Testing Gravity at the micro scale
Gravity is the weakest of the fundamental interactions but probably the most important one because of its ubiquitous nature which determines the space/time geometry around us. Experiments on gravity have always attracted enormous interest, especially today in the quest of deviations from General Relativity and of possible scenarios beyond the Standard Model. In this work we exploit new microscopic quantum probes of gravity constituted by ultracold Strontium atoms confined in the valleys of a periodic array of potential wells produced by a vertically-aligned laser beam. We perform an accurate measurement of the Earth's gravity and verify that the result obtained with this microscopic quantum system is consistent with the one measured with a macroscopic classical gravimeter. In our new technique atoms exchange quanta of energy with the time-modulated laser field: resonant quantum tunneling, which is observed experimentally, occurs once the energy quanta equal the gravitational potential between neighboring potential wells, which are vertically separated by multiples of the laser wavelength. Our results open interesting prospects for testing gravitational redshift and Newtonian law at micrometer scale and can also find applications for future compact, high precision quantum sensors of gravity and time.
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LW12140
Classical single-electron dynamics observed on the surface of liquid helium
For the first time, the transport of electrons through a small constriction, or 'point contact', has been measured
in the classical regime. Unlike in metals or semiconductors, where interactions between electrons are compromised by the
surrounding lattice of atoms, the electrostatic interaction between electrons floating above a liquid helium surface
is 'unscreened' and therefore strong. Hence, these surface electrons behave, in general, as a two-dimensional system of
classical charged particles. In this work, we measured the transport of such surface electrons through a small
constriction at the center of a microchannel filled with superfluid helium. The width of the constriction was controlled
using nanofabricated electrodes submerged beneath the helium surface. As the constriction was opened, a step-like
increase in the surface electron current was observed each time an additional electron was able to pass through the constriction.
The first step in the current therefore corresponded to electrons passing through the constriction in single-file.
Remarkably, we find that these dynamics are similar to those observed in crowds of human pedestrians moving through
bottlenecks, rather than in electron transport in metallic or semiconductor point-contact devices.
