http://www.paper.edu.cn
-1-
Entanglement Sudden Death and Manipulation in
Double-Quantum-Dot Driven by Cavity Fields with
Phonon Baths
1
Li Junqi, Liang Jiuqing
Institute of Theoretical Physics, Shanxi University, Taiyuan, Shanxi, China (030006)
E-mail:ljq811209@yahoo.com.cn
Abstract
The entanglement dynamics of excitons in the two-level double-quantum-dot driven by cavity
fields is investigated with the particular attention on the effect of phonon bath which makes an open
two-qubit system of the quantum-dot and cavity-field. The time-evolution of the concurrence,
which is the entanglement measure of mixed states for the open system, is obtained explicitly as a
parameter function of exciton-photon couplings
1,2
, the phonon-populations
1,2
N
, and the
Huang-Rhys factors
1,2
. The entanglement sudden death (ESD) is found and is seen to be
manipulated by the parameters
1,2
,
1,2
N
, and
1,2
as well. We moreover demonstrate the
condition to suppress the ESD sufficiently.
Keywords: entanglement, concurrence, bath
1. Introduction
Entanglement is the most characteristic trait of quantum mechanics and plays a central role in the
quantum computing process which thus has triggered lot of studies on the theoretical and practical
aspects in many fields such as cavity quantum electrodynamic (CQED) [1], BEC system [2], and
Josephoson system [3] etc. Developments in semiconductor nanotechnology have shown that excitons
in quantum dots (QDs) constitute an alternative two-level qubit system instead of the usual two-level
atoms. In general, these small QDs are characterized by strong exciton-phonon interactions [4, 5].
Recently, the entanglement of excitons interacting with an external broadband two-mode seqeezed
vacuum in the low excitation density regime was investigated [6, 7] and multipartite entanglement of
the exciton-photon coupling system was also demonstrated [8]. However, the dephasing noise plays an
important role in the quantum dot-cavity field system [9] due to the exciton-phonon interaction, which
may lead to disentanglement. The schemes [6-8] that generated entanglement based on exciton CQED,
the exciton-phonon interaction was ignored. Recently, the significant effect of the exciton-phonon
interaction on quantum system was considered in the strong coupling region [10, 11].
As much as we know, the entanglement manipulation by the exciton-photon couplings
1,2
and the
Huang-Rhys factors
1,2
with the effect of phonon-bath has not been investigated yet for the
two-qubit system of double-quantum-dot driven by two cavity fields. Based on the canonical
transformation an effective Jaynes-Cumming-like Hamiltonian is derived, from which we obtain the
time-evolution of the reduced density matrix and the corresponding concurrence for a given initial
entangled-state
0
Ψ
. The ESD firstly reported by Yu and Eberly [12] is found, which is considered as
a new kind of nonlocal decoherence with abruptly and nonsmoothly vanishing entanglement in a finite
time-period due to the dephasing noise described by phonon baths. The ESD has been demonstrated
experimentally based on an optical experiment-setup [13].
1
This work were supported by the Natural Science Foundation of China under Grant Nos.10475053
and
Specialized Research Fund for the Doctoral Program of Higher Education under Grant Nos. 20040108007.