States Of Atomic Systems Research Articles

Quantum-enhanced sensing on optical transitions through finite-range interactions.

The control over quantum states in atomic systems has led to the most precise optical atomic clocks so far1-3. Their sensitivity is bounded at present by the standard quantum limit, a fundamental floor set by quantum mechanics for uncorrelated particles, which can-nevertheless-be overcome when operated with entangled particles. Yet demonstrating a quantum advantage in real-world sensors is extremely challenging. Here we illustrate a pathway for harnessing large-scale entanglement in an optical transition using 1D chains of up to 51 ions with interactions that decay as a power-law function of the ion separation. We show that our sensor can emulate many features of the one-axis-twisting (OAT) model, an iconic, fully connected model known to generate scalable squeezing4 and Greenberger-Horne-Zeilinger-like states5-8. The collective nature of the state manifests itself in the preservation of the total transverse magnetization, the reduced growth of the structure factor, that is, spin-wave excitations (SWE), at finite momenta, the generation of spin squeezing comparable with OAT (a Wineland parameter9,10 of -3.9 ± 0.3 dB for only N = 12 ions) and the development of non-Gaussian states in the form of multi-headed cat states in the Q-distribution. We demonstrate the metrological utility of the states in a Ramsey-type interferometer, in which we reduce the measurement uncertainty by -3.2 ± 0.5 dB below the standard quantum limit for N = 51 ions.

Thermal contribution to measured g-factors in alkali atoms

In this paper, we consider a one-loop thermal correction to the g-factors of the ground and low-lying excited states in atomic systems with one valence s electron. As an example, we carried out calculations for Rb and Cs atoms, where optical measurements of transition frequencies set the metrological level of accuracy. With the development of atomic systems as the most accurate tool for spectroscopic experiments, it has become increasingly important to improve the accuracy of measuring the electron g-factor, which is currently at10−12. The rapid progress in this field in recent years requires analysis not only of various relativistic, quantum electrodynamics, and other effects, but also theoretical studies of phenomena stimulated by the external thermal environment. We can expect that the thermal contribution to the g-factor calculated in our work may be of interest in the near future.

Challenges for Variational Reduced-Density-Matrix Theory: Total Angular Momentum Constraints.

The variational two-electron reduced density matrix (v2RDM) method is generalized for the description of total angular momentum (J) and projection of total angular momentum (MJ) states in atomic systems described by nonrelativistic Hamiltonians, and it is shown that the approach exhibits serious deficiencies. Under ensemble N-representability constraints, v2RDM theory fails to retain the appropriate degeneracies among various J states for fixed spin (S) and orbital angular momentum (L), and for fixed L, S, and J, the manifold of MJ states is not necessarily degenerate. Moreover, a substantial energy error is observed for a system for which the two-electron reduced density matrix is exactly ensemble N-representable; in this case, the error stems from violations in pure-state N-representability conditions. Unfortunately, such violations do not appear to be good indicators of the reliability of energies from v2RDM theory in general. Several states are identified for which energy errors are near zero and yet pure-state conditions are clearly violated.

Autoionization and Dressing of Excited Excitons by Free Carriers in Monolayer WSe_{2}.

We experimentally demonstrate dressing of the excited exciton states by a continuously tunable Fermi sea of free charge carriers in a monolayer semiconductor. It represents an unusual scenario of two-particle excitations of charged excitons previously inaccessible in conventional material systems. We identify excited state trions, accurately determine their binding energies in the zero-density limit for both electron- and hole-doped regimes, and observe emerging many-body phenomena at elevated doping. Combining experiment and theory we gain access to the intra-exciton coupling facilitated by the interaction with free charge carriers. We provide evidence for a process of autoionization for quasiparticles, a unique scattering pathway available for excited states in atomic systems. Finally, we demonstrate a complete transfer of the optical transition strength from the excited excitons to dressed Fermi-polaron states as well as the associated light emission from their nonequilibrium populations.

The Development of a Parallel Algorithm and Program for Solving the Stationary Many-Body Schrodinger Equation by the Monte Carlo Method on the Example of S States of Atomic Systems

This paper is devoted to the development of a specialized oriented to the use of supercomputers algorithm for solving the stationary multiparticle Schrodinger equation - the eigenvalues problem and the corresponding eigenfunctions of many-electron systems (atoms, molecules, ions) - and their software implementation. The algorithm under development is based on several methods for numerical solving of eigenvalue problems by the Monte Carlo method (MCM) which are used in the calculation of neutron transport problems in nuclear reactors. MCM for the integral form of the stationary Schrodinger equation looks very attractive, since it is intrinsically parallel and very convenient for calculations on multiprocessor systems. The paper presents an algorithm for calculating many-electron atomic systems with zero orbital angular momentum on multiprocessor systems. As a result of the research, an approach that contains a theoretical prediction of the boundaries of fundamental regions - those in which the wave function is of a constant sign - was proposed. The problem of electronic fluctuations introduced by the use of normalization algorithms was also solved to prevent unlimited growth (fall) in the number of particles in the packet. The new approach refuses normalization and assumes the existence of a corridor for the number of particles in the packet.

