On-demand generation of indistinguishable polarization-entangled photon pairs

Journal name:
Nature Photonics
Year published:
Published online


An on-demand source of indistinguishable and entangled photon pairs is a fundamental component of various quantum information applications, including optical quantum computing, quantum repeaters, quantum teleportation and quantum communication1. Parametric downconversion2, 3 and four-wave mixing sources4 of entangled photons have shown high degrees of entanglement and indistinguishability, but the probabilistic nature of their generation process also creates zero or multiple photon pairs following a Poissonian distribution. This limits their use in complex algorithms where many qubits and gate operations are required. Here, we simultaneously show ultrahigh purity (g(2)(0) < 0.004), high entanglement fidelity (0.81 ± 0.02), high two-photon interference non-post selective visibilities (0.86 ± 0.03 and 0.71 ± 0.04) and on-demand generation (efficiency εpair = 0.86 ± 0.08) of polarization-entangled photon pairs from a single semiconductor quantum dot. Through a two-photon resonant excitation scheme, the biexciton population is deterministically prepared by a π-pulse (εbiexciton = 0.98 ± 0.07). Applied on a quantum dot showing no exciton fine-structure splitting, this results in the deterministic generation of indistinguishable entangled photon pairs.

At a glance


  1. Two-photon biexciton excitation scheme for a quantum dot exhibiting no excitonic fine-structure splitting.
    Figure 1: Two-photon biexciton excitation scheme for a quantum dot exhibiting no excitonic fine-structure splitting.

    a, A shaped laser is brought to resonance with the virtual biexciton TPE state, the energy of which lies between the exciton and biexciton emission lines. Two radiative recombination paths are possible to the ground state |0right fence via one of two bright exciton states |Xright fence. The polarizations of the two photons are determined by the intermediate exciton state. b, Above-GaAs-bandgap excitation spectrum. The presence of the trion is due to charge capture in the quantum dot. c, Emission spectrum under biexciton direct TPE. Only the exciton and biexciton can be observed, with the same intensities. No trion line is observed. This confirms that excitonic and biexcitonic photons are always emitted as pairs and that the exciton population cannot be transferred to the trion state by capture of charge before the radiative cascade is over. It is worth noting that the generation efficiency of the biexciton increases by a factor of ~4 from non-resonant (in saturation) to resonant excitation (see Supplementary Section 4). The large peak between the exciton and biexciton emission lines is due to some residual scattered laser light.

  2. Autocorrelation histograms, under resonant excitation.
    Figure 2: Autocorrelation histograms, under resonant excitation.

    a, Excitonic photons. b, Biexcitonic photons. Both sets of data are acquired with the biexciton being resonantly excited with π-pulses. The data are presented without correction. The raw antibunching values were measured as gX(2) (0)= 0.022 ± 0.018 and gXX(2) (0) = 0.021 ± 0.018, and after correction for APD dark count contribution, they were gX(2) (0) = 0.004 ± 0.018 and gXX(2) (0)= 0.003 ± 0.018.

  3. Integrated intensities, under resonant excitation.
    Figure 3: Integrated intensities, under resonant excitation.

    a,b, Integrated intensities for the biexcitonic emission line (a) and the excitonic emission line (b) versus the square root of the pump power (proportional to the excitation pulse area). The abscissa is renormalized in π-units such that the first biexciton intensity maximum, which corresponds to the first rotation from |0right fence to |XXright fence in the Bloch sphere, is reached for a pulse area equal to π. In the Supplementary Section 4 we evaluate that, for a π-pulse, the |XXright fence is prepared with a fidelity of 0.98 ± 0.07 and that 0.86 ± 0.08 of the excitation pulses generate a photon pair.

  4. Biexciton-exciton polarization-dependent cross-correlation histograms under resonant excitation.
    Figure 4: Biexciton–exciton polarization-dependent cross-correlation histograms under resonant excitation.

    ac, Results for the linear basis (a), the diagonal basis (b) and the circular basis (c). An antibunching is observed when the biexcitonic and excitonic photons are projected in orthogonal polarizations in the linear and diagonal bases. A bunching is observed for parallel polarizations. In the circular basis, the opposite is observed. The relative areas of the zero delay peaks from these six histograms are used to derive the cross-polarization contrasts. For clarity, data corresponding to orthogonal polarization configurations are time-shifted.

  5. Two-photon interference histograms, obtained under resonant excitation.
    Figure 5: Two-photon interference histograms, obtained under resonant excitation.

    a,b, Results for excitonic photons (a) and biexcitonic photons (b). On both graphs, the coloured plots correspond to the two-photon interference pattern of the parallel-polarized single photons and the grey graphs correspond to the two-photon interference of cross-polarized single photons. When photons arrive at the beamsplitter in parallel polarization (that is, they are indistinguishable), the central peak is strongly suppressed. The grey histograms are used to quantify the central peak suppression and to extract the visibilities of the two-photon interference. Side peaks were also used for cross-checking the extracted values. They were evaluated to 0.86 ± 0.03 for XX and 0.71 ± 0.04 for X after dark count and set-up imperfection corrections.


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Author information

  1. These authors contributed equally to this work

    • M. Müller &
    • S. Bounouar


  1. Institut für Halbleiteroptik und Funktionelle Grenzflächen, Universität Stuttgart, Allmandring 3, 70569 Stuttgart, Germany

    • M. Müller,
    • S. Bounouar,
    • K. D. Jöns &
    • P. Michler
  2. Institut für Theoretische Physik III, Universität Bayreuth, Universitätsstraße 30, 95440 Bayreuth, Germany

    • M. Glässl


M.M., S.B., K.D.J. and P.M. conceived and designed the experiments. M.M., S.B. and K.D.J. performed the experiments. M.M. and S.B. analysed the data. M.G. carried out the theoretical calculations. S.B. and P.M. wrote the manuscript with input from the other authors.

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