortens the process time to control the SLM with a minimal time delay, eliminating the need for repeated re-optimization of the hologram for the SLM.

Giorgio Guizzetti, Maddalena Patrini

K. von Arx, Qisi Wang, S. Mustafi et al.

Abstract In high-temperature cuprate superconductors, stripe order refers broadly to a coupled spin and charge modulation with a commensuration of eight and four lattice units, respectively. How this stripe order evolves across optimal doping remains a controversial question. Here we present a systematic resonant inelastic x-ray scattering study of weak charge correlations in La2−x Sr x CuO4 and La1.8−x Eu0.2Sr x CuO4. Ultra high energy resolution experiments demonstrate the importance of the separation of inelastic and elastic scattering processes. Long-range temperature-dependent stripe order is only found below optimal doping. At higher doping, short-range temperature-independent correlations are present up to the highest doping measured. This transformation is distinct from and preempts the pseudogap critical doping. We argue that the doping and temperature-independent short-range correlations originate from unresolved electron–phonon coupling that broadly peaks at the stripe ordering vector. In La2−x Sr x CuO4, long-range static stripe order vanishes around optimal doping and we discuss both quantum critical and crossover scenarios.

Scarlett Gauthier, Gayane Vardoyan, Stephanie Wehner

Entanglement between quantum network nodes is often produced using intermediary devices—such as heralding stations—as a resource. When scaling quantum networks to many nodes, requiring a dedicated intermediary device for every pair of nodes introduces high costs. Here, we propose a cost-effective architecture to connect many quantum network nodes via a central quantum network hub called an entanglement generation switch (EGS). The EGS allows multiple quantum nodes to be connected at a fixed resource cost, by sharing the resources needed to make entanglement. We propose an algorithm called the rate control protocol, which moderates the level of competition for access to the hub's resources between sets of users. We proceed to prove a convergence theorem for rates yielded by the algorithm. To derive the algorithm we work in the framework of network utility maximization and make use of the theory of Lagrange multipliers and Lagrangian duality. Our EGS architecture lays the groundwork for developing control architectures compatible with other types of quantum network hubs as well as system models of greater complexity.

Lei Wu, Shengwei Chi, Huakun Zuo et al.

Abstract Lifshitz transition (LT) refers to an abrupt change in the electronic structure and Fermi surface and is associated to a variety of emergent quantum phenomena. Amongst the LTs observed in known materials, the field-induced LT has been rare and its origin remains elusive. To understand the origin of field-induced LT, it is important to extend the material basis beyond the usual setting of heavy fermion metals. Here, we report on a field-induced LT in PrAlSi, a magnetic Weyl semimetal candidate with localized 4f electrons, through a study of magnetotransport up to 55 T. The quantum oscillation analysis reveals that across a threshold field B * ≈ 14.5 T the oscillation frequency (F 1 = 43 T) is replaced by two new frequencies (F 2 = 62 T and F 3 = 103 T). Strikingly, the LT occurs well below the quantum limit, with obvious temperature-dependent oscillation frequency and field-dependent cyclotron mass. Our work not only enriches the rare examples of field-induced LTs but also paves the way for further investigation of the interplay among topology, magnetism, and electronic correlation.

Jiarui Zhao, Menghan Song, Yang Qi et al.

Abstract The Mermin-Wagner theorem states that spontaneous continuous symmetry breaking is prohibited in systems with short-range interactions at spatial dimension D ≤ 2. For long-range interactions with a power-law form (1/r α ), the theorem further forbids ferromagnetic or antiferromagnetic order at finite temperature when α ≥ 2D. However, the situation for α ∈ (2, 4) at D = 2 is not covered by the theorem. To address this, we conduct large-scale quantum Monte Carlo simulations and field theoretical analysis. Our findings show spontaneous breaking of S U(2) symmetry in the ferromagnetic Heisenberg model with 1/r α -form long-range interactions at D = 2. We determine critical exponents through finite-size analysis for α < 3 (above the upper critical dimension with Gaussian fixed point) and 3 ≤ α < 4 (below the upper critical dimension with non-Gaussian fixed point). These results reveal new critical behaviors in 2D long-range Heisenberg models, encouraging further experimental studies of quantum materials with long-range interactions beyond the Mermin-Wagner theorem’s scope.

Feng Du, Lin Yang, Zhiyong Nie et al.

Abstract The combination of magnetic symmetries and electronic band topology provides a promising route for realizing topologically nontrivial quasiparticles, and the manipulation of magnetic structures may enable the switching between topological phases, with the potential for achieving functional physical properties. Here, we report measurements of the electrical resistivity of EuCd2As2 under pressure, which show an intriguing insulating dome at pressures between p c1 ~ 1.0 GPa and p c2 ~ 2.0 GPa, situated between two regimes with metallic transport. The insulating state can be fully suppressed by a small magnetic field, leading to a colossal negative magnetoresistance on the order of 105%, accessible via a modest field of ~ 0.2 T. First-principles calculations reveal that the dramatic evolution of the resistivity under pressure can be attributed to consecutive transitions of EuCd2As2 from a magnetic topological insulator to a trivial insulator, and then to a Weyl semimetal, with the latter resulting from a pressure-induced change in the magnetic ground state. Similarly, the colossal magnetoresistance results from a field-induced polarization of the magnetic moments, transforming EuCd2As2 from a trivial insulator to a Weyl semimetal. These findings underscore weak exchange couplings and weak magnetic anisotropy as ingredients for discovering tunable magnetic topological materials with desirable functionalities.