Engineering quantum hyperentangled states in atomic systems

Hyperentangled states have boosted many quantum informatics tasks tremendously due to their high information content per quantum entity. Until now, however, the engineering and manipulation of such states were limited to photonic systems only. In present article, we propose generating atomic hyperentanglement involving atomic internal states as well as atomic external momenta states. Hypersuperposition, hyperentangled cluster, Bell and Greenberger–Horne–Zeilinger states are engineered deterministically through resonant and off-resonant Bragg diffraction of neutral two-level atoms. Based on the characteristic parameters of the atomic Bragg diffraction, such as comparatively large interaction times and spatially well-separated outputs, such decoherence resistant states are expected to exhibit good overall fidelities and offer the evident benefits of full controllability, along with extremely high detection efficiency, over the counterpart photonic states comprised entirely of flying qubits.

Observation of chiral edge states with neutral fermions in synthetic Hall ribbons.

Chiral edge states are a hallmark of quantum Hall physics. In electronic systems, they appear as a macroscopic consequence of the cyclotron orbits induced by a magnetic field, which are naturally truncated at the physical boundary of the sample. Here we report on the experimental realization of chiral edge states in a ribbon geometry with an ultracold gas of neutral fermions subjected to an artificial gauge field. By imaging individual sites along a synthetic dimension, encoded in the nuclear spin of the atoms, we detect the existence of the edge states and observe the edge-cyclotron orbits induced during quench dynamics. The realization of fermionic chiral edge states opens the door for edge state interferometry and the study of non-Abelian anyons in atomic systems.

Visualizing edge states in atomic systems

Quantum Simulation![Figure][1] Illustration of atoms in a synthetic lattice PHOTO: EMILY EDWARDS Visualizing edge states in atomic systems Simulating the solid state using ultracold atoms is an appealing research approach. In solids, however, the charged electrons are susceptible to an

Visualizing edge states with an atomic Bose gas in the quantum Hall regime

Bringing ultracold atomic gases into the quantum Hall regime is challenging. We engineered an effective magnetic field in a two-dimensional lattice with an elongated-strip geometry, consisting of the sites of an optical lattice in the long direction and of three internal atomic spin states in the short direction. We imaged the localized states of atomic Bose-Einstein condensates in this strip; via excitation dynamics, we further observed both the skipping orbits of excited atoms traveling down the system's edges, analogous to edge magnetoplasmons in two-dimensional electron systems, and a dynamical Hall effect for bulk excitations. Our technique involves minimal heating, which will be important for spectroscopic measurements of the Hofstadter butterfly and realizations of Laughlin's charge pump.

Dynamic resonances in the autoionization Rydberg states of atomic systems

Contemporary views on the formation of dynamic nonlinear resonances in isolated intermediate Rydberg quasi-molecular complexes formed by a single elementary act upon the slow collision highly excited atoms are discussed. A relation between the emergence of dynamic resonance and the quasi-intersection of atomic terms is revealed in the quasi-classical approximation. Relationships between the widths of dynamic resonances and the dipole matrix element leading to the corresponding quasi-intersections are determined. The physical reasons for the dynamic chaos regime are formulated. A quasi-classical statistical description is given of the diffusion ionization of an atomic complex with a dense network of quasi-intersections of terms. Development of the stochastic instability of the Rydberg electron trajectories due charge exchange inside the collision complex is considered. The effect the narrowing region of stochastic motion has when passing through the Coulomb convergence of the levels with a simultaneous drop in the ionization rate of quasi-molecular systems is predicted for external statistical magnetic and electric fields under conditions of Forster resonance.

Synthetic spin-orbit interactions and magnetic fields in ring-cavity QED

The interactions between light and matter are strongly enhanced when atoms are placed in high-finesse quantum cavities, offering tantalizing opportunities for generating exotic new quantum phases. In this work we show that both spin-orbit interactions and strong synthetic magnetic fields result when a neutral atom is confined within a ring cavity, whenever the internal atomic states are coupled to two off-resonant counter-propagating modes. We diagonalize the resulting cavity polariton Hamiltonian and find characteristic spin-orbit dispersion relations for a wide range of parameters. An adjustable uniform gauge potential is also generated, which can be converted into a synthetic magnetic field for neutral atoms by applying an external magnetic field gradient. Very large synthetic magnetic fields are possible as the strength is proportional to the (average) number of photons in each of the cavity modes. The results suggest that strong-coupling cavity quantum electrodynamics can be a useful environment for the formation of topological states in atomic systems.

Calculation method for the continuum states of atomic systems

AbstractIn the present work, we develop a calculational method of solving the scattering equations for spherically symmetric potentials by expanding the solutions on Coulomb functions. We utilize a multistep integration scheme together with the standard partial wave analysis in a region where the potential term dominates. The method applies to any physical problem expressed as [∇ 2 + V(r) + k 2]ψ(r) = 0, while the extension of the method to more general scattering problems is briefly discussed. At present, we demonstrate a two-step Coulomb-fitted integration scheme by calculating the short-range scattering phase shifts for various potentials V (r).

