Experimentalphysik Nanoelektronik (Schönenberger)Head of Research Unit Prof. Dr.Christian SchönenbergerOverviewMembersPublicationsProjects & CollaborationsProjects & Collaborations OverviewMembersPublicationsProjects & Collaborations Projects & Collaborations 34 foundShow per page10 10 20 50 QUSTEC PhD fellowship - Spectroscopy of Subgap States in Semiconducting Nanowires with Proximitized Superconductivity Research Project | 4 Project MembersOriginal Title: Quantum transport in superconductor-semiconductor nanowire hybrid devices with axially built-in quantum dots as spectrometers Abstract: The project is motivated by the recent excitement of the appearance of topological phases and Majorana bound states (MBSs) in semiconducting nanowires (NWs) with strong spin-orbit interaction (SOI) coupled to a superconductor (SC) in magnetic field. To unravel the emergence of MBSs in single and coupled NWs, we develop new probes with which the proximity gap and proximity-induced bound states can be quantified. Our approach is based on measuring both DC and AC transport, the latter also at GHz frequencies using reflectometry. As a complementary test, we can also study the microwave radiation in the GHz domain emitted by the quantum device. With the current project we aim to deepen our understanding of the superconductive proximity effect in a NW with strong SOI by studying the evolution of the gap spectroscopically. For the latter we exploit quantum dots (QDs) as spectrometers. Here, the QDs are established by heteroepitaxy during growth. This is done in collaboration with Prof. Lucia Sorba from CNR-Nano at Pisa, where the InAs NWs are grown (see figure). These QDs are very promising due to the large confinement potential. We further plan to test different SCs beyond Al, e.g. Pd and MoRe, and optimize the evaporation together with collaborators from the Niels-Bohr Institute in Copenhagen. p.s. in the meantime the material system was changed to 2D InAs quantum proximitized from above by a thin Al layer. This material is provided by the Mafra group (Purdue Univ. USA). Two-dimensional semiconductor platforms for superconductor hybrid nanostructures Research Project | 2 Project MembersWe aim to develop a new material platform for nanoelectronic devices, with a strong focus on superconducting hybrid systems based on two-dimensional (2D) semiconducting layered materials (2D-SC) with a strong intrinsic spin-orbit interaction (SOI). We will establish standard surface bulk and 1D side-contacts in encapsulated 2D-SCs and perform "standard" experiments in this new type of structures, for example the measurement of a Josephson current, weak (anti-) localization and the quantum Hall effect. These experiments will form the basis for first Majorana bound state devices in a new type of geometry, and develop first topgate-defined nanostructures, with the aim to fabricate gate-tunable quantum dots and Cooper pair splitters. This project will pave the way towards deterministic double nanowire devices expected to host Parafermions, a generalization of Majorana bound states and many other more exotic superconductor-semiconductor hybrid structures. Andreev qubits for scalable quantum computation Research Project | 7 Project MembersOur goal is to establish the foundations of a radically new solid state platform for scalable quantum computation, based on Andreev qubits. This platform is implemented by utilizing the discrete superconducting quasiparticle levels (Andreev levels) that appear in weak links between superconductors. Each Andreev level can be occupied by zero, one, or two electrons. The even occupation manifold gives rise to the first type of Andreev qubit, which has recently been demonstrated by some of the consortium members. We will characterize and mitigate the factors limiting the coherence of this qubit to promote these proof of concept experiments towards a practical technology. The odd occupation state gives rise to a second type of qubit, the Andreev spin qubit, with an unprecedented functionality: a direct coupling between a single localized spin and the supercurrent across the weak link. Further harnessing the odd occupation state, we will investigate the so far unexplored scheme of fermionic quantum computation, with the potential of efficiently simulating electron systems in complex molecules and novel materials. The recent scientific breakthrough by the Copenhagen node of depositing of superconductors with clean interfaces on semiconductor nanostructures opened a realistic path to implement the Andreev qubit technology. In these devices, we can tune the qubit frequency by electrostatic gating, which brings the required flexibility and scalability to this platform. We will demonstrate single- and two-qubit control of Andreev qubits, and benchmark the results against established scalable solid-state quantum technologies, in particular semiconductor spin qubits and superconducting quantum circuits. To carry out this research program, we rely on the instrumental combination of experimentalists, theorists and material growers, together having the necessary expertise on all aspects of the proposed research. High Performance Transmission Electron Microscope for Present and Future Nanomaterials Research Project | 9 Project MembersThe rise of nanoscience and nanotechnology would not have been happened without the impressive development of instruments that allow to resolve structure on the nanometer scale with atomic resolution. Examples are scanning-probe and electron microscopy techniques. In recent years, several major breakthroughs gave rise to an exceptional boost in the performance of today's electron microscopy (EM), both for solid-state and soft (e.g. biological) materials: 1) high-resolution through image corrections, 2) fast and highly efficient electron detectors, 3) efficient artifact-free sample fabrication (cryo-EM and FIBEM), and 4) 3D tomography and image reconstruction. This has given a leap to what can be imaged today, allowing for example to reconstruct the atomic structure of single proteins and image complex interfaces in solid-state materials with atomic scale. The University of Basel (UBAS) is nationally and internationally recognized as a leader in nanoscience and nanotechnology. It was the leading house of the National Center in Competence and Research (NCCR) on Nanoscience, which later became the Swiss Nanoscience Institute (SNI), the institution that submits the current proposal. UBAS is also co-leading the NCCR Molecular Systems Engineering and the NCCR QSIT on Quantum Science (both together with ETHZ). Nanoscience is a focus area in the research portfolio of UBAS and instrumental for the recent development of quantum science. The present proposal to the SNF R'Equip scheme has been put together by key researchers at UBAS who work on current topics in nanoscience and nanotechnology in various disciplines from quantum science, material science, polymer chemistry to