Quantum Optics
The development of many optical quantum technologies is dependent on the availability of solid-state single quantum emitters with near-perfect optical coherence. Light-emitting defects in diamond and quantum dots grown by molecular beam epitaxy have demonstrated transform-limited emission linewidths. However, they are limited in terms of production scalability and reproducibility between individual emitters. Utzat et al. now show that perovskite quantum dots can overcome these limitations and provide unprecedented versatility for the generation of indistinguishable single photons or entangled photon pairs for quantum information processing.
Science , this issue p. [1068][1]
[1]: /lookup/doi/10.1126/science.aau7392
Quantum Optics
The development of many optical quantum technologies is dependent on the availability of solid-state single quantum emitters with near-perfect optical coherence. Light-emitting defects in diamond and quantum dots grown by molecular beam epitaxy have demonstrated transform-limited emission linewidths. However, they are limited in terms of production scalability and reproducibility between individual emitters. Utzat et al. now show that perovskite quantum dots can overcome these limitations and provide unprecedented versatility for the generation of indistinguishable single photons or entangled photon pairs for quantum information processing.
Metal-halide perovskite nanocrystals (PNCs) have emerged as leading candidates for next-generation quantum emitters, offering a unique combination of high photoluminescence quantum yield, tunable emission, short radiative lifetimes, and record-high single-photon purity under ambient conditions. These properties, together with low-cost and scalable solution-phase fabrication, position PNCs as attractive alternatives to traditional epitaxial and colloidal quantum dots. In this Review, we outline the physical parameters that define quantum emission in PNCs, compare their performance to other established and emerging quantum emitters, and assess the key figures of merit, including photostability, single-photon purity, and photon indistinguishability, required for practical quantum applications. We discuss underlying mechanisms affecting PNC emission behavior and highlight recent advances in improving their quantum emitting properties through synthetic and photonic engineering approaches. While challenges related to environmental stability and photon indistinguishability remain, emerging strategies, such as surface passivation, metal ion doping, and coupling with electromagnetic nano- and micro-cavities, are steadily closing the gap between PNCs and ideal quantum light sources.
Quantum emitters serve as essential on-demand photonic resources, generating quantum states of light such as single photons and entangled photon pairs while serving as interfaces between light and matter. Buried in the solid state, quantum emitters enable a straightforward adoption of advanced nanofabrication techniques, facilitating precise engineering of their photonic environment for scalable quantum technologies. In this review, we introduce the fundamentals of quantum emitters and the key metrics characterising their performance. We highlight three material platforms: quantum dots, defect centres in diamond, and defect centres in silicon carbide. We summarise the recent developments of these platforms and discuss their advancements in quantum applications, including quantum communication, computation, and sensing. Finally, we provide a comparison across the three platforms, along with an outlook on future directions and potential challenges.
For the past fifteen years, single semiconductor quantum dots, often referred to as solid-state artificial atoms, have been at the forefront of various research direction lines for experimental quantum information science, in particular in the development of practical sources of quantum states of light. Here we review the research to date, on the tailoring of the emission properties from single quantum dots producing single photons, indistinguishable single photons and entangled photon pairs. Finally, the progress and future prospects for applications of single dots in quantum information processing is considered.
Among different solid-state emitters of quantum light, epitaxial GaAs quantum dots (QDs) have recently emerged as nearly-ideal sources of triggered polarization entangled photon pairs [1]. This property, combined with the strongly suppressed probability of multiphoton emission under resonant excitation [2] has allowed the implementation of quantum teleportation using photons subsequently emitted by a single QD [3]. In this talk I will discuss the peculiar properties of GaAs QDs [4,5], their performance as emitters of both single and entangled photons, as well as possible methods to engineer their light emission characteristics [1,4] to meet the demanding requirements imposed by photonic quantum technologies. [1] D. Huber et al. Phys. Rev. Lett. 121, 033902 (2018). [2] L. Schweickert et al. Appl. Phys. Lett. 112, 093106 (2018). [3] M. Reindl et al. Science Adv. (2018). [4] X. Yuan et al. Nat. Comm. 9, 3058 (2018). [5] M. Reindl et al. https://arxiv.org/abs/1901.11251.
Quantum Optics
Single-photon emitters are of interest for many applications, such as quantum sensing and quantum secure communication. Although efficient on-demand solid-state sources based on quantum dots, defect color centers in diamond, and single molecules are available, most of these systems require cryogenic temperatures for optimal performance. Ripka et al. used a cloud of warm excited rubidium atoms confined to a gas cell and exploited the exaggerated interaction of Rydberg states to generate single photons on demand. The results demonstrate the viability of atomic gases for application in the development of quantum technologies.
Science , this issue p. [446][1]
[1]: /lookup/doi/10.1126/science.aau1949
The goal of this Special Topic is to provide new insights in the physics of single quantum emitters and single-photon detectors and their possible use for quantum photonic applications. The perspective article of Vural and others discusses the challenges for multi-source quantum implementations based on self-assembled InGaAs quantum dots. Decoherence and spectral diffusion processes in quantum dots, which limit the photon indistinguishability, are considered in their article. In their article, Anderson and others have investigated the noise sources that affect InAs/InP quantum dots emitting in the telecom C-band by comparing their behavior on a wetting layer for Stranski-Krastanov grown quantum dots with a nearly wetting layer-free environment achieved with the droplet epitaxy growth mode. They show that the droplet epitaxy growth mode is beneficial for a low-noise environment, which is a pre-condition for the generation of highly coherent photons.