Plasmonic nanostructures for shrinking structured light to access forbidden transitions

Plasmonic nanostructures have considerable applicability in light–matter interactions owing to their capacity for strong field confinement and enhancement. Nanogap structures allow us to tailor electric field distributions at the nanoscale, bridging the differences in size and shape of atomic and light structures. In this study, we demonstrated that a plasmonic tetramer structure can squeeze structured light into a nanoscale area, in which a strong field gradient allows access to forbidden transitions. Numerical simulations showed that the gold tetramer structure on a glass substrate possesses a plasmonic eigenmode, which forms structured light with a quadrupole profile in the nanogap region at the center of the tetramer. The top–down technique employed using electron-beam lithography allows us to produce a gap size of approximately 50 nm, which supports plasmonic resonance in the near-infrared regime. In addition, we demonstrated an array architecture in which a collective lattice resonance enhances the intensity of the quadrupole field in multiple lattice units. This study highlights the possibility of accessing multipolar transitions in a combined system of structured light and plasmonic nanostructures. Our findings may lead to new platforms for spectroscopy, sensing, and light sources that take advantage of the full electronic spectrum of an emitter.

Dynamical evolution of voids with surrounding gravitational tidal field

ABSTRACT The void ellipticity distribution today can be well explained by the tidal field. Going a step further from the overall distribution, we investigate individuality on the tidal response of void shape in non-linear dynamical evolution. We perform an N-body simulation and trace individual voids using particle ID. The voids are defined based on Voronoi tessellation and watershed algorithm, using public code vide. A positive correlation is found between the time variation of void ellipticity and tidal field around a void if the void maintains its constituent particles. Such voids tend to have smaller mass densities. Conversely, not a few voids significantly deform by particle exchange, rather than the tidal field. Those voids may prevent us from correctly probing a quadrupole field of gravity out of a void shape.

Mass-selective removal of ions from Paul traps using parametric excitation

We study a method for mass-selective removal of ions from a Paul trap by parametric excitation. This can be achieved by applying an oscillating electric quadrupole field at twice the secular frequency $$\omega _{\text {sec}}$$ ω sec using pairs of opposing electrodes. While excitation near the resonance with the secular frequency $$\omega _{\text {sec}}$$ ω sec only leads to a linear increase of the amplitude with excitation duration, parametric excitation near $$2\, \omega _{\text {sec}}$$ 2 ω sec results in an exponential increase of the amplitude. This enables efficient removal of ions from the trap with modest excitation voltages and narrow bandwidth, therefore, substantially reducing the disturbance of ions with other charge-to-mass ratios. We numerically study and compare the mass selectivity of the two methods. In addition, we experimentally show that the barium isotopes with 136 and 137 nucleons can be removed from small ion crystals and ejected out of the trap while keeping $$^{138}\text {Ba}^{+}$$ 138 Ba + ions Doppler cooled, corresponding to a mass selectivity of better than $$\Delta m / m = 1/138$$ Δ m / m = 1 / 138 . This method can be widely applied to ion trapping experiments without major modifications since it only requires modulating the potential of the ion trap.

Quantitative Susceptibility Mapping of Magnetic Quadrupole Moments

We modeled the magnetic field up to the quadrupole term to investigate not only the average susceptibility (dipole), but also the susceptibility distribution (quadrupole) contribution. Expanding the magnetic field up to the 2nd order provides the quadrupole (0th: monopole, 1st: dipole). Numerical simulations were performed to investigate the quadrupole contribution with subvoxel nonuniformity. Conventional dipole and our dipole + quadrupole models were compared in the simulation, the phantom and human brain. Furthermore, the quadrupole field was compared with the anisotropic susceptibility field in the dipole tensor model. In a nonuniformity case, numerical simulations showed a nonnegligible quadrupole field contribution. Our study showed a difference between the two methods in the susceptibility map at the edges; both the phantom and human studies showed sharper structural edges with the dipole + quadrupole model. Quadrupole moments showed contrast mainly at the structural boundaries. The quadrupole moment field contribution was smaller but nonnegligible compared to the anisotropic susceptibility contribution. Nonuniform and uniform source distributions can be separately considered by quadrupole expansion, which were mixed together in the dipole model. In the presence of nonuniformity, the susceptibility maps may be different between the two models. For a comprehensive field model, the quadrupole might need to be considered along with susceptibility anisotropy and microstructure effects.

Realisation and Characterisation the BEC for 87Rb Atoms

The Bose-Einstein condensate (BEC) is created in a magnetic trap in the Quadrupole-Ioffe configuration (QUIC). This kind of trap combines an anti-Helmholtz quadrupole field with an offset field produced by a single coil perpendicular to the quadrupole field axis to suppress Majorana transitions. In the quadrupole trap evaporative cooling is performed by using radio frequency, reaching the phase transition to a BEC in the QUIC trap. By using Time of Flight (TOF) technique, the expansion velocity is measured with and which lead to temperature of and It is roughly around the recoil temperature.