Model of a PT symmetric Bose-Einstein condensate in a delta-functions double well

The observation of PT symmetry in a coupled optical wave guide system that involves a complex refractive index has been demonstrated impressively in the experiment by R\"uter el al. (Nat. Phys. 6, 192, 2010). This is, however, only an optical analogue of a quantum system, and it would be highly desirable to observe the manifestation of PT symmetry and the resulting properties also in a real, experimentally accessible, quantum system. Following a suggestion by Klaiman et al. (Phys. Rev. Lett. 101, 080402, 2008), we investigate a PT symmetric arrangement of a Bose-Einstein condensate in a double well potential, where in one well cold atoms are injected while in the other particles are extracted from the condensate. We investigate, in particular, the effects of the nonlinearity in the Gross-Pitaevskii equation on the PT properties of the condensate. To study these effects we analyze a simple one-dimensional model system in which the condensate is placed into two PT symmetric delta-function traps. The analysis will serve as a useful guide for studies of the behaviour of Bose-Einstein condensates in realistic PT symmetric double wells.Comment: 5 pages, 3 figures (one redundant figure removed), minor changes in the discussio

Resonance wave functions located at the Stark saddle point

We calculate quantum mechanically exact wave functions of resonances in spectra of the hydrogen atom in crossed external fields and prove the existence of long-lived decaying quantum states localized at the Stark saddle point. A spectrum of ground and excited states reproducing the nodal patterns expected from simple quadratic and cubic expansions of the potential in the vicinity of the saddle point can be identified. The results demonstrate the presence of resonances in the vicinity of the saddle predicted by simple approximations.Comment: 7 pages, 6 figures, two figures revised, minor changes in the tex