  We study Unruh phenomena for a qudit detector coupled to a quantized scalar
field, comparing its response to that of a standard qubit-based Unruh-DeWitt
detector. We show that there are limitations to the utility of the detailed
balance condition as an indicator for Unruh thermality of higher-dimensional
qudit detector models. This can be traced to the fact that a qudit has multiple
possible transition channels between its energy levels, in contrast to the
2-level qubit model. We illustrate these limitations using two types of qutrit
detector models based on the spin-1 representations of $SU(2)$ and the
non-Hermitian generalization of the Pauli observables (the Heisenberg-Weyl
operators).

Quantum Physics;General Relativity and Quantum Cosmology;High Energy Physics - Theory