molecular biology, and, who make use of EM available within the SNI. The principle investigators, who submit this proposal together, do research that relies on the availability of state-of-the-art nanoimaging tools, such as a transmission electron microscope (TEM). The proposal outlines a convincing case for the purchase of special, unique TEM that combines state-of-the-art (and fast) atomic resolution imaging with material analysis using EDX and scanning TEM (STEM). This combination is unique and crucial for the University of Basel to stay at the forefront of science. Georg H. Endress Postdoctoral Fellow Dr. Artem Kononov Research Project | 3 Project MembersThe project is concerned with topological insulators and unconventional superconductivity induced by proximity effect or of intrinsic nature in 2D van der Waals heterostructures. It is funded as a Georg H. Endress Postdoctoral Fellowship. TopSupra / Engineered Topological Superconductivity in van der Waals Heterostructures Research Project | 1 Project MembersTopological matter is a new research focus with great perspectives. These are insulators with an inverted "negative" bandgap and a conducting surface state. While the surface state in a topological insulator (TI) is composed of chiral fermions carrying charge and spin, in topological superconductors it is pinned to zero energy due to particle-hole symmetry and composed of fermions that carry neither charge nor spin. Instead, they are non-abelian fermions, Majorana and parafermions (MF/PF), that have been proposed for topological quantum computing. Evidence for MFs have been found in nanowires. However, the scaling-up challenge requires a platform in which networks of MFs can be realized. Here, we propose to use graphene-based van der Waals heterostructure for this purpose. The unprecedented versatility is enabled by combining high-mobility graphene with other layered materials, such as transition-metal dichalcogenide, few-layer ferromagnets and superconductors (SCs). This allows to design topological systems , e.g. the quantum spin, anomalous and valley Hall effect, by combining Zeeman energy, spin-orbit and pairing interaction. We will design 2D quantum matter using different approaches, including strain tuning and the dressing of the bandstructure by photon-fields (Floquet TI), and couple it to SCs to induce topological superconductivity. We will use our expertise from studies of Cooper-pair splitters to not only add pairing in a single edge-state, but also between different edge-states, beneficial for obtaining MFs and more exotic quasiparticles. We will apply advanced high-frequency techniques, e.g. emission and noise - in addition to local tunneling spectroscopy - to characterize the in-gap states and to prove their topological nature . We will deliver a versatile technology with which new states of matter can be obtained in a platform which can be engineered in a top-down manner into networks allowing for quantum-state manipulation of MFs and PFs. Graphene flagship WP2 Core 2 Research Project | 3 Project MembersThe PI is part of WP2 on Spintronics in Graphene: WP2 in CORE2 targets the demonstration of the technological potential of graphene and related two-dimensional materials for spintronic applications, including the concept of spin-based field effect transistors (spin-FET) and technologies based on spin-torque mechanisms including nano oscillators (commercial products developed by the SME NanOsc), innovative memory (spin transfer torque MRAM and spin orbit torque MRAM) and spin logic components. The WP will be structured around 3 tasks, including a device-oriented task of optimization and upscaling of the demonstrators developed by the consortium (task 2.1), a full task on the fabrication, characterization and optimization of spin torque based nano oscillators (task 2.2) driven by the SME NanOsc and supported by engineering developments at CUT, ICN2, and IMEC together with simulation support by CEA, UCL and ICN2, and a more exploratory research task (task 2.3) led by RUG, in which new materials, interfaces (graphene/transition metal dichalcogenides (TMDC), graphene/topological insulators) and heterostructures will be investigated for their potential in opto(spin)electronics, spin filtering (achieving large TMR) or spin-torque physics. All three tasks are divided in subtasks led by one partner and associating others for targeted objectives. WP2 will also increase collaborations with other WPs (WP3 and WP10) concerning the enhancement of the spin-orbit coupling on graphene devices by various ways and the clarification of spin lifetime tunability by spin orbit coupling (SOC)-proximity effects (with WP3) and the fabrication of clean 2D materials-based heterostructures and their technology integration in core blocks of spintronic devices in a fab environment (WP3 and WP10). Topological quantum states in double nanowire devices ERA-NET Research Project | 3 Project MembersTopological quantum computing (TQC) is an emerging field with strong benefits for prospective applications, since it provides an elegant way around decoherence. The theory of TQC progressed very rapidly during the last decade from various qubit realizations to scalable computational protocols. However, the experimental realizations of these concepts lag behind. Important experimental milestones have been achieved recently, by demonstrating the first signatures of Majorana states which are the simplest non-Abelian anyons. However, to realize fully topologically protected universal quantum computation, more exotic anyons, such as parafermions are required. Thus, the unambiguous demonstration of parafermion states will have a great impact on the development of universal quantum computation. The experimental realization of parafermions is challenging, since they are based on the combination of various ingredients, such as crossed Andreev reflection, electron-electron or spin-orbit interaction, and high quality quantum conductors. Thus, the investigation of all these ingredients is essential and timely to achieve further experimental progress. The team of SuperTop is composed of six leading groups with strong and complementary experimental background in these areas with the aim to realize parafermions in double nanowire-based hybrid devices (DNW) for the first time. The main objectives of SuperTop are: a) development of different DNW geometries, which consist of two parallel 1D spin-orbit nanowires coupled by a thin superconductor stripe and b) investigation of the emerging exotic bound states at the superconductor/semiconductor interface of the DNW. SuperTop first grows state-of-the-art InAs and InSb based nanostructures, in particular InAs nanowires (NWs) with in-situ grown epitaxial superconducting layer, NWs with built-in InP barriers and InSb nanoflakes. Based on these high quality materials, different device geometries of DNW are fabricated and the emerging novel states are investigated. The