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Résumé |
When a quantum system is subjected to a continuous measurement,
its evolution becomes stochastic and in a proper limit, it can be described
by a continuous equation with Gaussian noise. On the other hand, it is
known since Bohr that a quantum system subjected to successive von Neumann
measurements undergoes rare quantum jumps. The objective of this talk is to
show how this simple jumpy behavior can be obtained as a limit of the finer
continuous picture. Starting from repeated interaction schemes, my first
objective will be to introduce smoothly the formalism of quantum
trajectories to explain what a continuous measurement even means in a
quantum context. Then I will show, numerically, heuristically and perhaps
even analytically that when the measurement rate increases, the evolution
of a continuously monitored quantum system becomes "jumpy". I will show how
the jump rates can be computed from the system parameters in the general
case and I will finally demonstrate on an example that the continuous
picture is much finer than what the naive quantum jump limit would suggest
even in the infinitely strong measurement limit. |
