A palm hovering over a hot stove feels the heat even when the surrounding air seems cool. Something similar happens to electrons in the Aharonov–Bohm effect: the particle senses an electric voltage even though it enters a region where the field has already been switched off. The electric version of the effect, where a voltage (scalar potential) changes over time and shifts the phase of the electron wave, has so far existed only on paper. No one has run an experiment with shielded, time-varying potentials.
The authors of the new work propose to close this gap. The idea is to send single electrons through an interferometer and apply a short voltage pulse to a shielded region. If the scalar part of the potential is not just a mathematical convenience but a real field, the electron will feel it and produce a characteristic phase shift. This shift depends on the pulse frequency not as a sine (the usual contribution) but as one minus cosine. The two signals are orthogonal: they can be separated by smoothly varying the frequency.
The experiment will require picosecond precision — the pulse timing is comparable to the electron's transit through the device. Such technology already exists. Essentially, the experiment asks a question that has hung in the air since 1959: Is the Lorenz condition just a convenient choice or a fundamental law? The answer may show that “empty” space is not so empty, and electrons sense what we have grown used to calling invisible. Like a palm over a cooling stove — the heat is gone, but its trace can still be caught.
The electric Aharonov–Bohm effect is like warming your hands over a stove that has been turned off: the heat is already gone, but the wave of warmth hasn't reached your palms yet. Only here, instead of heat, it's electric voltage, and instead of palms, it's an electron.