Interplay between Photogenerated Charges and Microwave Losses in Quantum Dot Hybrid Systems

Quantum processing units (QPUs) based on quantum dots are currently limited in qubit scalability due to the inherent number of control gates and fabrication inconsistencies. Photogenerated charges trapped inside gate-defined quantum dots offer a promising platform for spin qubits, addressing those two limitations. However, this technique introduces new challenges, particularly in hybrid systems with superconducting coplanar waveguide resonators, where photogenerated charges can act as loss channels due to their uncontrolled creation throughout the semiconductor.

To address this, we combine two strategies to confine charge generation exclusively to the quantum dot region. First, the heterostructure is selectively etched away, leaving the active region only under the control gates. Second, a GRIN lens mounted on a piezo stack delivers light with 2-micron precision, ensuring targeted charge generation.

This talk will discuss the effectiveness of these techniques and their implications for future photopopulated quantum dot development.