# Hy-Q Seminar: Thomas Descamps

### Thin semiconductor membrane for optical coupling of a gate-defined quantum dot to an electrostatically-defined exciton trap

###### Thomas Descamps, JARA-FIT Institute Quantum Information, Forschungszentrum Jülich GmbH and RWTH Aachen University, 52074 Aachen, Germany
Interfacing stationary matter qubits with photonic qubits is a major milestone towards the realization of a quantum network [1]. Spin qubit in GaAs gate-defined quantum dots (GDQD) is a promising candidate since it meets all the quantum computing requirements and can interact with photons. In this presentation, I will present a scheme to integrate an electrostatically-defined and optically active quantum dot at tunnel coupling distance to a GDQD [2]. This dot serves as intermediary between the photonic qubit and the spin qubit. Based on the quantum-confined Stark effect, the optically active dot traps excitons in the maxima of a local electric field applied across the heterostructure with fabricated metal gates [3]. As a result, thinning heterostructure down to a membrane without degrading its optical and transport properties is of primary importance for the implementation of this scheme.
In this talk, I will discuss the preliminary steps towards this goal. After detailing the fabrication of the membrane devices, I will present a customized dry dilution refrigerator allowing optical excitation to characterize and operate them. Doped and undoped membranes were both investigated to assess the feasibility of the aforementioned scheme. In doped membrane, the mobility of the two-dimensional electron gas (2DEG) can reach over $1 \times 10^{6}$ cm$^{2}$V$^{-1}$s$^{-1}$, close to the value on substrate. Quantum point contacts and Coulomb oscillations were also observed. Besides, exciton traps can be made provided depletion of the 2DEG. In undoped membranes, a 2DEG can be accumulated by positively biasing a metal top-gate voltage and exciton trap can also be fabricated.

[1] Kimble, H. The quantum internet. Nature 453, 1023–1030 (2008)
[2] Benjamin J. et al. Transfer of a quantum state from a photonic qubit to a gate-defined quantum dot. Physical Review B, 99(20), dec 2019
[3] Schinner G. J. et al. Confinement and interaction of single indirect excitons in a voltage-controlled trap formed inside double InGaAs quantum wells. Physical Review Letters, 110(12), mar 2013.