Abstract
We consider some of the obstacles that will have to be overcome in order to perform a direct measurement of the gravitational free-fall of positronium atoms. Foremost among these are the production of positronium atoms in a cryogenic environment, efficient excitation of these atoms to suitably long-lived Rydberg states, and their subsequent control via the interaction of their large electric dipole moments with inhomogeneous electric fields. Recent developments in all of these areas can be directly applied to a positronium free-fall gravity measurement, making such an endeavour both timely and feasible.
Highlights
The idea that the universe originated in a primordial cosmic explosion is well established
An experimental programme currently underway at University College London (UCL) has as its long-term goal a gravitational free-fall measurement of positronium atoms along the lines suggested by Mills and Leventhal.[3]
There are some considerable challenges that have to be met in order to perform this experiment, these are (i) production of a positron pulse with spatio-temporal characteristics suitable for interfacing with a focused laser, (ii) efficient conversion of such a positron pulse into slow positronium atoms in a cryogenic environment, (iii) optical excitation of the positronium atoms to sufficiently long lived states and, (iv) implementation of atom-optics to produce a slow focused Ps beam
Summary
The idea that the universe originated in a primordial cosmic explosion (known as the Big Bang) is well established. The observed predominance of matter in the universe today contradicts this hypothesis This imbalance may result from a fundamental asymmetry between the properties of matter and antimatter that has not yet been understood, and which would presumably have to involve CPT violating effects. There are some speculations that the absence of observed antimatter in the Universe may be related This is an Open Access article published by World Scientific Publishing Company. An experimental programme currently underway at University College London (UCL) has as its long-term goal a gravitational free-fall measurement of positronium atoms along the lines suggested by Mills and Leventhal.[3] There are some considerable challenges that have to be met in order to perform this experiment, these are (i) production of a positron pulse with spatio-temporal characteristics suitable for interfacing with a focused laser,. In the last decade or so there have been many advances that apply directly to these tasks; the increasing use of pulsed positron beams derived from traps,[4] the development of new positron-positronium converters,[5,6] pulsed laser excitation[7] and associated detection techniques,[8] and methods for the manipulation of Rydberg atoms using inhomogeneous electric fields[9,10] all offer increased capabilities useful in a measurement of the free-fall of positronium
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