  Femtosecond torsional relaxation processes experimentally detected and
recently reported by Clark et al. (Nature Phys. 8,225 (2012)) are theoretically
dissected with a Hilbert/Fock quantum physical (QP) framework incorporating
entanglement of photon/matter base states overcoming standard semi-classic
vibrational descriptions. The quantum analysis of a generic Z/E (cis/trans)
isomerization in abstract QP terms shed light to fundamental roles played by
photonic spin and excited electronic singlet coupled to triplet states. It is
shown that one photon activation cannot elicit femtosecond phenomenon, while a
two-photon pulse would do. Estimated time scales for the two-photon case
indicate the process to lie between a slower than electronic Franck-Condon-like
transition yet faster than (semi-classic) vibration relaxation ones.
