Developing a bright, deterministic source of entangled photon pairs has been an outstanding scientific and technological challenge. Semiconductor quantum dots are a promising candidate for this task. A new device combining a circular Bragg resonator and a piezoelectric actuator achieves high brightness and entanglement fidelity simultaneously, overcoming previous limitations. This breakthrough enhances quantum dot applications in entanglement-based quantum communication protocols.
Developing a bright, deterministic source of entangled photon pairs has been an outstanding scientific and technological challenge. Semiconductor quantum dots are a promising candidate for this task. A new device combining a circular Bragg resonator and a piezoelectric actuator achieves high brightness and entanglement fidelity simultaneously, overcoming previous limitations. This breakthrough enhances quantum dot applications in entanglement-based quantum communication protocols.
A quantum-light source that delivers photons with a high brightness and a high degree of entanglement is fundamental for the development of efficient entanglement-based quantum-key distribution systems. Among all possible candidates, epitaxial quantum dots are currently emerging as one of the brightest sources of highly entangled photons. However, the optimization of both brightness and entanglement currently requires different technologies that are difficult to combine in a scalable manner. In this work, we overcome this challenge by developing a novel device consisting of a quantum dot embedded in a circular Bragg resonator, in turn, integrated onto a micromachined piezoelectric actuator. The resonator engineers the light-matter interaction to empower extraction efficiencies up to 0.69(4). Simultaneously, the actuator manipulates strain fields that tune the quantum dot for the generation of entangled photons with corrected fidelities to a maximally entangled state up to 0.96(1). This hybrid technology has the potential to overcome the limitations of the key rates that plague QD-based entangled sources for entanglement-based quantum key distribution and entanglement-based quantum networks. Supplementary Information: The online version contains supplementary material available at 10.1186/s43593-024-00072-8.
Entanglement between particles is a crucial resource in quantum information processing, an important example of which is the exploitation of entangled photons in quantum communication protocols. Among the different available sources of entangled photons, semiconductor quantum dots (QDs) excel owing to their deterministic emission properties, potential for electrical injections, and direct compatibility with semiconductor manufacturing techniques. Despite the great promises, QD-based sources are far from being ideal. In particular, such sources present several critical issues, which require the overcoming of challenges pertaining to spectral tunability, entanglement fidelity, photon indistinguishability and brightness. In this article, we will discuss the potential solutions to these problems and review the recent progress in the field.
An outstanding goal in quantum optics and scalable photonic quantum technology is to develop a source that each time emits one and only one entangled photon pair with simultaneously high entanglement fidelity, extraction efficiency, and photon indistinguishability. By coherent two-photon excitation of a single InGaAs quantum dot coupled to a circular Bragg grating bull's-eye cavity with a broadband high Purcell factor of up to 11.3, we generate entangled photon pairs with a state fidelity of 0.90(1), pair generation rate of 0.59(1), pair extraction efficiency of 0.62(6), and photon indistinguishability of 0.90(1) simultaneously. Our work will open up many applications in high-efficiency multiphoton experiments and solid-state quantum repeaters.
Semiconductor quantum dots (QDs) have emerged as a premier solid-state platform for the deterministic generation of nonclassical light, offering a compelling pathway toward scalable quantum photonic systems. While single-photon emission from QDs has reached a high level of maturity, the realization of high-fidelity entangled photon-pair sources remains an active and rapidly evolving frontier. In this review, we survey the recent progress in QD-based entangled photon sources, highlighting the conceptual evolution from the established biexciton-exciton cascade to the emerging paradigm of spontaneous two-photon emission. We further examine how advances in nanophotonic architectures and coherent control strategies are redefining fundamental performance limits, enabling concurrent improvements in source brightness, coherence, and entanglement fidelity. Finally, we discuss the key physical and technological challenges that must be addressed to bridge the gap between laboratory demonstrations and large-scale deployment. We conclude by outlining the future opportunities for integrating QD-based entangled photon sources into practical quantum communication, computation, and sensing platforms.
Semiconductor quantum dots (QDs) have emerged as a premier solid-state platform for the deterministic generation of nonclassical light, offering a compelling pathway toward scalable quantum photonic systems. While single-photon emission from QDs has reached a high level of maturity, the realization of high-fidelity entangled photon-pair sources remains an active and rapidly evolving frontier. In this review, we survey the recent progress in QD-based entangled photon sources, highlighting the conceptual evolution from the established biexciton–exciton cascade to the emerging paradigm of spontaneous two-photon emission. We further examine how advances in nanophotonic architectures and coherent control strategies are redefining fundamental performance limits, enabling concurrent improvements in source brightness, coherence, and entanglement fidelity. Finally, we discuss the key physical and technological challenges that must be addressed to bridge the gap between laboratory demonstrations and large-scale deployment. We conclude by outlining the future opportunities for integrating QD-based entangled photon sources into practical quantum communication, computation, and sensing platforms.
Quantum technology promises to revolutionize various aspects of information processing, communication, and data security, by surpassing the capabilities of classical systems. Central to these advancements are photons, due to their resilience to external influence and ease of transport in air and glass fibers. However, attenuation in glass fiber cores hinders the realization of a worldwide quantum network. To circumvent this limit, the use of quantum repeaters for long-distance communication is required. Pivotal to the realization of quantum repeaters are entangled photons, enabling the distribution of entanglement across intermediate nodes, eventually extending the range of the envisioned quantum network. Despite the availability of numerous photon sources, stringent requirements–such as deterministic photon generation with high purity, high indistinguishability, high efficiency and a high degree of entanglement–hinder the realization of quantum repeaters, as they need to be fulfilled within the same device. Epitaxial quantum dots have emerged as promising candidates for generating pairs of entangled photons with a high purity and a high degree of entanglement. These semiconductor nanostructures, often referred to as “artificial atoms,” confine charge carriers and discretize energy levels like atoms but in a manipulable solid state environment. They exhibit exceptional emission characteristics owing to their high quantum efficiency and tunability via external fields such as electric, magnetic, and strain fields. Nevertheless, the fact that they are embedded in a semiconductor matrix with high refractive index limits their brightness due to challenging light extraction. This PhD thesis investigates the potential of strain-tuned GaAs droplet-etched quantum dots–a system known to generate highly entangled photon pairs–embedded within a photonic cavity, aiming to enhance light extraction efficiency, for an ideal entangled photon source. Device fabrication involves bonding the semiconductor with a micromachined piezoelectric substrate for strain-tuning quantum dots and their deterministic integration with a circular Bragg grating resonator, known as a “bullseye cavity.” Key advancements include cryogenic photoluminescence imaging for precise quantum dot localization, achieving high spatial overlap of the confined excitons with the resonator’s mode volume. Furthermore, postfabrication tuning of the resonator mode via wet chemical etching is employed to optimize spectral overlap. The achievements enable significant Purcell enhancement and high extraction efficiency. Simultaneously, multi-axial strain tuning the quantum dot emission eliminates entanglement degradation caused by the anisotropic exchange interaction of charge carriers. Such an entangled photon source additionally allows to experimentally reveal the limits of entanglement set by the excitation type. Finally, with optimized excitation conditions, a near-ideal entangled photon pair source is realized, which may surpass any other quantum emitter in terms of simultaneous brightness and degree of entanglement. The advancements presented within this PhD thesis represent a significant step towards the integration of quantum dot-based entangled photon sources into real-world quantum technology applications, facilitating the realization of a quantum internet.