Papers by Wolfgang Ertmer
We review recent theoretical models and experiments dealing with the diffraction of neutral atoms... more We review recent theoretical models and experiments dealing with the diffraction of neutral atoms by a reflection grating, formed by a standing evanescent wave. We analyze diffraction mechanisms proposed for normal and grazing incidence, point out their scopes and confront the theory with experiment.
We present a novel technique for the precise measurement of absolute local gravity with a quantum... more We present a novel technique for the precise measurement of absolute local gravity with a quantum gravimeter based on an atom chip. Atom interferometry utilizes the interference of matter waves interrogated by laser light to read out inertial forces. Today’s generation of these devices typically operate with test mass samples, that consists of ensembles of laser cooled atoms. Their performance is limited by the velocity spread and finite-size of the test masses that impose systematic uncertainties at the level of a few μGal [1]. Rather than laser cooled atoms we employ quantum degenerate ensembles, so called Bose-Einstein condensates [2], as ultra-sensitive probes for gravity. These sources offer unique properties that will allow to overcome the current limitations in the next generation of sensors. Furthermore, atom-chip technology offers the possibility to generate Bose-Einstein condensates in a fast and reliable way.
New Journal of Physics, 2018
If the boundary conditions of the quantum vacuum are changed in time, quantum field theory predic... more If the boundary conditions of the quantum vacuum are changed in time, quantum field theory predicts that real, observable particles can be created in the initially empty modes. Here, we realize this effect by changing the boundary conditions of a spinor Bose-Einstein condensate, which yields a population of initially unoccupied spatial and spin excitations. We prove that the excitations are created as entangled pairs by certifying continuous-variable entanglement within the many-particle output state.
Acta Physica Polonica A, 2006
Cold atomic gases placed in optical lattices enable studies of simple condensed matter theory mod... more Cold atomic gases placed in optical lattices enable studies of simple condensed matter theory models with parameters that may be tuned relatively easily. When the optical potential is randomized (e.g. using laser speckle to create a random intensity distribution) one may be able to observe Anderson localization of matter waves for non-interacting bosons, the so-called Bose glass in the presence of interactions, as well as the Fermi glass or quantum spin glass for mixtures of fermions and bosons.
Nuclear Physics B - Proceedings Supplements, 2007
La pubblicazione è resa disponibile sotto le norme e i termini della licenza di deposito, secondo... more La pubblicazione è resa disponibile sotto le norme e i termini della licenza di deposito, secondo quanto stabilito dalla Policy per l'accesso aperto dell'Università degli Studi di Firenze (https://www.sba.unifi.it/upload/policy-oa-2016-1.pdf)
Conference Digest. 2000 International Quantum Electronics Conference (Cat. No.00TH8504)
ABSTRACT
Physical Review A, 2013
We present an analytical model for the theoretical analysis of spin dynamics and spontaneous symm... more We present an analytical model for the theoretical analysis of spin dynamics and spontaneous symmetry breaking in a spinor Bose-Einstein condensate (BEC). This allows for an excellent intuitive understanding of the processes and provides good quantitative agreement with the experimental results of Scherer et al. [Phys. Rev. Lett. 105, 135302 (2010)]. It is shown that the dynamics of a spinor BEC initially prepared in an unstable Zeeman state m F = 0 (|0) can be understood by approximating the effective trapping potential for the state |±1 with a cylindrical box potential. The resonances in the creation efficiency of these atom pairs can be traced back to excitation modes of this confinement. The understanding of these excitation modes allows for a detailed characterization of the symmetry-breaking mechanism, showing how a twofold spontaneous breaking of spatial and spin symmetry can occur. In addition, a detailed account of the experimental methods for the preparation and analysis of spinor quantum gases is given.
Physical Review Letters, 2003
We analyze the operation of quantum gates for neutral atoms with qubits that are delocalized in s... more We analyze the operation of quantum gates for neutral atoms with qubits that are delocalized in space, i.e., the computational basis states are defined by the presence of a neutral atom in the ground state of one out of two trapping potentials. The implementation of single qubit gates as well as a controlled phase gate between two qubits is discussed and explicit calculations are presented for rubidium atoms in optical microtraps. Furthermore, we show how multi-qubit highly entangled states can be created in this scheme.
Physical Review Letters, 1999
Dark solitons in cigar-shaped Bose-Einstein condensates of 87 Rb are created by a phase imprintin... more Dark solitons in cigar-shaped Bose-Einstein condensates of 87 Rb are created by a phase imprinting method. Coherent and dissipative dynamics of the solitons has been observed.