topological character, quantum phase transition, coherence time, coupling strength to QED as key features of the engineered new states are planned to be addressed by various cutting-edge low temperature measurement techniques (e.g. non-local spectroscopy, noise, current-phase relationship measurement or integration into coplanar resonators). The experimental team of SuperTop is supported by in-house theoretical experts of TQC, who will contribute to the interpretation of the results and development of technologically feasible topologically protected quantum architectures. SuperTop first grows state-of-the-art InAs and InSb based nanostructures, in particular InAs nanowires (NWs) with in-situ grown epitaxial superconducting layer, NWs with built-in InP barriers and InSb nanoflakes. Based on these high quality materials, different device geometries of DNW are fabricated and the emerging novel states are investigated. The topological character, quantum phase transition, coherence time, coupling strength to QED as key features of the engineered new states are planned to be addressed by various cutting-edge low temperature measurement techniques (e.g. non-local spectroscopy, noise, current-phase relationship measurement or integration into coplanar resonators).The experimental team of SuperTop is supported by in-house theoretical experts of TQC, who will contribute to the interpretation of the results and development of technologically feasible topologically protected quantum architectures. van der Waals 2D semiconductor nanostructures with superconducting contacts Research Project | 4 Project MembersThe combination of semiconducting nanostructures with standard superconducting materials hold great promises for finding new physical phenomena, as well as for applications in quantum information processing. Currently, strong efforts are made to demonstrate and exploit Majorana bound states (MBSs), i.e. protected zero-energy states at the ends of a topologically non-trivial superconductor. The latter is obtained by combining one-dimensional (1D) semiconducting nanowires (NWs) with a large spin-orbit interaction (SOI) with conventional superconductors. In very similar electronic devices our group already demonstrated Cooper pair splitting (CPS) [5,6], believed to be a source of spatially separated entangled electrons. However, these 1D systems are strongly limiting the device geometry and scalability, because the NWs are deposited randomly and have a considerable height, which makes the fabrication of thin superconducting contacts challenging. While standard semiconducting heterostructures like AlGaAs/AlAs are difficult to combine with superconducting or ferromagnetic contacts, graphene is a more versatile platform, but lacks the energy gap necessary for simple gate confinement, and has only a small SOI. Other 2D layered materials (LMs), like MoS2 or WSe2, have a large SOI, exhibit appreciable energy gaps, can have good transport properties [9] and can probably be contacted by thin metal contacts, all of which makes them ideal candidates for scalable and complex electronic devices based on SOI and superconductivity. The general aim of this project is to develop a semiconductor electronics platform based on large-SOI 2D layered materials, which allow us to obtain quantum confinement by electrical gating and a strong coupling to metallic superconductors and ferromagnetic materials. We will develop two specific device types: A) Majorana and Parafermion devices, and B) gate-defined quantum dots (QDs), in four project phases summarized below. Understanding and engineering of phonon propagation in nanodevices by employing energy resolved phonon emission and adsorption spectroscopy Research Project | 3 Project MembersWith this PhD project we address phononics in nanodevices, a new field with great prospects for applications relating to sound and heat. While there is excellent control over electromagnetic degrees of freedom, the control of phonon transport in nanostructures is in its infancy. We propose a new scheme with which phonon transport in nanowires (NWs) can be studied with high spectroscopic resolution. This is done by embedding quantum dots (QDs) into the NW. Inelastic transport through states in the QDs can be used to both emit and detect phonons. This can be done energy resolved, allowing to characterize the energy-dependent phonon transmission. Once established, a periodic axial material modulation can be realized during NW growth, allowing to tune the phonon bandstructure. A challenging milestone would be the demonstration and engineering of phononic band-gaps. 1234 1...4 OverviewMembersPublicationsProjects & Collaborations
Projects & Collaborations 34 foundShow per page10 10 20 50 QUSTEC PhD fellowship - Spectroscopy of Subgap States in Semiconducting Nanowires with Proximitized Superconductivity Research Project | 4 Project MembersOriginal Title: Quantum transport in superconductor-semiconductor nanowire hybrid devices with axially built-in quantum dots as spectrometers Abstract: The project is motivated by the recent excitement of the appearance of topological phases and Majorana bound states (MBSs) in semiconducting nanowires (NWs) with strong spin-orbit interaction (SOI) coupled to a superconductor (SC) in magnetic field. To unravel the emergence of MBSs in single and coupled NWs, we develop new probes with which the proximity gap and proximity-induced bound states can be quantified. Our approach is based on measuring both DC and AC transport, the latter also at GHz frequencies using reflectometry. As a complementary test, we can also study the microwave radiation in the GHz domain emitted by the quantum device. With the current project we aim to deepen our understanding of the superconductive proximity effect in a NW with strong SOI by studying the evolution of the gap spectroscopically. For the latter we exploit quantum dots (QDs) as spectrometers. Here, the QDs are established by heteroepitaxy during growth. This is done in collaboration with Prof. Lucia Sorba from CNR-Nano at Pisa, where the InAs NWs are grown (see figure). These QDs are very promising due to the large confinement potential. We further plan to test different SCs beyond Al, e.g. Pd and MoRe, and optimize the evaporation together with collaborators from the Niels-Bohr Institute in Copenhagen. p.s. in the meantime the material system was changed to 2D InAs quantum proximitized from above by a thin Al layer. This material is provided by the Mafra group (Purdue Univ. USA). Two-dimensional semiconductor platforms for superconductor hybrid nanostructures Research Project | 2 Project MembersWe aim to develop a new material platform for nanoelectronic devices, with a strong focus on superconducting hybrid systems based on two-dimensional (2D) semiconducting layered materials (2D-SC) with a strong intrinsic spin-orbit interaction (SOI). We will establish standard surface bulk and 1D side-contacts in encapsulated 2D-SCs