Applied Physics and Materials Science Special Seminar

Abstract:

In the quest to observe and exploit ever-faster physical phenomena, ultrashort light pulses with a few optical cycles play a crucial role. Precisely controlling the light waveform allows us to manipulate and study processes on a sub-cycle timescale of the laser pulse. Such waveform control opens prospects for technological applications, especially for on-chip signal processing at speeds that exceed by orders of magnitude the current gigahertz clock rates of processors - opening the realm of petahertz electronics. In my talk, I will present how the electric field of laser pulses can be used to build ultrafast light-wave electronics and how the underlying processes can be used to observe and control novel solid-state quantum processes.

Using a strong light field, it is possible to steer electrons on complex electron trajectories inside 2D materials, such as graphene [1- 3]. Due to the fast timescale involved, the electron dynamics is described fully quantum mechanically, which allows the electron to drive like a matter wave through the band structure. In the vicinity of the band gap, the electron wavefunction can be split into conduction and valence band states. Because these transition events act as electron beam splitters, we have built a light-field-driven electron interferometer akin to a Mach-Zehnder interferometer for light. The quantum phase accumulated in the beam-split state determines in which output port the electron ends up: in the valence or the conduction band, and defines the direction and amount of injected photocurrent [1,2]. Additionally, by tailoring the electron trajectory with the light field, we can map the accumulated quantum phase and turn the interference on and off, thus, representing an optical analog of a field-effect transistor [3].

Although the band structure of graphene allows quantum control most simply, it is even more fascinating to extend the concept of light-field controlled electron dynamics to tailored quantum materials and topologically protected materials. These materials are promising candidates for Floquet engineering or non-dissipative topological quantum electronics [4, 5]. Based on bismuth selenide, I demonstrate that the topologically protected conducting surface states are ideally suited to coherently drive electrons inside of solids [5]. Additionally, I demonstrate that light-field-driven electron dynamics are ideally suited to measure the coherence lifetime of the electrons after excitation [6,7], to build a novel quantum sensor for the electro-optical reconstruction of the band structure, to control the charge on the attosecond timescale across material interfaces [8] and to built light-field driven logic gates [2].

Looking forward, I will discuss how to bridge the gap between ultrafast phenomena, photonics, quantum materials, and quantum optics towards Wavetronics: Lightfield-driven quantum electronics on a chip. The primary goal will be to harness strong light fields to dynamically control and imprint information on electrons on the fastest possible timescale. This includes strategies to read out the quantum phase by developing advanced ultrafast spectroscopy tools such as light-field-driven electron interferometry. Access to the quantum phase and understanding lightwave-driven processes in tailored quantum materials will allow new insights into material properties, which will ultimately help to develop electronics operating at optical clock rates.

[1] Higuchi T., Heide C., et. al. Nature 550, 224-228 (2017) [2] Boolakee T., Heide C., et al. , Nature 605, 251-255 (2022)

[3] Heide C., et. al PRL 121, 207401 (2018) [4] Kobayashi Y, Heide C., et al. Nature Physics, 1-6 (2023)

[5] Heide C., Kobayashi Y, et al. Nature Photonics 16, 620-624 (2022) [6] Heide C., Eckstein T., et. al., Nano Letters, 21, 9403 (2021)

[7] Heide C., Kobayashi Y, et. al. Optica 9, 512-516 (2022) [8] Heide C. et. al. Nature Photonics 14, 219–222 (2020)

More about the Speaker:

Christian Heide received his PhD from Friedrich-Alexaner University in Erlangen- Nuremberg, Germany, in 2020 with distinction. Since 2020, he has been working with Profs. Tony Heinz, David Reis, and Shambhu Ghimire at the Stanford PULSE Institute. Since 2021, he is a Feodor Lynen Fellow of the Alexander von Humboldt Foundation. Christian's research interests include coherent control of electrons on the fastest possible timescale. This comprises the design and development of light-field-driven electronics and the development of advanced spectroscopy tools to probe novel quantum phenomena. Christian was awarded the best dissertation award by the German Physical Society (DPG) and by the German Society for Applied Optics.