  Magnons enable transferring a magnetic moment or spin over macroscopic
distance. In quantum Hall ferromagnet, it has been predicted in the early 90s
that spin and charges are entangled, meaning that any change of the spin
texture modifies the charge distribution. As a direct consequence of this
entanglement, magnons carry an electric dipole moment. Here we report the first
evidence of the existence of this electric dipole moment in a graphene quantum
Hall ferromagnet using a Mach-Zehnder interferometer as a quantum sensor. By
propagating towards the interferometer through an insulating bulk, the magnon
electric dipole moment modifies the Aharonov-Bohm flux through the
interferometer, changing both its phase and its visibility. In particular, we
relate the phase shift to the sign of this electric dipole moment, and the
exponential loss of visibility to the flux of emitted magnons. Finally, we
probe the emission energy threshold of the magnons close to filling factor v=1.
Approaching v=0, we observe that the emission energy threshold diminishes
towards zero, which might be linked to the existence of gapless mode in the
canted-antiferromagnetic (CAF) phase at v=0. The detection and manipulation of
magnons based on their electric dipole open the field for a new type of
coherent magnon quantum circuits that will be electrostatically controlled.
