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arXiv:2207.02035 · Applied Physics Letters

Near-unity efficiency and photon indistinguishability for the “hourglass” single-photon source using suppression of the background emission

Benedek Gaál, Martin Arentoft Jacobsen, Luca Vannucci, Julien Claudon, Jean‐Michel Gérard, Niels Gregersen

Published Oct 24, 2022• 10 citations
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Abstract

An on-going challenge within scalable optical quantum information processing is to increase the collection efficiency ε and the photon indistinguishability η of the single-photon source toward unity. Within quantum dot-based sources, the prospect of increasing the product εη arbitrarily close to unity was recently questioned. In this work, we discuss the influence of the trade-off between efficiency and indistinguishability in the presence of phonon-induced decoherence, and we show that the photonic “hourglass” design allows for improving εη beyond the predicted maximum for the standard micropillar design subject to this trade-off. This circumvention of the trade-off is possible thanks to control of the spontaneous emission into background radiation modes, and our work highlights the importance of engineering of the background emission in future pursuits of near-unity performance of quantum dot single-photon sources.

DOI
10.1063/5.0107624

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An on-going challenge within scalable optical quantum information processing is to increase the collection efficiency ε and the photon indistinguishability η of the single-photon source toward unity. Within quantum dot-based sources, the prospect of increasing the product εη arbitrarily close to unity was recently questioned. In this work, we discuss the influence of the trade-off between efficiency and indistinguishability in the presence of phonon-induced decoherence, and we show that the photonic “hourglass” design allows for improving εη beyond the predicted maximum for the standard micropillar design subject to this trade-off. This circumvention of the trade-off is possible thanks to control of the spontaneous emission into background radiation modes, and our work highlights the importance of engineering of the background emission in future pursuits of near-unity performance of quantum dot single-photon sources.
Single-photon sources with near-unity efficiency and indistinguishability play a major role in the development of quantum technologies. However, on-demand excitation of the emitter imposes substantial limitations to the source performance. Here, we show that coherent two-color pumping allows for population inversion arbitrarily close to unity in bulk quantum dots thanks to a decoupling effect between the emitter and its phonon bath. Driving a micropillar single-photon source with this scheme, we calculate very high photon emission into the cavity mode (0.95 photons per pulse) together with excellent indistinguishability (0.975) in a realistic configuration, thereby removing the limitations imposed by the excitation scheme on single-photon source engineering.
We present a numerical investigation of the performance of the micropillar cavity single-photon source in terms of collection efficiency and indistinguishability of the emitted photons in the presence of non-Markovian phonon-induced decoherence. We analyze the physics governing the efficiency using a single-mode model, and we optimize efficiency $\ensuremath{\varepsilon}$ and the indistinguishability $\ensuremath{\eta}$ on an equal footing by computing $\ensuremath{\varepsilon}\ensuremath{\eta}$ as function of the micropillar design parameters. We show that $\ensuremath{\varepsilon}\ensuremath{\eta}$ is limited to $\ensuremath{\sim}0.96$ for the ideal geometry due to an inherent tradeoff between efficiency and indistinguishability. Finally, we subsequently consider the influence of realistic fabrication imperfections and Markovian pure dephasing noise on the performance.
The key challenge to scalable optical quantum computing, boson sampling, and quantum metrology is sources of single photons with near-unity system efficiency and simultaneously near-perfect indistinguishability in all degrees of freedom (including spectral, temporal, spatial, and polarization). However, previous high-indistinguishability solid-state single-photon sources had to rely on polarization filtering that reduced the system efficiency by at least 50%. Here, we overcome this challenge by developing a new single-photon source based on a coherently driven quantum dot embedded in an elliptical micropillar. The asymmetric cavity lifts the polarization degeneracy into two orthogonal linearly polarized modes with a suitable energy separation. We design an excitation-collection scheme that allows the creation and collection of single photons with an indistinguishability of 0.976(1) and a degree of polarization of 91%. Our method provides a solution of combining near-unity system efficiency and indistinguishability compatible with background-free resonant excitation, and opens the way to truly optimal single-photon sources for scalable photonic quantum technologies.
An optimal single-photon source should deterministically deliver one, and only one, photon at a time, with no trade-off between the source's efficiency and the photon indistinguishability. However, all reported solid-state sources of indistinguishable single photons had to rely on polarization filtering, which reduced the efficiency by 50%, fundamentally limiting the scaling of photonic quantum technologies. Here, we overcome this long-standing challenge by coherently driving quantum dots deterministically coupled to polarization-selective Purcell microcavities. We present two examples: narrowband, elliptical micropillars and broadband, elliptical Bragg gratings. A polarization-orthogonal excitation–collection scheme is designed to minimize the polarization filtering loss under resonant excitation. We demonstrate a polarized single-photon efficiency of 0.60 ± 0.02 (0.56 ± 0.02), a single-photon purity of 0.975 ± 0.005 (0.991 ± 0.003) and an indistinguishability of 0.975 ± 0.006 (0.951 ± 0.005) for the micropillar (Bragg grating) device. Our work provides promising solutions for truly optimal single-photon sources combining near-unity indistinguishability and near-unity system efficiency simultaneously. Single-photon sources with a single-photon efficiency of 0.60, a single-photon purity of 0.975 and an indistinguishability of 0.975 are demonstrated. This is achieved by fabricating elliptical resonators around site-registered quantum dots.
Semiconductor quantum dots (QDs) coupled with optical microcavities provide an excellent platform for generating high-performance single-photon sources. However, the current microcavity structures are difficult to solve the tradeoff between single-photon purity and indistinguishability without additional filtering, due to challenges in suppressing broad phonon sideband spectrum and two-photon emission in the practical experiments. To address these issues, we have developed a novel asymmetric microcavity that supports two nondegenerate polarized modes, both resonant with a single quantum dot. One cavity mode is broadband and is used for excitation to reduce two-photon emission intensity, while the other is narrowband and is used for collection to enhance the indistinguishability of single-photon sources. This asymmetric microcavity also has the ability to overcome at least half of the photon efficiency loss under polarization filtering. Moreover, our model has employed an excitation pulse that resonates with cavity modes eliminating spectral distortion of intracavity fields, and efficiently achieving deterministic population inversion of QDs compared to an elliptical cavity. Our scheme paves the way to develop the excellent performance single-photon sources with higher brightness, near-unity purity, and indistinguishability without any additional filtering in practical experiments.