  Over the past century, a large community within theoretical physics has been
seeking a unified framework for quantum gravity. Yet, to date, there is still
no experimental evidence of any non-classical features of gravity. While
traditional experimental proposals would usually require immensely challenging
Planck scale experiments, recent table-top protocols based on low-energy
quantum control have opened a new avenue into the investigation of
non-classical gravity. An approach that has sparked high interest, both in
terms of experimental feasibility and of theoretical implications, is the
indirect witnessing of non-classical gravity through the detection of its
capacity to act as an entangling channel. Most discussions have been centred on
the entanglement generation between two gravitationally coupled massive
systems. In this work, we instead examine the entangling capacity of the
gravitational interaction between two light pulses, we explain the main
experimental and theoretical advantages of having a photonic protocol, and lay
out the steps leading to the determination of the entangling phase, using the
path integral formalism and linearised gravity. We establish a closed form
formula for the entangling phase and provide an estimated order of magnitude of
the average photon number required for the generation of appreciable phase.
