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There are currently proposals to test the weak equivalence principle for antimatter by studying the motion of antiprotons, negative hydrogen ions, positrons, and electrons under gravity. The motions of such charged particles are affected by residual gas, radiation, and electric and magnetic fields, as well as gravity. The electric fields are particularly sensitive to the state of the "shielding" container. This paper reviews, and extends where necessary, the physics of these extraneous influences on the motion of charged particles under gravity. The effects considered include residual gas scattering; wall potentials due to patches, stress, thermal gradients, and contamination states; and image-charge-induced dissipation.

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The authors report measurements of surface patch potential profiles on polycrystalline Cu and Au surfaces in high vacuum after previous exposure to air. These results are relevant to experiments to measure the gravitational acceleration of charged particles inside vertical metallic drift tubes. Axial potential variations due to patch potentials on the drift tube surface limit the accuracy of these experiments. They discuss the problems due to non-uniform contamination by adsorbates, which generally produces patches over length scales larger than the crystallite size. Their observations show that, given sufficient time, patch potential variations are generally smoothed out, apparently due to preferential adsorption of background contaminants.

The scalar version of the Aharonov-Bohm effect predicts a phase shift for de Broglie waves due to the action of a scalar potential in an otherwise field-free (i.e., force-free) region of space. Unlike the more familiar effect due to the magnetic vector potential, the scalar effect has hitherto remained unverified due, presumably, to technical difficulties in electron interferometry. Rather than using electrons acted on by electrostatic potentials, we have performed an analogous interferometry experiment with thermal neutrons subject to pulsed magnetic fields. The expected phase shifts have been observed to a high degree of accuracy.PACS numbers: 03.65.Bz, 42.50.-p In classical electrodynamics, potentials are merely a convenient mathematical tool for calculating electromagnetic fields of force. In quantum mechanics, however, potentials have a primary physical significance and are an essential ingredient which cannot be readily eliminated from the Schrodinger equation. In a paper entitled "Significance of Electromagnetic Potentials in Quantum Theory" published in 1959, Aharonov and Bohm [1] proposed two types of actual electron interference experiments aimed at exhibiting these conclusions. The phenomena predicted came to be known as the AharonovBohm (AB) effect, and have given rise to a literature of almost 400 journal articles over the last thirty-odd years.The essence of the AB experiments [2] is that electrons suffer phase shifts in passing through regions of space of zero fields but nonzero potentials. The effects are of two types, the usual magnetic (or vector) AB effect, and the less often cited electric (or scalar) AB effect which is conceptually quite simple. It concerns the phase shift caused by the scalar potential V= -eU in the Schrodinger equation:(H 0 +V)yr=ihdifr/dt.(1) Figure 1 (a) shows a divided electron wave packet traveling down two conducting cylinders which act as Faraday cages, i.e., have a field-free interior irrespective of their electrostatic potentials U\ and Ui* To exhibit the scalar AB effect, the potential of cylinder 2 alone is pulsed during a time when the wave packet is contained inside it. In spite of the absence of a force at all times, a relative phase shift A# is expected, A = (\/h)feU 2 (t)dt.(2)The correctness of this AB prediction is of such importance to the consistency of quantum mechanics [3] that the actual experiment deserves a serious attempt. However, such an experiment has not yet been performed because of technical difficulties with existing types of electron interferometers. The closely related experiment of Mateucci and Pozzi [4] involves forces acting on the electron and is not, therefore, a clear-cut test of the effect. Realizations with protons or ions are hindered by the lack of suitable interferometers for such particles.In the present experiment with neutrons, the phase shift is due to a scalar potential, V s -JI * B, which is the analog of V*= -eU, the scalar potential in the scalar AB effect for electrons. (This parallels a previous situation in which th...

We show that ground-state Zeeman coherence prepared by two-photon Raman transitions in alkali atoms results in steep controllable and sign-reversible dispersion. Pulse propagation with small negative as well as positive group velocity of light (Ϫc/5100 and c/41 000) in a Cs vapor cell is reported. Energy exchange between copropagating light components through long-lived Zeeman coherence with enhanced absorption or transmission has been observed.

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