arXiv subjects

Christoph Weiss

Publications and source records attributed to Christoph Weiss.

At least 37 records · Page 2Linked to original sources

arXiv2012

Nonlocal quantum superpositions of bright matter-wave solitons and dimers

The scattering of bright quantum solitons at barrier potentials in one-dimensional geometries is investigated. Such protocols have been predicted to lead to the creation of nonlocal quantum superpositions. The centre-of-mass motion of these bright matter-wave solitons generated from attractive Bose-Einstein condensates can be analysed with the effective potential approach. An application to the case of two particles being scattered at a delta potential allows analytical calculations not possible for higher particle numbers as well as a comparison with numerical results. Both for the dimer and a soliton with particle numbers on the order of N = 100, we investigate the signatures of the coherent superposition states in an interferometric setup and argue that experimentally an interference pattern would be particularly well observable in the centre-of-mass density. Quantum superposition states of ultra-cold atoms are interesting as input states for matter-wave interferometry as they could improve signal-to-noise ratios.

cond-mat.quant-gas↗

arXiv2012

Elastic scattering of a quantum matter-wave bright soliton on a barrier

We consider a one-dimensional matter-wave bright soliton, corresponding to the ground bound state of N particles of mass m having a binary attractive delta potential interaction on the open line. For a full N-body quantum treatment, we derive several results for the scattering of this quantum soliton on a short-range, bounded from below, external potential, restricting to the low energy, elastic regime where the centre-of-mass kinetic energy of the incoming soliton is lower than the internal energy gap of the soliton, that is the minimal energy required to extract particles from the soliton.

cond-mat.quant-gas↗

arXiv2012

Effective time-reversal via periodic shaking

For a periodically shaken optical lattice, effective time-reversal is investigated numerically. For interacting ultra-cold atoms, the scheme of [J. Phys. B 45, 021002 (2012)] involves a quasi-instantaneous change of both the shaking-amplitude and the sign of the interaction. As the wave function returns to its initial state with high probability, time-reversal is ideal to distinguish pure quantum dynamics from the dynamics described by statistical mixtures.

cond-mat.quant-gas↗

arXiv2012

Quantum theory of bright matter wave solitons in harmonic confinement

This paper investigates bright quantum-matter-wave solitons beyond the Gross-Pitaevskii equation (GPE). As proposals for interferometry and creating nonlocal quantum superpositions have been formed, it has become necessary to investigate effects not present in mean-field models. We investigate the effect of harmonic confinement on the internal degrees of freedom, as the ratio of zero-point harmonic oscillator length to classical soliton length, for different numbers of atoms. We derive a first-order energy correction for the addition of a harmonic potential to the many-body wave function and use this to create a variational technique based on energy minimization of this wave function for an arbitrary number of atoms, and include numerics based on diagonalization of the Hamiltonian in a basis of harmonic oscillator Fock states. Finally we compare agreement between a Hartree product ground state and the Bethe ansatz solution with a Gaussian envelope localizing the center of mass and show a region of good agreement.

cond-mat.quant-gas↗

arXiv2011

Distinguishing mesoscopic quantum superpositions from statistical mixtures in periodically shaken double wells

For Bose-Einstein condensates in double wells, N-particle Rabi-like oscillations often seem to be damped. Far from being a decoherence effect, the apparent damping can indicate the emergence of quantum superpositions in the many-particle quantum dynamics. However, in an experiment it would be difficult to distinguish the apparent damping from decoherence effects. The present paper suggests using controlled periodic shaking to quasi-instantaneously switch the sign of an effective Hamiltonian, thus implementing an `echo' technique which distinguishes quantum superpositions from statistical mixtures. The scheme for the effective time-reversal is tested by numerically solving the time-dependent N-particle Schrodinger equation.

cond-mat.quant-gas↗

arXiv2011

Fractional photon-assisted tunnelling of ultra-cold atoms in periodically shaken double-well lattices

