Quantum transport

The everlasting trend to miniaturize classical electronic devices has guaranteed progress over half a century. This evolution is now reaching its fundamental limits due to the granularity of matter and the quantum nature of the electron dynamics, which modifies the circuit properties on extremely short length and time scales. Therefore, future progress of electronics will be increasingly based on the coherent quantum dynamics of individual states. This development is often denoted as the second quantum revolution.


Transport spectroscopy is applied as a tool to explore the dynamics of nanoscale semiconductor quantum circuits, typically at very low temperatures. The aim of this research is to utilize the coherent superposition of quantum states and to pave the way for future technologies such as quantum simulators or quantum computers. Therefore, the coherent dynamics of individual electronic quantum excitations and of their interactions is investigated on a fundamental level.


The investigated nanostructures are fabricated using state-of-the-art cleanroom facilities. The surface of semiconductor heterostructures or nanowires is patterned by optical and electron beam lithography. In this way, nanoscale electrical contacts and metal electrodes are created to shape the local electrostatic potential within a conducting sheet using the electric-field effect. The circuit components include interacting quantum point contacts, coupled quantum dots, ballistic structures, and hybrid devices such as quantum dots coupled to on-chip phonon resonators.


Information processing is always based on non-equilibrium operations, while quantum control and coherence are closely related to interactions on the microscopic level. Hence, aiming at full control while minimizing decoherence, the main focus of this research covers the dynamics, the interaction, and the coherence of non-equilibrium excitations in quantum circuits.



2 Author M. Geier , J. Freudenfeld , J. T. Silva , V. Umansky , D. Reuter , A. D. Wieck , P. W. Brouwer , S. Ludwig

Electrostatic potential shape of gate defined quantum point contacts

Source Phys. Rev. B , 101 , 165429 ( 2020 )
DOI : 10.1103/PhysRevB.101.165429 | Download: PDF | 3178 Cite : Bibtex RIS
M. Geier, J. Freudenfeld, J. T. Silva, V. Umansky, D. Reuter, A. D. Wieck, P. W. Brouwer, and S. Ludwig

1 Author J. Freudenfeld , M. Geier , V. Umansky , P. W. Brouwer , S. Ludwig

Coherent Electron Optics with Ballistically Coupled Quantum Point Contacts

Source Phys. Rev. Lett. , 125 , 107701 ( 2020 )
DOI : 10.1103/PhysRevLett.125.107701 | Download: PDF | 3101 Cite : Bibtex RIS
J. Freudenfeld, M. Geier, V. Umansky, P. W. Brouwer, and S. Ludwig


Prof. Dr. Holger T. Grahn

Head of Department 

+49 30 20377-318