  We propose a new method to optically levitate a macroscopic mirror with two
vertical Fabry-P{\'e}rot cavities linearly aligned. This configuration gives
the simplest possible optical levitation in which the number of laser beams
used is the minimum of two. We demonstrate that reaching the standard quantum
limit (SQL) of a displacement measurement with our system is feasible with
current technology. The cavity geometry and the levitated mirror parameters are
designed to ensure that the Brownian vibration of the mirror surface is smaller
than the SQL. Our scheme provides a promising tool for testing macroscopic
quantum mechanics.
