Near-optimal single-photon sources in the solid state

Journal name:
Nature Photonics
Year published:
Published online


The scaling of optical quantum technologies requires efficient, on-demand sources of highly indistinguishable single photons. Semiconductor quantum dots inserted into photonic structures are ultrabright single-photon sources, yet the indistinguishability is limited by charge noise. Parametric downconversion sources provide highly indistinguishable photons but are operated at very low brightness to maintain high single-photon purity. To date, no technology has provided a bright source generating near-unity indistinguishability and pure single photons. Here, we report such devices made of quantum dots in electrically controlled cavities. Application of an electrical bias on the deterministically fabricated structures is shown to strongly reduce charge noise. Under resonant excitation, an indistinguishability of 0.9956 ± 0.0045 is demonstrated with g(2)(0) = 0.0028 ± 0.0012. The photon extraction of 65% and measured brightness of 0.154 ± 0.015 make this source 20 times brighter than any source of equal quality. This new generation of sources opens the way to new levels of complexity and scalability in optical quantum technologies.

At a glance


  1. Electrically controlled single-photon sources.
    Figure 1: Electrically controlled single-photon sources.

    a, Schematic of the devices under study: a micropillar coupled to a QD is connected to a surrounding circular frame by four one-dimensional wires. The top p-contact is defined on a large mesa adjacent to the frame. The n-contact is deposited on the back of the sample. b, Optical microscope image showing 18 connected pillar sources electrically controlled through the metallic contact defined on the 300 × 300 µm2 diode. c, Photoluminescence map of a connected device: the bright emission at the centre of the device arises from the deterministically coupled QD. d, Emission intensity as a function of bias and energy, showing the Stark tuning of the exciton transition (X) within the cavity mode (CM) resonance (dashed line).

  2. Characteristics of single-photon source QD1 under non-resonant excitation.
    Figure 2: Characteristics of single-photon source QD1 under non-resonant excitation.

    a, Second-order autocorrelation histogram of device QD1 at 2.45Psat showing pure single-photon emission with g(2)(0) = 0.024 ± 0.007. b, Correlation histogram measuring the indistinguishability of photons successively emitted by QD1 (with an acquisition time of 8 min). c, Summary of the source properties as a function of excitation power: from top to bottom: purity (g(2)(0)); indistinguishability (M); and brightness (collected photons per pulse). Error bars are deduced from assuming Poissonian statistics in detected events.

  3. Characteristics of single-photon source QD3 under resonant excitation.
    Figure 3: Characteristics of single-photon source QD3 under resonant excitation.

    a, Schematic of the cross-polarization excitation/detection set-up implemented for resonant fluorescence measurements and single-photon statistics analysis. Temporally shaped laser pulses are sent from the top of the pillars and focused using a microscope objective. The emission is collected through the same objective in a confocal geometry. A polarizing beamsplitter (PBS) and half-wave plate allows the separation of crossed polarized emission from the excitation. b, Second-order autocorrelation histogram of device QD3 at 0.75Pπ showing pure single-photon emission with g(2)(0) = 0.0028 ± 0.0012. c,d, Correlation histograms measuring the indistinguishability of photons successively emitted by the QD3. The photons are sent to the HOM beamsplitter with the same polarization (c) or orthogonal polarization (d). The acquisition time is 10 min for each curve. e, Summary of the source properties as a function of excitation power: from top to bottom: purity (g(2)(0)); indistinguishability (M); and brightness (collected photons per pulse). Error bars are deduced from assuming Poissonian statistics in detected events.

  4. Comparison with other QD and SPDC single-photon sources.
    Figure 4: Comparison with other QD and SPDC single-photon sources.

    Comparison of state-of-the-art QD-based single-photon sources (blue symbols, the corresponding reference is indicated in the label), high-quality SPDC heralded single-photon sources (grey symbols) and the devices reported in the present work (red symbols). QD1 and QD2 correspond to the measurements under non-resonant excitation presented in Fig. 2 and Supplementary Fig. 2, respectively. QD3 and QD4 correspond to measurements under resonant excitation shown in Fig. 3 and Supplementary Fig. 1, respectively. See text for a detailed discussion.


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Author information

  1. These authors contributed equally to this work

    • N. Somaschi,
    • V. Giesz &
    • L. De Santis


  1. CNRS-LPN Laboratoire de Photonique et de Nanostructures, Université Paris-Saclay, Route de Nozay, 91460 Marcoussis, France

    • N. Somaschi,
    • V. Giesz,
    • L. De Santis,
    • S. L. Portalupi,
    • C. Antón,
    • J. Demory,
    • C. Gómez,
    • I. Sagnes,
    • N. D. Lanzillotti-Kimura,
    • A. Lemaítre,
    • L. Lanco &
    • P. Senellart
  2. Université Paris-Sud, Université Paris-Saclay, F-91405 Orsay, France

    • L. De Santis
  3. Centre for Engineered Quantum Systems, Centre for Quantum Computer and Communication Technology, School of Mathematics and Physics, University of Queensland, Brisbane, Queensland 4072, Australia

    • J. C. Loredo,
    • M. P. Almeida &
    • A. G. White
  4. Université Grenoble Alpes, F-38000 Grenoble, France

    • G. Hornecker,
    • T. Grange &
    • A. Auffeves
  5. CNRS, Institut Néel, ‘Nanophysique et Semiconducteurs’ Group, F-38000 Grenoble, France

    • G. Hornecker,
    • T. Grange &
    • A. Auffeves
  6. Département de Physique, Université Paris Diderot, 4 rue Elsa Morante, 75013 Paris, France

    • L. Lanco
  7. Département de Physique, Ecole Polytechnique, Université Paris-Saclay, F-91128 Palaiseau, France

    • P. Senellart


Optical measurements on the QD devices were conducted primarily by V.G., N.S. and L.d.S., with help from L.L., S.L.P. and P.S. The electrically controlled samples were fabricated by N.S. with help from C.A. The sample was grown by C.G. and A.L., and the etching was performed by I.S. The measurements on the SPDC sources and analysis of that data were conducted by J.C.L. and M.P.A, with help from A.G.W. Theoretical support for the experiment was provided by G.H., T.G. and A.A. The project was conducted by P.S. with help from L.L. All authors discussed the results and participated in manuscript preparation.

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