Physical Review Letters, 2005
We investigate, both experimentally and theoretically, possible routes towards Anderson-like loca... more We investigate, both experimentally and theoretically, possible routes towards Anderson-like localization of Bose-Einstein condensates in disordered potentials. The dependence of this quantum interference effect on the nonlinear interactions and the shape of the disorder potential is investigated. Experiments with an optical lattice and a superimposed disordered potential reveal the lack of Anderson localization. A theoretical analysis shows that this absence is due to the large length scale of the disorder potential as well as its screening by the nonlinear interactions. Further analysis shows that incommensurable superlattices should allow for the observation of the crossover from the nonlinear screening regime to the Anderson localized case within realistic experimental parameters.
Physical Review Letters, 2003
We measure the intensity correlation function of two interfering spatially displaced copies of a ... more We measure the intensity correlation function of two interfering spatially displaced copies of a phase fluctuating Bose-Einstein Condensate (BEC). It is shown that this corresponds to a measurement of the phase correlation properties of the initial condensate. Analogous to the method used in the stellar interferometer experiment of Hanbury Brown and Twiss, we use spatial intensity correlations to determine the phase coherence lengths of elongated BECs. We find good agreement with our prediction of the correlation function and confirm the expected coherence length.
Physical Review Letters, 2010
Physical Review Letters, 2009
We analyze the spinor dynamics of a 87 Rb F = 2 condensate initially prepared in the mF = 0 Zeema... more We analyze the spinor dynamics of a 87 Rb F = 2 condensate initially prepared in the mF = 0 Zeeman sublevel. We show that this dynamics, characterized by the creation of correlated atomic pairs in mF = ±1, presents an intriguing multi-resonant magnetic field dependence induced by the trap inhomogeneity. This dependence is directly linked to the most unstable Bogoliubov spin excitations of the initial mF = 0 condensate, showing that, in general, even a qualitative understanding of the pair creation efficiency in a spinor condensate requires a careful consideration of the confinement.
Physical Review A, 2010
Spin-changing collisions may lead under proper conditions to the parametric amplification of matt... more Spin-changing collisions may lead under proper conditions to the parametric amplification of matter waves in spinor Bose-Einstein condensates. Magnetic dipole-dipole interactions, although typically very weak in alkaline atoms, are shown to play a very relevant role in the amplification process. We show that these interactions may lead to a strong dependence of the amplification dynamics on the angle between the trap axis and the magneticfield orientation. We analyze as well the important role played by magnetic-field gradients, which modify also strongly the amplification process. Magnetic-field gradients must be hence carefully controlled in future experiments, in order to observe clearly the effects of the dipolar interactions in the amplification dynamics.
Physical Review A, 2011
We report on a simple novel trapping scheme for the generation of Bose-Einstein condensates of 87... more We report on a simple novel trapping scheme for the generation of Bose-Einstein condensates of 87 Rb atoms. This scheme employs a near-infrared single beam optical dipole trap combined with a weak magnetic quadrupole field as used for magneto-optical trapping to enhance the confinement in axial direction. Efficient forced evaporative cooling to the phase transition is achieved in this weak hybrid trap via reduction of the laser intensity of the optical dipole trap at constant magnetic field gradient.
Physical Review A, 2003
The lifetime of the metastable 3 P 2 state of neon has been determined as 14.73(14) s ͓decay rate... more The lifetime of the metastable 3 P 2 state of neon has been determined as 14.73(14) s ͓decay rate 0.067 90(64) s Ϫ1 ] by measuring the decay in fluorescence of an ensemble of 20 Ne atoms trapped in a magnetooptical trap ͑MOT͒. Due to low background gas pressure (pϽ5ϫ10 Ϫ11 mbar) and low relative excitation to the 3 D 3 state ͑0.5 % excitation probability͒ only small corrections have to be included in the lifetime extrapolation. Together with a careful analysis of residual loss mechanisms in the MOT a lifetime determination to high precision is achieved.
Physical Review A, 1993
The diffraction theory of a reflection grating for atoms based on a standing light wave is develo... more The diffraction theory of a reflection grating for atoms based on a standing light wave is developed in a particular dressed-state approximation. The basis states take into account internal and external atomic degrees of freedom simultaneously and correspond to diffraction orders in the ...
Physical Review A, 2008
We present a detailed analysis of the dynamics of Bloch oscillations of Bose-Einstein condensates... more We present a detailed analysis of the dynamics of Bloch oscillations of Bose-Einstein condensates in disordered lattice potentials. Due to the disorder and the interparticle interactions these oscillations undergo a dephasing, reflected in a damping of the center of mass oscillations, which should be observable under realistic experimental conditions. The interplay between interactions and disorder is far from trivial, ranging from an interaction-enhanced damping due to modulational instability for strong interactions, to an interaction-reduced damping due to a dynamical screening of the disorder potential.
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Papers by Wolfgang Ertmer