A practical all optical quantum calculator/simulator is expected to need a number of gates which will be extraordinarily high. A key challenge towards the achievement of an optical quantum computer is that of a “deterministic” source of entangled photons, designed to be compatible with standard cleanroom processing and integration technology. This paper discuss how a relatively “niche” QD system (site-controlled Pyramidal quantum dots, grown by metalorganic vapour phase epitaxy in etched GaAs (111)B tetrahedral recesses) actually offer a number of unexpected potentiality for entangled photon emission.
A practical all optical quantum calculator/simulator is expected to need a number of gates which will be extraordinarily high. A key challenge towards the achievement of an optical quantum computer is that of a “deterministic” source of entangled photons, designed to be compatible with standard cleanroom processing and integration technology. This paper discuss how a relatively “niche” QD system (site-controlled Pyramidal quantum dots, grown by metalorganic vapour phase epitaxy in etched GaAs (111)B tetrahedral recesses) actually offer a number of unexpected potentiality for entangled photon emission.
Practical realisation of quantum information science is a challenge being addressed by researchers employing various technologies. One of them is based on quantum dots (QD), usually referred to as artificial atoms. Being capable to emit single and polarization entangled photons, they are attractive as sources of quantum bits (qubits) which can be relatively easily integrated into photonic circuits using conventional semiconductor technologies. However, the dominant self-assembled QD systems suffer from asymmetry related problems which modify the energetic structure. The main issue is the degeneracy lifting (the fine-structure splitting, FSS) of an optically allowed neutral exciton state which participates in a polarization-entanglement realisation scheme. The FSS complicates polarization-entanglement detection unless a particular FSS manipulation technique is utilized to reduce it to vanishing values, or a careful selection of intrinsically good candidates from the vast number of QDs is carried out, preventing the possibility of constructing vast arrays of emitters on the same sample. In this work, site-controlled InGaAs QDs grown on (111)B oriented GaAs substrates prepatterned with 7.5 μm pitch tetrahedrons were studied in order to overcome QD asymmetry related problems. By exploiting an intrinsically high rotational symmetry, pyramidal QDs were shown as polarization-entangled photon sources emitting photons with the fidelity of the expected maximally entangled state as high as 0.721. It is the first site-controlled QD system of entangled photon emitters. Moreover, the density of such emitters was found to be as high as 15% in some areas: the density much higher than in any other QD system. The associated physical phenomena (e.g., carrier dynamic, QD energetic structure) were studied, as well, by different techniques: photon correlation spectroscopy, polarization-resolved microphotoluminescence and magneto-photoluminescence.
In recent years it has been realized that quantum entanglement could have many applications in the nascent field of quantum information technology [1]. While most existing sources for entangled photons rely on nonlinear optical effects [2], triggered entangled photons provide the benefit of being event-ready for application. The radiative decay of biexcitons in a quantum dot (QD) has been proposed [3] and recently demonstrated [4,5,6] as a source of triggered polarization-entangled photon pairs. However, in most cases the anisotropy-induced exciton fine structure splitting destroys this entanglement. The key to the generation of entangled photon pairs in a QD is therefore the suppression of the exciton polarization splitting. Seeded self-ordering, which involves the self-formation of nanostructures at nucleation sites introduced by a substrate patterning process [7], is particularly attractive because it allows for control over the size and shape of the QD. In particular, pyramidal QDs grown in this way on (111)B GaAs substrates have a higher symmetry (C3v) [8] as compared with self-assembled Stranski-Krastanow QDs (C2v). This feature makes them a prime candidate for efficient sources of entangled photons.
Fast, high efficiency and low error single-photon sources are required for the implementation of a number of quantum information processing applications. The fastest triggered single-photon sources to date have been demonstrated using epitaxially grown semiconductor quantum dots (QDs), which can be conveniently integrated with optical microcavities. Recent advances in QD technology, including demonstrations of high temperature and telecommunications wavelength single-photon emission, have made QD single-photon sources more practical. Here we discuss the applications of single-photon sources and their various requirements, before reviewing the progress made on a QD platform in meeting these requirements.
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.
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.