Abstract
We examine the influence of environmental interactions on simple quantum
systems by obtaining the exact reduced dynamics of a qubit coupled to a
one-dimensional spin bath. In contrast to previous studies, both the qubit-bath
coupling and the nearest neighbor intrabath couplings are taken as the
spin-flip XX-type. We first study the Rabi oscillations of a single qubit with
the spin bath prepared in a spin coherent state, finding that nonresonance and
finite intrabath interactions have significant effects on the qubit dynamics.
Next, we discuss the bath-induced decoherence of the qubit when the bath is
initially in the ground state, and show that the decoherence properties depend
on the internal phases of the spin bath. By considering two independent copies
of the qubit-bath system, we finally probe the disentanglement dynamics of two
noninteracting entangled qubits. We find that entanglement sudden death appears
when the spin bath is in its critical phase. We show that the single-qubit
decoherence factor is an upper bound for the two-qubit concurrence.
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