Extracts from the Internet

Measurement of space-time curvature by its influence on the wave function of individual atoms

As distinct from free fall acceleration expressed in terms of the gravitational potential gradient, the gravitational tidal forces depend on second derivatives of the potential and are related to the space-time curvature. The space-time curvature has already been measured using three separate atomic interferometers in which the atomic states were not quantum-coherent among themselves. In the new experiment performed by M.A. Kasevich (Stanford University, USA) and his colleagues, the effect of gravitational tidal forces on the wave function of individual atoms in one interferometer was measured for the first time. A freely falling cloud of ultracold gas of 87Rb atoms experienced an impact of laser pulses transferring the atoms into different states of motion. This splitting into trajectories is analogous to the occurrence of different interferometer arms. The wave function of atoms flying simultaneously through two arms experienced the difference of gravitational forces on the scale of 10 cm. The tidal forces were generated by an 84-kg lead weight, and the interference of output atoms was observed using a CCD matrix from the scattering by photon atoms. Thus, from the difference of the wave-function phase shift it became possible to measure the variations of gravitational acceleration by 10-10 g. Such atomic interferometer can be applied to verify the gravitation theories and to seek minerals by gravitational anomalies. Source: Phys. Rev. Lett. 118 183602 (2017)

Nonmonotonic behavior of Casimir force

The experimental measurement of the Casimir force between two surfaces covered by periodic T-shaped protrusions was due to H.B. Chan (the Hong Kong University of Science and Technology) and his colleagues. The surfaces, the devices for their motion (electrostatic actuators) and the sensors were fabricated on a single silicon plate by the methods of lithography and etching. This allowed the obtained surfaces to feature precise protrusion leveling. The Casimir force gradient was measured from the frequency shift of the silicon-rod mechanical oscillations. When the surfaces came closer to each other and the protrusions on them began going one behind another, the Casimir force twice changed the sign thus transforming from attractive to repulsive in the intermediate distance region. The repulsive character of the Casimir force in such a configuration was theoretically predicted by A. Rodriguez (Princeton University) and his colleagues in 2008. This experiment was the first to demonstrate the nonmonotonic character of the Casimir force. The repulsive Casimir force may appear to be useful in nanomechanics for reduction of surface adhesion. Source: Nature Photonics 11 97 (2017)

Control of the quantum state of a molecular ion

The possibility of controlling the quantum state of trapped ions is of importance for many applications. For monatomic ions a great progress was achieved in this issue, whereas with molecular ions there are difficulties because of a large number of quantum levels. C.-w. Chou (the National Institute of Standards and Technology, USA) with colleagues elaborated a new method based on a simultaneous Pauli trapping of molecular 40CaH+ and atomic 40Ca+ ions. Laser photons induced interlevel transitions and a 40CaH+ molecule assumed progressive motion which was translated to the atomic ion through Coulomb interaction. The state of 40Ca+ is easier to measure (from the photon scattering), which made it possible to indirectly determine the state of the molecular ion. Through a series of measurements and laser actions the 40CaH+ ion was transferred to desired quantum states, including superposition of rotational levels with prescribed orientation of the rotation axis. Source: Nature 545 203 (2017)

Laser cooling of triatomic molecules

J. Doyle (Harvard University, USA) with colleagues developed a new method of polyatomic molecule cooling in a molecular beam referred to as “Sisyphus method”. Cooled by lasing the molecules rise to the top of the interaction potential graph, roll down to the state in which cooling is ineffective, but then, affected by the magnetic field, are again transferred to the initial state, and this process repeats many times (up to about 200 times in the described experiment) according as the molecules fly through the laser beams that are repeatedly reflected from the mirrors and cross the beams. The method was demonstrated on an example of triatomic SrOH molecules. The gas of SrOH molecules in the beam was cooled in one of the transverse directions by two orders of magnitude to a temperature of ≈750 µK. Source: Phys. Rev. Lett. 118 173201 (2017)

Observation of fast radio bursts

The origin of fast radio bursts, cosmic radio emission millisecond pulses with a large dispersion measure, has not yet been clarified and is being intensely studied to date. The radiation polarization of the burst FRB 150215 that came from the direction close to the Galactic disc has been investigated using the radio telescope in the Australian Parkes Observatory. The radiation is linearly polarized at the level of 43 ± 5 %, and its specific feature is a small angle of Faraday rotation. A possible explanation may be either an opposite direction of the magnetic field in different regions along the line of sight, which leads to compensation, or else it may be a low electron column density. The burst FRB 121102 which yields repeated pulses is also under study. The survey in the optical and IR ranges established that FRB 121102 is generated in the region of active star formation on the periphery of the irregular dwarf galaxy. A steady compact radio source which is likely to relate to the burst is projected to the same region. Conditions in the Galaxy are favorable for explosions of powerful supernovae, and therefore this localization testifies in favor of burst origin on young neutron stars or magnetars. A high-luminosity (58 ± 6 Jy ms) burst was registered with the new telescope ASKAP consisting of 36 antennas. Its observation confirms the existence of a separate population of ultra-bright (>20 Jy ms) bursts which are already six. A new method of observations was applied allowing an instantaneous coverage of a large effective area of celestial sphere — 160 sq. deg. Sources: arXiv:1705.02911 [astro-ph.HE], arXiv:1705.07698 [astro-ph.HE], arXiv:1705.07581 [astro-ph.HE]

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