and perform "standard" experiments in this new type of structures, for example the measurement of a Josephson current, weak (anti-) localization and the quantum Hall effect. These experiments will form the basis for first Majorana bound state devices in a new type of geometry, and develop first topgate-defined nanostructures, with the aim to fabricate gate-tunable quantum dots and Cooper pair splitters. This project will pave the way towards deterministic double nanowire devices expected to host Parafermions, a generalization of Majorana bound states and many other more exotic superconductor-semiconductor hybrid structures. Andreev qubits for scalable quantum computation Research Project | 7 Project MembersOur goal is to establish the foundations of a radically new solid state platform for scalable quantum computation, based on Andreev qubits. This platform is implemented by utilizing the discrete superconducting quasiparticle levels (Andreev levels) that appear in weak links between superconductors. Each Andreev level can be occupied by zero, one, or two electrons. The even occupation manifold gives rise to the first type of Andreev qubit, which has recently been demonstrated by some of the consortium members. We will characterize and mitigate the factors limiting the coherence of this qubit to promote these proof of concept experiments towards a practical technology. The odd occupation state gives rise to a second type of qubit, the Andreev spin qubit, with an unprecedented functionality: a direct coupling between a single localized spin and the supercurrent across the weak link. Further harnessing the odd occupation state, we will investigate the so far unexplored scheme of fermionic quantum computation, with the potential of efficiently simulating electron systems in complex molecules and novel materials. The recent scientific breakthrough by the Copenhagen node of depositing of superconductors with clean interfaces on semiconductor nanostructures opened a realistic path to implement the Andreev qubit technology. In these devices, we can tune the qubit frequency by electrostatic gating, which brings the required flexibility and scalability to this platform. We will demonstrate single- and two-qubit control of Andreev qubits, and benchmark the results against established scalable solid-state quantum technologies, in particular semiconductor spin qubits and superconducting quantum circuits. To carry out this research program, we rely on the instrumental combination of experimentalists, theorists and material growers, together having the necessary expertise on all aspects of the proposed research. High Performance Transmission Electron Microscope for Present and Future Nanomaterials Research Project | 9 Project MembersThe rise of nanoscience and nanotechnology would not have been happened without the impressive development of instruments that allow to resolve structure on the nanometer scale with atomic resolution. Examples are scanning-probe and electron microscopy techniques. In recent years, several major breakthroughs gave rise to an exceptional boost in the performance of today's electron microscopy (EM), both for solid-state and soft (e.g. biological) materials: 1) high-resolution through image corrections, 2) fast and highly efficient electron detectors, 3) efficient artifact-free sample fabrication (cryo-EM and FIBEM), and 4) 3D tomography and image reconstruction. This has given a leap to what can be imaged today, allowing for example to reconstruct the atomic structure of single proteins and image complex interfaces in solid-state materials with atomic scale. The University of Basel (UBAS) is nationally and internationally recognized as a leader in nanoscience and nanotechnology. It was the leading house of the National Center in Competence and Research (NCCR) on Nanoscience, which later became the Swiss Nanoscience Institute (SNI), the institution that submits the current proposal. UBAS is also co-leading the NCCR Molecular Systems Engineering and the NCCR QSIT on Quantum Science (both together with ETHZ). Nanoscience is a focus area in the research portfolio of UBAS and instrumental for the recent development of quantum science. The present proposal to the SNF R'Equip scheme has been put together by key researchers at UBAS who work on current topics in nanoscience and nanotechnology in various disciplines from quantum science, material science, polymer chemistry to molecular biology, and, who make use of EM available within the SNI. The principle investigators, who submit this proposal together, do research that relies on the availability of state-of-the-art nanoimaging tools, such as a transmission electron microscope (TEM). The proposal outlines a convincing case for the purchase of special, unique TEM that combines state-of-the-art (and fast) atomic resolution imaging with material analysis using EDX and scanning TEM (STEM). This combination is unique and crucial for the University of Basel to stay at the forefront of science. Georg H. Endress Postdoctoral Fellow Dr. Artem Kononov Research Project | 3 Project MembersThe project is concerned with topological insulators and unconventional superconductivity induced by proximity effect or of intrinsic nature in 2D van der Waals heterostructures. It is funded as a Georg H. Endress Postdoctoral Fellowship. TopSupra / Engineered Topological Superconductivity in van der Waals Heterostructures Research Project | 1 Project MembersTopological matter is a new research focus with great perspectives. These are insulators with an inverted "negative" bandgap and a conducting surface state. While the surface state in a topological insulator (TI) is composed of chiral fermions carrying charge and spin, in topological superconductors it is pinned to zero energy due to particle-hole symmetry and composed of fermions that carry neither charge nor spin. Instead, they are non-abelian fermions, Majorana and parafermions (MF/PF), that have been proposed for topological quantum computing. Evidence for MFs have been found in nanowires. However, the scaling-up challenge requires a platform in which networks of MFs can be realized. Here, we propose to use graphene-based van der Waals heterostructure for this purpose. The unprecedented versatility is enabled by combining high-mobility graphene with other layered materials, such as transition-metal dichalcogenide, few-layer ferromagnets and superconductors (SCs). This allows to design topological systems , e.g. the quantum spin, anomalous and valley Hall effect, by combining Zeeman energy, spin-orbit and pairing interaction. We will design 2D quantum matter using different approaches, including strain tuning and the dressing of the bandstructure by photon-fields (Floquet TI), and couple it to SCs to induce topological superconductivity. We will use our expertise from studies of Cooper-pair splitters to not only add pairing in a single edge-state, but also between different