Prof. Dr. Gabriel Aeppli

Head of Photon Science Division (PSD)

Paul Scherrer Institute
Forschungsstrasse 111
5232 Villigen PSI

Gabriel Aeppli is professor of physics at ETH Zürich and EPF Lausanne, and head of the Photon Science Division of the Paul Scherrer Institut. All of his degrees are from MIT and include a BSc in Mathematics and Electrical Engineering, and MSc and PhD in Electrical Engineering. A large fraction of his career was in industry, where, starting as a work-study student at IBM and after his PhD moving to Bell Laboratories and then NEC, he worked on problems ranging from liquid crystals to magnetic data storage. He was subsequently co-founder and director of the London Centre for Nanotechnology and Quain Professor at University College London. Aeppli also cofounded the Bio-Nano Consulting Company, of which he remains a non-executive director. He is a frequent advisor to numerous private and public entities worldwide (including China, Australia, Europe and the US) engaged in the funding, evaluation and management of science and technology. Honors include the Mott Prize of the Institute of Physics (London), the Oliver Buckley prize of the American Physical Society, the Néel Medal/International Magnetism Prize of the International Union of Pure and Applied Physics, and election to the (US) National Academy of Sciences, the American Academy of Arts and Sciences, and the Royal Society (London).
Aeppli’s scientific research is currently focused on the applications of nanotechnology and photon science to biomedicine and quantum information processing. Projects include the development of optical and microwave tools for medical diagnostics and pharmacology, where we are interested in new drug-target and antibody-antigen binding assays. We pay particular attention to obtaining specific, quantitative results, as well as to ease of use and (eventual) low cost for our engineered systems. Photons are also at the heart of efforts to control and read out quantum states in solids, including especially silicon, for which we exploit coherent, tunable pulses of THz radiation from a free electron laser. Our most recent work (2015) describes the electrical detection of coherent orbital superpositions in a commercial silicon wafer. A related topic is adiabatic quantum computing, where calculations are performed by mapping problems onto networks of bits, and then relaxing the networks via quantum mechanics. This procedure is most easily modeled in the limits of very large networks using magnets (although programmable medium size networks containing of order 1000 bits are now being implemented using superconducting junctions), where the bits correspond to Ising spins with either up or down magnetization, and quantum mechanics is introduced via a “transverse” field, which allows tunneling between the up and down states.
Coherent superpositions of three states for phosphorous donors in silicon prepared using THz radiation, Chick, Steven, Stavrias, N., Saeedi, K., Redlich, B., Greenland, P. T., Matmon, G., Naftaly, M., Pidgeon, C. R., Aeppli, G. and Murdin, B, Nature Communications 8, 16038 (2017) Superposition of orbital eigenstates is crucial to quantum technology utilising atoms, such as atomic clocks and quantum computers, and control over the interaction between atoms and their neighbours is an essential ingredient for both gating and readout. The simplest coherent wavefunction control uses a 2-eigenstate admixture, but more control over the spatial distribution of the wavefunction can be obained by increasing the number of states in the wavepacket. Here we demonstrate THz laser pulse control of Si:P orbitals using multiple orbital state admixtures, which implies we can now control the strength and duration of the interaction of the atom with different neighbours. This could simplify surface code networks which require spatially controlled interaction between atoms, and we propose an architecture that might take advantage of this.

Nondestructive imaging of atomically thin nanostructures buried in silicon, Georg Gramse, Alexander Kölker, Tingbin Lim, Taylor J. Z. Stock, Hari Solanki, Steven R. Schofield, Enrico Brinciotti, Gabriel Aeppli, Ferry Kienberger and Neil J. Curson, Science Advances, 28 Jun 2017, Vol. 3, no. 6, e1602586, DOI: 10.1126/sciadv.1602586 It is now possible to create atomically thin regions of dopant atoms in silicon patterned with lateral dimensions ranging from the atomic scale to micrometers. These structures are likely also to serve as key components of devices for next-generation classical and quantum information processing. Until now, their characteristics could only be inferred from destructive techniques and/or final electronic device performance; this severely limits engineering and manufacture based on atomic-scale lithography. Here, we use scanning microwave microscopy to image and electronically characterize three-dimensional phosphorus nanostructures fabricated via scanning tunneling microscope–based lithography.

