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arXiv · 2601.00966

Four-Photon Interference with a High-Efficiency Quantum Dot Source

Alistair J. Brash·Luke Brunswick·Mark R. Hogg·Catherine L. Phillips·Malwina A. Marczak·Timon L. Baltisberger·Sascha R. Valentin·Arne Ludwig·Richard J. Warburton
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Abstract

While two-photon Hong-Ou-Mandel interference visibility has become a standard metric for single-photon sources, many optical quantum technologies require the generation and manipulation of larger photonic states. To date, efficiency limitations have prevented scaling quantum dot-based interference to the coalescence of more than two photons at a single beamsplitter. We overcome this limitation by combining a state-of-the-art quantum dot source with deterministic demultiplexing, enabling the direct observation of quantum interference fringes arising from up to four photons. We measure high mean interference contrasts of $93.0 \pm 0.1~\%$ for two photons, and $84.1 \pm 1.0~\%$ for four photons, with the complex fringe structure fully reproduced by a theoretical model. These results reveal the existence of "deep fringes" whose minima are unaffected by distinguishable photons, rendering the maximum contrast of four-photon interference highly sensitive to multi-photon emission but robust against photon distinguishability. We predict that these phenomena will extend to interference of larger numbers of photons, with relevance across a range of potential optical quantum technologies. A Fisher information analysis demonstrates that interference fringes from our source can exhibit phase sensitivity beyond the standard quantum limit, illustrating potential applications in quantum metrology.

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Alistair J. Brash, Luke Brunswick, Mark R. Hogg, Catherine L. Phillips, Malwina A. Marczak, Timon L. Baltisberger, Sascha R. Valentin, Arne Ludwig, Richard J. Warburton. 2026-01-02. Four-Photon Interference with a High-Efficiency Quantum Dot Source. https://arxiv.org/abs/2601.00966

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