arXiv subjects

Peter Schmelcher

Publications and source records attributed to Peter Schmelcher.

At least 145 records · Page 8Linked to original sources

arXiv2016

Analysis of classical phase space and energy transfer for two rotating dipoles in an electric field

We explore the classical dynamics of two interacting rotating dipoles that are fixed in the space and exposed to an external homogeneous electric field. Kinetic energy transfer mechanisms between the dipoles are investigated varying both the amount of initial excess kinetic energy of one of them and the strength of the electric field. In the field-free case, and depending on the initial excess energy an abrupt transition between equipartition and non-equipartition regimes is encountered. The study of the phase space structure of the system as well as the formulation of the Hamiltonian in an appropriate coordinate frame provide a thorough understanding of this sharp transition. When the electric field is turned on, the kinetic energy transfer mechanism is significantly more complex and the system goes through different regimes of equipartition and non-equipartition of the energy including chaotic behavior.

nlin.CD↗

arXiv2016

Collective excitations of dipolar gases based on local tunneling in superlattices

The collective dynamics of a dipolar fermionic quantum gas confined in a one-dimensional double-well superlattice is explored. The fermionic gas resides in a paramagnetic-like ground state in the weak interaction regime, upon which a new type of collective dynamics is found when applying a local perturbation. This dynamics is composed of the local tunneling of fermions in separate supercells, and is a pure quantum effect, with no classical counterpart. Due to the presence of the dipolar interactions the local tunneling transports through the entire superlattice, giving rise to a collective dynamics. A well-defined momentum-energy dispersion relation is identified in the ab-initio simulations demonstrating the phonon-like behavior. The phonon-like characteristic is also confirmed by an analytical description of the dynamics within a semiclassical picture.

cond-mat.quant-gas↗

arXiv2016

Stretching and bending dynamics in triatomic ultralong-range Rydberg molecules

We investigate polyatomic ultralong-range Rydberg molecules consisting of three ground state atoms bound to a Rydberg atom via $s$- and $p$-wave interactions. By employing the finite basis set representation of the unperturbed Rydberg electron Green's function we reduce the computational effort to solve the electronic problem substantially. This method is subsequently applied to determine the potential energy surfaces of triatomic systems in electronic $s$- and $p$-Rydberg states. Their molecular geometry and resulting vibrational structure are analyzed within an adiabatic approach that separates the vibrational bending and stretching dynamics. This procedure yields information on the radial and angular arrangement of the nuclei and indicates in particular that kinetic couplings between bending and stretching modes induce a linear structure in triatomic $l=0$ ultralong-range Rydberg molecules.

physics.atom-ph↗

arXiv2016

Freezing, accelerating and slowing directed currents in real time with superimposed driven lattices

We provide a generic scheme offering real time control of directed particle transport in superimposed driven lattices. This scheme allows to accelerate, slow and freeze the transport on demand, by switching one of the lattices subsequently on and off. The underlying physical mechanism hinges on a systematic opening and closing of channels between transporting and non-transporting phase space structures upon switching, and exploits cantori structures which generate memory effects in the population of these structures. Our results should allow for real time control of cold thermal atomic ensembles in optical lattices, but might also be useful as a design principle for targeted delivery of molecules or colloids in optical devices.

nlin.CD↗

arXiv2016

Exciton absorption in narrow armchair graphene nanoribbons

We develop an analytical approach to the exciton optical absorption for narrow gap armchair graphene nanoribbons (AGNR). We focus on the regime of dominant size quantization in combination with the attractive electron-hole interaction. An adiabatic separation of slow and fast motions leads via the two-body Dirac equation to the isolated and coupled subband approximations. Discrete and continuous exciton states are in general coupled and form quasi Rydberg series of purely discrete and resonance type character. Corresponding oscillator strengths and widths are derived. We show that the exciton peaks are blue-shifted, become broader and increase in magnitude upon narrowing the ribbon. At the edge of a subband the singularity related to the 1D density of states is transformed into finite absorption via the presence of the exciton. Our analytical results are in good agreement with those obtained by other methods including numerical approaches. Estimates of the expected experimental values are provided for realistic AGNRs.