High-resolution non-destructive three-dimensional imaging of integrated circuits, Mirko Holler, Manuel Guizar-Sicairos, Esther H. R. Tsai, Roberto Dinapoli, Elisabeth Müller, Oliver Bunk, Jörg Raabe & Gabriel Aeppli, Nature 543, 402–406, 16 March 2017, doi:10.1038/nature21698 Modern nanoelectronics has advanced to a point at which it is impossible to image entire devices and their interconnections non-destructively because of their small feature sizes and the complex three-dimensional structures resulting from their integration on a chip. Here we demonstrate that X-ray ptychography—a high-resolution coherent diffractive imaging technique—can create three-dimensional images of integrated circuits of known and unknown designs with a lateral resolution in all directions down to 14.6 nanometres. Our experiments represent a major advance in chip inspection and reverse engineering over the traditional destructive electron microscopy and ion milling techniques.

Fast diffusion of water nanodroplets on graphene, Ming Ma, Gabriele Tocci, Angelos Michaelides & Gabriel Aeppli, Nature Materials 15, 66–71 (2016), doi:10.1038/nmat4449 Diffusion across surfaces generally involves motion on a vibrating but otherwise stationary substrate. Here, using molecular dynamics, we show that a layered material such as graphene opens up a new mechanism for surface diffusion whereby adsorbates are carried by propagating ripples in a motion similar to surfing. For water nanodroplets, we demonstrate that the mechanism leads to exceedingly fast diffusion that is 2–3 orders of magnitude faster than the self-diffusion of water molecules in liquid water. We also reveal the underlying principles that regulate this new mechanism for diffusion and show how it also applies to adsorbates other than water, thus opening up the prospect of achieving fast and controllable motion of adsorbates across material surfaces more generally.

Surface-stress sensors for rapid and ultrasensitive detection of active free drugs in human serum, Joseph W. Ndieyira, Natascha Kappeler, Stephen Logan, Matthew A. Cooper, Chris Abell, Rachel A. McKendry & Gabriel Aeppli, Nature Nanotechnology 9, 225–232 (2014), doi:10.1038/nnano.2014.33 There is a growing appreciation that mechanical signals can be as important as chemical and electrical signals in biology. To include such signals in a systems biology description for understanding pathobiology and developing therapies, quantitative experiments on how solution-phase and surface chemistry together produce biologically relevant mechanical signals are needed. Because of the appearance of drug-resistant hospital ‘superbugs’, there is currently great interest in the destruction of bacteria by bound drug–target complexes that stress bacterial cell membranes. Here, we use nanomechanical cantilevers as surface-stress sensors, together with equilibrium theory, to describe quantitatively the mechanical response of a surface receptor to different antibiotics in the presence of competing ligands in solution. The findings further enhance our understanding of the biophysical mode of action of the antibiotics and will help develop better treatments, including choice of drugs as well as dosages, against pathogens.

Quantum engineering at the silicon surface using dangling bonds, S. R. Schofield, , P. Studer, , C. F. Hirjibehedin, , N. J. Curson, G. Aeppli & D. R. Bowler, Nature Communications 4, Article number: 1649 (2013), doi:10.1038/ncomms2679 Individual atoms and ions are now routinely manipulated using scanning tunnelling microscopes or electromagnetic traps for the creation and control of artificial quantum states. For applications such as quantum information processing, the ability to introduce multiple atomic-scale defects deterministically in a semiconductor is highly desirable. Here we use a scanning tunnelling microscope to fabricate interacting chains of dangling bond defects on the hydrogen-passivated silicon (001) surface. We image both the ground-state and the excited-state probability distributions of the resulting artificial molecular orbitals, using the scanning tunnelling microscope tip bias and tip-sample separation as gates to control which states contribute to the image.

Potential for spin-based information processing in a thin-film molecular semiconductor, Marc Warner, Salahud Din, Igor S. Tupitsyn, Gavin W. Morley, A. Marshall Stoneham, Jules A. Gardener, Zhenlin Wu, Andrew J. Fisher, Sandrine Heutz, Christopher W. M. Kay & Gabriel Aeppli, Nature 503, 504–508, 28 November 2013, doi:10.1038/nature12597 Organic semiconductors are studied intensively for applications in electronics and optics, and even spin-based information technology, or spintronics. Fundamental quantities in spintronics are the population relaxation time (T1) and the phase memory time (T2): T1 measures the lifetime of a classical bit, in this case embodied by a spin oriented either parallel or antiparallel to an external magnetic field, and T2 measures the corresponding lifetime of a quantum bit, encoded in the phase of the quantum state. Here we establish that these times are surprisingly long for a common, low-cost and chemically modifiable organic semiconductor, the blue pigment copper phthalocyanine, in easily processed thin-film form of the type used for device fabrication.
Quantum phase transitions in transverse field spin models: from statistical physics to quantum information, Amit Dutta, Gabriel Aeppli, Bikas K. Chakrabarti, Uma Divakaran, Thomas F. Rosenbaum, Diptiman Sen (v3) Cambridge University Press, Cambridge, 2015. ISBN: 9781107068797