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Determination of a state of a quantum system from results of measurements. (English. Russian original) Zbl 0967.81004
Probl. Inf. Transm. 35, No. 4, 359-368 (1999); translation from Probl. Peredachi Inf. 35, No. 4, 84-94 (1999).
Summary: It is shown that for determining a pure state of a quantum system (in a finite- or infinite-dimensional case), it suffices to measure four certain observables, and any two of them are not sufficient. Another problem considered is the determination of a mixed state in the finite-dimensional case where the space dimension \(N\) is not a prime number.
81P15 Quantum measurement theory, state operations, state preparations