  Recently, Bennett et al. [Eur. J. Phys. 37:014001, 2016] presented a
physically-motivated and explicitly gauge-independent scheme for the
quantisation of the electromagnetic field in flat Minkowski space. In this
paper we generalise this field quantisation scheme to curved spacetimes.
Working within the standard assumptions of quantum field theory and only
postulating the physicality of the photon, we derive the Hamiltonian, H, and
the electric and magnetic field observables, E and B, without having to invoke
a specific gauge. As an example, we quantise the electromagnetic field in the
spacetime of an accelerated Minkowski observer, Rindler space, and demonstrate
consistency with other field quantisation schemes by reproducing the Unruh
effect.
