The QUIC Seminar Series presents ....

Who: Dr. Asher Peres
What: QUIC Seminar
What: QUIC Seminar "Dual quantum and classical descriptions of a measuring apparatus"
When: Friday, July 31, 1998 at 2:00pm
Where:Rm. 114, E. Bridge

The measuring process is the interface of classical and quantum phenomena. A measuring apparatus must be described by quantum mechanics while it interacts with the quantum system under observation. Then, it has to be given a classical description so that the result of the measurement appears as objective reality. Alternatively, that apparatus may be treated at all times by quantum mechanics. In that case, it never achieves the "objective" status, but it can be measured by a second apparatus which has such a dual description.

This work examines whether these two different descriptions of the same apparatus are mutually consistent. It is proved that if the dynamical variable used in the first apparatus is represented by an operator of the Weyl-Wigner type (for example, if it is a linear coordinate), then the conversion from quantum to classical terminology does not affect the final result. However, if the first apparatus encodes the measurement in a different type of operator (e.g., the phase operator), the two methods of calculation may give different results.

The conclusion is that not every physical system is a legitimate measuring apparatus. The quantum measurement problem has a satisfactory solution only if the measuring apparatus is properly built.

This work was done in collaboration with Ori Hay. It was supported by the Gerard Swope Fund, and the Fund for Encouragement of Research.