  While the coherent control of two level quantum systems ---qubits--- is now
standard, their continuum electronic equivalents ---flying qubits--- are much
less developed. A first step in this direction has been achieved in DC
interferometry experiments. Here, we propose a simple setup to perform the
second step, the spectroscopy of these flying qubits, by measuring the DC
response to a high frequency AC voltage drive. Using two different concurring
approaches --- Floquet theory and time-dependent simulations --- and three
different models --- an analytical model, a simple microscopic model and a
realistic microscopic model --- we predict the power-frequency map of the
multi-terminal device. We argue that this spectroscopy provides a direct
measurement of the flying qubit characteristic frequencies and a key validation
for more advanced quantum manipulations.
