2 research outputs found
Dynamics of Collective Decoherence and Thermalization
We analyze the dynamics of N interacting spins (quantum register)
collectively coupled to a thermal environment. Each spin experiences the same
environment interaction, consisting of an energy conserving and an energy
exchange part.
We find the decay rates of the reduced density matrix elements in the energy
basis. We show that if the spins do not interact among each other, then the
fastest decay rates of off-diagonal matrix elements induced by the energy
conserving interaction is of order N^2, while that one induced by the energy
exchange interaction is of the order N only. Moreover, the diagonal matrix
elements approach their limiting values at a rate independent of N.
For a general spin system the decay rates depend in a rather complicated (but
explicit) way on the size N and the interaction between the spins.
Our method is based on a dynamical quantum resonance theory valid for small,
fixed values of the couplings. We do not make Markov-, Born- or weak coupling
(van Hove) approximations
Resonance Theory of Decoherence and Thermalization
We present a rigorous analysis of the phenomenon of decoherence for general
level systems coupled to reservoirs. The latter are described by free
massless bosonic fields. We apply our general results to the specific cases of
the qubit and the quantum register. We compare our results with the explicitly
solvable case of systems whose interaction with the environment does not allow
for energy exchange (non-demolition, or energy conserving interactions). We
suggest a new approach which applies to a wide variety of systems which are not
explicitly solvable