  The Standard Quantum Limit (SQL) for the measurement of a free mass position
is illustrated, along with two necessary conditions for breaching it. A
measurement scheme that overcomes the SQL is engineered. It can be achieved in
three-steps: i) a pre-squeezing stage; ii) a standard von Neumann measurement
with momentum-position object-probe interaction and iii) a feedback. Advantages
and limitations of this scheme are discussed. It is shown that all of the three
steps are needed in order to overcome the SQL. In particular, the von Neumann
interaction is crucial in getting the right state reduction, whereas other
experimentally achievable Hamiltonians, as, for example, the radiation-pressure
interaction, lead to state reductions that on the average cannot overcome the
SQL.
