For oscillatory high-amplitude potentials it is known that the linear Schrödinger operator leads to exponentially localized ground states. This localization result can be quantified explicitly in terms of geometric parameters and the degree of disorder within the potential. In the present paper we study the influence of the amplitude and the importance of the periodicity in the nonlinear setting of the Gross-Pitaevskii equation which models ultracold bosonic gases.
Gross-Pitaevskii equationQuantum-physical processes related to ultracold bosonic gases -so-called Bose-Einstein condensates -can in certain regimes be mathematically described by the Gross-Pitaevskii equation [7]. The corresponding eigenvalue problem is then related to the formation of ground states and excited states of such condensates. For oscillatory and disordered potentials surprising phenomena such as Anderson localization occur. We are particularly interested in such localization properties of the ground state, which is the minimal-energy solution of the problemFor simplicity, we consider homogeneous Dirichlet boundary conditions, i.e., u ∈ H 1 0 (Ω). The parameter δ ≥ 0 controls the non-linearity whereas V is a high-amplitude potential that oscillates on a small scale ε. Moreover, the potential V ∈ L ∞ (D) remains within the boundsProperties of the ground state are discussed in [6]. The aim of this paper is to study the influence of the non-linearity (in form of the parameter δ) and the amplitude of the potential (parameter β) on the possible localization of the ground state.
Numerical resultsFor the numerical experiments, we introduce three prototypical potentials. The first potential V 1 is periodic and oscillates continuously between the values α and β. Since the influence of the lower bound is negligible, we fix α = 1 throughout all experiments. In two space dimensions the first potential reads V 1 (x, y) := α + β−α 2 1 + sin(2πx/ε) sin(2πy/ε) .The second and third potential are both piecewise constant (on an ε-mesh). The potential V 2 takes independently the value α or β with probability 1 2 each (coin toss). V 3 takes independent random values uniformly distributed in the interval [α, β], cf. Fig. 1. (a) periodic potential V1 (b) checkerboard potential V2 (c) random potential V3 Fig. 1: Realizations of the three potentials V1, V2, and V3.