edge-states, beneficial for obtaining MFs and more exotic quasiparticles. We will apply advanced high-frequency techniques, e.g. emission and noise - in addition to local tunneling spectroscopy - to characterize the in-gap states and to prove their topological nature . We will deliver a versatile technology with which new states of matter can be obtained in a platform which can be engineered in a top-down manner into networks allowing for quantum-state manipulation of MFs and PFs. Graphene flagship WP2 Core 2 Research Project | 3 Project MembersThe PI is part of WP2 on Spintronics in Graphene: WP2 in CORE2 targets the demonstration of the technological potential of graphene and related two-dimensional materials for spintronic applications, including the concept of spin-based field effect transistors (spin-FET) and technologies based on spin-torque mechanisms including nano oscillators (commercial products developed by the SME NanOsc), innovative memory (spin transfer torque MRAM and spin orbit torque MRAM) and spin logic components. The WP will be structured around 3 tasks, including a device-oriented task of optimization and upscaling of the demonstrators developed by the consortium (task 2.1), a full task on the fabrication, characterization and optimization of spin torque based nano oscillators (task 2.2) driven by the SME NanOsc and supported by engineering developments at CUT, ICN2, and IMEC together with simulation support by CEA, UCL and ICN2, and a more exploratory research task (task 2.3) led by RUG, in which new materials, interfaces (graphene/transition metal dichalcogenides (TMDC), graphene/topological insulators) and heterostructures will be investigated for their potential in opto(spin)electronics, spin filtering (achieving large TMR) or spin-torque physics. All three tasks are divided in subtasks led by one partner and associating others for targeted objectives. WP2 will also increase collaborations with other WPs (WP3 and WP10) concerning the enhancement of the spin-orbit coupling on graphene devices by various ways and the clarification of spin lifetime tunability by spin orbit coupling (SOC)-proximity effects (with WP3) and the fabrication of clean 2D materials-based heterostructures and their technology integration in core blocks of spintronic devices in a fab environment (WP3 and WP10). Topological quantum states in double nanowire devices ERA-NET Research Project | 3 Project MembersTopological quantum computing (TQC) is an emerging field with strong benefits for prospective applications, since it provides an elegant way around decoherence. The theory of TQC progressed very rapidly during the last decade from various qubit realizations to scalable computational protocols. However, the experimental realizations of these concepts lag behind. Important experimental milestones have been achieved recently, by demonstrating the first signatures of Majorana states which are the simplest non-Abelian anyons. However, to realize fully topologically protected universal quantum computation, more exotic anyons, such as parafermions are required. Thus, the unambiguous demonstration of parafermion states will have a great impact on the development of universal quantum computation. The experimental realization of parafermions is challenging, since they are based on the combination of various ingredients, such as crossed Andreev reflection, electron-electron or spin-orbit interaction, and high quality quantum conductors. Thus, the investigation of all these ingredients is essential and timely to achieve further experimental progress. The team of SuperTop is composed of six leading groups with strong and complementary experimental background in these areas with the aim to realize parafermions in double nanowire-based hybrid devices (DNW) for the first time. The main objectives of SuperTop are: a) development of different DNW geometries, which consist of two parallel 1D spin-orbit nanowires coupled by a thin superconductor stripe and b) investigation of the emerging exotic bound states at the superconductor/semiconductor interface of the DNW. SuperTop first grows state-of-the-art InAs and InSb based nanostructures, in particular InAs nanowires (NWs) with in-situ grown epitaxial superconducting layer, NWs with built-in InP barriers and InSb nanoflakes. Based on these high quality materials, different device geometries of DNW are fabricated and the emerging novel states are investigated. The topological character, quantum phase transition, coherence time, coupling strength to QED as key features of the engineered new states are planned to be addressed by various cutting-edge low temperature measurement techniques (e.g. non-local spectroscopy, noise, current-phase relationship measurement or integration into coplanar resonators). The experimental team of SuperTop is supported by in-house theoretical experts of TQC, who will contribute to the interpretation of the results and development of technologically feasible topologically protected quantum architectures. SuperTop first grows state-of-the-art InAs and InSb based nanostructures, in particular InAs nanowires (NWs) with in-situ grown epitaxial superconducting layer, NWs with built-in InP barriers and InSb nanoflakes. Based on these high quality materials, different device geometries of DNW are fabricated and the emerging novel states are investigated. The topological character, quantum phase transition, coherence time, coupling strength to QED as key features of the engineered new states are planned to be addressed by various cutting-edge low temperature measurement techniques (e.g. non-local spectroscopy, noise, current-phase relationship measurement or integration into coplanar resonators).The experimental team of SuperTop is supported by in-house theoretical experts of TQC, who will contribute to the interpretation of the results and development of technologically feasible topologically protected quantum architectures. van der Waals 2D semiconductor nanostructures with superconducting contacts Research Project | 4 Project MembersThe combination of semiconducting nanostructures with standard superconducting materials hold great promises for finding new physical phenomena, as well as for applications in quantum information processing. Currently, strong efforts are made to demonstrate and exploit Majorana bound states (MBSs), i.e. protected zero-energy states at the ends of a topologically non-trivial superconductor. The latter is obtained by combining one-dimensional (1D) semiconducting nanowires (NWs) with a large spin-orbit interaction (SOI) with conventional superconductors. In very similar electronic devices our group already demonstrated Cooper pair splitting (CPS) [5,6], believed to be a source of spatially separated entangled electrons. However, these 1D systems are strongly limiting the device geometry and scalability, because the NWs are deposited randomly and have a considerable height, which makes the fabrication of thin