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arXiv:2608.28353

Crystal-phase quantum dots in AlGaAs nanowires

Rohan Radhakrishnan, Rodion Reznik, Gilles Patriarche, Lorenzo Leandro, Igor Ilkiv, Anna Andreeva, Artem Khrebtov, George Cirlin, Nika Akopian

cond-mat.mes-hallphysics.opticsquant-phSubmitted Aug 28, 2026• Announced Aug 31, 2026
arXivHTMLPDF

Abstract

Crystal-phase quantum dots (CPQDs)$\unicode{x2014}$quantum dots in nanowires defined by crystal structure rather than material composition$\unicode{x2014}$constitute the only platform capable of fabricating quantum-dot arrays with the ultimate precision of a single atomic layer. This intrinsic control yields perfectly aligned quantum dots with atomically sharp interfaces, providing a unique pathway toward scalable quantum-dot-based photonic quantum technologies. To date, CPQDs have been studied primarily in binary semiconductors, such as InP and GaAs, where their emission linewidths are typically in the meV range, thereby limiting their technological potential. Here, we report, for the first time, CPQDs in AlGaAs nanowires and show bright single-photon emission with linewidths as narrow as 61 $μeV$ and low background emission, demonstrating optical quality well beyond typical CPQDs. We attribute this performance to a type-I band alignment, as suggested by an exciton lifetime of 1 ns, significantly shorter than that typically observed in type-II CPQDs. Additionally, we observe an exciton fine-structure splitting and a Zeeman splitting, as commonly observed in standard type-I self-assembled quantum dots.

Comments
Main text: 18 pages, 4 figures / Supplementary Materials: 8 pages, 3 figures

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Crystal-phase quantum dots (CPQDs)\unicodex2014\unicode{x2014}\unicodex2014quantum dots in nanowires defined by crystal structure rather than material composition\unicodex2014\unicode{x2014}\unicodex2014constitute the only platform capable of fabricating quantum-dot arrays with the ultimate precision of a single atomic layer. This intrinsic control yields perfectly aligned quantum dots with atomically sharp interfaces, providing a unique pathway toward scalable quantum-dot-based photonic quantum technologies. To date, CPQDs have been studied primarily in binary semiconductors, such as InP and GaAs, where their emission linewidths are typically in the meV range, thereby limiting their technological potential. Here, we report, for the first time, CPQDs in AlGaAs nanowires and show bright single-photon emission with linewidths as narrow as 61 μeVμeVμeV and low background emission, demonstrating optical quality well beyond typical CPQDs. We attribute this performance to a type-I band alignment, as suggested by an exciton lifetime of 1 ns, significantly shorter than that typically observed in type-II CPQDs. Additionally, we observe an exciton fine-structure splitting and a Zeeman splitting, as commonly observed in standard type-I self-assembled quantum dots.
Optical quantum dots (QDs) are central to photonic quantum technologies, with fabrication approaches tailored to different spectral ranges. A key challenge, however, is the realization of a unified platform$\unicode{x2014}$a single growth method combined with a host material offering a designable architecture$\unicode{x2014}$enabling wavelength tunability across the full emission range and co-integration of multiple quantum dots. Here, we introduce AlGaAs nanowires as a universal host for GaAs, InGaAs, and InAs QDs. Building on our previous demonstration of high-quality GaAs QDs, we realize InGaAs QDs with tunable emission by varying the growth duration from 2 to 5 s, achieving emission at 780 and 920 nm. We further showcase the platform's versatility for multi-quantum-dot devices by co-integrating two InGaAs QDs, as well as GaAs and InGaAs QDs within a single nanowire. Finally, we initiate a first step toward pure InAs QDs by growing a pristine InAs segment on AlGaAs nanowires, demonstrating material compatibility.
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Nanowires offer new opportunities for nanoscale and integrated quantum optics; the quantum dot geometry in semiconducting nanowires as well as the material composition and environment can be engineered with unprecedented freedom to improve the light extraction efficiency. Quantum dots in nanowires are shown to be efficient single photon sources, in addition because of the very small fine structure splitting, we demonstrate the generation of entangled pairs of photons from a nanowire and discuss the limits to entanglement fidelity. Another type of nanowire under study in our group is superconducting nanowires for single photon detection, reaching efficiencies, time resolution and dark counts beyond currently available detectors. We will discuss our first attempts at combining semiconducting nanowire based single photon emitters and superconducting nanowire single photon detectors on a chip to realize integrated quantum circuits.
Epitaxial quantum dots (QDs) are widely recognised as one of the best quantum light sources, given their good stability, brightness, quantum efficiency and coherence. To reach such properties, QDs are protected from potentially detrimental surface states by a relatively thick capping layer, typically exceeding 50nm. This prevents the implementation of near-field effects, like plasmonic-based ones, that can dramatically increase the light-matter interaction, since the control of the spontaneous emission dynamics and directionality of the emission can only occur if the emitter is in close proximity (typically tens of nanometers or less) from the metallic structures. In this work, we report the growth and optical characterisation of InAs/GaAs QDs with GaAs capping layer thickness of 10nm, 20nm, and a more standard 95nm. Remarkably, we observe emission linewidths up to 5 times smaller than previously reported, with unperturbed excitonic lifetimes. These results demonstrate that the epitaxial QD's high optical quality can be maintained even when the emitters are at reduced distances from the surface, opening the path for the exploration of near-field light-matter interactions with coherent and stable emitters, suitable for quantum technology applications.
The development of quantum materials for single-photon emission is crucial for the advancement of quantum information technology. Although significant advancement has been witnessed in recent years for single photon sources in near infrared band (λ~700-1000 nm), several challenges have yet to be addressed for ideal single photon emission at the telecommunication band. In this study, we present a droplet-epitaxy strategy for O-band to C-band single-photon source based semiconductor quantum dots (QDs) using metal-organic vapor-phase epitaxy (MOVPE). Via investigating the growth conditions of the epitaxial process, we have successfully synthesized InAs/InP QDs with narrow emission lines spanning a broad spectral range of λ~1200-1600 nm. The morphological and optical properties of the samples were characterized using atomic force microscopy and micro photoluminescence spectroscopy. The recorded single-photon purity of a plain QD structure reaches (g(2)(0) = 0.16), with a radiative recombination lifetime as short as 1.5 ns. This work provides a crucial platform for future research on integrated microcavity enhancement techniques and coupled QDs with other quantum photonics in the telecom bands, offering significant prospects for quantum network applications.
High Resolution Image Download MS PowerPoint Slide Entangled photon pairs at telecom wavelengths are essential for quantum communication, distributed computing, and quantum-enhanced sensing. The telecom O-band offers low chromatic dispersion and fiber loss, which is ideal for long-distance networks. Site-controlled nanowire quantum dots have emerged as a promising platform for generating single and entangled photons, offering high extraction efficiency and scalability. However, their operation has largely been restricted to the visible and first near-infrared (NIR-I) windows. Here, we demonstrate a bright source of entangled photon pairs in the telecom O-band based on site-controlled nanowire quantum dots. We measure a fine-structure splitting of 4.6 μeV, confirming suitability for high-fidelity polarization entanglement. Quantum-state tomography of the biexciton–exciton cascade reveals a maximum fidelity of 85.8 ± 1.1% to the Φ + Bell state and a maximum concurrence of 75.1 ± 2.1%. This work establishes nanowire quantum dots as viable entangled photon sources at telecom, advancing scalable quantum technologies for fiber-based networks.