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Physical Review A

Entanglement for excitons in two quantum dots placed in two separate single-mode cavities

Gao‐xiang Li, Hua-Tang Tan, Shao‐ping Wu, Yaping Yang

Published Sep 29, 2004• 16 citations
Publisher

Abstract

The dynamical behavior of entanglement for excitons in two quantum dots placed in two separately single-mode optical cavities driven by an external broadband two-mode squeezed vacuum is studied in the low exciton density regime. It is found that if the field in the two separate cavities is initially prepared in a pure two-mode squeezed vacuum state, the excitons in the two quantum dots can evolve into a pure entangled state only when the dissipation of the cavities and exciton modes is negligible. When the effect of the dissipation is included, the excitons will be in a two-mode Gaussian entangled mixed state whose properties are decided by the externally driven field and the initial field. The dependence of the entanglement property of the excitons in the two quantum dots on the squeezing properties of the fields in the two cavities is also discussed.

DOI
10.1103/physreva.70.034307

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The dynamical behavior of entanglement for excitons in two quantum dots placed in two separately single-mode optical cavities driven by an external broadband two-mode squeezed vacuum is studied in the low exciton density regime. It is found that if the field in the two separate cavities is initially prepared in a pure two-mode squeezed vacuum state, the excitons in the two quantum dots can evolve into a pure entangled state only when the dissipation of the cavities and exciton modes is negligible. When the effect of the dissipation is included, the excitons will be in a two-mode Gaussian entangled mixed state whose properties are decided by the externally driven field and the initial field. The dependence of the entanglement property of the excitons in the two quantum dots on the squeezing properties of the fields in the two cavities is also discussed.
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.
The dynamical behavior of purity and entanglement for excitions in three 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 excitions in the three quantum dots can evolve into a pure entangled state only when the dissipation of the cavity and excitions is negligible. When the injected field into the cavity is a squeezed vacuum, the excitions will be in a three_mode Gaussian entangled mixed state even in the long time limit .Analytical expressions are derived showing the dependence of the purity and entanglement property of the excitions in the three 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.
We investigate entanglement transfer from two separate cavities to the excitons in two quantum dots separately placed in the two cavities. The cavity fields and the excitons are treated as two continuous-variable (CV) subsystems. The time-dependent characteristic functions in the Wigner representation for the two subsystems are analytically obtained. Under the conditions that one of the two CV subsystems is initially prepared in a two-mode squeezed vacuum state and the other in its lowest energy state, we show that the entanglement reciprocation between the cavity fields and the excitons is realizable.
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.
Squeezing properties of two-mode excitons in a system of two coupled quantum dots and cavity QED is investigated.The effect of the different initial cavity field states on two-mode excitons normal squeezing and sum squeezing has been discussed.A conclusion has also been obtained through calculating.It is that when the cavity field is initial prepared in coherent states,two-mode excitons normal squeezing do not exist as well as the sum squeezing.It indicates that the two quadrature components of the excitons amplitude possess the same quantum fluctuation.However,in the case that cavity field is in the vacuum squeezed state,no matter how normal squeezing or sum squeezing,either of the two quadrature component of the excitons amplitude are always of squeezing,it implies that quantum noise can be effective restrained in the case.Otherwise,the maximum squeezing in both situations is determined by the initial cavity field squeezing factor r.After comparing normal squeezing and sum squeezing,we can find that two-mode excitons normal squeezing is larger than sum squeezing.