Precise criterion for excited states of the lithiumlike systems

By using the accurate inequalities of the electron density at the nucleus and radial expectation values for atomic systems derived by Gálvez and Porras, we separately construct two sets of precise criterion of the wave function, they are another precise criterion independent of energy to test quality of the wave function. In this paper, we use the excited states of lithiumlike systems as research objects and examine the upper bound of the electron density at the nucleus and radial expectation value for the lithiumlike systems 1s23s state, R6 defined by the upper bounds of the electron density at the nucleus and R4 defined by the upper bounds of radial expectation value for the lithium atom 1s23s state in different calculation methods are also tested，at the same time we check up the upper bound of the electron density at the nucleus and radial expectation value for double excited states of the lithium atom. Research has shown that these two sets of inequalities can be used as precise criterion for wave function of energy states of atomic systems.

Entanglement and the SU(2) phase states in atomic systems

We show that a system of $2n$ identical two-level atoms interacting with n cavity photons manifests entanglement and that the set of entangled states coincides with the so-called SU(2) phase states. In particular, violation of classical realism in terms of the Greenberger-Horne-Zeilinger and Clauser-Horne-Shimoni-Holt conditions is proved. We discuss a property of entanglement expressed in terms of local measurements. We also show that generation of entangled states in the atom-photon systems under consideration strongly depends on the choice of initial conditions and that the parasitic influence of cavity detuning can be compensated through the use of Kerr medium.

The theory of two-electron atoms: between ground state and complete fragmentation

Since the first attempts to calculate the helium ground state in the early days of Bohr-Sommerfeld quantization, two-electron atoms have posed a series of unexpected challenges to theoretical physics. Despite the seemingly simple problem of three charged particles with known interactions, it took more than half a century after quantum mechanics was established to describe the spectra of two-electron atoms satisfactorily. The evolution of the understanding of correlated two-electron dynamics and its importance for doubly excited resonance states is presented here, with an emphasis on the concepts introduced. The authors begin by reviewing the historical development and summarizing the progress in measuring the spectra of two-electron atoms and in calculating them by solving the corresponding Schr\"odinger equation numerically. They devote the second part of the review to approximate quantum methods, in particular adiabatic and group-theoretical approaches. These methods explain and predict the striking regularities of two-electron resonance spectra, including propensity rules for decay and dipole transitions of resonant states. This progress was made possible through the identification of approximate dynamical symmetries leading to corresponding collective quantum numbers for correlated electron-pair dynamics. The quantum numbers are very different from the independent particle classification, suitable for low-lying states in atomic systems. The third section of the review describes modern semiclassical concepts and their application to two-electron atoms. Simple interpretations of the approximate quantum numbers and propensity rules can be given in terms of a few key periodic orbits of the classical three-body problem. This includes the puzzling existence of Rydberg series for electron-pair motion. Qualitative and quantitative semiclassical estimates for doubly excited states are obtained for both regular and chaotic classical two-electron dynamics using modern semiclassical techniques. These techniques set the stage for a theoretical investigation of the regime of extreme excitation towards the three-body breakup threshold. Together with periodic orbit spectroscopy, they supply new tools for the analysis of complex experimental spectra.

Quintet States in Atomic Systems

Quintet states in atomic and ionic systems are fascinating and are rare and elusive to optical studies. This brief communication reviews our observation of specific quintet states in the N+, O2+ and Ar4+ systems via electron-capture processes in high-resolution translational energy spectroscopy. In particular, the metastable [3s3p3 5S0] state of Ar4+, which is not listed in comprehensive spectroscopic tables, has been identified and located at an energy of 7.7 eV above the 3P ground state.

Density functional calculations of positron annihilation lifetimes from positron bound states in atoms

Positron annihilation from positron bound states in atomic systems has been investigated by using density functional theory. The shifts of the positron lifetime have been analysed in terms of competing influences of correlation potentials. The results suggest that inclusion of electron - positron correlation is crucial in the assignment of positron orbitals to lifetime components in density functional investigations of bound states of the positron in negative and neutral atomic systems. The eigenvalues of positron bound states consistently correspond to the positron annihilation lifetimes in our calculations.

An attempt to use correlated wavefunctions to determine autoionizing states. I. 2P0 resonances in the lithium atom

The correlated-configuration saddle point method is proposed as a tool for rather high accuracy determination of autoionizing states in atomic systems. The method is based on the method of superposition of correlated configurations, elaborated previously by one of the authors and on the mini-max principle. The positions of the six lowest 2P0 resonances in the lithium atom have been determined. The results are better than those obtained by other authors and a comparison with experiments is in general satisfactory.

A novel method to determine vibrational energy states of atomic systems

Vibrations of atomic systems, including zero-point motions, can be investigated by nuclear reactions. This novel technique, based on the Doppler principle, yields information on the energetic and orientational states of the target.