ABSTRACT. We study the stability of the standing wave solutions of a Gross-Pitaevskii equation describing Bose-Einstein condensation of dipolar quantum gases and characterize their orbit. As an intermediate step, we consider the corresponding constrained minimization problem and establish existence, symmetry and uniqueness of the ground state solutions.
INTRODUCTIONSince the experimental realization of the first Bose-Einstein condensate (BEC) by Eric Cornell and Carl Wieman in 1995, tremendous efforts have been undertaken by mathematicians to exploit this achievement especially in atomic physics and optics. In the last years, a new kind of quantum gases with dipolar interaction, which acts between particles as a permanent magnetic or electric dipole moment has attracted the attention of a lot of scientists. The interactions between particles are both long-range and non-isotropic. Describing the corresponding BEC via Gross Pitaevskii approximation, one gets the following nonlinear Schrödinger equation (1.1) i ∂ t ψ = − 2 2m ∆ψ + g|ψ| 2 ψ + d 2 (K * |ψ| 2 )ψ + V (x)ψ, t ∈ R, x ∈ R 3 , where |g| = 4π 2 N |a| m , N ∈ N is the number of particles, m denotes the mass of individual particles and a its corresponding scattering length. The external potential V (x) describes the electromagnetic trap and has the following harmonic confinementThe factor d 2 denotes the strength of the dipole moment in Gaussian units andwhere θ = θ(x) is the angle between x ∈ R 3 and the dipole axis n ∈ R 3 . The local term g|ψ| 2 ψ describes the short-range interaction forces between particles, while the non-local potential K * |ψ| 2 describes their long-range dipolar interactions. For the mathematical analysis, it is more convenient to rescale (1.1) into the following dimensionless formThis work was supported by the French ANR projects SchEq (ANR-12-JS01-0005-01) and BoND (ANR-13-BS01-0009-01). , and a 0 = m .In the following, we assume that λ 1 and λ 2 are two given real-valued parameters.In [5], the authors have studied the existence and uniqueness of the equation (1.3) with initial condition ψ 0 ∈ H 1 (R 3 ),They have established that (1.4) has a unique, global solution if λ 1 4 3 πλ 2 0. They called this situation stable regime, referring to the fact that no singularity in formed in finite time. In this paper, we study another notion of stability, that is, the stability of standing waves. They have also showed that in the unstable regime (λ 1 < 4 3 πλ 2 ), finite time blow up may occur, hence the denomination.The evidence of blow-up relies on a function for which the corresponding energy is strictly negative ([5, Lemma 5.1]). They concluded using the virial approach of Zakharov and Glassey. Some refinements of the above result have been discussed in [5, Proposition 5.4].The most important issue in view of the applications of (1.4) in atomic physics and quantum optics seems to be the study of ground state solutions of (1.4). These solutions are the "only" observable states in experiments. A standing wave solution of (1.4) is a wave func...