@article{WeissWilkens1997,
  author    = {Weiss, Christoph and Wilkens, Martin},
  title     = {Particle number counting statistics in ideal Bose gases},
  year      = {1997},
  abstract  = {We discuss the exact particle number counting statistics of degenerate ideal Bose gases in the microcanonical, canonical, and grand-canonical ensemble, respectively, for various trapping potentials. We then invoke the Maxwell's Demon ensemble [P. Navez et al., Phys. Rev. Lett.(1997)] and show that for large total number of particles the root-mean-square fluctuation of the condensate occupation scales delta n0 proportional to [T/Tc]r Ns with scaling exponents r=3/2, s=1/2 for the 3D harmonic oscillator trapping potential, and r=1, s=2/3 for the 3D box. We derive an explicit expression for r and s in terms of spatial dimension D and spectral index sigma of the single- particle energy spectrum. Our predictions also apply to systems where Bose-Einstein condensation does not occur. We point out that the condensate fluctuations in the microcanonical and canonical ensemble respect the principle of thermodynamic equivalence.},
  language  = {en}
}
@article{WilkensWeiss1997,
  author    = {Wilkens, Martin and Weiss, Christoph},
  title     = {Particle number fluctuations in an ideal Bose gas},
  year      = {1997},
  abstract  = {We analyse occupation number fluctuations of an ideal Bose gas in a trap which is isolated from theenvironment with respect to particle exchange (canonical ensemble). We show that in contrast to the predictions of thegrand- canonical ensemble, the counting statistics of particles in the trap ground state changes from monotonously decreasing above the condensation temperature to single-peaked below that temperature. For the exactly solvable case of a harmonic oscillator trapping potential in one spatial dimension we extract a Landau-Ginzburg functional which - despite the non- interacting nature of the system - displays the characteristic behaviour of a weakly interacting Bose gas. We also compare our findings with the usual treatment which is base on the grand-canonical ensemble. We show that for an ideal Bose gas neither are the grand-canonical and canonical ensemble thermodynamically equivalent, nor the grand-canonical ensemble can be viewed as a small system in diffusive contact with a particle reservoir.},
  language  = {en}
}
@article{PowerPfauWilkens1997,
  author    = {Power, W. L. and Pfau, T. and Wilkens, Martin},
  title     = {Loading atoms into a surface trap: simulations of an experimental scheme},
  year      = {1997},
  abstract  = {We present simulations of a scheme for the continuous loading of pre-cooled atoms into the lowest energy states of an optical surface trap. The atoms fall under gravity towards the surface of a prism where evanescent waves are used to decelerate the falling atoms and to pump them into a trapped state in an optical standing wave. The simulations are performed using the Monte-Carlo wavefunction technique and are designed to represent the proposed experimental scheme as closely as is practically possible. The probabilities of atoms being pumped into the different trapped states have been calculated as a function of the properties of the braking and pumping fields. The effective temperature of the final distribution of the atoms is calculated in order to find the change in phase-space density.},
  language  = {en}
}
@article{OehbergSurkovTittonenetal.1997,
  author    = {{\"O}hberg, P. and Surkov, E. L. and Tittonen, I. and Stenholm, Stig and Wilkens, Martin and Shlyapnikov, G. V.},
  title     = {Low-energy elementary excitations of a trapped Bose-condensed gas},
  year      = {1997},
  abstract  = {We develop a method of finding analytical sotutions of the Bogolyubov-de Gennes equations for the excitations of a Bose condensate in the Thomas-Fermi regime in harmonic traps of any asymmetry and introduce a classification of eigenstates. In the case of cylindrical symmetry we emphasize the presence of an accidental degeneracy in the excitation spectrum at certain values of the projection of orbital angular momentum on the symmetry axis and discuss possible consequences of the degeneracy in the context of new signatures of Bose- Einstein condensation},
  language  = {en}
}
@article{JavanainenWilkens1997,
  author    = {Javanainen, Juha and Wilkens, Martin},
  title     = {Phase and Phase Diffusion of a Split Bose-Einstein Condensate},
  year      = {1997},
  abstract  = {We analyze theoretically an experiment in which a trapped Bose-Einstein condensate is cut in half, and the parts are subsequently allowed to interfere. If the delay cutting and atom detection is small, the interference pattern of the two halves of the condensate is the same in every experiment. However, for longer delays the spatial phase of the interference shows random fluctuations from one experiment to the other. This phase diffusion is characterized quantitatively.},
  language  = {en}
}
@article{StenholmWilkens1997,
  author    = {Stenholm, Stig and Wilkens, Martin},
  title     = {Jumps in quantum theory},
  year      = {1997},
  abstract  = {In this paper we review the discussion about quantum jumps. We sketch the historical background before we present the recent revival of this problem originating in the field of atomic investigations. We present both the theoretical methods and their motivations, the relevance to experiments and an attempt at a preliminary discussion of the role of these developments in our fundamental understanding of quantum physics.},
  language  = {en}
}
@article{PowerTanWilkens1997,
  author    = {Power, W. L. and Tan, S. M. and Wilkens, Martin},
  title     = {A scheme for the simultaneous measurement of atomic position and momentum},
  year      = {1997},
  abstract  = {We propose an optical scheme for the simultaneous measurement of the position and momentum of a single atom. The scheme involves the coupling of the atom of two light fields with different spatical and polarization characteristics. The proposed technique is closely related to the Arthurs-Kelly measurement scheme; the principal difference is that in the present case the electromagnetic fields rather than from shifts in the position of a pointer.},
  language  = {en}
}
@article{JanickeWilkens1998,
  author    = {Janicke, U. and Wilkens, Martin},
  title     = {Atomic matter wave amplification by optical pumping},
  year      = {1998},
  abstract  = {The atom laser (or `Boser') is a device that delivers a beam of atomic de Broglie waves with high coherence and monochromaticity. In this review, we concentrate on an all-optical scheme of an atom laser that is based on optical pumping. The model is first presented in terms of kinetic equations, and its relation to the ordinary laser and the Bose-Einstein condensation is discussed. We then derive a master equation for the quantum statistics dynamics of the atom laser. Neglecting photon reabsorption processes, the master equation is solved and the counting statistics is computed. Finally, the effects of the inelastic reabsorption processes are investigated for the particular case of two atoms. It is shown that the onset of atom-lasing is suppressed in large resonators, but may be achieved in small and/or low-dimensional resonators.},
  language  = {en}
}
@article{BuschEnglertRzazewskietal.1998,
  author    = {Busch, Thomas and Englert, Bertold-Georg and Rzazewski, Kazimierz and Wilkens, Martin},
  title     = {Two cold atoms in a harmonic trap},
  year      = {1998},
  abstract  = {Two ultracold atoms moving in a trap interact weakly at a very short distance. This interaction can be modeled by a properly regularized contact potential. We solve the corresponding time-independent Schr{\"o}dinger equation under the assumption of a parabolic, spherically symmetric trapping potential.},
  language  = {en}
}
@article{LeonhardtWilkens1998,
  author    = {Leonhardt, Ulf and Wilkens, Martin},
  title     = {Aharonov-Bohm scattering of neutral atoms},
  year      = {1998},
  abstract  = {We study the scattering of quantum particles in the presence of an Aharonov-Bohm vortex and in an arbitrary cylindrically symmetric potential. In particular we address the scattering of atoms carrying dipole moments induced by an electrically charged wire and a homogeneous magnetic field. We argue that, despite the strong attraction of the wire, an Aharoniv-Bohm effect will be visible.},
  language  = {en}
}