superconducting contacts challenging. While standard semiconducting heterostructures like AlGaAs/AlAs are difficult to combine with superconducting or ferromagnetic contacts, graphene is a more versatile platform, but lacks the energy gap necessary for simple gate confinement, and has only a small SOI. Other 2D layered materials (LMs), like MoS2 or WSe2, have a large SOI, exhibit appreciable energy gaps, can have good transport properties [9] and can probably be contacted by thin metal contacts, all of which makes them ideal candidates for scalable and complex electronic devices based on SOI and superconductivity. The general aim of this project is to develop a semiconductor electronics platform based on large-SOI 2D layered materials, which allow us to obtain quantum confinement by electrical gating and a strong coupling to metallic superconductors and ferromagnetic materials. We will develop two specific device types: A) Majorana and Parafermion devices, and B) gate-defined quantum dots (QDs), in four project phases summarized below. Understanding and engineering of phonon propagation in nanodevices by employing energy resolved phonon emission and adsorption spectroscopy Research Project | 3 Project MembersWith this PhD project we address phononics in nanodevices, a new field with great prospects for applications relating to sound and heat. While there is excellent control over electromagnetic degrees of freedom, the control of phonon transport in nanostructures is in its infancy. We propose a new scheme with which phonon transport in nanowires (NWs) can be studied with high spectroscopic resolution. This is done by embedding quantum dots (QDs) into the NW. Inelastic transport through states in the QDs can be used to both emit and detect phonons. This can be done energy resolved, allowing to characterize the energy-dependent phonon transmission. Once established, a periodic axial material modulation can be realized during NW growth, allowing to tune the phonon bandstructure. A challenging milestone would be the demonstration and engineering of phononic band-gaps. 1234 1...4
QUSTEC PhD fellowship - Spectroscopy of Subgap States in Semiconducting Nanowires with Proximitized Superconductivity Research Project | 4 Project MembersOriginal Title: Quantum transport in superconductor-semiconductor nanowire hybrid devices with axially built-in quantum dots as spectrometers Abstract: The project is motivated by the recent excitement of the appearance of topological phases and Majorana bound states (MBSs) in semiconducting nanowires (NWs) with strong spin-orbit interaction (SOI) coupled to a superconductor (SC) in magnetic field. To unravel the emergence of MBSs in single and coupled NWs, we develop new probes with which the proximity gap and proximity-induced bound states can be quantified. Our approach is based on measuring both DC and AC transport, the latter also at GHz frequencies using reflectometry. As a complementary test, we can also study the microwave radiation in the GHz domain emitted by the quantum device. With the current project we aim to deepen our understanding of the superconductive proximity effect in a NW with strong SOI by studying the evolution of the gap spectroscopically. For the latter we exploit quantum dots (QDs) as spectrometers. Here, the QDs are established by heteroepitaxy during growth. This is done in collaboration with Prof. Lucia Sorba from CNR-Nano at Pisa, where the InAs NWs are grown (see figure). These QDs are very promising due to the large confinement potential. We further plan to test different SCs beyond Al, e.g. Pd and MoRe, and optimize the evaporation together with collaborators from the Niels-Bohr Institute in Copenhagen. p.s. in the meantime the material system was changed to 2D InAs quantum proximitized from above by a thin Al layer. This material is provided by the Mafra group (Purdue Univ. USA).
Two-dimensional semiconductor platforms for superconductor hybrid nanostructures Research Project | 2 Project MembersWe aim to develop a new material platform for nanoelectronic devices, with a strong focus on superconducting hybrid systems based on two-dimensional (2D) semiconducting layered materials (2D-SC) with a strong intrinsic spin-orbit interaction (SOI). We will establish standard surface bulk and 1D side-contacts in encapsulated 2D-SCs and perform "standard" experiments in this new type of structures, for example the measurement of a Josephson current, weak (anti-) localization and the quantum Hall effect. These experiments will form the basis for first Majorana bound state devices in a new type of geometry, and develop first topgate-defined nanostructures, with the aim to fabricate gate-tunable quantum dots and Cooper pair splitters. This project will pave the way towards deterministic double nanowire devices expected to host Parafermions, a generalization of Majorana bound states and many other more exotic superconductor-semiconductor hybrid structures.
Andreev qubits for scalable quantum computation Research Project | 7 Project MembersOur goal is to establish the foundations of a radically new solid state platform for scalable quantum computation, based on Andreev qubits. This platform is implemented by utilizing the discrete superconducting quasiparticle levels (Andreev levels) that appear in weak links between superconductors. Each Andreev level can be occupied by zero, one, or two electrons. The even occupation manifold gives rise to the first type of Andreev qubit, which has recently been demonstrated by some of the consortium members. We will characterize and mitigate the factors limiting the coherence of this qubit to promote these proof of concept experiments towards a practical technology. The odd occupation state gives rise to a second type of qubit, the Andreev spin qubit, with an unprecedented functionality: a direct coupling between a single localized spin and the supercurrent across the weak link. Further harnessing the odd occupation state, we will investigate the so far unexplored scheme of fermionic quantum computation, with the potential of efficiently simulating electron systems in complex molecules and novel materials. The recent scientific breakthrough by the Copenhagen node of depositing of superconductors with clean interfaces on semiconductor nanostructures opened a realistic path to implement the Andreev qubit technology. In these devices, we can tune the qubit frequency by electrostatic gating, which brings the required flexibility and scalability to this platform. We will demonstrate single- and two-qubit control of Andreev qubits, and benchmark the results against established scalable solid-state quantum technologies, in particular semiconductor spin qubits and superconducting quantum circuits. To carry out this research program, we rely on the instrumental combination of experimentalists, theorists and material growers, together having the necessary expertise on all aspects of the proposed research.