Jiarui Zhao, Bin-Bin Chen, Yan-Cheng Wang et al.

Abstract We develop a nonequilibrium increment method in quantum Monte Carlo simulations to obtain the Rényi entanglement entropy of various quantum many-body systems with high efficiency and precision. To demonstrate its power, we show the results on a few important yet difficult (2 + 1)d quantum lattice models, ranging from the Heisenberg quantum antiferromagnet with spontaneous symmetry breaking, the quantum critical point with O(3) conformal field theory (CFT) to the toric code $${{\mathbb{Z}}}_{2}$$ Z 2 topological ordered state and the Kagome $${{\mathbb{Z}}}_{2}$$ Z 2 quantum spin liquid model with frustration and multi-spin interactions. In all these cases, our method either reveals the precise CFT data from the logarithmic correction or extracts the quantum dimension in topological order, from the dominant area law in finite-size scaling, with very large system sizes, controlled errorbars, and minimal computational costs. Our method, therefore, establishes a controlled and practical computation paradigm to obtain the difficult yet important universal properties in highly entangled quantum matter.

Anna Galler, Semih Ener, Fernando Maccari et al.

Abstract Cerium-based intermetallics are currently attracting much interest as a possible alternative to existing high-performance magnets containing scarce heavy rare-earth elements. However, the intrinsic magnetic properties of Ce in these systems are poorly understood due to the difficulty of a quantitative description of the Kondo effect, a many-body phenomenon where conduction electrons screen out the Ce-4f moment. Here, we show that the Ce-4f shell in Ce–Fe intermetallics is partially Kondo screened. The Kondo scale is dramatically enhanced by nitrogen interstitials suppressing the Ce-4f contribution to the magnetic anisotropy, in striking contrast to the effect of nitrogenation in isostructural intermetallics containing other rare-earth elements. We determine the full temperature dependence of the Ce-4f single-ion anisotropy and show that even unscreened Ce-4f moments contribute little to the room-temperature intrinsic magnetic hardness. Our study thus establishes fundamental constraints on the potential of cerium-based permanent magnet intermetallics.

Lee Braine, Daniel J. Egger, Jennifer Glick et al.

In this article, we extend variational quantum optimization algorithms for quadratic unconstrained binary optimization problems to the class of mixed binary optimization problems. This allows us to combine binary decision variables with continuous decision variables, which, for instance, enables the modeling of inequality constraints via slack variables. We propose two heuristics and introduce the transaction settlement problem to demonstrate them. Transaction settlement is defined as the exchange of securities and cash between parties and is crucial to financial market infrastructure. We test our algorithms using classical simulation as well as real quantum devices provided by IBM quantum.

V. A. Babenko, N. M. Petrov

On the basis of the Yukawa potential we study the pion-nucleon coupling constants for the neutral and charged pions assuming that nuclear forces at low energies are mainly determined by the exchange of virtual pions. We obtain the charged pseudovector pion-nucleon coupling constant f2π± = 0.0804(7) by making the use of experimental low-energy scattering parameters for the singlet pp- and np-scattering, and also by use of the neutral pseudovector pion-nucleon coupling constant f2π0 = 0.0749(7). Corresponding value of the charged pseudoscalar pion-nucleon coupling constant g2π0 / 4π = 14.55(13) is also determined. This calculated value of the charged pseudoscalar pion-nucleon coupling constant is in fully agreement with the experimental constant g2π0 / 4π = 14.52(26) obtained by the Uppsala Neutron Research Group. Our results show considerable charge splitting of the pion-nucleon coupling constant.

M. F. Mitrokhovich, V. T. Kupryashkin, L. P. Sidorenko

On installation of coincidences of -quanta with electrons and with law energy electrons about zero area the spatial correlation of the direction emitting Auger-electrons and electron of internal conversion was investigated at the 152Eu decay. Auger-electrons were registered on ео-electrons of the secondary electron emission (еICео-coincidences). It was established, that Auger-electrons of M-series, as well as electrons “shake-off” at -decay and internal conversion, are strongly correlated at the direction of movement with the direction of movement of basic particle (-particle, conversion electron), moving together mainly in the forward hemisphere. The intensity of correlated М-Auger radiation in range energy 1000 - 1700 eV is equal to intensity of correlated radiation “shake-off” electron from internal conversion in this range. The assumption, that the presence of spatial correlat-ing Auger-electron and conversion electron caused by current components of electron-electron interaction of particles in the final state is made.

Klavs Hansen

A. T. Rudchik, O. V. Gerashchenko, A. A. Rudchik et al.

Angular distributions of the 7Li + 14N elastic and inelastic scattering as well as the 7Li(14N, Х) reactions with production of 13, 15, 16N + 8, 6, 5Li, 11, 12, 13, 14С + 10, 9, 8, 7Ве, 10, 11, 12В + 11, 10, 9В nuclei and others were measured at Elab (14N) = 80 MeV. The data were analyzed within the optical model and coupled-reaction-channels method. The elastic and inelastic scattering, reorientations of 7Li and 14N in ground and excited states as well as the prominent one- and two-step transfers were included in a channels-coupling-scheme. The 7Li + 14N optical potential parameters for ground and excited states of 7Li and 14N as well as deformation parameters of these nuclei were deduced. The contributions of one and two-step transfers in the 7Li + 14N elastic and inelastic scattering channels were estimated.

C.T. Chantler