  In a recent paper [Southall et al., Locally-acting mirror Hamiltonians,
arXiv:1908.07597 (2021)], we showed that it is possible to design
locally-acting mirror Hamiltonians which only affect incoming but do not change
the dynamics of outgoing wave packets. To better justify our approach, this
paper presents a systematic quantisation of the electromagnetic field in
position space. Starting from the assumption that the basic building blocks of
the electromagnetic field in one dimension are localised bosonic wave packets
with a clear direction of propagation -- so-called bosons localised in position
(BLiPs) -- we identify the relevant Schroedinger equation and construct Lorentz
covariant electric and magnetic field observables. Our description contains the
standard description of the quantised electromagnetic field which is shown to
apply to a subspace of states.
