  A which-way device is one which is designed to detect which of 2 paths is
taken by a quantum particle, whether Schr\"odinger's cat is dead or alive. One
possible such device is represented by an Aharonov-Bohm ring with a quantum dot
on one branch. A charged cantilever or spring is brought close to the dot as a
detector of the presence of an electron. The conventional view of such a device
is that any change in the state of the cantilever implies a change in the
electron state which will in turn destroy the interference effects. In this
paper we show that it is in fact possible to change the state of the oscillator
while preserving the quantum interference phenomenon.
