Quantum decoherence and measurement in small spin systems

M. A. Novotny, Fengping Jin, Hans A. De Raedt +1 more

We study the case of a small quantum spin system S with a non-degenerate groundstate coupled to a small quantum spin bath. Finite temperature measures for both quantum decoherence and thermalization are studied. The computational results, obtained from exact diagonalization, compare well with a recent perturbation theory prediction, even when the system and bath are of comparable sizes.

V. V. Dobrovitski

Dube, M., Philip C. E. Stamp

We consider the quantum dynamics of two spin-1/2 systems, each coupled to a bath of oscillators, so that a bath-mediated coupling is generated between the spins. We find that the interactions destroys any coherent motion of the 2 spins, even if the coupling of each spin to the bath is quite weak, unless the interaction is extremely small. This is because the dynamic mutual bias between the spins blocks any coherent transitions between nearly degenerate states. In many quantum measurement operations this means that decoherence effects will be much stonger during the actual measurement

Hans A. De Raedt, V. V. Dobrovitski

Philip C. E. Stamp

Hylke C. Donker, Hans A. De Raedt, Mikhail I. Katsnelson

We study the decoherence process of a four spin-1/2 antiferromagnet that is coupled to an environment of spin-1/2 particles. The preferred basis of the antiferromagnet is discussed in two limiting cases and we identify two exact pointer states. Decoherence near the two limits is examined whereby entropy is used to quantify the robustness of states against environmental coupling. We find that close to the quantum measurement limit, the self-Hamiltonian of the system of interest can become dynamically relevant on macroscopic timescales. We illustrate this point by explicitly constructing a state that is more robust than (generic) states diagonal in the system-environment interaction Hamiltonian.