  We present a scheme for achieving macroscopic quantum superpositions in
optomechanical systems by using single photon postselection and detecting them
with nested interferometers. This method relieves many of the challenges
associated with previous optical schemes for measuring macroscopic
superpositions, and only requires the devices to be in the weak coupling
regime. It requires only small improvements on currently achievable device
parameters, and allows observation of decoherence on a timescale unconstrained
by the system's optical decay time. Prospects for observing novel decoherence
mechanisms are discussed.
