N. Somaschi, V. Giesz, L. De Santis, J. C. Loredo, M. P. Almeida, G. Hornecker, S. L. Portalupi, T. Grange, C. Antón, J. Demory, C. Gómez, I. Sagnes, N. D. Lanzillotti-Kimura, A. Lemaítre, A. Auffeves, A. G. White, L. Lanco & P. Senellart.
The scaling of optical quantum technologies requires efficient, on-demand sources of highly indistinguishable single photons. We had demonstrated in 2013 that semiconductor quantum dots inserted into photonic structures were ultrabright single-photon sources, yet the indistinguishability wass limited by charge noise. Parametric downconversion sources provide highly indistinguishable photons but are operated at very low brightness to maintain high single-photon purity.
Until this work, no technology had provided a bright source generating near-unity indistinguishability and pure single photons. We have fabricated 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.
Figure: 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: Photoluminescence map of a connected device: the bright emission at the centre of the device arises from the deterministically coupled QD. 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). 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).
Figure: Comparison of state-of-the-art QD-based single-photon sources prior to our work (blue symbols, the corresponding reference is indicated in the label), high-quality SPDC heralded single-photon sources (grey symbols) and the devices reported in our Nature Photonics 2016 (red symbols).