  A complete, non-demolition procedure is established for measuring multi-qubit
entangled states, such as the Bell-states and the GHZ-states, which is
essential in certain processes of quantum communication, computation, and
teleportation. No interaction between the individual parts of the entangled
system, nor with any environment is required. A small probe (e.g. a single
qubit) takes care of all interaction with the system, and is used repeatedly.
The probe-qubit interaction is of the simplest form, and only this one type of
interaction is required to perform a complete measurement. The process may be
divided into elementary local operations and interactions, taking place
sequentially as the probe visits each of the qubits. A shuttle mode is
described, which may be repeated indefinitely. By the quantum Zeno effect, the
entangled states can be maintained until released in a predictable state. This
shuttle process is stable, and self-correcting, by virtue of the standard
measurements performed repeatedly on the probe.
