  The characterisation of Quantum Channel Discrimination (QCD) offers critical
insight for future quantum technologies in quantum metrology, sensing and
communications. The task of multi-channel discrimination creates a scenario in
which the discrimination of multiple quantum channels can be equated to the
idea of pattern recognition, highly relevant to the tasks of quantum reading,
illumination and more. Whilst the optimal quantum strategy for many scenarios
is an entangled idler-assisted protocol, the extension to a multi-hypothesis
setting invites the exploration of discrimination strategies based on
unassisted, multipartite probe states. In this work, we expand the space of
possible quantum enhanced protocols by formulating general classes of
unassisted multi-channel discrimination protocols which are not assisted by
idler modes. Developing a general framework for idler-free protocols, we
perform an explicit investigation in the bosonic setting, studying prominent
Gaussian channel discrimination problems for real world applications. Our
findings uncover the existence of strongly quantum advantageous, idler-free
protocols for the discrimination of bosonic loss and environmental noise. This
circumvents the necessity for idler assistance to achieve quantum advantage in
some of the most relevant discrimination settings, significantly loosening
practical requirements for prominent quantum sensing applications.
