| 1. |
- Becher, Christoph, et al.
(author)
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2023 roadmap for materials for quantum technologies
- 2023
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In: Materials for Quantum Technology. - : IOP Publishing. - 2633-4356. ; 3:1
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Journal article (peer-reviewed)abstract
- Quantum technologies are poised to move the foundational principles of quantum physics to the forefront of applications. This roadmap identifies some of the key challenges and provides insights on material innovations underlying a range of exciting quantum technology frontiers. Over the past decades, hardware platforms enabling different quantum technologies have reached varying levels of maturity. This has allowed for first proof-of-principle demonstrations of quantum supremacy, for example quantum computers surpassing their classical counterparts, quantum communication with reliable security guaranteed by laws of quantum mechanics, and quantum sensors uniting the advantages of high sensitivity, high spatial resolution, and small footprints. In all cases, however, advancing these technologies to the next level of applications in relevant environments requires further development and innovations in the underlying materials. From a wealth of hardware platforms, we select representative and promising material systems in currently investigated quantum technologies. These include both the inherent quantum bit systems and materials playing supportive or enabling roles, and cover trapped ions, neutral atom arrays, rare earth ion systems, donors in silicon, color centers and defects in wide-band gap materials, two-dimensional materials and superconducting materials for single-photon detectors. Advancing these materials frontiers will require innovations from a diverse community of scientific expertise, and hence this roadmap will be of interest to a broad spectrum of disciplines.
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| 2. |
- Gerhardt, Stefan, et al.
(author)
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Optomechanical tuning of the polarization properties of micropillar cavity systems with embedded quantum dots
- 2020
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In: Physical Review B. - 2469-9950 .- 2469-9969. ; 101:24
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Journal article (peer-reviewed)abstract
- Strain tuning emerged as an appealing tool for tuning of fundamental optical properties of solid-state quantum emitters. In particular, the wavelength and fine structure of quantum dot states can be tuned using hybrid semiconductor-piezoelectric devices. Here, we show how an applied external stress can directly impact the polarization properties of coupled InAs quantum dot-micropillar cavity systems. In our experiment, we find that we can reversibly tune the anisotropic polarization splitting of the fundamental microcavity mode by approximately 60 mu eV. We discuss the origin of this tuning mechanism, which arises from an interplay between elastic deformation and the photoelastic effect in our micropillar. Finally, we exploit this effect to tune the quantum dot polarization optomechanically via the polarization-anisotropic Purcell effect. Our work paves the way for optomechanical and reversible tuning of the polarization and spin properties of light-matter-coupled solid-state systems.
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| 3. |
- Ginés, Laia, et al.
(author)
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High Extraction Efficiency Source of Photon Pairs Based on a Quantum Dot Embedded in a Broadband Micropillar Cavity
- 2022
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 129:3
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Journal article (peer-reviewed)abstract
- The generation of photon pairs in quantum dots is in its nature deterministic. However, efficient extraction of photon pairs from the high index semiconductor material requires engineering of the photonic environment. We report on a micropillar device with 69.4(10)% efficiency that features broadband operation suitable for extraction of photon pairs. Opposing the approaches that rely solely on Purcell enhancement to realize the enhancement of the extraction efficiency, our solution exploits a suppression of the emission into the modes other than the cavity mode. Furthermore, the design of the device can be further optimized to allow for an extraction efficiency of 85%.
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| 4. |
- Ginés, Laia, et al.
(author)
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Time-bin entangled photon pairs from quantum dots embedded in a self-aligned cavity
- 2021
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In: Optics Express. - 1094-4087. ; 29:3, s. 4174-4180
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Journal article (peer-reviewed)abstract
- We introduce a scalable photonic platform that enables efficient generation of entangled photon pairs from a semiconductor quantum dot. Our system, which is based on a self-aligned quantum dot- micro-cavity structure, erases the need for complex steps of lithography and nanofabrication. We experimentally show collection efficiency of 0.17 combined with a Purcell enhancement of up to 1.7. We harness the potential of our device to generate photon pairs entangled in time bin, reaching a fidelity of 0.84(5) with the maximally entangled state. The achieved pair collection efficiency is 4 times larger than the state-of-the art for this application. The device, which theoretically supports pair extraction efficiencies of nearly 0.5 is a promising candidate for the implementation of bright sources of time-bin, polarization- and hyper entangled photon pairs in a straightforward manner.
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| 5. |
- Jurkat, Jonathan, et al.
(author)
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Technological implementation of a photonic Bier-Glas cavity
- 2021
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In: Physical Review Materials. - 2475-9953. ; 5:6
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Journal article (peer-reviewed)abstract
- In this paper, we introduce a quantum photonic device, which we term the photonic Bier-Glas cavity. We discuss its fabrication and functionality, which is based on the coupling of integrated In(Ga)As quantum dots to a broadband photonic cavity resonance. By design, the device architecture uniquely combines the Purcell enhancement of a photonic micropillar structure with a broadband photonic mode shaping of a vertical, tapered waveguide, making it an interesting candidate to enable the efficient extraction of entangled photon pairs. We detail the epitaxial growth of the heterostructure as well as the necessary lithography steps to approach a GaAsbased photonic device with a height exceeding 15 mu m, supported on a pedestal that can be as thin as 20 nm. We further describe its key performance parameters using a Fourier-modal method. Finally, we present an optical characterization, which confirms the presence of broadband optical resonances, in conjunction with amplified spontaneous emission of single photons.
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| 6. |
- Koutny, Dominik, et al.
(author)
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Deep learning of quantum entanglement from incomplete measurements
- 2023
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In: Science Advances. - 2375-2548. ; 9:29
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Journal article (peer-reviewed)abstract
- The quantification of the entanglement present in a physical system is of paramount importance for fundamental research and many cutting-edge applications. Now, achieving this goal requires either a priori knowledge on the system or very demanding experimental procedures such as full state tomography or collective measurements. Here, we demonstrate that, by using neural networks, we can quantify the degree of entanglement without the need to know the full description of the quantum state. Our method allows for direct quantification of the quantum correlations using an incomplete set of local measurements. Despite using undersampled measurements, we achieve a quantification error of up to an order of magnitude lower than the state-of-the-art quantum tomography. Furthermore, we achieve this result using networks trained using exclusively simulated data. Last, we derive a method based on a convolutional network input that can accept data from various measurement scenarios and perform, to some extent, independently of the measurement device.
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| 7. |
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| 8. |
- Schimpf, Christian, et al.
(author)
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Hyperfine interaction limits polarization entanglement of photons from semiconductor quantum dots
- 2023
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In: Physical Review B. - 2469-9950 .- 2469-9969. ; 108:8
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Journal article (peer-reviewed)abstract
- Excitons in quantum dots are excellent sources of polarization-entangled photon pairs, but a quantitative understanding of their interaction with the nuclear spin bath is still missing. Here we investigate the role of hyperfine energy shifts using experimentally accessible parameters and derive an upper limit to the achievable entanglement fidelity. Our results are consistent with all available literature, indicate that spin noise is often the dominant process limiting the entanglement in InGaAs quantum dots, and suggest routes to alleviate its effect.
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