ERC Grants

Dissipation spectroscopy: Nanomechanical dissipation, experienced by oscillating tip-based Force Microscopy (AFM) instruments, provides an innovative probe of the physics of classical and quantum materials, solids, surfaces. My group made, in the last decade, well-recognized experimental and conceptual advances by exploiting and adapting advanced AFM techniques, especially the ultra-sensitive pendulum-AFM, (p-AFM, dissipation sensitivity ~0.1 aW, force sensitivity ~ 10-12N) detecting collective phenomena and phase transitions including structural, electronic, magnetic. This dissipation spectroscopy was applied so far mostly at the equilibrium physics of 3D classical solids. The challenge: I propose to extend nanomechanical dissipation spectroscopy to pick up much weaker effects caused by non-equilibrium perturbations, by nanomanipulations, and by quantum effects in carefully picked case studies. Such as measuring the imperceptible wind force exerted on a noncontact tip by a thermal or electrical current in the surface below, or the minute mechanical cost of creating and dismantling a single spin Kondo state, or a topological surface state. Risks, benefits, relevance: None of this was done before, so despite our experience and good feasibility estimates there is some risk. The benefits however will be substantial. Thermal and electrical migration of defects and impurities is important in materials, and electrical contacts. The dragging, peeling, sensing of 2D systems like graphene nanoribbons and twisted bilayers is hot. And quantum dissipation is pertinent to the limiting factor of quantum information processes. To do all this by nanomechanics will be unique. The opportunity: My group is ready to put its expertise in these exciting new problems, once I can through an Advanced Grant secure the instrumental and experimental human resources, as well as the theoretical support of additional beneficiary SISSA, indispensable in such a frontier context.

2 002 833 €

Start date: 2019-05-01, End date: 2024-04-30

Topological 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. In-stead, 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 in 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.

2 497 577 €

Start date: 2018-07-01, End date: 2023-06-30

The main goal of this theory project is to propose engineered topological phases emerging only in strongly interacting systems and to identify the most feasible systems for experimental implementation. First, we will focus on setups hosting topological states localized at domain walls in one-dimensional channels such as parafermions, which are a new class of non-Abelian anyons and most promising candidates for topological quantum computing schemes. Second, in the framework of weakly coupled wires and planes, we will develop schemes for novel fractional topological phases in two- and three-dimensional interacting systems. To achieve these two goals, my team will identify necessary ingredients such as strong electron-electron interactions, helical magnetic order, or crossed Andreev proximity-induced superconductivity and address each of them separately. Later, we combine them to lead us to the desired topological phases and states. On our way to the main goal, as test cases, we will also study non-interacting analogies of the proposed effects such as Majorana fermions and integer topological insulators and pay close attention to the rapid experimental progress to come up with the most feasible proposals. We will study transport properties, scanning tunneling and atomic force microscopy. Especially for systems driven out of equilibrium, we will develop a Floquet-Luttinger liquid technique. We will explore the stability of engineered topological phases, error rates of topological qubits based on them, and computation schemes allowing for a set of universal qubit gates. We will strive to find a reasonable balance between topological stability and experimental feasibility of setups. Our main theoretical tools are Luttinger liquid techniques (bosonization and renormalization group), Green functions, Floquet formalism, and numerical simulations in non-interacting test models.

1 158 403 €

Start date: 2018-01-01, End date: 2022-12-31

In the last decades, the power to control photons and electrons paved the way for extraordinary technological developments in electronic and optoelectronic applications. The same degree of control is still lacking with quantized lattice vibrations, i.e. phonons. Phonons are the carriers of heat and sound. The understanding and ability to manipulate phonons as quantum particles in solids enable the control of coherent phonon transport, which is of fundamental interest and could also be exploited in applications. Logic operations can be realized with the manipulation of phonons both in their coherent and incoherent form in order to switch, amplify, and route signals, and to store information. If brought to a mature level, phononic devices can become complementary to the conventional electronics, opening new opportunities. I envision to realize each part of this technology exploiting phonons and to bring them together in an integrated circuit on chip: a phononic integrated circuit. The objective of the proposal is: A: the realization of coherent phonon source and detector; B: the realization of phonon computation with the use of thermal logic gates; C: the realization of phonon based quantum and thermal memories. To this end it is crucial to engineer nanoscale heterostructures with suitable interfaces, and to engineer the phonon spectrum and the interface thermal resistance. Phonons will be launched, probed and manipulated with a combination of pump-probe experiments and resistive thermal measurements on chip. The proposed research will be of great relevance for fundamental research as well as for technological applications in the field of sound and thermal management.

1 488 388 €

Start date: 2018-01-01, End date: 2022-12-31

Atomic ensembles are routinely prepared and manipulated in the quantum regime using the powerful techniques of laser cooling and trapping. To achieve similar control over the vibrations of nanofabricated mechanical oscillators is a goal that is vigorously pursued, which recently led to the first observations of ground-state cooling and quantum behavior in such systems. In this project, we will explore the new conceptual and experimental possibilities offered by hybrid systems in which the vibrations of a mechanical oscillator are coupled to an ensemble of ultracold atoms. An optomechanics setup and an ultracold atom experiment will be connected by laser light to generate long-distance Hamiltonian interactions between the two systems. This modularapproach avoids the technical complications of combining a cryogenic optomechanics experiment and a cold atom experiment into a highly integrated setup. At the same time, it allows to investigate intriguing conceptual questions associated with the remote control of quantum systems. The coupled mechanical-atomic system will be used for a range of experiments on quantum control and quantum metrology of mechanical vibrations. We will implement new schemes for ground-state cooling of mechanical vibrations that overcome some of the limitations of existing techniques, explore coherent mechanical-atomic interactions and Einstein-Podolsky-Rosen entanglement, and use such entanglement for measurements of mechanical vibrations beyond the standard quantum limit. The extensive experience of the PI in atomic quantum metrology and hybrid optomechanics will be a valuable asset in this endeavor. Besides the interesting perspective of observing quantum phenomena in engineered mechanical devices that are visible to the bare eye, the project will open up new avenues for quantum measurement of mechanical vibrations with potential impact on the development of mechanical quantum sensors and transducers for accelerations, forces and fields.

