  Beyond their use as numerical tools, quantum trajectories can be ascribed a
degree of reality in terms of quantum measurement theory. In fact, they arise
naturally from considering continuous observation of a damped quantum system. A
particularly useful form of quantum trajectories is as linear (but non-unitary)
stochastic Schrodinger equations. In the limit where a strong local oscillator
is used in the detection, and where the system is not driven, these quantum
trajectories can be solved. This gives an alternate derivation of the
probability distributions for completed homodyne and heterodyne detection
schemes. It also allows the previously intractable problem of real-time
adaptive measurements to be treated. The results for an analytically soluble
example of adaptive phase measurements are presented, and future developments
discussed.
