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Journal of Huaihua University

Linear Entropy Evolution of Coherent Excitonic States in Coupled Exciton-photon System

Kehui Song

Published Jan 1, 2007• 0 citations
OpenAlex

Abstract

Some investigations have been made about the evolution of the linear entropies for coherent excitonic states in the system of two coupled large semiconduction quantum dots mediated by a single-mode cavity field.The linear entropy attains the ideal case of being a periodic function of gt,it shows maximally entangled coherent exciton states can be generated in the case.The effects of the zero-temperature environment on the linear entropy of excitonic coherent state are also studied.

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Some investigations have been made about the evolution of the linear entropies for coherent excitonic states in the system of two coupled large semiconduction quantum dots mediated by a single-mode cavity field.The linear entropy attains the ideal case of being a periodic function of gt,it shows maximally entangled coherent exciton states can be generated in the case.The effects of the zero-temperature environment on the linear entropy of excitonic coherent state are also studied.
The dynamics of the entanglement for coherent excitonic states in the system of two, coupled, large semiconductor quantum dots ${(R/a}_{B}\ensuremath{\gg}1)$ mediated by a single-mode cavity field is investigated. Maximally entangled coherent excitonic states can be generated by cavity field initially prepared in odd coherent state. The entanglement of the excitonic coherent states between two dots reaches maximum when no photon is present in the cavity. The effects of the zero-temperature environment on the entanglement of excitonic coherent state are also studied using the concurrence for two subsystems of the excitons.
The relation between the excitonic purity and the concurrence in a system of two coupled large semiconduction quantum dots mediated by a single-mode cavity field is investigated by using linear entropy theory. The results show the difference in describing two modes of excitonic entanglement between linear entropy and concurrence. The relation between nonclassical property of cavity field and the entanglement degree of excitons is also discussed. The results show that two modes of exciton can reach maximal entanglement when the cavity exhibits an antibunching effect.
The dynamical behaviors of the entanglement for the excitons in a system of two coupled quantum dots and a single-mode cavity field are investigated for two different initial conditions by means of the concurrence.It is shown that the direct coupling between the dots can reduce the degree of the entanglement for the excitons.For the initial cavity field being in the odd-coherent state,the degree of their entanglement decreases with the increase of the coherent intensity of cavity field.There is a trade-off for excitonic entanglement when cavity field is initially prepared in the even-coherent state.The relation between the average photon numbers of cavity field and quasi-maximally entangled excitonic coherent states is studied.
We study the dynamics of entanglement and mixedness of the excitons in a system of the two driven quantum dots coupled to a single-model cavity field by means of the concurrence and the linear entropy.We show that in the absence of the external driving field,excitonic entanglement and mixedness exhibit a periodic oscillation.When the external field is applied,state entanglement and mixedness will reduce,but if the Ω/g is selected a reasonable value,we can effectively suppress the mixedness and prepare a pure excitonic entangled state.
Recently a pair of vertically aligned quantum dots has been suggested as optically driven quantum gate. The later is built when two different particles, an electron and a hole, are created optically. The two particles form entangled states. We study theoretically the dynamics of a single heavy hole exciton confined in a small vertically coupled quantum dot. We use harmonic potentials to model the confining of electrons and holes and calculate the exciton's energy spectrum using the Hund-Mulliken approach, and including the Coulomb interaction. The entanglement may be controlled by the application of external electric field. At certain times of dynamical evolution one can generate a maximally entangled coherent exciton state by initially preparing the quantum dots in a superposition of coherent state. In ideal situations, entangled quantum states would not decohere during processing and transmission of quantum information. However, a real quantum system is inevitably influenced by its environment. Since, we study the decoherence effect caused by the interaction of the confined carriers with the acoustic phonon effects. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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.