  Due to their high energy, hot electrons in quantum Hall edge states can be
considered as single particles that have the potential to be used for quantum
optics-like experiments. Unlike photons, however, electrons typically undergo
scattering processes in transport, which results in a loss of coherence and
limits their ability to show quantum-coherent behaviour. Here we study
theoretically the decoherence mechanisms of hot electrons in a Mach-Zehnder
interferometer, and highlight the role played by both acoustic and optical
phonon emission. We discuss optimal choices of experimental parameters and show
that high visibilities of $\gtrsim 85\%$ are achievable in hot-electron devices
over relatively long distances of 10 $\mu$m. We also discuss energy filtration
techniques to remove decoherent electrons and show that this can increase
visibilities to over $95\%$. This represents an improvement over Fermi-level
electron quantum optics, and suggests hot-electron charge pumps as a platform
for realising quantum-coherent nanoelectronic devices.
