Free electrons with a helical phase front, referred to as "twisted"
electrons, possess an orbital angular momentum (OAM) and, hence, a quantized
magnetic dipole moment along their propagation direction. This intrinsic
magnetic moment can be used to probe material properties. Twisted electrons
thus have numerous potential applications in materials science. Measuring this
quantity often relies on a series of projective measurements that subsequently
change the OAM carried by the electrons. In this Letter, we propose a
nondestructive way of measuring an electron beam's OAM through the interaction
of this associated magnetic dipole with a conductive loop. Such an interaction
results in the generation of induced currents within the loop, which are found
to be directly proportional to the electron's OAM value. Moreover, the electron
experiences no OAM variations and only minimal energy losses upon the
measurement, and, hence, the nondestructive nature of the proposed technique.Comment: 5 pages, 3 figures, and supplemental material that is comprised of
text and 4 figure