  We study theoretically the detection of the topological phase transition
occurring in Rashba nanowires with proximity-induced superconductivity using a
quantum dot. The bulk states lowest in energy of such a nanowire have a spin
polarization parallel or antiparallel to the applied magnetic field in the
topological or trivial phase, respectively. We show that this property can be
probed by the quantum dot created at the end of the nanowire by external gates.
By tuning one of the two spin-split levels of the quantum dot to be in
resonance with nanowire bulk states, one can detect the spin polarization of
the lowest band via transport measurement. This allows one to determine the
topological phase of the Rashba nanowire independently of the presence of
Majorana bound states.
