  VO$_{2}$ is a model material system which exhibits a metal to insulator
transition at 67$^\circ$C. This holds potential for future ultrafast switching
in memory devices, but typically requires a purely electronic process to avoid
the slow lattice response. The role of lattice vibrations is thus important,
but it is not well understood and it has been a long-standing source of
controversy. We use a combination of ultrafast spectroscopy and ab initio
quantum calculations to unveil the mechanism responsible for the transition. We
identify an atypical Peierls vibrational mode which acts as a trigger for the
transition. This rules out the long standing paradigm of a purely electronic
Mott transition in VO$_{2}$; however, we found a new electron-phonon pathway
for a purely reversible electronic transition in a true bi-stable fashion under
specific conditions. This transition is very atypical, as it involves purely
charge-like excitations and requires only small nuclear displacement. Our
findings will prompt the design of future ultrafast electro-resistive
non-volatile memory devices.

Strongly Correlated Electrons;Materials Science;Quantum Physics