There exist nonorthogonal quantum measurements that are perfectly repeatable.
We show that, contrary to the widespread belief, in quantum mechanics repeatable measurements are not necessarily described by orthogonal projectors--the customary paradigm of observable. Nonorthogonal repeatability, however, occurs only for infinite dimensions. We also show that, when a nonorthogonal repeatable measurement is performed, the measured system retains some "memory" of the number of times that the measurement has been performed.
Buscemi
F
F
QUIT Group, Unità INFM and Dipartimento di Fisica A. Volta, Università di Pavia, via A. Bassi 6, I-27100 Pavia, Italy.
D'Ariano
G M
GM
Perinotti
P
P