Relaxation of a two-level system strongly coupled to a reservoir: Anomalously slow decoherence - art. no. 033809

摘要

Relaxation of a two-level system (TLS) into a resonant infinite-temperature reservoir with a Lorentzian is studied The reservoir is described by a complex Gaussian-Markovian field coupled to the nondiagonal elements of the TLS Hamiltonian. The theory can be relevant for electromagnetic interactions in microwave high-Q cavities and muon spin depolarization. Analytical results are obtained for the strong-coupling regime, Ohm (0)much greater than nu, where Ohm (0) is the rms coupling amplitude (Rabi frequency) and nu is the width of the reservoir spectrum. In this regime, the population difference and half of the initial coherence decay with two characteristic rates: most of the decay occurs at t similar to Ohm (-1)(0), the relaxation being reversible for t much less than(Ohm (2)(0)nu)(-1/3), whereas for t much greater than(Ohm (2)(0)nu)(-1/3) the relaxation becomes irreversible and is practically over. The other half of the coherence decays with a rate on the order of nu, which may be slower by orders of magnitude than the time scale of the population relaxation. The above features are explained by the fact that at t much less than nu (-1), the reservoir temporal fluctuations are effectively one-dimensional (adiabatic). Moreover, we identify the pointer basis, in which the reduction of the state vector occurs. The pointer states depend on the initial phase of the reservoir. [References: 55]