Coupling between Rydberg states and Landau levels of electrons trapped on liquid helium

We investigate the coupling between Rydberg states of electrons trapped on a liquid Helium surface and Landau levels induced by a perpendicular magnetic field. We show that this realises a prototype quantum system equivalent to an atom in a cavity, where their coupling strength can be tuned by a parallel magnetic field. We determine experimentally the renormalisation of the atomic transition energies induced by the coupling to the cavity, which can be seen as an analogue of the Lamb shift. When the coupling is sufficiently strong the transition between the ground and first excited Rydberg states splits into two resonances corresponding to dressed states with vacuum and one photon in the cavity. Our results are in quantitative agreement with the energy shifts predicted by the effective atom in a cavity model where all parameters are known with high accuracy

Circular-Polarization-Dependent Study of Microwave-Induced Conductivity Oscillations in a Two-Dimensional Electron Gas on Liquid Helium

The polarization dependence of photoconductivity response at cyclotron-resonance harmonics in a nondegenerate two-dimensional (2D) electron system formed on the surface of liquid helium is studied using a setup in which a circular polarization of opposite directions can be produced. Contrary to the results of similar investigations reported for semiconductor 2D electron systems, for electrons on liquid helium, a strong dependence of the amplitude of magnetoconductivity oscillations on the direction of circular polarization is observed. This observation is in accordance with theoretical models based on photon-assisted scattering and, therefore, it solves a critical issue in the dispute over the origin of microwave-induced conductivity oscillations.Comment: 5 pages, 4 figure

Sliding of Electron Crystal of Finite Size on the Surface of Superfluid He-4 Confined in a Microchannel

We present a new study of the nonlinear transport of a two-dimensional electron crystal on the surface of liquid helium confined in a 10 micrometer-wide channel in which the effective length of the crystal can be varied from 10 to 215 micrometers. At low driving voltages, the moving electron crystal is strongly coupled to deformation of the liquid surface arising from resonant excitation of surface capillary waves, ripplons, while at higher driving voltages the crystal decouples from the deformation. We find strong dependence of the decoupling threshold of the driving electric field acting on the electrons, on the size of the crystal. In particular, the threshold electric field significantly decreases when the length of the crystal becomes shorter than 25 micrometers. We explain this effect as arising from weakening of surface deformations due to radiative loss of resonantly-excited ripplons from an electron crystal of finite size, and we account for the observed effect using an instructive analytical model.Comment: 5 figure

Antimatter Bounds by Anti-Asteroids annihilations on Planets and Sun

The existence of antimatter stars in the Galaxy as possible signature for inflationary models with non-homogeneous baryo-synthesis may leave the trace by antimatter cosmic rays as well as by their secondaries (anti-planets and anti-meteorites) diffused bodies in our galactic halo. The anti-meteorite flux may leave its explosive gamma signature by colliding on lunar soil as well as on terrestrial, jovian and solar atmospheres. However the propagation in galaxy and the consequent evaporation in galactic matter gas suppress the lightest (m < 10^(-2)g) anti-meteorites. Anisotropic annihilation of larger anti-meteorites within a narrow mass window, maybe rarely deflected, bounced by the galactic gas disk, escaping detection in our solar system. Nevertheless heaviest anti-meteorites (m > 10^(-1)g up to 10^(6)g) are unable to be deflected by the thin galactic gas surface annihilation; they might hit the Sun (or rarely Jupiter) leading to an explosive gamma event and a spectacular track with a bouncing and even a propelling annihilation on cromosphere and photosphere. Their anti-nuclei annihilation in pions and their final hard gammas showering may be observabe as a "solar flare" at a rate nearly comparable to the observed ones. From their absence we may infer bounds on antimatter-matter ratio near or below 10^(-9) limit: already recorded data in BATSE catalog might be applied.Comment: 6 pages, more accurate estimate and minor correction