High Performance Transmission Electron Microscope for Present and Future Nanomaterials Research Project | 9 Project MembersThe rise of nanoscience and nanotechnology would not have been happened without the impressive development of instruments that allow to resolve structure on the nanometer scale with atomic resolution. Examples are scanning-probe and electron microscopy techniques. In recent years, several major breakthroughs gave rise to an exceptional boost in the performance of today's electron microscopy (EM), both for solid-state and soft (e.g. biological) materials: 1) high-resolution through image corrections, 2) fast and highly efficient electron detectors, 3) efficient artifact-free sample fabrication (cryo-EM and FIBEM), and 4) 3D tomography and image reconstruction. This has given a leap to what can be imaged today, allowing for example to reconstruct the atomic structure of single proteins and image complex interfaces in solid-state materials with atomic scale. The University of Basel (UBAS) is nationally and internationally recognized as a leader in nanoscience and nanotechnology. It was the leading house of the National Center in Competence and Research (NCCR) on Nanoscience, which later became the Swiss Nanoscience Institute (SNI), the institution that submits the current proposal. UBAS is also co-leading the NCCR Molecular Systems Engineering and the NCCR QSIT on Quantum Science (both together with ETHZ). Nanoscience is a focus area in the research portfolio of UBAS and instrumental for the recent development of quantum science. The present proposal to the SNF R'Equip scheme has been put together by key researchers at UBAS who work on current topics in nanoscience and nanotechnology in various disciplines from quantum science, material science, polymer chemistry to molecular biology, and, who make use of EM available within the SNI. The principle investigators, who submit this proposal together, do research that relies on the availability of state-of-the-art nanoimaging tools, such as a transmission electron microscope (TEM). The proposal outlines a convincing case for the purchase of special, unique TEM that combines state-of-the-art (and fast) atomic resolution imaging with material analysis using EDX and scanning TEM (STEM). This combination is unique and crucial for the University of Basel to stay at the forefront of science.
Georg H. Endress Postdoctoral Fellow Dr. Artem Kononov Research Project | 3 Project MembersThe project is concerned with topological insulators and unconventional superconductivity induced by proximity effect or of intrinsic nature in 2D van der Waals heterostructures. It is funded as a Georg H. Endress Postdoctoral Fellowship.
TopSupra / Engineered Topological Superconductivity in van der Waals Heterostructures Research Project | 1 Project MembersTopological matter is a new research focus with great perspectives. These are insulators with an inverted "negative" bandgap and a conducting surface state. While the surface state in a topological insulator (TI) is composed of chiral fermions carrying charge and spin, in topological superconductors it is pinned to zero energy due to particle-hole symmetry and composed of fermions that carry neither charge nor spin. Instead, they are non-abelian fermions, Majorana and parafermions (MF/PF), that have been proposed for topological quantum computing. Evidence for MFs have been found in nanowires. However, the scaling-up challenge requires a platform in which networks of MFs can be realized. Here, we propose to use graphene-based van der Waals heterostructure for this purpose. The unprecedented versatility is enabled by combining high-mobility graphene with other layered materials, such as transition-metal dichalcogenide, few-layer ferromagnets and superconductors (SCs). This allows to design topological systems , e.g. the quantum spin, anomalous and valley Hall effect, by combining Zeeman energy, spin-orbit and pairing interaction. We will design 2D quantum matter using different approaches, including strain tuning and the dressing of the bandstructure by photon-fields (Floquet TI), and couple it to SCs to induce topological superconductivity. We will use our expertise from studies of Cooper-pair splitters to not only add pairing in a single edge-state, but also between different edge-states, beneficial for obtaining MFs and more exotic quasiparticles. We will apply advanced high-frequency techniques, e.g. emission and noise - in addition to local tunneling spectroscopy - to characterize the in-gap states and to prove their topological nature . We will deliver a versatile technology with which new states of matter can be obtained in a platform which can be engineered in a top-down manner into networks allowing for quantum-state manipulation of MFs and PFs.
Graphene flagship WP2 Core 2 Research Project | 3 Project MembersThe PI is part of WP2 on Spintronics in Graphene: WP2 in CORE2 targets the demonstration of the technological potential of graphene and related two-dimensional materials for spintronic applications, including the concept of spin-based field effect transistors (spin-FET) and technologies based on spin-torque mechanisms including nano oscillators (commercial products developed by the SME NanOsc), innovative memory (spin transfer torque MRAM and spin orbit torque MRAM) and spin logic components. The WP will be structured around 3 tasks, including a device-oriented task of optimization and upscaling of the demonstrators developed by the consortium (task 2.1), a full task on the fabrication, characterization and optimization of spin torque based nano oscillators (task 2.2) driven by the SME NanOsc and supported by engineering developments at CUT, ICN2, and IMEC together with simulation support by CEA, UCL and ICN2, and a more exploratory research task (task 2.3) led by RUG, in which new materials, interfaces (graphene/transition metal dichalcogenides (TMDC), graphene/topological insulators) and heterostructures will be investigated for their potential in opto(spin)electronics, spin filtering (achieving large TMR) or spin-torque physics. All three tasks are divided in subtasks led by one partner and associating others for targeted objectives. WP2 will also increase collaborations with other WPs (WP3 and WP10) concerning the enhancement of the spin-orbit coupling on graphene devices by various ways and the clarification of spin lifetime tunability by spin orbit coupling (SOC)-proximity effects (with WP3) and the fabrication of clean 2D materials-based heterostructures and their technology integration in core blocks of spintronic devices in a fab environment (WP3 and WP10).
