STAGE offre de stage : Electron tunneling time and its fluctuations

Challenging our classical intuition, quantum tunneling has fascinated physicists for decades. Very soon after its discovery, it raised the question of how much time do particles spend under the classically forbidden barrier. Despite its simplicity, such a question is ill defined in terms of quantum observables and does not admit a single answer, thus triggering over the past decades a bunch of different definitions corresponding to different (thought) scenarios.
Following a proposal by Büttiker & collaborators [1], we will address this question from the perspective of a well-defined observable: that is, measuring the spectrum of time fluctuations of the number of particles residing within the classically forbidden barrier. The idea is to exploit semiconducting 2D electron gases where electrostatically coupled metallic gates are used to generate the electrostatic potential barrier upon which the electrons are scattered. Moreover, we will equally use them to collect the mirror influence-charges fluctuating in response to the tunneling electrons residing within the electrostatic barrier. Despite its conceptual simplicity, implementing such a scenario is a formidable task since it demands collecting a tiny radiofrequency (RF) signal emitted by a huge output-impedance source in a sub-Kelvin (dilution) refrigerator. We will build upon the group’s expertise in RF design and ultra-low noise measurements in cryogenic environments in order to overcome this challenge, notably implementing recently developed high impedance RF matching circuits [2] allowing us to efficiently collect the signal into a RF detection chain.
The student will participate to the radiofrequency design of the samples, to their fabrication in a clean-room environment, and to their measurement exploiting low noise measurement techniques both in the near DC and the few GHz range. He will become familiar with sub-Kelvin cryogenic techniques as well.

References:
[1] Pedersen, van Langen, and Büttiker, Phys. Rev. B 57, 1838 (1998)
[2] Rolland et al., https://arxiv.org/abs/1810.06217
[3] Anthore et al., Phys. Rev. X 8, 031075 (2018)
[4] Altimiras, Portier and Joyez, Phys. Rev. X 6, 031002 (2016)