Wechselwirkung zwischen mesoskopischen Strukturen im Nichtgleichgewicht
Final Report Abstract
Within this project my research team experimentally studied fundamental questions related to electron interactions in out of equilibrium mesoscopic semiconductor circuits. These studies are important for the development of miniature electrical classical or quantum circuits for future information processing applications. Our material system where GaAs/AlGaAs based heterostructures containing a two-dimensional electron system. We employed electron-beam-lithography to design surface metal gates and used the electric field effect to modify and control the potential landscape inside the two-dimensional electron system. Solid state nanostructures, like ours, are exposed to multiple interaction effects between electrons and photons, phonons, uncontrolled charges (charge noise), nuclear spins and more. These interactions become particularly important if the device is driven out of thermal equilibrium. It is essential to understand the underlying physics in order to fully control interacting quantum circuits and minimize their dephasing. In case of classical applications the related energy relaxation is central to the charge carrier dynamics. Exploring these effects was the aim of the project. We planned to study the interaction of hot, i.e. highly excited, electrons moving ballistically through a degenerate Fermi liquid of cold electrons. Building on these experiments, as a next step, we planned to investigate the interaction between driven nanostructures including the backaction between a qubit and its detector but also dephasing of the driven qubit by environmental influences. Before the start of the project we had already studied the interaction between hot ballistic electrons and acoustic phonons. Within the project we studied interaction between hot ballistic electrons and optical phonons as well as the electron-electron interaction. All these experiments demonstrate a high degree of control of hot electrons in mesoscopic devices. By studying the exchange of energy between hot electrons and other excitations in the solid we have laid a foundation for future application oriented research. We originally intended to also study the emission of plasmons by hot electrons, but this turned out to be difficult in pure transport experiments and our results were not conclusive and we did not publish them. To study the environmental influences on a driven qubit, we completely characterized a double QD charge qubit including its dephasing environment by Landau-Zener interferometry. By a direct comparison with a complete model we found that its coherence time at 20 mK is entirely limited by the electron-phonon interaction. With the goal to improve the qubits coherence by engineering the electron-phonon interaction we investigated coherent phonon absorption in a double dot. We found that it is, e.g., possible to protect a qubit from phonons by engineering destructive interference in the electron-phonon interaction. Interestingly, in this study we also found, that a double QD can be employed as single phonon emitter or detector. Based on our results it even seems feasible to make use of coherent phonons controlled via the electron phonon coupling for information processing. Symmetry properties are essential for quantum information, as pure quantum systems obey spatio-time symmetry which excludes information processing. We have studied several ways to break and control symmetries in driven (non-equilibrium) QD systems. Our results suggest interesting perspectives for quantum information and simulation applications. In another project we investigated exchange correlations, which cause the so-called 0.7-anomaly in QPCs, i.e. short 1D constrictions in a 2D system. Together with our theory collaborators, led by Prof. Jan von Delft, we where able to fully explain this historical problem. The electrons are jostling similar to a crowd of people trying to enter a theater through a narrow door. In case of the electrons, the van-Hove singularity of the 1D density of states near the band bottom gives rise to the jostle. We have recently started to also study such narrow constrictions in phototransport measurements.
Publications
- An Electron-Avalanche Amplifier based on the Electronic Venturi Effect. Phys. Rev. B 82, 161416, 1 – 4 (Rapid Communications) (2010)
D. Taubert, G. J. Schinner, H. P. Tranitz, W. Wegscheider, C. Tomaras, S. Kehrein, and S. Ludwig
(See online at https://doi.org/10.1103/PhysRevB.82.161416) - Accurate Determination of Energy Scales in Few-Electron Double Quantum Dots. Rev. Sci. Inst. 82, 123905, 1 – 6 (2011)
D. Taubert, D. Schuh, W. Wegscheider, and S. Ludwig
(See online at https://doi.org/10.1063/1.3673003) - An Electron Jet Pump: the Venturi Effect of a Fermi Liquid. J. Appl. Phys. 109, 102412, 1 – 5 (2011)
D. Taubert, G. J. Schinner, C. Tomaras, H. P. Tranitz, W. Wegscheider, and S. Ludwig
(See online at https://doi.org/10.1063/1.3577959) - Relaxation of Hot Electrons in a Degenerate Two-Dimensional Electron System: Transition to One-Dimensional Scattering. Phys. Rev. B 83, 235404, 1 – 13 (2011)
D. Taubert, C. Tomaras, G. J. Schinner, H. P. Tranitz, W. Wegscheider, S. Kehrein, and S. Ludwig
(See online at https://doi.org/10.1103/PhysRevB.83.235404) - Quantum Interference and Phonon-Mediated Back-Action in Lateral Quantum-Dot Circuits. Nature Physics 8, 522 – 527 (2012)
G. Granger, D. Taubert, C. E. Young, L. Gaudreau, A. Kam, S. A. Studenikin, P. Zawadzki, D. Harbusch, D. Schuh, W. Wegscheider, Z. R. Wasilewski, A. A. Clerk, S. Ludwig, and A. S. Sachrajda
(See online at https://doi.org/10.1038/NPHYS2326) - The Microscopic Origin of the 0.7-Anomaly in Quantum Point Contacts. Nature 501, 73 – 78 (2013)
Florian Bauer, Jan Heyder, Enrico Schubert, David Borowsky, Daniela Taubert, Benedikt Bruognolo, Dieter Schuh, Werner Wegscheider, Jan von Delft, and Stefan Ludwig
(See online at https://doi.org/10.1038/nature12421) - Landau-Zener interference at bichromatic driving. Phys. Rev. B 92, 245422, 1 – 12 (2015)
F. Forster, M. Mühlbacher„ R. Blattmann, D. Schuh, W. Wegscheider, S. Ludwig, and S. Kohler
(See online at https://doi.org/10.1103/PhysRevB.92.245422) - Lissajous Rocking Ratchet: Realization in a Semiconductor Quantum Dot. prl 115, 106801, 1 – 5 (2015)
S. Platonov, B. Kästner, H.W. Schumacher, S. Kohler, and S. Ludwig
(See online at https://doi.org/10.1103/PhysRevLett.115.106801) - On the Relation between the 0.7-Anomaly and the Kondo Effect: Geometric Crossover between a Quantum Point Contact and a Kondo Quantum Dot. Phys. Rev. B 92, 195401, 1 – 19 (2015)
J. Heyder, F. Bauer, E. Schubert, D. Borowsky, D. Schuh, W. Wegscheider, J. v. Delft, and S. Ludwig
(See online at https://doi.org/10.1103/PhysRevB.92.195401) - Mesoscopic Field-Effect-Induced Devices in Depleted Two-Dimensional Electron Systems. Phys. Rev. Applied 8, 064015, 1 – 8 (2017)
N. Bachsoliani, S. Platonov, A.D. Wieck, and S. Ludwig
(See online at https://doi.org/10.1103/PhysRevApplied.8.064015)
