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arXiv:quant-ph/0507027 · Physical Review A

Complete disentanglement by partial pure dephasing

Katarzyna Roszak, Paweł Machnikowski

Published Feb 6, 2006• 102 citations
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Abstract

We study the effect of pure dephasing on the entanglement of a pair of two-level subsystems (qubits). We show that partial dephasing induced by a super-Ohmic reservoir, corresponding to well-established properties of confined charge states and phonons in semiconductors, may lead to complete disentanglement. We show also that the disentanglement effect increases with growing distance between the two subsystems.

DOI
10.1103/physreva.73.022313

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We study the effect of pure dephasing on the entanglement of a pair of two-level subsystems (qubits). We show that partial dephasing induced by a super-Ohmic reservoir, corresponding to well-established properties of confined charge states and phonons in semiconductors, may lead to complete disentanglement. We show also that the disentanglement effect increases with growing distance between the two subsystems.
We study entanglement generated between a qubit and a super-ohmic bosonic bath due to their joint evolution which leads to pure dephasing of the qubit. We tune the parameters of the interaction, so that the decoherence is quantitatively independent of the number of bosonic modes taken into account (and corresponds to realistic decoherence seen in small excitonic quantum dots coupled to an environment of phonons) and investigate, how the entanglement generated depends on the size of the environment. A second parameter of interest is the mixedness of the initial state of the environment which is controlled by temperature. We show analytically that for a pure initial state of the environment (zero temperature here), entanglement does not depend on environment size. At finite temperatures (mixed initial state of the environment), the generated entanglement decreases with the increase of environment size. This effect is stronger for larger temperatures, when the environment is initially more mixed, but in the limit of an infinitely large environment, no entanglement is created at any finite temperature.
This work investigates the impact of decoherence induced by pure dephasing and phonon-assisted tunneling mechanisms on the optical and quantum properties of two quantum dots. Special attention is given to the density matrix at steady state, and a detailed analysis of populations, coherences, optical transitions and the emission spectrum is performed. Additionally, we study the influence of both phonon-decoherence mechanisms on bipartite entanglement and the degree of mixedness of the system. In particular, our findings indicate that the phonon-assisted tunneling mechanism partially affects the coherences of the system and quantum properties when the imbalance of phonon absorption and emission is significant. Conversely, the pure dephasing mechanism does not affect the populations but strongly entangles the quantum dots and the reservoir, inducing maximally mixed states and significantly reducing the spectral splitting in the emission spectrum of the system.