@article{HenkelSauerProukakis2017,
  author    = {Henkel, Carsten and Sauer, Tim-O and Proukakis, N. P.},
  title     = {Cross-over to quasi-condensation: mean-field theories and beyond},
  series = {Journal of physics : B, Atomic, molecular and optical physics},
  volume    = {50},
  journal   = {Journal of physics : B, Atomic, molecular and optical physics},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {0953-4075},
  doi       = {10.1088/1361-6455/aa6888},
  pages     = {19},
  year      = {2017},
  abstract  = {We analyze the cross-over of a homogeneous, weakly interacting Bose gas in one dimension from the ideal gas into the dense quasi-condensate phase. We review a number of mean-field theories, perturbative or self-consistent, and provide accurate evaluations of equation of state, density fluctuations, and correlation functions. A smooth crossover is reproduced by classical-field simulations based on the stochastic Gross-Pitaevskii equation and the Yang-Yang solution to the one-dimensional Bose gas.},
  language  = {en}
}
@article{SchiefeleHenkel2011,
  author    = {Schiefele, Juergen and Henkel, Carsten},
  title     = {Bosonic enhancement of spontaneous emission near an interface},
  series = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics},
  volume    = {375},
  journal   = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics},
  number    = {3},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0375-9601},
  doi       = {10.1016/j.physleta.2010.11.058},
  pages     = {680 -- 684},
  year      = {2011},
  abstract  = {We show how the spontaneous emission rate of an excited two-level atom placed in a trapped Bose-Einstein condensate of ground-state atoms is enhanced by bosonic stimulation. This stimulation depends on the overlap of the excited matter-wave packet with the macroscopically occupied condensate wave function, and provides a probe of the spatial coherence of the Bose gas. The effect can be used to amplify the distance-dependent decay rate of an excited atom near an interface.},
  language  = {en}
}
@misc{Sauer2015,
  type      = {Master Thesis},
  author    = {Sauer, Tim-Oliver},
  title     = {Quasi-condensation in low-dimensional Bose gases},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-87247},
  school      = {Universit{\"a}t Potsdam},
  pages     = {154},
  year      = {2015},
  abstract  = {The subject of the present thesis is the one-dimensional Bose gas. Since long-rang order is destroyed by infra-red fluctuations in one dimension, only the formation of a quasi-condensate is possible, which exhibits suppressed density fluctuations, but whose phase fluctuates strongly. It is shown that modified mean-field theories based on a symmetry-breaking approach can even characterise phase coherence properties of such a quasi-condensate properly. A correct description of the transition from the degenerate ideal Bose gas to the quasi-condensate, which is a smooth cross-over rather than a phase transition, is not possible though. Basic conditions for the applicability of the theories are not fulfilled in this regime, such that the existence of a critical point is predicted. The theories are compared on the basis of their excitation sprectum, equation of state, density fluctuations and related correlation functions. High-temperature expansions of the corresponding integrals are derived analytically for the numerical evaluation of the self-consistent integral equations. Apart from that, the Stochastic Gross-Pitaevskii equation (SGPE), a non-linear Langevin equation, is analysed numerically by means of Monte-Carlo simulations and the results are compared to those of the mean-field theories. In this context, a lot of attention is payed to the appropriate choice of the parameters. The simulations prove that the SGPE is capable of describing the cross-over properly, but highlight the limitations of the widely used local density approximation as well.},
  language  = {en}
}
@phdthesis{Schiefele2011,
  author    = {Schiefele, J{\"u}rgen},
  title     = {Casimir-Polder interaction in second quantization},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-54171},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {The Casimir-Polder interaction between a single neutral atom and a nearby surface, arising from the (quantum and thermal) fluctuations of the electromagnetic field, is a cornerstone of cavity quantum electrodynamics (cQED), and theoretically well established. Recently, Bose-Einstein condensates (BECs) of ultracold atoms have been used to test the predictions of cQED. The purpose of the present thesis is to upgrade single-atom cQED with the many-body theory needed to describe trapped atomic BECs. Tools and methods are developed in a second-quantized picture that treats atom and photon fields on the same footing. We formulate a diagrammatic expansion using correlation functions for both the electromagnetic field and the atomic system. The formalism is applied to investigate, for BECs trapped near surfaces, dispersion interactions of the van der Waals-Casimir-Polder type, and the Bosonic stimulation in spontaneous decay of excited atomic states. We also discuss a phononic Casimir effect, which arises from the quantum fluctuations in an interacting BEC.},
  language  = {en}
}
@unpublished{Rafler2008,
  author    = {Rafler, Mathias},
  title     = {Martin-Dynkin Boundaries of the Bose Gas},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-51667},
  year      = {2008},
  abstract  = {The Ginibre gas is a Poisson point process defined on a space of loops related to the Feynman-Kac representation of the ideal Bose gas. Here we study thermodynamic limits of different ensembles via Martin-Dynkin boundary technique and show, in which way infinitely long loops occur. This effect is the so-called Bose-Einstein condensation.},
  language  = {en}
}