  We present results of extensive finite-temperature Quantum Monte Carlo
simulations on a SU(2) symmetric S=1/2 quantum antiferromagnet with a four-spin
interaction [Sandvik, Phys. Rev. Lett. 98, 227202 (2007)]. Our simulations,
which are free of the sign-problem and carried out on lattices containing in
excess of 1.6 X 10^4 spins, indicate that the four-spin interaction destroys
the N\'eel order at an unconventional z=1 quantum critical point, producing a
valence-bond solid paramagnet. Our results are consistent with the `deconfined
quantum criticality' scenario.
