arXiv subjects

Peter Schmelcher

Publications and source records attributed to Peter Schmelcher.

At least 235 records · Page 13Linked to original sources

arXiv2007

One-dimensional Rydberg Gas in a Magnetoelectric Trap

We study the quantum properties of Rydberg atoms in a magnetic Ioffe-Pritchard trap which is superimposed by a homogeneous electric field. Trapped Rydberg atoms can be created in long-lived electronic states exhibiting a permanent electric dipole moment of several hundred Debye. The resulting dipole-dipole interaction in conjunction with the radial confinement is demonstrated to give rise to an effectively one-dimensional ultracold Rydberg gas with a macroscopic interparticle distance. We derive analytical expressions for the electric dipole moment and the critical linear density of Rydberg atoms.

physics.atom-ph↗

arXiv2007

Ultracold Rydberg Atoms in a Ioffe-Pritchard Trap

We discuss the properties of ultracold Rydberg atoms in a Ioffe-Pritchard magnetic field configuration. The derived two-body Hamiltonian unveils how the large size of Rydberg atoms affects their coupling to the inhomogeneous magnetic field. The properties of the compound electronic and center of mass quantum states are thoroughly analyzed. We find very tight confinement of the center of mass motion in two dimensions to be achievable while barely changing the electronic structure compared to the field free case. This paves the way for generating a one-dimensional ultracold quantum Rydberg gas.

physics.atom-ph↗

arXiv2007

Magnetically controlled current flow in coupled-dot arrays

Quantum transport through an open periodic array of up to five dots is investigated in the presence of a magnetic field. The device spectrum exhibits clear features of the band structure of the corresponding one-dimensional artificial crystal which evolves with varying field. A significant magnetically controlled current flow is induced with changes up to many orders of magnitude depending on temperature and material parameters. Our results put forward a simple design for measuring with current technology the magnetic subband formation of quasi one-dimensional Bloch electrons.

cond-mat.mes-hall↗

arXiv2007

Quantum dynamics of two bosons in an anharmonic trap: Collective vs internal excitations

This work deals with the effects of an anharmonic trap on an interacting two-boson system in one dimension. Our primary focus is on the role of the induced coupling between the center of mass and the relative motion as both anharmonicity and the (repulsive) interaction strength are varied. The ground state reveals a strong localization in the relative coordinate, counteracting the tendency to fragment for stronger repulsion. To explore the quantum dynamics, we study the system's response upon (i) exciting the harmonic ground state by continuously switching on an additional anharmonicity, and (ii) displacing the center of mass, this way triggering collective oscillations. The interplay between collective and internal dynamics materializes in the collapse of oscillations, which are explained in terms of few-mode models.

cond-mat.other↗

arXiv2007

Scattering Dynamics of Driven Closed Billiards

We investigate the classical scattering dynamics of the driven elliptical billiard. Two fundamental scattering mechanisms are identified and employed to understand the rich behavior of the escape rate. A long-time algebraic decay which can be tuned by varying the driving amplitude is established. Pulsed escape rates and decelerated escaping particles are generic properties of the harmonically breathing billiard. This suggests time-dependent billiards as prototype systems to study the nonequilibrium evolution of classical ensembles encountering a multitude of scattering processes off driven targets.

nlin.CD↗

arXiv2007

Formation of Ultracold Heteronuclear Dimers in Electric Fields

The formation of ultracold molecules via stimulated emission followed by a radiative deexcitation cascade in the presence of a static electric field is investigated. By analyzing the corresponding cross sections, we demonstrate the possibility to populate the lowest rotational excitations via photoassociation. The modification of the radiative cascade due to the electric field leads to narrow rotational state distributions in the vibrational ground state. External fields might therefore represent an additional valuable tool towards the ultimate goal of quantum state preparation of molecules.

quant-ph↗

arXiv2006

Excitations of Few-Boson Systems in 1-D Harmonic and Double Wells

We examine the lowest excitations of one-dimensional few-boson systems trapped in double wells of variable barrier height. Based on a numerically exact multi-configurational method, we follow the whole pathway from the non-interacting to the fermionization limit. It is shown how, in a purely harmonic trap, the initially equidistant, degenerate levels are split up due to interactions, but merge again for strong enough coupling. In a double well, the low-lying spectrum is largely rearranged in the course of fermionization, exhibiting level adhesion and (anti-)crossings. The evolution of the underlying states is explained in analogy to the ground-state behavior. Our discussion is complemented by illuminating the crossover from a single to a double well.

