312 research outputs found
Quantum and classical correlations in high temperature dynamics of two coupled large spins
We study dynamical correlations of two coupled large spins depending on the
time and on the spin quantum numbers. In the high-temperature approximation, we
obtain analytical expressions for the mutual informations, quantum and
classical parts of correlations. The latter was obtained performing the
non-orthogonal projective (POVM) measurements onto the spin coherent states of
two spins or one spin, as well as by means of the orthogonal projective
measurement of von Neumann. Contribution from quantum correlations is much less
than that from classical ones and decreasing with the increase in spin quantum
numbers at short times. However, it is not so in a time equal to half of the
quantum period.Comment: 10 pages, 3 figures, Corrected typos in formula
On the time-optimal implementation of quantum Fourier transform for qudits represented by quadrupole nucleus
We consider the problem of time-optimal realization of the quantum Fourier
transform gate for a single qudit with number of levels d from 3 to 8. As a
qudit the quadrupole nucleus with spin I > 1/2 controlled by NMR is considered.
We calculate the dependencies of the gate error on the duration of
radio-frequency pulse obtained by numerical optimization using Krotov-based
algorithm. It is shown that the dependences of minimum time of QFT gate
implementation on qudit dimension are different for integer and half-integer
spins.Comment: 6 pages, 5 figures, report for the International Symposium "Quantum
Informatics-2012" (QI-2012), Zvenigorod, Moscow region, October 01-05, 201
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