  We generalize a recently developed scheme for monitoring coherent quantum
dynamics with good time-resolution and low backaction [Reuther et al., Phys.
Rev. Lett. 102, 033602 (2009)] to the case of more complex quantum dynamics of
one or several qubits. The underlying idea is to measure with lock-in
techniques the response of the quantum system to a high-frequency ac field. We
demonstrate that this scheme also allows one to observe quantum dynamics with
many frequency scales, such as that of a qubit undergoing Landau-Zener
transitions. Moreover, we propose how to measure the entanglement between two
qubits as well as the collective dynamics of qubit arrays.
