  The periodically kicked quantum rotor is known for non-classical effects such
as quantum localisation in angular momentum space or quantum resonances in
rotational excitation. These phenomena have been studied in diverse systems
mimicking the kicked rotor, such as cold atoms in optical lattices, or coupled
photonic structures. Recently, it was predicted that several solid state
quantum localisation phenomena - Anderson localisation, Bloch oscillations, and
Tamm-Shockley surface states - may manifest themselves in the rotational
dynamics of laser-kicked molecules. Here, we report the first observation of
rotational Bloch oscillations in a gas of nitrogen molecules kicked by a
periodic train of femtosecond laser pulses. A controllable detuning from the
quantum resonance creates an effective accelerating potential in angular
momentum space, inducing Bloch-like oscillations of the rotational excitation.
These oscillations are measured via the temporal modulation of the refractive
index of the gas. Our results introduce room-temperature laser-kicked molecules
as a new laboratory for studies of localisation phenomena in quantum transport.
