Sub-Nano Assemblers

Could anybody out there give me the parameters of a machine (not
unlike proposed nano-assemblers) which is able to construct artifacts
much, much smaller than what is sought by researchers into
nanotechnology.  Where I'm looking is this:

    Micro-assemblers:  building artifacts out of materials
    Nano-assemblers:  building materials out of molecules
    Pico-assemblers:  building molecules out of atoms
    Femto-assemblers:  building atoms out of subatomic particles
    Atto-assemblers:  building subatomic particles out of quarks and
leptons
    Zepto-assemblers:  building quarks and leptons out of
superstrings, twistors, etc.

What level of difficulty are any of these assemblers?  Completely
impossible and violations of every law from conservation of energy to
Heisenberg's Uncertainty Principle?  Or just really, really difficult?
 How would tunneling be handled, or would that in fact be the process
by which they operate?  How would they be constructed?  Since logic
circuits are essentially impossible at such ranges, would the
sub-Nano-assemblers be temporary tools of larger assemblers, or could
the sub-Nano-assemblers communicate like distributed nodes in a
network, forming a processor though they are too small to be
processors themselves?  If this thread sparks you or you have comment,
please e-mail me or reply to this post.