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Physica status solidi. C, Conferences and critical reviews/Physica status solidi. C, Current topics in solid state physics

Single entangled photon pair emission from an InGaAs/GaAs quantum dot up to temperatures of 30 K

R. Hafenbrak, Sven M. Ulrich, L. Wang, Armando Rastelli, Oliver G. Schmidt, Peter Michler

Published Oct 27, 2008• 1 citation
Publisher

Abstract

Abstract Photon pairs emitted from the biexciton‐exciton cascade of a single self‐assembled InGaAs/GaAs quantum dot can be polarization‐entangled. The degree of entanglement is reduced by the fine structure splitting of the involved exciton level. We measure this splitting in high resolution using a scanning Fabry‐Pérot interferometer. By quantum state tomographywe can determine the twophoton polarization state.We are able to verify the conditions of entangled or classically correlated photon pairs in full consistence with the observed fine structure splittings. The entanglement remains relatively unaffected for elevated sample temperatures where we observe reliable entanglement up to 30 K. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

DOI
10.1002/pssc.200880333

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Abstract Photon pairs emitted from the biexciton‐exciton cascade of a single self‐assembled InGaAs/GaAs quantum dot can be polarization‐entangled. The degree of entanglement is reduced by the fine structure splitting of the involved exciton level. We measure this splitting in high resolution using a scanning Fabry‐Pérot interferometer. By quantum state tomographywe can determine the twophoton polarization state.We are able to verify the conditions of entangled or classically correlated photon pairs in full consistence with the observed fine structure splittings. The entanglement remains relatively unaffected for elevated sample temperatures where we observe reliable entanglement up to 30 K. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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The radiative biexciton-exciton decay in a semiconductor quantum dot (QD) has the potential of being a source of triggered polarization-entangled photon pairs. However, in most cases the anisotropy-induced exciton fine structure splitting destroys this entanglement. Here, we present measurements on improved QD structures, providing both significantly reduced inhomogeneous emission linewidths and near-zero fine structure splittings. A high-resolution detection technique is introduced which allows us to accurately determine the fine structure in the photoluminescence emission and therefore select appropriate QDs for quantum state tomography. We were able to verify the conditions of entangled or classically correlated photon pairs in full consistence with observed fine structure properties. Furthermore, we demonstrate reliable polarization-entanglement for elevated temperatures up to 30 K. The fidelity of the maximally entangled state decreases only a little from 72% at 4 K to 68% at 30 K. This is especially encouraging for future implementations in practical devices. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Abstract We theoretically investigate the production of polarization‐entangled photons through the biexciton cascade decay in a single semiconductor quantum dot. A biexciton radiatively decays through two intermediate exciton states, where polarization‐entangled photons are emitted if the two decay paths differ in polarization but are indistinguishable otherwise. This ideal performance is usually spoiled by the electron–hole exchange interaction splitting the intermediate exciton states by a small amount and consequently attaching a which‐path information to the photon frequencies. We discuss post‐selection schemes to mask this which‐path information to an outside observer. We show how spectral filtering and time shifts at a single photon level affect the photon state. Here the solid state environment plays a crucial role in the effective measurement of intermediate exciton states. Evaluating our analytical results with realistic quantum dot parameters we quantify the applicability of suggested protocols for solid‐state based quantum cryptography. Our results indicate, that a high degree of entanglement is only reached by spectral alignment of the exciton states. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Abstract Entangled photon pairs are emitted from a biexciton decay cascade of single quantum dots when spectral filtering is applied. We show this by experimentally measuring the density matrix of the polarization state of the photon pair emitted from a continuously pumped quantum dot. The matrix clearly satisfies the Peres criterion for entanglement. By applying in addition a temporal window, the quantum dot becomes an entangled light source. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Abstract We present the results of recent experiments designed to manipulate the splitting in quantum dots, to eradicate the which‐path information that prevents entangled photon emission. We demonstrate that dots with splitting within the homogeneous linewidth can be grown directly by carefully controlling the thickness of the dot layer. Polarization dependent correlation measurements on these dots show characteristic features of entanglement, only present for dots with small splitting. Our results indicate that for the first time, we have observed triggered entangled photon pair emission from a quantum dot. The ability to trigger the emission of just one photon pair has advantages over other schemes to generate entangled photons, including scalability of the applications. Finally, we note that the device, once optimized, could be implemented by a simple LED‐like structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
We have studied photon correlation measurements on the photoluminescence (PL) of a self‐assembled single GaAs quantum dots (QD) under 8 K. The QD exhibited several peaks on the PL spectra arising from the recombination of multi‐excitonic complexes. Photon correlation measurements show several photon pairs emitted from the cascade of neutral and charged biexcitons. The photon pairs of the neutral biexcitons did not exhibit entanglement due to anisotropy of the QD, while we succeeded in observing the entanglement from the photon pairs from the charged biexcitons. This result can be understood by considering the energy structure of the charged states having Kramers doublets in the anisotropic QD.