Decoherence by a chaotic many-spin bath.pdfVIP

a r X i v : q u a n t - p h / 0 4 0 6 0 0 1 v 1 3 1 M a y 2 0 0 4 Decoherence by a chaotic many-spin bath J. Lages, V. V. Dobrovitski, and B. N. Harmon Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames IA 50011, USA We numerically investigate decoherence of a two-spin system (central system) by a bath of many spins 1/2. By carefully adjusting parameters, the dynamical regime of the bath has been varied from quantum chaos to regular, while all other dynamical characteristics have been kept practically intact. We explicitly demonstrate that for a many-body quantum bath, the onset of quantum chaos leads to significantly faster and stronger decoherence compared to an equivalent non-chaotic bath. Moreover, the non-diagonal elements of the system’s density matrix decay differently for chaotic and non-chaotic baths. Therefore, knowledge of the basic parameters of the bath (strength of the system-bath interaction, bath’s spectral density of states) is not always sufficient, and much finer details of the bath’s dynamics can strongly affect the decoherence process. PACS numbers: 05.45.Pq, 03.65.Yz, 75.10.Nr, 03.67.-a Real physical systems are never isolated. Interaction of a quantum system with its environment leads to de- coherence: the initial pure state of the system quickly decays into an incoherent mixture of several states [1, 2]. Modern experiments provide much information about the decoherence dynamics of single (or few) ions [3], Cooper pairs [4], or spins [5], and require a comprehensive theory for adequate understanding. Decoherence is also a ma- jor obstacle to building a practical quantum computer, which, for a wide class of problems, is exponentially more efficient than classical computers [6]. Interaction of a quantum computer with the bath leads to a fast genera- tion of errors, and an accurate theory is needed to find a way of controlling this process. Decoherence is a complex quantum many-body phe- nomenon, and its det