Description From The Literature
A. Lupascu et al. give this description:
In quantum mechanics, the process of measurement is a subtle interplay between extraction of information and disturbance of the state of the quantum system. A quantum non-demolition (QND) measurement minimizes this disturbance by using a particular system—detector interaction that preserves the eigenstates of a suitable operator of the quantum system. This leads to an ideal projective measurement.
On the other hand, it has been argued that the usage of the term QND does not add anything to the usual notion of a strong quantum measurement and can moreover be confusing because of the two different interpretations of demolition in a quantum system (losing the quantum state vs. losing the particle). :
Read more about this topic: Quantum Nondemolition Measurement
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