Can a single electron have a quantized orbital angular momentum in the direction of propagation in free space? I trying to understand the article about quantized orbital angular momentum in electron vortex beams. The article is not important per se, as there are many others. But I'm reading it as if an electron in free space may have quantized orbital angular momentum, yet the experiments are done with a beam (packets) of electrons.
My question is, can we have experimentally, a single electron with quantized angular momentum in the direction of propagation in free space or are there other constraints?
 A: Yes, a single electron can have angular momentum in free space.

Electrons can also possess quantized canonical orbital angular momentum which
  does not depend on the presence of a magnetic field.  This is well known in the case of
  bound states in atoms and quantum dots [6], in which there is a confining potential,
  however recently it was discovered that
  free
  electrons can be imprinted with orbital
  angular  momentum. 
In this paper, we show that the total orbital angular momentum of the electron
  is  described  by  the  parallel  axis  theorem.   This  angular  momentum  comprises  the
  canonical and diamagnetic components,  which are associated with rotation relative
  to  the  centre  of  mass  of  the  wavefunction,  and  a  cyclotron  component  which  has
  expectation value equal to that for the classical orbit.  Interestingly, for free electrons
  all  three  of  these  components  can  have  similar  magnitude.

Quoted from Parallel axis theorem for free-space electron wavefunctions, Greenshields et al., 2015.
