Measurement of the Abraham Force and Its Predicted QED Corrections in Crossed Electric and Magnetic Fields

We report the observation by a new method of mechanical momentum transferred to gas phase atoms and molecules upon application of crossed oscillating electric and static magnetic fields. We identify this momentum as the microscopic analogue of the classical Abraham force. Two QED predictions of additional magnetoelectrically induced mechanical momentum are addressed. One of them is experimentally refuted; the other is found to be currently below our experimental detection.

Figure 1

Schematic setup of the experiment. A magnetic field $B$ is applied perpendicular to the drawing, and high voltage at frequency $\omega$ is applied to the electrodes of the cell. The pressures at the cell ends are detected by microphones Mic $A$ and Mic $B$. The pressure difference is detected by the lock-in amplifier LIA. The effective interaction length $L$ between the gas and the fields is defined in the text.

Figure 2

Magnetoelectric acoustic pressure observed in nitrogen gas. Top panel: 6.15 kHz, 1 atm, $E=370\mathrm{kV}/\mathrm{m}$. Middle panel: 6.15 kHz, 1 atm, $B=1.14\mathrm{T}$. Bottom panel: 1 atm. Solid lines are linear fits to the data, dashed lines theoretical predictions.

Figure 3

Polarizability for different atoms and molecules as deduced from magnetoelectrically generated pressure, as a function of the literature values. Solid line corresponds to the classical Abraham force prediction.