Topological quantum states in double nanowire devices ERA-NET Research Project | 3 Project MembersTopological quantum computing (TQC) is an emerging field with strong benefits for prospective applications, since it provides an elegant way around decoherence. The theory of TQC progressed very rapidly during the last decade from various qubit realizations to scalable computational protocols. However, the experimental realizations of these concepts lag behind. Important experimental milestones have been achieved recently, by demonstrating the first signatures of Majorana states which are the simplest non-Abelian anyons. However, to realize fully topologically protected universal quantum computation, more exotic anyons, such as parafermions are required. Thus, the unambiguous demonstration of parafermion states will have a great impact on the development of universal quantum computation. The experimental realization of parafermions is challenging, since they are based on the combination of various ingredients, such as crossed Andreev reflection, electron-electron or spin-orbit interaction, and high quality quantum conductors. Thus, the investigation of all these ingredients is essential and timely to achieve further experimental progress. The team of SuperTop is composed of six leading groups with strong and complementary experimental background in these areas with the aim to realize parafermions in double nanowire-based hybrid devices (DNW) for the first time. The main objectives of SuperTop are: a) development of different DNW geometries, which consist of two parallel 1D spin-orbit nanowires coupled by a thin superconductor stripe and b) investigation of the emerging exotic bound states at the superconductor/semiconductor interface of the DNW. SuperTop first grows state-of-the-art InAs and InSb based nanostructures, in particular InAs nanowires (NWs) with in-situ grown epitaxial superconducting layer, NWs with built-in InP barriers and InSb nanoflakes. Based on these high quality materials, different device geometries of DNW are fabricated and the emerging novel states are investigated. The topological character, quantum phase transition, coherence time, coupling strength to QED as key features of the engineered new states are planned to be addressed by various cutting-edge low temperature measurement techniques (e.g. non-local spectroscopy, noise, current-phase relationship measurement or integration into coplanar resonators). The experimental team of SuperTop is supported by in-house theoretical experts of TQC, who will contribute to the interpretation of the results and development of technologically feasible topologically protected quantum architectures. SuperTop first grows state-of-the-art InAs and InSb based nanostructures, in particular InAs nanowires (NWs) with in-situ grown epitaxial superconducting layer, NWs with built-in InP barriers and InSb nanoflakes. Based on these high quality materials, different device geometries of DNW are fabricated and the emerging novel states are investigated. The topological character, quantum phase transition, coherence time, coupling strength to QED as key features of the engineered new states are planned to be addressed by various cutting-edge low temperature measurement techniques (e.g. non-local spectroscopy, noise, current-phase relationship measurement or integration into coplanar resonators).The experimental team of SuperTop is supported by in-house theoretical experts of TQC, who will contribute to the interpretation of the results and development of technologically feasible topologically protected quantum architectures.
van der Waals 2D semiconductor nanostructures with superconducting contacts Research Project | 4 Project MembersThe combination of semiconducting nanostructures with standard superconducting materials hold great promises for finding new physical phenomena, as well as for applications in quantum information processing. Currently, strong efforts are made to demonstrate and exploit Majorana bound states (MBSs), i.e. protected zero-energy states at the ends of a topologically non-trivial superconductor. The latter is obtained by combining one-dimensional (1D) semiconducting nanowires (NWs) with a large spin-orbit interaction (SOI) with conventional superconductors. In very similar electronic devices our group already demonstrated Cooper pair splitting (CPS) [5,6], believed to be a source of spatially separated entangled electrons. However, these 1D systems are strongly limiting the device geometry and scalability, because the NWs are deposited randomly and have a considerable height, which makes the fabrication of thin superconducting contacts challenging. While standard semiconducting heterostructures like AlGaAs/AlAs are difficult to combine with superconducting or ferromagnetic contacts, graphene is a more versatile platform, but lacks the energy gap necessary for simple gate confinement, and has only a small SOI. Other 2D layered materials (LMs), like MoS2 or WSe2, have a large SOI, exhibit appreciable energy gaps, can have good transport properties [9] and can probably be contacted by thin metal contacts, all of which makes them ideal candidates for scalable and complex electronic devices based on SOI and superconductivity. The general aim of this project is to develop a semiconductor electronics platform based on large-SOI 2D layered materials, which allow us to obtain quantum confinement by electrical gating and a strong coupling to metallic superconductors and ferromagnetic materials. We will develop two specific device types: A) Majorana and Parafermion devices, and B) gate-defined quantum dots (QDs), in four project phases summarized below.
Understanding and engineering of phonon propagation in nanodevices by employing energy resolved phonon emission and adsorption spectroscopy Research Project | 3 Project MembersWith this PhD project we address phononics in nanodevices, a new field with great prospects for applications relating to sound and heat. While there is excellent control over electromagnetic degrees of freedom, the control of phonon transport in nanostructures is in its infancy. We propose a new scheme with which phonon transport in nanowires (NWs) can be studied with high spectroscopic resolution. This is done by embedding quantum dots (QDs) into the NW. Inelastic transport through states in the QDs can be used to both emit and detect phonons. This can be done energy resolved, allowing to characterize the energy-dependent phonon transmission. Once established, a periodic axial material modulation can be realized during NW growth, allowing to tune the phonon bandstructure. A challenging milestone would be the demonstration and engineering of phononic band-gaps.
