PhD defense rehearsal: Highly integrated RF electronics for readout of superconducting circuits

by Robert Gartmann (KIT-IPE)

Monday Oct 26, 2026, 2:00 PM → 3:00 PM Europe/Berlin

Seminarraum EG + zoom (IPE)

Robert Gartmann will present his PhD thesis. The presentation will be held in German.

Abstract:

Microintegration through lithography of superconducting circuits enables the formation of qubits and quantum sensors, promising advances in several scientific fields. Qubits, leveraging quantum superposition and entanglement, facilitate simulation and modelling of quantum processes. Quantum computing establishes new algorithms that drastically reduce the asymptotic execution runtime from exponential to polynomial time. Furthermore, detectors can benefit from the cryogenic environment through low ambient noise levels and the macroscopic wave function property of superconducting materials.

Future experiments require channel counts of sensors and qubits in the thousands. Handling the necessary signals for operation and readout at high resolution and fidelity imposes challenges on the full signal processing chain, which spans from room temperature to the millikelvin domain. To limit the number of lines and heat conduction to the sample, frequency division multiplexing (FDM) increases the channel count through waveguide connections. Their substantial bandwidth supports elaborate analogue and concurrent microwave signal transmission. The high-throughput data acquisition (DAQ) electronics are typically founded on software-defined radio (SDR) with a field-programmable gate array (FPGA) core. As the latter is a digital-only device, there is a need for analog-to-digital converters (ADCs) and digital-to-analog converters (DACs), subsequently requiring conversion to RF. At Institute for Data Processing and Electronics (IPE), such a flexible SDR for superconducting cryogenic circuits is developed, albeit without custom integrated RF electronics yet. Therefore, capability expansion of the analogue RF stage is needed, towards higher channel counts and channel density through increased instantaneous bandwidth. This serves as a foundation for present and upcoming experiments and applications.

The development of the analogue RF signal conditioning hardware is presented in this thesis, to refine and advance both current and proposed developments in cryogenic electronics interfacing. While starting from general criteria and drafting of requirements, it culminates in the creation of two pieces of hardware for two use cases: cryogenic quantum sensor readout and qubit characterisation. Multiple evaluation printed circuit boards (PCBs) are also introduced, with advanced methodology and measurements. This thesis guides through the concepts, schematic capture and PCB routing, manufacturing, assembly and finally verification of the full systems in use. Besides synthetic characterisation and validation throughout the chapters, each also contains multiple real world experiments, demonstrating the newly gained capabilities of simultaneous 400 channel readout and standalone qubit entanglement.

The main challenges and intricacies along the way enable a thorough understanding for future scalability. The thesis therefore establishes an essential contribution for utilisation of the SDR and beyond in future projects.