April 2024

Abstracts of the Quantum Center Lunch Seminar

Date: Thursday, April 4, 2024
Place: ETH Zurich, Hönggerberg, HPF G 6
Time: 12:00 - 13:30

Spin-orbit coupling in bilayer graphene/transition-metal dichalcogenide quantum devices

Jonas Gerber - The Ensslin Nanophysics Group (Ensslin group), ETH Zurich

A high spin-orbit coupling (SOC) is beneficial for driving qubits fast. While graphene exhibits relatively low SOC values, typically ranging from 40-80 µeV [1,2], its integration with transition-metal dichalcogenides (TMDs) presents a promising possibility for enhancing SOC [3,4,5] while preserving high electronic mobility [6].

Our study examines the properties of quantum point contacts and quantum dots in bilayer graphene/TMD heterostructures. We observe a significant enhancement of the SOC in the bilayer graphene, reaching up to 1.4meV. Moreover, we demonstrate the capability to tune the SOC strength by manipulating the position of the charge carriers in the bilayer graphene relative to the TMD layer.

This increased SOC strength combined with the tunability of SOC in bilayer graphene/TMD heterostructures holds great potential for future quantum computing and spintronics applications.

[1] L. Banszerus, et al. Phys. Rev. Lett. 124, 177701 (2020).
[2] A. Kurzmann, et al. Nat. Commun. 12, 6004 (2021).
[3] A. Avsar, et al. Nat Commun. 5, 4875 (2014).
[4] Z. Wang, et al. Phys. Rev. X 6, 041020 (2016).
[5] M. Gmitra, and J. Fabian. Phys. Rev. Lett. 119, 146401 (2017).
[6] A. V. Kretinin, et al. Nano Lett. 14, 3270-3276 (2014).

Quantum squeezing in a nonlinear mechanical oscillator

Matteo Fadel - Hybrid Quantum Systems (Chu Group), ETH Zurich

Mechanical degrees of freedom are natural candidates for continuous-variable quantum information processing and bosonic quantum simulations. These applications, however, require the engineering of squeezing and nonlinearities in the quantum regime. In our work, we demonstrate ground state squeezing of a gigahertz-frequency mechanical resonator coupled to a superconducting qubit. This is achieved by parametrically driving the qubit, which results in an effective two-phonon drive. In addition, we show that the resonator mode inherits a nonlinearity from the off-resonant coupling with the qubit, which can be tuned by controlling the detuning. We thus realize a mechanical squeezed Kerr oscillator, where we demonstrate the preparation of non-Gaussian quantum states of motion with Wigner function negativities and high quantum Fisher information. This shows that our results also have applications in quantum metrology and sensing.