91 research outputs found
Solid-state ensemble of highly entangled photon sources at rubidium atomic transitions
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
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
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 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 0.09). High single
photon purity is maintained from 4 K (g(0) = 0.07 0.02) up to
80 K (g(0) = 0.11 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
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
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Quantum dot-based broadband optical antenna for efficient extraction of single photons in the telecom O-band
Long-distance fiber-based quantum communication relies on efficient non-classical light sources operating at telecommunication wavelengths. Semiconductor quantum dots are promising candidates for on-demand generation of single photons and entangled photon pairs for such applications. However, their brightness is strongly limited due to total internal reflection at the semiconductor/vacuum interface. Here we overcome this limitation using a dielectric antenna structure. The non-classical light source consists of a gallium phosphide solid immersion lens in combination with a quantum dot nanomembrane emitting single photons in the telecom O-band. With this device, the photon extraction is strongly increased in a broad spectral range. A brightness of 17% (numerical aperture of 0.6) is obtained experimentally, with a single photon purity of (2)(0)=0.049±0.02 at saturation power. This brings the practical implementation of quantum communication networks one step closer
Temperature-dependent coercive field measured by a quantum dot strain gauge
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
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
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
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
MoSe and WSe under biaxial strain. We observe a marked
enhancement(reduction) on the WSe triplet trion valley polarization with
compressive(tensile) strain while the trion in MoSe 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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