  The null conformal boundary $\mathscr{I}$ of Minkowski spacetime $\mathbb{M}$
plays a special role in scattering theory, as it is the locus where massless
particle states are most naturally defined. We construct quantum fields on
$\mathscr{I}$ which create these massless states from the vacuum and transform
covariantly under Poincar\'e symmetries. Since the latter symmetries act as
Carrollian conformal isometries of $\mathscr{I}$, these quantum fields are
Carrollian conformal fields. This group theoretic construction is intrinsic to
$\mathscr{I}$ by contrast to existing treatments in the literature. However we
also show that the standard relativistic massless quantum fields in
$\mathbb{M}$, when pulled back to $\mathscr{I}$, provide a realisation of these
Carrollian conformal fields. This correspondence between bulk and boundary
fields should constitute a basic entry in the dictionary of flat holography.
Finally we show that $\mathscr{I}$ provides a natural parametrisation of the
massless particles as described by irreducible representations of the
Poincar\'e group, and that in an appropriate conjugate basis they indeed
transform like Carrollian conformal fields.
