Abstract
Measurements are ordinarily described with respect to absolute “Newtonian” time. In reality, however, the switching-on of the measuring device at the instance of the measurement requires a timing device. Hence the classical time t must be replaced by a suitable quantum time variable τ of a physical clock. The main issue raised in this paper is that while doing so, we can no longer neglect the back reaction due to the measurement on the clock. For a von Neumann measurement model, this back reaction yields a bound on the accuracy of the measurement. When this bound is violated the result of a measurement is generally not an eigenvalue of the observable, and furthermore, the state of the system after the measurement is generally not a pure state. We argue that as a consequence, a subclass of observables in a closed system cannot be realized by a von Neumann–like measurement.
Original language | English |
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Pages (from-to) | 7 |
Number of pages | 1 |
Journal | Physical Review A - Atomic, Molecular, and Optical Physics |
Volume | 62 |
Issue number | 4 |
DOIs | |
State | Published - 2000 |