S. Ludwig; "The Role of Phonons for the Back-Action of a Quantum-point-Contact Charge Detector", Sept. 15, 11:00, FENS 2019
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  • S. Ludwig; "The Role of Phonons for the Back-Action of a Quantum-point-Contact Charge Detector", Sept. 15, 11:00, FENS 2019

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Faculty of Engineering and Natural Sciences







The role of phonons for the back–action of a quantum–point–contact charge detector



S. Ludwig


Center for NanoScience and Fakultät für Physik, Ludwig-Maximilians-Universität,


Geschwister-Scholl-Platz 1, 80539 München, Germany



Interactions between nanoscale devices are a key component for solid–state based quantum information processing. For instance the capacitive coupling between a biased quantum point contact (QPC) and quantum dots (QD) is utilized for charge detection of a qubit. In this context, the back–action of a QPC is often associated with direct Coulomb forces between fluctuating charges at the QPC and electrons in the QD [1,2]. On the other hand a driven QPC emits energy, e. g. in the form of phonons. In this talk I will discuss possible back–action mechanisms and present measurements that prove that back–action in a solid state environment can be mediated by phonons.



We have established a technique to make back–action directly visible in low frequency


measurements of the charge stability diagram of tunnel–coupled QDs [3]. Based on this


method I will first demonstrate the back–action of driven QPCs on double QDs in the


non–equilibrium regime. Then I will present a phonon–spectroscopy measurement that


strongly indicates the importance of phonons for non–equilibrium interactions in a mesoscopic environment [4]. Backscattering of an electron defines an upper bound of the


energy that can be transferred between an electron and an acoustic phonon (in two dimensions). This limit results in observable features that allow us to determine which part


of the back–action of a QPC can be linked to phonon–mediated processes.



The electron–phonon scattering processes relevant for the phonon–mediated interaction


happens in the leads of the driven QPC and stands in direct competition with other scattering mechanisms, e. g. electron–electron scattering. In this context I will present data showing an avalanche amplification effect caused by electron–electron scattering.





[1] E. Onac, F. Balestro, L. H. Willems van Beveren, U. Hartmann, Y.V. Nazarov, L.P.


Kouwenhoven, Phys. Rev. Lett. 96, 176601 (2006).


[2] S. Gustavsson, M. Studer, R. Leturcq, T. Ihn, K. Ensslin, D.C. Driscoll, A.C. Gossard, Phys. Rev. Lett. 99, 206804 (2007).


[3] D. Taubert, M. Pioro–Ladriere, D. Schröer, D. Harbusch, A. S. Sachrajda, S. Ludwig, Phys. Rev. Lett. 100, 176805 (2008).


[4] G. J. Schinner, H. P. Tranitz, W. Wegscheider, J. P. Kotthaus, S. Ludwig, Phys. Rev. Lett. 102, 186801 (2009).



September 15, 2009, 11:00, FENS 2019