  We demonstrate qubit state measurement for ~160 Cesium atoms in a 3D optical
lattice based on coherent spatial splitting of the atoms' wavefunctions. The
measurement fidelity is 0.9994, essentially independent of the number of qubits
measured. The detection scheme is reminiscent of the Stern-Gerlach experiment,
but carried out in light traps. The measurement causes no loss, which allows us
to demonstrate re-initialization of the 3D qubit array after state measurement,
including the replacement of an atom lost to a background gas collision.