Fractional photon-assisted tunnelling is investigated both numerically and analytically in a double-well lattice. While integer photon-assisted tunnelling is a single-particle effect, fractional photon-assisted tunnelling is an interaction-induced many-body effect. Double-well lattices with few particles in each double well are ideal to study this effect far from the mean-field effects. It is predicted that the 1/4-resonance is observable in such systems. Fractional photon-assisted tunnelling provides a physically relevant model for which N-th order time-dependent perturbation theory can be large although all previous orders are small.

cond-mat.quant-gas↗

arXiv2011

Fractional photon-assisted tunneling in an optical superlattice: large contribution to particle transfer

Fractional photon-assisted tunneling is investigated both analytically and numerically for few interacting ultra-cold atoms in the double-wells of an optical superlattice. This can be realized experimentally by adding periodic shaking to an existing experimental setup [Phys. Rev. Lett. 101, 090404 (2008)]. Photon-assisted tunneling is visible in the particle transfer between the wells of the individual double wells. In order to understand the physics of the photon-assisted tunneling, an effective model based on the rotating wave approximation is introduced. The validity of this effective approach is tested for wide parameter ranges which are accessible to experiments in double-well lattices. The effective model goes well beyond previous perturbation theory approaches and is useful to investigate in particular the fractional photon-assisted tunneling resonances. Analytic results on the level of the experimentally realizable two-particle quantum dynamics show very good agreement with the numerical solution of the time-dependent Schrödinger equation. Far from being a small effect, both the one-half-photon and the one-third-photon resonance are shown to have large effects on the particle transfer.

cond-mat.quant-gas↗

arXiv2011

Spatial two-particle NOON-states in periodically shaken three-well potentials

Few-particle dynamics in a three-well potential are investigated numerically. It is shown that periodically shaking the potential can considerably increase the fidelity of emerging spatial quantum superpositions. Such NOON-states are important for quantum interferometry. If the two particles initially sit in the middle well, the probability to return to this state can distinguish pure quantum dynamics from statistical mixtures. The numeric implementation of decoherence via particle losses shows clear differences from the pure quantum behaviour. A three-well lattice could be an ideal system for experimental realisations.

cond-mat.quant-gas↗

arXiv2010

Reproducible mesoscopic superpositions of Bose-Einstein condensates and mean-field chaos

In a parameter regime for which the mean-field (Gross-Pitaevskii) dynamics becomes chaotic, mesoscopic quantum superpositions in phase space can occur in a double-well potential which is shaken periodically. For experimentally realistic initial states like the ground state of some 100 atoms, the emergence of mesoscopic quantum superpositions in phase space is investigated numerically. It is shown to be reproducible even if the initial conditions slightly change. While the final state is not a perfect superposition of two distinct phase-states, the superposition is reached an order of magnitude faster than in the case of the collapse and revival phenomenon. Furthermore, a generator of entanglement is identified.

cond-mat.quant-gas↗

arXiv2010

Exploiting and engineering the optical field-enhancement in metal nanoparticle based circuits

We study the impact of optical field-enhancement effects on the optoelectronic properties of metal nanoparticle arrays. Applying a focused ion beam lithography in combination with an electron beam deposition technique we can pattern electrical contacts in a way to give rise to an electromagnetic field-enhancement. A further field-enhancement is achieved by the plasmon resonance of the particles. Both effects are directly observed in the photoconductance of the arrays.

cond-mat.mes-hall↗

arXiv2009

Scattering tightly bound dimers off a scattering potential

The motion of two attractively interacting atoms in an optical lattice is investigated in the presence of a scattering potential. The initial wavefunction can be prepared by using tightly bound exact two-particle eigenfunction for vanishing scattering potential. This allows to numerically simulate the dynamics in the generation of two-particle Schrodinger cat states using a scheme recently proposed for scattering of quantum matter wave solitons.

cond-mat.quant-gas↗

arXiv2009

Fractional photon-assisted tunneling for Bose-Einstein condensates in a double well

