Month: July 2011

Localization effects induced by decoherence in superpositions of many-spin quantum states | Phys. Rev. A 84, 012320 (2011)

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Localization effects induced by decoherence in superpositions of many-spin quantum states

Gonzalo A. Álvarez* and Dieter Suter†

Fakultät Physik, Technische Universität Dortmund, Dortmund, Germany

Received 23 March 2011; published 18 July 2011

The spurious interaction of quantum systems with their environment known as decoherence leads, as a function of time, to a decay of coherence of superposition states. Since the interactions between system and environment are local, they can also cause a loss of spatial coherence: correlations between spatially distant parts of the system are lost and the equilibrium states can become localized. This effect limits the distance over which quantum information can be transmitted, e.g., along a spin chain. We investigate this issue in a nuclear magnetic resonance quantum simulator, where it is possible to monitor the spreading of quantum information in a three-dimensional network: states that are initially localized on individual spins (qubits) spread under the influence of a suitable Hamiltonian apparently without limits. If we add a perturbation to this Hamiltonian, the spreading stops and the system reaches a limiting size, which becomes smaller as the strength of the perturbation increases. This limiting size appears to represent a dynamical equilibrium. We present a phenomenological model to describe these results.

©2011 American Physical Society

via Phys. Rev. A 84, 012320 (2011): Localization effects induced by decoherence in superpositions of many-spin quantum states.

Time evolution of the Multiple Quantum Coherence (MQC) distribution of the density matrix . The main panel shows the time evolution of the MQC spectrum. The inset shows the time evolution of its standard deviation.
Time evolution of the Multiple Quantum Coherence (MQC) distribution of the density matrix . The main panel shows the time evolution of the MQC spectrum. The inset shows the time evolution of its standard deviation.
Time evolution of the MQC distribution under a perturbation p = 0.108. The main panel shows the time evolution of the MQC spectrum. The inset shows the time evolution of the standard deviation σ for the unperturbed case compared with the perturbed case. This comparison shows directly the localization.
Time evolution of the MQC distribution under a perturbation p = 0.108. The main panel shows the time evolution of the MQC spectrum. The inset shows the time evolution of the standard deviation σ for the unperturbed case compared with the perturbed case. This comparison shows directly the localization.
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