91 research outputs found

    Solid-state ensemble of highly entangled photon sources at rubidium atomic transitions

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    Semiconductor InAs/GaAs quantum dots grown by the Stranski-Krastanov method are among the leading candidates for the deterministic generation of polarization entangled photon pairs. Despite remarkable progress in the last twenty years, many challenges still remain for this material, such as the extremely low yield (<1% quantum dots can emit entangled photons), the low degree of entanglement, and the large wavelength distribution. Here we show that, with an emerging family of GaAs/AlGaAs quantum dots grown by droplet etching and nanohole infilling, it is possible to obtain a large ensemble (close to 100%) of polarization-entangled photon emitters on a wafer without any post-growth tuning. Under pulsed resonant two-photon excitation, all measured quantum dots emit single pairs of entangled photons with ultra-high purity, high degree of entanglement (fidelity up to F=0.91, with a record high concurrence C=0.90), and ultra-narrow wavelength distribution at rubidium transitions. Therefore, a solid-state quantum repeater - among many other key enabling quantum photonic elements - can be practically implemented with this new material

    Wavelength-tunable entangled photons from silicon-integrated III–V quantum dots

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    Many of the quantum information applications rely on indistinguishable sources of polarization-entangled photons. Semiconductor quantum dots are among the leading candidates for a deterministic entangled photon source; however, due to their random growth nature, it is impossible to find different quantum dots emitting entangled photons with identical wavelengths. The wavelength tunability has therefore become a fundamental requirement for a number of envisioned applications, for example, nesting different dots via the entanglement swapping and interfacing dots with cavities/atoms. Here we report the generation of wavelength-tunable entangled photons from on-chip integrated InAs/GaAs quantum dots. With a novel anisotropic strain engineering technique based on PMN-PT/silicon micro-electromechanical system, we can recover the quantum dot electronic symmetry at different exciton emission wavelengths. Together with a footprint of several hundred microns, our device facilitates the scalable integration of indistinguishable entangled photon sources on-chip, and therefore removes a major stumbling block to the quantum-dot-based solid-state quantum information platforms

    A solid-state source of single and entangled photons at diamond SiV−^--center transitions operating at 80K

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    Large-scale quantum networks require the implementation of long-lived quantum memories as stationary nodes interacting with qubits of light. Epitaxially grown quantum dots hold great potential for the on-demand generation of single and entangled photons with high purity and indistinguishability. Coupling these emitters to memories with long coherence times enables the development of hybrid nanophotonic devices incorporating the advantages of both systems. Here we report the first GaAs/AlGaAs quantum dots grown by droplet etching and nanohole infilling method, emitting single photons with a narrow wavelength distribution (736.2 ±\pm 1.7 nm) close to the zero-phonon line of Silicon-vacancy centers. Polarization entangled photons are generated via the biexciton-exciton cascade with a fidelity of (0.73 ±\pm 0.09). High single photon purity is maintained from 4 K (g(^(2^2)^)(0) = 0.07 ±\pm 0.02) up to 80 K (g(^(2^2)^)(0) = 0.11 ±\pm 0.01), therefore making this hybrid system technologically attractive for real-world quantum photonic applications

    Local droplet etching on InAlAs/InP surfaces with InAl droplets

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    GaAs quantum dots (QDs) grown by local droplet etching (LDE) have been studied extensively in recent years. The LDE method allows for high crystallinity, as well as precise control of the density, morphology, and size of QDs. These properties make GaAs QDs an ideal candidate as single photon and entangled photon sources at short wavelengths (<800 nm). For technologically important telecom wavelengths, however, it is still unclear whether LDE grown QDs can be realized. Controlling the growth conditions does not enable shifting the wavelength of GaAs QDs to the telecom region. New recipes will have to be established. In this work, we study Indium–Aluminum (InAl) droplet etching on ultra-smooth In0.55Al0.45As surfaces on InP substrates, with a goal to lay the foundation for growing symmetrical and strain-free telecom QDs using the LDE method. We report that both droplets start to etch nanoholes at a substrate temperature above 415 °C, showing varying nanohole morphology and rapidly changing density (by more than one order of magnitude) at different temperatures. Al and In droplets are found to not intermix during etching, and instead etch nanoholes individually. The obtained nanoholes show a symmetric profile and very low densities, enabling infilling of lattice-matched InGaAs QDs on InxAl1−xAs/InP surfaces in further works

    Temperature-dependent coercive field measured by a quantum dot strain gauge

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    Coercive fields of piezoelectric materials can be strongly influenced by environmental temperature. We investigate this influence using a hetero-structure consisting of a single crystal piezoelectric film and a quantum dots containing membrane. Applying electric field leads to a physical deformation of the piezoelectric film, thereby inducing strain in the quantum dots and thus modifying their optical properties. The wavelength of the quantum dot emission shows butterfly-like loops, from which the coercive fields are directly derived. The results suggest that coercive fields at cryogenic temperatures are strongly increased, yielding values several tens of times larger than those at room temperature. We adapt a theoretical model to fit the measured data with very high agreement. Our work provides an efficient framework for predicting the properties of ferroelectric materials and advocate their practical applications, especially at low temperatures. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.nanolett.7b0413

    Statistical limits for entanglement swapping with semiconductor entangled photon sources

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    Semiconductor quantum dots are promising building blocks for quantum communication applications. Al- though deterministic, efficient, and coherent emission of entangled photons has been realized, implementing a practical quantum repeater remains outstanding. Here we explore the statistical limits for entanglement swapping with sources of polarization-entangled photons from the commonly used biexciton-exciton cascade. We stress the necessity of tuning the exciton fine structure, and explain why the often observed time evolution of photonic entanglement in quantum dots is not applicable for large quantum networks. We identify the critical, statistically distributed device parameters for entanglement swapping based on two sources. A numerical model for benchmarking the consequences of device fabrication, dynamic tuning techniques, and statistical effects is developed, in order to bring the realization of semiconductor-based quantum networks one step closer to reality. ©2022 American Physical Societ

    Entanglement Swapping with Semiconductor-Generated Photons Violates Bell’s Inequality

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    Transferring entangled states between photon pairs is essential in quantum communication. Semiconductor quantum dots are the leading candidate for generating polarization-entangled photons deterministically. Here we show for the first time swapping of entangled states between two pairs of photons emitted by a single dot. A joint Bell measurement heralds the successful generation of the Bell state Ψ+, yielding a fidelity of 0.81±0.04 and violating the CHSH and Bell inequalities. Our photon source matches atomic quantum memory frequencies, facilitating implementation of hybrid quantum repeaters.BMBF/Q.comERC/QD-NOMSIFW Excellence Progra

    Strain control of exciton and trion spin-valley dynamics in monolayer transition metal dichalcogenides

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    The electron-hole exchange interaction is a fundamental mechanism that drives valley depolarization via intervalley exciton hopping in semiconductor multi-valley systems. Here, we report polarization-resolved photoluminescence spectroscopy of neutral excitons and negatively charged trions in monolayer MoSe2_2 and WSe2_2 under biaxial strain. We observe a marked enhancement(reduction) on the WSe2_2 triplet trion valley polarization with compressive(tensile) strain while the trion in MoSe2_2 is unaffected. The origin of this effect is shown to be a strain dependent tuning of the electron-hole exchange interaction. A combined analysis of the strain dependent polarization degree using ab initio calculations and rate equations shows that strain affects intervalley scattering beyond what is expected from strain dependent bandgap modulations. The results evidence how strain can be used to tune valley physics in energetically degenerate multi-valley systems
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