Half-integer photon-resonances in a periodically shaken double well are investigated on the level of the N-particle quantum dynamics. Contrary to non-linear mean-field equations, the linear N-particle Schrodinger equation does not contain any non-linearity which could be the origin of such resonances. Nevertheless, analytic calculations on the N-particle level explain why such resonances can be observed even for particle numbers as low as N = 2. These calculations also demonstrate why fractional photon resonances are not restricted to half-integer values.

cond-mat.quant-gas↗

arXiv2009

Manipulation of quantum particles in rapidly oscillating potentials by inducing phase hops

Analytical calculations show that the mean-motion of a quantum particle trapped by a rapidly oscillating potential can be significantly manipulated by inducing phase hops, i.e., by instantaneously changing the potential's phase. A phase hop can be visualized as being the result of a collision with an imaginary particle which can be controlled. Several phase hops can have accumulating effects on the particle's mean-motion, even if they transform the particle's Hamiltonian into its initial one. The theoretical predictions are verified by numerical simulations for the one-dimensional Paul-trap.

cond-mat.other↗

arXiv2009

Photon-assisted tunneling in optical lattices: Ballistic transport of interacting boson pairs

In a recent experiment [PRL 100, 040404 (2008)] an analog of photon-assisted tunneling has been observed for a Bose-Einstein condensate in an optical lattice subject to a constant force plus a sinusoidal shaking. Contrary to previous theoretical predictions, the width of the condensate was measured to be proportional to the square of the effective tunneling matrix element, rather than a linear dependence. For a simple model of two interacting bosons in a one-dimensional optical lattice, both analytical and numerical calculations indicate that such a transition from a linear to a quadratic dependence can be interpreted through the ballistic transport and the corresponding exact dispersion relation of bound boson pairs.

cond-mat.other↗

arXiv2008

Bose-Einstein condensates in a double well: mean-field chaos and multi-particle entanglement

A recent publication [Phys. Rev. Lett. 100, 140408 (2008)] shows that there is a relation between mean-field chaos and multi-particle entanglement for BECs in a periodically shaken double well. 'Schrodinger-cat' like mesoscopic superpositions in phase-space occur for conditions for which the system displays mean-field chaos. In the present manuscript, more general highly-entangled states are investigated. Mean-field chaos accelerates the emergence of multi-particle entanglement; the boundaries of stable regions are particularly suited for entanglement generation.

cond-mat.other↗

arXiv2008

Creation and detection of a mesoscopic gas in a non-local quantum superposition

We investigate the scattering of a quantum matter wave soliton on a barrier in a one dimensional geometry and we show that it can lead to mesoscopic Schrödinger cat states, where the atomic gas is in a coherent superposition of being in the half-space to the left of the barrier and being in the half-space to the right of the barrier. We propose an interferometric method to reveal the coherent nature of this superposition and we discuss in details the experimental feasibility.

cond-mat.other↗

arXiv2008

Differences between mean-field dynamics and N-particle quantum dynamics as a signature of entanglement

A Bose-Einstein condensate in a tilted double-well potential under the influence of time-periodic potential differences is investigated in the regime where the mean-field (Gross-Pitaevskii) dynamics become chaotic. For some parameters near stable regions, even averaging over several condensate oscillations does not remove the differences between mean-field and N-particle results. While introducing decoherence via piecewise deterministic processes reduces those differences, they are due to the emergence of mesoscopic entangled states in the chaotic regime.

cond-mat.other↗

arXiv2007

Generation of mesoscopic superpositions of a binary Bose-Einstein condensate in a slightly asymmetric double well

A previous publication [Europhysics Letters 78, 10009 (2007)] suggested to coherently generate mesoscopic superpositions of a two-component Bose-Einstein condensate in a double well under perfectly symmetric conditions. However, already tiny asymmetries can destroy the entanglement properties of the ground state. Nevertheless, even under more realistic conditions, the scheme is demonstrated numerically to generate mesoscopic superpositions.

cond-mat.other↗