Entangled photon pairs (EPP) can be produced through the biexciton ( XX ) – exciton ( X ) radiative decay cascade in semiconductor quantum dots (QD) [1-3]. In existing devices, the requirement to enforce degeneracy of the intermediate excitonic states, whose degeneracy is lifted by the anisotropic exchange splitting (AES) [2-5], has led to remedies that include the application of large external magnetic fields , or the materials engineering of individual dots [3, 4]. Such schemes are impractical if large arrays of integrated EPP sources are to be constructed for quantum information applications.
In the work presented here we propose a scheme for EPP generation that does not require the removal of the AES. By application of a lateral electric field to an individual, pre-positioned InAs quantum dot on a patterned InP substrate, we engineer the quantum dot to introduce Hidden Symmetry within the s-shell. In such circumstances the biexciton binding energy vanishes, “which path” information for the XX - X radiative cascade is not available through a photon energy measurement and polarization entanglement is produced even if AES is still present. Photoluminescence measurements as a function of applied lateral electric field will be presented for individual InAs/InP quantum dots emitting close to \lambda=1300nm. The nucleation sites of these dots can be controlled with nanometer precision using an in-situ, ‘nanotemplate deposition’ technique , so that it is possible to build control structures, such as electrostatic gates, around individual QDs. Such a capability is a pre-requisite if arrays of such dots are to be employed for quantum information applications. Our measurements demonstrate the removal of the biexciton binding energy, a reduction of the AES, quenching of the neutral exciton emission and the appearance of new, normally forbidden transitions involving an s-shell electron and p-shell hole. Full Configuration-Interaction calculations will be presented that explain how the biexciton binding energy can be removed through manipulation of the electron-hole Coulomb interaction and consequent introduction of Hidden Symmetry.
 O. Benson, C. Santori, M. Pelton, Y. Yamamoto, Phys. Rev. Lett. 84 , 2513-2516(2000).
 R. M. Stevenson et al. , Nature 439 , 179-182 (2006).
 N. Akopian et al. , Phys. Rev. Lett. 96 , 130501 (2006).
 A. Greilich et al. , Phys. Rev. B 73 , 045323 (2006).
 K. Kowalik et al. , Appl. Phys. Lett. 86 , 041907 (2005).
 D. Chithrani, R. L. Williams, J. Lefebvre, P. J. Poole, and G. C. Aers, Appl. Phys. Lett. 84 , 978 (2004).
Joint QUINF Seminar and Quantum Optics/AMO Seminar