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РАЗНОЕ
How behavior of systems with sparse spectrum can be predicted on a quantum computer
Yu. I. Ozhigov Insitute of Physics and Technology, Russian Academy of Sciences, Moscow
Аннотация:
Call a spectrum of Hamiltonian
$H$ sparse if each eigenvalue can be quickly restored within
$\varepsilon$ from its rough approximation within
$\varepsilon_1$ by means of some classical algorithm. It is shown how a behavior of system with sparse spectrum up to time
$T={(1-\rho)}/{14\varepsilon}$ can be predicted on a quantum computer with the time complexity
$t={4}/{(1-\rho)\varepsilon_1}$ plus the time of classical algorithm, where
$\rho$ is the fidelity. The quantum knowledge of Hamiltonian eigenvalues is considered as the new Hamiltonian
$W_H$ whose action on each eigenvector of
$H$ gives the corresponding eigenvalue. Speedup of an evolution for systems with the sparse spectrum is possible because for such systems the Hamiltonian
$W_H$ can be quickly simulated on the quantum computer. For an arbitrary system (even in the classical case) its behavior cannot be predicted on a quantum computer even for one step ahead. By this method we can also restore the history with the same efficiency.
PACS:
03.67.Lx Поступила в редакцию: 01.04.2002
Исправленный вариант: 30.10.2002
Язык публикации: английский