cond-mat.mes-hall↗

arXiv2016

Dynamics of Local Symmetry Correlators for Interacting Many-Particle Systems

Recently (PRL 113, 050403 (2014)) the concept of local symmetries in one-dimensional stationary wave propagation has been shown to lead to a class of invariant two-point currents that allow to generalize the parity and Bloch theorem. In the present work we establish the theoretical framework of local symmetries for higher-dimensional interacting many-body systems. Based on the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy we derive the equations of motion of local symmetry correlators which are off-diagonal elements of the reduced one-body density matrix at symmetry related positions. The natural orbital representation yields equations of motion for the convex sum of the local symmetry correlators of the natural orbitals as well as for the local symmetry correlators of the individual orbitals themselves. An alternative integral representation with a unique interpretation is provided. We discuss special cases, such as the bosonic and fermionic mean field theory and show in particular that the invariant two-point currents are recovered in the case of the non-interacting one-dimensional stationary wave propagation. Finally we derive the equations of motion for anomalous local symmetry correlators which indicate the breaking of a global into a local symmetry in the stationary non-interacting case.

quant-ph↗

arXiv2016

Diffusion and transport in locally disordered driven lattices

We study the effect of disorder on the particle density evolution in a classical Hamiltonian driven lattice setup. If the disorder is localized within a finite sub-domain of the lattice, the emergence of strong tails in the density distribution which even increases towards larger positions is shown, thus yielding a highly non Gaussian particle density evolution. As the key underlying mechanism we identify the conversion between different components of the unperturbed systems mixed phase space which is induced by the disorder. Based on the introduction of individual conversion rates between chaotic and regular components, a theoretical model is developed which correctly predicts the scaling of the particle density. The effect of disorder on the transport properties is studied where a significant enhancement of the transport for cases of localized disorder is shown, thereby contrasting strongly the merely weak modification of transport for global disorder.

nlin.CD↗

arXiv2016

Bound and scattering states in harmonic waveguides in the vicinity of free space Feshbach resonances

The two-body bound and scattering properties in an one-dimensional harmonic waveguide close to free space magnetic Feshbach resonances are investigated based on the local frame transformation approach within a single partial wave approximation. An energy and magnetic field dependent free space phase shift is adopted in the current theoretical framework. For both $s$- and $p$-wave interaction, the least bound state in the waveguide dissociates into the continuum at the resonant magnetic field where the effective one-dimensional scattering length $a_{\rm 1D}$ diverges. Consequently, the association of atoms into molecules in the waveguide occurs when the magnetic field is swept adiabatically across the pole of $a_{\rm 1D}$. In the vicinity of broad $s$-wave resonances, the resonant magnetic field is nearly independent on the transverse confining frequency $ω_{\perp}$ of the waveguide. Close to $p$-wave and narrow $s$-wave resonances, the resonant magnetic field changes as $ω_{\perp}$ varies.

cond-mat.quant-gas↗

arXiv2016

Quench Dynamics of Two Coupled Ionic Zig-Zag Chains

We explore the non-equilibrium dynamics of two coupled zig-zag chains of trapped ions in a double well potential. Following a quench of the potential barrier between both wells, the induced coupling between both chains due to the long-range interaction of the ions leads to their complete melting. The resulting dynamics is however not exclusively irregular but leads to phases of motion during which various ordered structures appear with ions arranged in arcs, lines and crosses. We quantify the emerging order by introducing a suitable measure and complement our analysis of the ion dynamics using a normal mode analysis showing a decisive population transfer between only a few distinguished modes.

physics.class-ph↗

arXiv2016

Exposing local symmetries in distorted driven lattices via time-averaged invariants