cond-mat.other↗

arXiv2006

Resonances of the helium atom in a strong magnetic field

We present an investigation on the resonances of a doubly excited helium atom in a strong magnetic field covering the regime B = 0-100 a.u. A full-interaction approach which is based on an anisotropic Gaussian basis set of one-particle functions being nonlinearly optimized for each field strength is employed. Accurate results for a total of 17 resonances below the threshold of consisting of He+ in the N=2 state are reported in this work. This includes states with total magnetic quantum numbers M=0,-1,-2 and even z-parity. The corresponding binding energies are compared to approximate energies of two-particle configurations consisting of two hydrogen-like electrons in the strong field regime, thereby providing an understanding of the behavior of the energies of the resonances with varying field strength.

physics.atom-ph↗

arXiv2006

Negative Energy Resonances of Bosons in a Magnetic Quadrupole Trap

We investigate resonances of spin 1 bosons in a three-dimensional magnetic quadrupole field. Complementary to the well-known positive energy resonances it is shown that there exist short-lived, i.e. broad, negative energy resonances. The latter are characterized by an atomic spin that is aligned antiparallel to the local magnetic field direction. In contrast to the positive energy resonances the lifetimes of the negative energy resonances decreases with increasing total magnetic quantum number. We derive a mapping of the two branches of the spectrum.

physics.atom-ph↗

arXiv2006

Controlling ultracold Rydberg atoms in the quantum regime

We discuss the properties of Rydberg atoms in a magnetic Ioffe-Pritchard trap being commonly used in ultracold atomic physics experiments. The Hamiltonian is derived and it is demonstrated how tight traps alter the coupling of the atom to the magnetic field. We solve the underlying Schroedinger equation of the system within a given n-manifold and show that for a sufficiently large Ioffe field strength the 2n^2-dimensional system of coupled Schroedinger equations decays into several decoupled multicomponent equations governing the center of mass motion. An analysis of the fully quantized center of mass and electronic states is undertaken. In particular, we discuss the situation of tight center of mass confinement outlining the procedure to generate a low-dimensional ultracold Rydberg gas.

physics.atom-ph↗

arXiv2006

Correlations in Ultracold Trapped Few-Boson Systems: Transition from Condensation to Fermionization

We study the correlation properties of the ground states of few ultracold bosons, trapped in double wells of varying barrier height in one dimension. Extending previous results on the signature of the transition from a Bose-condensed state via fragmentation to the hard-core limit, we provide a deeper understanding of that transition by relating it to the loss of coherence in the one-body density matrix and to the emerging long-range tail in the momentum spectrum. These are accounted for in detail by discussing the natural orbitals and their occupations. Our discussion is complemented by an analysis of the two-body correlation function.

cond-mat.other↗

arXiv2006

Ultracold Few-Boson Systems in a Double-Well Trap

We investigate the transition of a quasi-one-dimensional few-boson system from a weakly correlated to a fragmented and finally a fermionized ground state. Our numerically exact analysis, based on a multi-configurational method, explores the interplay between different shapes of external and inter-particle forces. Specifically, we demonstrate that the addition of a central barrier to an otherwise harmonic trap may supports the system's fragmentation, with a symmetry-induced distinction between even and odd atom numbers. Moreover, the impact of inhomogeneous interactions is studied, where the effective coupling strength is spatially modulated. It is laid out how the ground state can be displaced in a controlled way depending on the trap and the degree of modulation. We present the one- and two-body densities and, beyond that, highlight the role of correlations on the basis of the natural occupations.

quant-ph↗

arXiv2005

N-Electron Giant Dipole States in Crossed Electric and Magnetic Fields

Multi-electron giant dipole resonances of atoms in crossed electric and magnetic fields are investigated. Stationary configurations corresponding to a highly symmetric arrangement of the electrons on a decentered circle are derived, and a normal-mode and stability analysis are performed. A classification of the various modes, which are dominated by the magnetic field or the Coulomb interactions, is provided. Based on the MCTDH approach, we carry out a six-dimensional wave-packet dynamical study for the two-electron resonances, yielding in particular lifetimes of more than 0.1 $μ$s for strong electric fields.

