  Microquasars (MQs) are binary systems composed by a star feeding mass to a
compact object through an accretion disk. The compact object, usually a black
hole, launches oppositely directed jets which are typically observed in our
galaxy through their broadband electromagnetic emission. These jets are
considered potential galactic neutrino sources. MQs can also have been formed
by the first generations of stars in the universe, i.e., Population III (Pop
III) stars, which are considered essential contributors to the ionization
processes that took place during the period of 'cosmic reionization'. In the
present work, we develop a model that accounts for the main particle processes
occurring within Pop III MQ jets, with the aim to obtain the diffuse neutrino
flux at the Earth [...] We find that, for a range of parameters suitable for
Pop III MQ jets, the most relevant site for neutrino production in the jets is
the base of the inner conical jet. Additionally, if protons accelerated at the
forward shock formed at terminal jet region can escape from the outer shell,
they would produce further neutrinos via $p{\gamma}$ interactions with the
cosmic microwave background (CMB). The latter contribution to the diffuse
neutrino flux turns out to be dominant in the range $10^7 {\rm GeV} \lesssim
E_{\nu} \lesssim 10^9 {\rm GeV}$, while the neutrinos produced in the inner jet
could only account for a small fraction of the IceCube flux for $E_{\nu}\sim
10^5$ GeV. The co-produced multiwavelength photon background is also computed
and it is checked to be in agreement with observations.
