Physics – Condensed Matter – Mesoscale and Nanoscale Physics
Scientific paper
2003-11-20
Physics
Condensed Matter
Mesoscale and Nanoscale Physics
5 pages revtex
Scientific paper
10.1103/PhysRevLett.92.120402
The unknown state $\hrho$ of a quantum system S is determined by letting it interact with an auxiliary system A, the initial state of which is known. A one-to-one mapping can thus be realized between the density matrix $\hrho$ and the probabilities of occurrence of the eigenvalues of a single and factorized observable of S+A, so that $\hrho$ can be determined by repeated measurements using a single apparatus. If S and A are spins, it suffices to measure simultaneously their $z$-components after a controlled interaction. The most robust setups are determined in this case, for an initially pure or a completely disordered state of A. They involve an Ising or anisotropic Heisenberg coupling and an external field.
Allahverdyan Armen E.
Balian Roger
Nieuwenhuizen Th. M.
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