  Quantum control of a system requires the manipulation of quantum states
faster than any decoherence rate. For mesoscopic systems, this has so far only
been reached by few cryogenic systems. An important milestone towards quantum
control is the so-called strong coupling regime, which in cavity optomechanics
corresponds to an optomechanical coupling strength larger than cavity decay
rate and mechanical damping. Here, we demonstrate the strong coupling regime at
room temperature between a levitated silica particle and a high finesse optical
cavity. Normal mode splitting is achieved by employing coherent scattering,
instead of directly driving the cavity. The coupling strength achieved here
approaches three times the cavity linewidth, crossing deep into the strong
coupling regime. Entering the strong coupling regime is an essential step
towards quantum control with mesoscopic objects at room temperature.