Time-averaged two-point currents are derived and shown to be spatially invariant within domains of local translation or inversion symmetry for arbitrary time-periodic quantum systems in one dimension. These currents are shown to provide a valuable tool for detecting deformations of a spatial symmetry in static and driven lattices. In the static case the invariance of the two-point currents is related to the presence of time-reversal invariance and/or probability current conservation. The obtained insights into the wavefunctions are further exploited for a symmetry-based convergence check which is applicable for globally broken but locally retained potential symmetries.

quant-ph↗

arXiv2016

Chaotic and ballistic dynamics in time-driven quasiperiodic lattices

We investigate the nonequilibrium dynamics of classical particles in a driven quasiperiodic lattice based on the Fibonacci sequence. An intricate transient dynamics of extraordinarily long ballistic flights at distinct velocities is found. We argue how these transients are caused and can be under- stood by a hierarchy of block decompositions of the quasiperiodic lattice. A comparison to the cases of periodic and fully randomized lattices is performed.

nlin.CD↗

arXiv2016

Ultralong-range triatomic Rydberg molecules in an electric field

We investigate the electronic structure of a triatomic Rydberg molecule formed by a Rydberg atom and two neutral ground-state atoms. Taking into account the $s$-wave and $p$-wave interactions we perform electronic structure calculations and analyze the adiabatic electronic potentials evolving from the Rb$(n=35, l\ge 3)$ Rydberg degenerate manifold. We hereby focus on three different classes of geometries of the Rydberg molecules, including symmetric, asymmetric and planar configurations. The metamorphosis of these potential energy surfaces in the presence of an external electric field is explored.

physics.atom-ph↗

arXiv2015

Two-body correlations and natural orbital tomography in ultracold bosonic systems of definite parity

The relationship between natural orbitals, one-body coherences and two-body correlations is explored for bosonic many-body systems of definite parity with two occupied single-particle states. We show that the strength of local two-body correlations at the parity-symmetry center characterizes the number state distribution and controls the structure of non-local two-body correlations. A recipe for the experimental reconstruction of the natural orbital densities and quantum depletion is derived. These insights into the structure of the many-body wave-function are applied to the predicted quantum-fluctuations induced decay of dark solitons.

cond-mat.quant-gas↗

arXiv2015

Ultralong-Range Rb-KRb Rydberg Molecules: Selected Aspects of Electronic Structure, Orientation and Alignment

We investigate the structure and features of an ultralong-range triatomic Rydberg molecule formed by a Rb Rydberg atom and a KRb diatomic molecule. In our numerical description, we perform a realistic treatment of the internal rotational motion of the diatomic molecule, and take into account the Rb($n, l\ge 3$) Rydberg degenerate manifold and the energetically closest neighboring levels with principal quantum numbers $n'>n$ and orbital quantum number $l\le2$. We focus here on the adiabatic electronic potentials evolving from the Rb($n, l\ge 3$) and Rb($n=26, l=2$) manifolds. The directional properties of the KRb diatomic molecule within the Rb-KRb triatomic Rydberg molecule are also analyzed in detail.

physics.atom-ph↗

arXiv2015

Effective intermittency and cross-correlations in the Standard Map

We define auto- and cross-correlation functions capable to capture dynamical characteristics induced by local phase space structures in a general dynamical system. These correlation functions are calculated in the Standard Map for a range of values of the non-linearity parameter $k$. Using a model of non-interacting particles, each evolving according to the same Standard Map dynamics and located initially at specific phase space regions, we show that for $0.6 < k \leq 1.2$ long-range cross-correlations emerge. They occur as an ensemble property of particle trajectories by an appropriate choice of the phase space cells used in the statistical averaging. In this region of $k$-values the single particle phase space is either dominated by local chaos ($k \leq k_c$ with $k_c \approx 0.97$) or it is characterized by the transition from local to global chaos ($k_c < k \leq 1.2$). Introducing suitable symbolic dynamics we demonstrate that the emergence of long-range cross-correlations can be attributed to the existence of an effective intermittent dynamics in specific regions of the phase space. Our findings further support the recently found relation of intermittent dynamics with the occurrence of cross-correlations (F.K. Diakonos, A.K. Karlis, and P. Schmelcher, Europhys. Lett. {\bf 105}, 26004 (2014)) in simple one-dimensional intermittent maps, suggesting its validity for two-dimensional Hamiltonian systems.