physics.atom-ph↗

arXiv2005

Quantum Scattering in Strong Cylindrical Confinement

A Green's function formalism to analyze the scattering properties in confined geometries is developed. This includes scattering from a central field inside the guide created e.g. by impurities. For atomic collisions our approach applies to the case of parabolic confinement and, with certain restrictions, also to an anharmonic one. The coupling between the angular momentum phase shifts $δ_l$ of a spherically symmetric scattering potential $V(r)$ due to the cylindrical confinement is analysed. Under these general conditions, a broad range of scattering energies covering many transversal excitations is considered and changes to the bound states of $V(r)$ are derived. For collisions between identical atoms, the boson-fermion and fermion-boson mappings are demonstrated.

quant-ph↗

arXiv2004

Impurity center in a semiconductor quantum ring in the presence of a radial electric field

The problem of an impurity electron in a quantum ring (QR) in the presence of a radially directed strong external electric field is investigated in detail. Both an analytical and a numerical approach to the problem are developed. The analytical investigation focuses on the regime of a strong wire-electric field compared to the electric field due to the impurity. An adiabatic and quasiclassical approximation is employed. The explicit dependencies of the binding energy of the impurity electron on the electric field strength, parameters of the QR and position of the impurity within the QR are obtained. Numerical calculations of the binding energy based on a finite-difference method in two and three dimensions are performed for arbitrary strengths of the electric field. It is shown that the binding energy of the impurity electron exhibits a maximum as a function of the radial position of the impurity that can be shifted arbitrarily by applying a corresponding wire-electric field. The maximal binding energy monotonically increases with increasing electric field strength. The inversion effect of the electric field is found to occur. An increase of the longitudinal displacement of the impurity typically leads to a decrease of the binding energy. Results for both low- and high-quantum rings are derived and discussed. Suggestions for an experimentally accessible set-up associated with the GaAs/GaAlAs QR are provided.

cond-mat.mes-hall↗

arXiv2004

Spectral Properties and Lifetimes of Neutral Spin-1/2-Fermions in a Magnetic Guide

We investigate the resonant motion of neutral spin-1/2-fermions in a magnetic guide. A wealth of unitary and anti-unitary symmetries is revealed in particular giving rise to a two-fold degeneracy of the energy levels. To compute the energies and decay widths of a large number of resonances the complex scaling method is employed. We discuss the dependence of the lifetimes on the angular momentum of the resonance states. In this context the existence of so-called quasi-bound states is shown. In order to approximately calculate the resonance energies of such states a radial Schrödinger equation is derived which improves the well-known adiabatic approximation. The effects of an additionally applied homogeneous Ioffe field on the resonance energies and decay widths are also considered. The results are applied to the case of the $^6\text{Li}$ atom in the $F=1/2$ hyperfine ground state.

physics.atom-ph↗

arXiv2004

Rydberg Atoms in a Magnetic Guide

We investigate electronically excited atoms in a magnetic guide. It turns out that the Hamiltonian describing this system possesses a wealth of both unitary as well as antiunitary symmetries that constitute an uncommon extensive symmetry group. One consequence is the two-fold degeneracy of any energy level. The spectral properties are investigated for a wide range of field gradients and the spatial distributions of the spin polarization are analyzed. Wave lengths, oscillator strengths and selection rules are provided for the corresponding electromagnetic transitions. The effects due to an additional homogeneous bias field constituting a Ioffe-Pritchard trap are explored equally.

physics.atom-ph↗

arXiv2004

Electronic Structure of Atoms in Magnetic Quadrupole Traps

We investigate the electronic structure and properties of atoms exposed to a magnetic quadrupole field. The spin-spatial as well as generalized time reversal symmetries are established and shown to lead to a two-fold degeneracy of the electronic states in the presence of the field. Low-lying as well as highly excited Rydberg states are computed and analyzed for a broad regime of field gradients. The delicate interplay between the Coulomb and various magnetic interactions leads to complex patterns of the spatial spin polarization of individual excited states. Electromagnetic transitions in the quadrupole field are studied in detail thereby providing the selection rules and in particular the transition wavelengths and corresponding dipole strengths. The peculiar property that the quadrupole magnetic field induces permanent electric dipole moments of the atoms is derived and discussed.

physics.atom-ph↗