One of the critical outcomes of the project is the demonstration of a world-record single-photon source, which also resulted in a patent. We used a quantum dot in the microcavity system to generate single photons. By optimizing different parts of the setup and carefully engineering an excitation method, we managed to generate single-photons states with record efficiency and coherence [1]. We achieved an end efficiency of 57%, which is 2.3 better than the prior state-of-the-art. To put it into context, our source outperforms other sources by seven orders of magnitude in a 20 photon experiment. These results have been published in Nature Nanotechnology. Figure 1 shows the comparison between the performance of our source and the other candidates.
As a new research direction, we investigated the chiral quantum optics with a quantum dot in the microcavity. We managed to realize a single-photon diode where a single quantum dot allows the propagation of photons in one direction while blocking their propagation in the opposite direction [2]. We achieved an isolation of 10 dB in our diode. We also showed that the propagation of photons in our diode is highly nonlinear; the diode can block single photons while it allows two-photon states to pass through. From the classical point of view, the diode showed an on-set of nonlinearity at 200 pW. From the quantum point of view, the transmitted photons show an autocorrelation function that is strongly bunched, a factor of 100 times compared to a laser field. These results have been accepted for publication in npj Quantum.
Recently, we investigated the quantum characteristics of GaAs quantum dots and showed that GaAs quantum dots could be made nearly noise-free [3]. We also measured the indistinguishability of photons generated from two independent GaAs quantum dots and observed two-photon interference visibility of 93%. This level of quantum interference requires that all the properties of the two quantum dots are identical and stable over the course of the measurement, around 4 hours. Such interference visibility is significantly better than the earlier reports on solid-state quantum emitters and matches the performance of single-photon sources based on ions and parametric down-conversion. Two-photon interference is at the heart of most of the proposals for photonic information processing, and our demonstration opens true prospects for photonic chips with multiple single-photon sources.
[1] N. Tomm, A. Javadi, N. Antoniadis, N. Najer, M. C. Lӧbl, A. R. Korsch, R. Schott, S. R. Valantin, A. D. Wieck, A. Ludwig, R. J. Warburton, "A Bright Source of Coherent Single Photons", Nature Nanotechnology 16, 399 (2021).
[4] N. O. Antoniadis, N. Tomm, T. Jakubczyk, R. Schott, S. R. Valentin, A. D. Wieck, A. Ludwig, R. J. Warburton, A. Javadi, "A chiral one-dimensional atom using a quantum dot in an open microcavity", npj Quantum Information 8, 27 (2022).
