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AIP conference proceedings

Polarization-entangled Photon Pairs From A Single GaAs Quantum Dot

Yusuke Arashida, T. Hanazawa, Yoshihiro Ogawa, F. Minami, Jisoon Ihm, Hyeonsik Cheong

Published Jan 1, 2011• 0 citations
Publisher

Abstract

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.

DOI
10.1063/1.3666460

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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.
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)
We measured the second order correlation function between single photons emitted from optically excited single self‐assembled quantum dots embedded in planar microcavities. We clearly distinguish between radiative recombination processes in the presence of a charge in the dot to recombination in its absence. We observed strong correlations of the linear polarization states of photons emitted by the recombining neutral biexcitons and the polarization states of consecutive recombining neutral excitons.
Single InAs quantum dot (QD) sample was grown by molecular-beam epitaxy (MBE). The Photoluminescences (PL) of the exciton and biexciton in a single QD were measured at 5 K. The PL intensity as a function of the laser excitation power, the fine structure splittings of the exciton and biexciton, and the corresponding linearly polarized emissions were analyzed. By means of Hanbury-Brown and Twiss (HBT) setup, the photon correlation between the PL of exciton and biexciton were measured, which is gave an evidence of the quantum cascade emissions between biexciton and exciton PL.
We report photon correlation measurements that reveal unique signatures of biexciton and charged exciton emissions in a single self-assembled InAs quantum dot. Biexciton emission exhibits both bunching and antibunching under continuous-wave excitation and only antibunching under pulsed excitation. Cross correlation between biexciton and single-exciton emissions reveals highly asymmetric features due to cascaded emission. Under our excitation conditions, no polarization correlations between the exciton and biexciton emissions were observed.
Summary form only given. A realization of time-bin entanglement obtained from quantum dots would join the strength of long distance transmission that characterizes this type of entanglement with the single photon state purity of the quantum dot emission. Compared with polarization entanglement from quantum dots this scheme does not require elimination of the fine structure splitting responsible for partial distinguishability of the quantum dot cascades [1].Here, we present our results on coherent and resonant excitation of quantum dots, creation of photon pairs, scattering free emission and measurement of the high purity of the emitted photons [2, 3]. In addition, we will show our measurements of the generated time-bin entanglement. To excite a single quantum dot we performed two-photon resonant excitation of the biexciton state. Here, we exploited the biexciton binding energy in order to use the laser light which was not resonant to any photon emitted from the quantum dot (Fig. 1a). Our measurements were performed on a single self-assembled InAs/GaAs quantum dot. We confirmed the resonant nature of the excitation by observing Rabi oscillations (Fig. 1b). Additionally, we performed Ramsey interference measurement and determined the coherence time of the ground-biexciton state superposition. These measurements show that we can coherently transfer the phase of the excitation laser onto the quantum dot system, a necessary requirement to obtain time-bin entanglement.To test the statistics of the emitted state we measured the auto-correlation of the emitted photons (Fig. 3c). Here, the auto-correlation parameter at zero delay was measured to be 0.012(1) without and 0.0073(8) with background subtraction. In addition, we performed a measurement to characterize the state emitted from a quantum dot using a witness-based criterion described in [4]. With this measurement we experimentally confirmed that the resonantly excited quantum dot emits a non-Gaussian state of light (Fig. 1d). This measurement is the first of this nature ever performed on a semiconductor single photon emitter.
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.