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Journal of the Physical Society of Japan

Time Evolution of an Exciton and a Photon Qubit Coupled with Each Other

Yoshiaki Rikitake, Hiroshi Imamura, Hiromichi Ebisawa

Published Dec 15, 2003• 1 citation
Publisher

Abstract

We theoretically study the time evolution of an exciton qubit (quantum dot) and a photon qubit (photonic cavity) coupled with each other. Special attention is paid to the effect of pure dephasing and energy dissipation in the quantum dot. We find that the pure dephasing brings about the oscillation of the entropy of the quantum dot with the half period of Rabi oscillation. Finite entanglement remains in the steady state. This state can be used for preparing the Bell state between photon and exciton qubits. The energy dissipation suppresses the amplitude of the oscillation of the entanglement between the exciton and photon qubits. We also find that the energy dissipation in the quantum dot changes the oscillation period of the entropy of the quantum dot.

DOI
10.1143/jpsj.72.3020

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The dynamical behavior of entanglement for excitons in two quantum dots placed in a cavity driven by a broadband squeezed vacuum is studied in the low exciton density regime. It is found that the excitons in two quantum dots can evolve into a pure entangled state only when the dissipation of the cavity and exciton modes is negligible. When the injected field into the cavity is a squeezed vacuum, the excitons will be in a two-mode Gaussian entangled mixed state even in the long time limit. Analytical expressions are derived, showing the dependence of the entanglement property of the excitons in two quantum dots on the squeezing properties of the initial state prepared in the cavity and the strength of two-photon correlations of the squeezed vacuum injected into the cavity.
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The time evolution of entanglement between two quantum dots (QDs) trapped inside a cavity driven by a coherent quantized field is studied. In the presence of dissipation, entanglement shows many interesting features such as sudden death and revival, and finite steady state value after sudden death. We also investigate dependence of entanglement on dot variables and its relation to bistability. It is found that entanglement vanishes when the cavity field intensity approaches the upper branch of the bistability curve. When the cavity is driven by a modulated field in the presence of dissipation, it can periodically generate entanglement, which is much larger than the maximum value attained in the steady-state for this system but the dots are never fully entangled.
We investigate the entanglement dynamics of two electron-spin qubits in the quantum-dot (QD)–microcavity system in the large-detuning limit and subjected to two different noise sources: electron-spin dephasing and relaxation. We show that when one of the two dots is prepared initially in the excited state, the created entanglement exhibits oscillatory behavior at the beginning of evolution and then completely disappears over time. For two QDs that are initially in either the Einstein–Podolsky–Rosen-Bell states or the Werner states, their entanglement evolution exhibits the same behavior in the presence of pure dephasing, but is completely different under the relaxation process. We also show that the interdot interaction induced by a single-mode cavity field does not contribute to the dynamics of entanglement for these Bell states and Werner states.