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Quantum Information and Computation

Coherence preservation in a Λ-type three-level atom

YangFei, CongShuang

Published May 1, 2011• 0 citations
Publisher

Abstract

Coherence preservation of a multilevel system subject to Markovian decoherence is studied. A Λ-type three-level atom is selected as the system model. Coherence preservation between a ground state a...
DOI
10.5555/2011406.2011410

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Coherence preservation of a multilevel system subject to Markovian decoherence is studied. A Lambda-type three-level atom is selected as the system model. Coherence preservation between a ground state and the excited state of such a system is defined as the control object. A control field is designed by means of constraining the constant coherence condition. For the singularities of the control field, we qualitatively analyze the breakdown time, i.e. the time of control diverging. We obtain the region in which the state stays to maintain coherence forever in the case that the three-level system is reduced to a two-level one. For other cases, we investigate how different parameters affect the breakdown time qualitatively. Numerical experiments are implemented on a three-level quantum system and the experimental results are analyzed.
The interpretation to the mechanism of interaction of light and matter is used in new quantum devices designing for the optical information storage.For reducing the unexpected decoherence effect in a Λ-typed three-level atom system,the master equation of an atomic system is investigated to find a set of states that have zero spontaneous decay rates.Two laser fields are introduced to prepare the decoherence-free state by using decoherence-free subspace(DFS) strategy to suppress spontaneous emission for the decoupling of the system's state and the environment.Theoretical analysis verifys its effectiveness to coherence-preserving.
The correlated dynamics of a three-level atom resonantly coupled to an electromagnetic cavity field is calculated (Λ, V , and L models). A diagrammatic representation of quantum dynamics is proposed for these models. As an example, Λ-atom dynamics is examined to demonstrate how the use of conventional von Neumann’s reduction leads to internal decoherence (disentanglement-induced decoherence) and to the absence of atomic coherence under multiphoton excitation. The predicted absence of atomic coherence is inconsistent with characteristics of an experimentally observed atom-photon entangled state. It is shown that the correlated reduction of a composite quantum system proposed in [18] qualitatively predicts the occurrence and evolution of atomic coherence under multiphoton excitation if a seed coherence is introduced into any subsystem (the atom or a cavity mode).