nlin.CD↗

arXiv2015

Correlated Quantum Dynamics of a Single Atom Collisionally Coupled to an Ultracold Finite Bosonic Ensemble

We explore the correlated quantum dynamics of a single atom, regarded as an open system, with a spatio-temporally localized coupling to a finite bosonic environment. The single atom, initially prepared in a coherent state of low energy, oscillates in a one-dimensional harmonic trap and thereby periodically penetrates an interacting ensemble of $N_A$ bosons, held in a displaced trap. We show that the inter-species energy transfer accelerates with increasing $N_A$ and becomes less complete at the same time. System-environment correlations prove to be significant except for times when the excess energy distribution among the subsystems is highly imbalanced. These correlations result in incoherent energy transfer processes, which accelerate the early energy donation of the single atom and stochastically favour certain energy transfer channels depending on the instantaneous direction of transfer. Concerning the subsystem states, the energy transfer is mediated by non-coherent states of the single atom and manifests itself in singlet and doublet excitations in the finite bosonic environment. These comprehensive insights into the non-equilibrium quantum dynamics of an open system are gained by ab-initio simulations of the total system with the recently developed Multi-Layer Multi-Configuration Time-Dependent Hartree Method for Bosons.

cond-mat.quant-gas↗

arXiv2015

Many-body processes in black and grey matter-wave solitons

We perform a comparative beyond mean-field study of black and grey solitonic excitations in a finite ensemble of ultracold bosons confined to a one-dimensional box. An optimized density-engineering potential is developed and employed together with phase-imprinting to cleanly initialize grey solitons. Based on our recently developed Multi-Layer Multi-Configuration Time-Dependent Hartree Method for Bosons, we demonstrate an enhancement of the quantum fluctuations limited lifetime of the soliton contrast with increasing soliton velocity. A natural orbital analysis reveals a two-stage process underlying the decay of the soliton contrast. The broken parity symmetry of grey solitons results in a local asymmetry of the orbital mainly responsible for the decay, which leads to a characteristic asymmetry of remarkably localized two-body correlations. The emergence and decay of these correlations as well as their displacement from the instantaneous soliton position are analysed in detail. Finally, the role of phase-imprinting for the many-body dynamics is illuminated and additional non-local correlations in pairs of counter-propagating grey solitons are unravelled.

cond-mat.quant-gas↗

arXiv2015

Shifts and widths of p-wave confinement induced resonances in atomic waveguides

We develop and analyze a theoretical model to study p-wave Feshbach resonances of identical fermions in atomic waveguides by extending the two-channel model of A.D. Lange et. al. [Phys. Rev. A 79, 013622 (2009)] and S. Saeidian et. al. [Phys. Rev. A 86, 062713 (2012)]. The experimentally known parameters of Feshbach resonances in free space are used as input of the model. We calculate the shifts and widths of p-wave magnetic Feshbach resonance of $^{40}$K atoms emerging in harmonic waveguides as p-wave confinement induced resonance (CIR). Particularly, we show a possibility to control the width and shift of the p-wave confinement induced resonance by the trap frequency and the applied magnetic field which could be used in corresponding experiments. Our analysis also demonstrates the importance of the inclusion of the effective radius in the computational schemes for the description of the p-wave CIRs contrary to the case of s-wave CIRs where the influence of this term is negligible.

cond-mat.quant-gas↗