1 498 961 €

Start date: 2016-01-01, End date: 2020-12-31

Advances in growth and fabrication of semiconductor nanostructures have led to both the production of exquisitely sensitive force transducers and the development of solid-state quantum devices. Force transducers, typically monolithic Si cantilevers, are central to techniques such as AFM, and MFM. On the other hand, quantum devices including quantum wells, quantum dots (QDs), and single electron transistors are essential to technologies like lasers, optical detectors, and in experiments on quantum information. These two types of devices have – until now – occupied distinct material systems and have, for the most part, not been combined. New developments in the growth of inorganic nanowires (NWs), however, are set to change the status quo. Researchers can now grow nanoscale structures from the bottom-up with unprecedented mechanical properties. Unlike traditional top-down cantilevers, which are etched or milled out of a larger block of material, bottom-up structures are assembled unit-by-unit to be almost defect-free on the atomic-scale. This near perfection gives NWs a much smaller mechanical dissipation than their top-down counterparts, while their higher resonance frequencies allow them to couple less strongly to common sources of noise. Meanwhile, layer-by-layer growth of NWs is rapidly developing such that both axial and radial heterostructures have now been realized. Such fine control allows for band-structure engineering and the production of devices including FETs, single photon sources, and QDs. NWs are also attractive hosts for optical emitters as their geometry favors the efficient extraction of photons. These properties and the fact that a NW can be integrated as the tip of an SPM make NWs extremely promising devices. We propose to develop the use of NWs as scanning multifunctional sensors. We intend to 1) use NW cantilevers as force transducers in high-resolution scanning force microscopy, and 2) use NW quantum devices as scanning sensors.

1 480 680 €

Start date: 2013-11-01, End date: 2018-10-31

“The quantum world is by far larger than the classical one. It is entanglement, closely linked to non-locality, that spans this larger space manifold. Entanglement plays a central role in emerging quantum technology aiming to harvest quantum space. From the experimentalist’s point of view working in nanoelectronics, there is no instrument on the shelf yet, that would measure the degree of entanglement. This we would like to change with QUEST. QUEST is a long term project with the goal to experimentally establish a continuous probe of entanglement generation in the electrical signal of quantum devices. It is set up in two parts: the realization of a highly efficient source of spin-entangled electron pairs and the exploration of different correlation measurements providing a measure of entanglement “on the fly”. During the last decade a wealth of theory proposals have appeared, addressing entanglement in electronic devices. The interaction of particles in solid-state devices provides a natural force for the appearance of entanglement. Examples are correlation between electrons and holes in the emission on a tunnel junction, or the “naturally” occurring Cooper pairs in s-wave superconductors. While first results on the realization of sources of entangled electron pairs have appeared recently, there are no experiments demonstrating entanglement in transport of any of those devices. We aim to change this and propose to implement high-bandwidth current correlation methods up to the forth moment, enabling to test Bell-inequality and quantum state tomo-graphy. Based on our long standing experience in the measurement of second-order correlations in nanodevices, we are well prepared for this very challenging goal.”

1 999 350 €

Start date: 2012-04-01, End date: 2017-03-31

Macroscopic control of quantum states is a major theme in much of modern physics because quantum coherence enables study of fundamental physics and has promising applications for quantum information processing. The potential significance of quantum computing is recognized well beyond the physics community. For electron spins in GaAs quantum dots, it has become clear that decoherence caused by interactions with the nuclear spins is a major challenge. We propose to investigate and reduce hyperfine induced decoherence with two complementary approaches: nuclear spin state narrowing and nuclear spin polarization. We propose a new projective state narrowing technique: a large, Coulomb blockaded dot measures the qubit nuclear ensemble, resulting in enhanced spin coherence times. Further, mediated by an interacting 2D electron gas via hyperfine interaction, a low temperature nuclear ferromagnetic spin state was predicted, which we propose to investigate using a quantum point contact as a nuclear polarization detector. Estimates indicate that the nuclear ferromagnetic transition occurs in the sub-Millikelvin range, well below already hard to reach temperatures around 10 mK. However, the exciting combination of interacting electron and nuclear spin physics as well as applications in spin qubits give ample incentive to strive for sub-Millikelvin temperatures in nanostructures. We propose to build a novel type of nuclear demagnetization refrigerator aiming to reach electron temperatures of 0.1 mK in semiconductor nanostructures. This interdisciplinary project combines Microkelvin and nanophysics, going well beyond the status quo. It is a challenging project that could be the beginning of a new era of coherent spin physics with unprecedented quantum control. This project requires a several year commitment and a team of two graduate students plus one postdoctoral fellow.

1 377 000 €

Start date: 2008-06-01, End date: 2013-05-31