One of the most important and topical challenges of quantum circuits is their scalability. Rapid Single Flux Quantum (RSFQ) technology is at the forefront of replacing current standardCMOS-based control architectures for a number of applications, including quantum computing and quantum sensor arrays. By condensing the control and readout to SFQ-based on-chip devices that are directly connected to the quantum systems, it is possible to minimise the total system overhead, improving scalability and integration. In this work, we present a novel RSFQ device that generates multi tone digital signals, based on complex pulse train sequences using a Circular Shift Register (CSR) and a comb filter stage. We show that the frequency spectrum of the pulse trains is dependent on a preloaded pattern on the CSR, as well as on the delay line of the comb filter stage. By carefully selecting both the pattern and delay, the desired tones can be isolated and amplified as required. Finally, we propose architectures where this device can be implemented to control and readout arrays of quantum devices, such as qubits and single photon detectors.
Electromagnetic filtering is essential for the coherent control, operation and readout of superconducting quantum circuits at milliKelvin temperatures. The suppression of spurious modesaround the transition frequencies of a few GHz is well understood and mainly achieved by on-chip and package considerations. Noise photons of higher frequencies — beyond the pair-breaking energies — cause decoherence, and require spectral engineering before reaching the packaged quantum chip. The external wires through the refrigerator down to the quantum circuit provides a direct path, and this article contains quantitative analysis and experimental data for noise photon flux through the coaxial filtered wiring. The coaxial cable attenuation and noise photon flux for typical wiring configurations are provided, and compact cryogenic microwave low-pass filters with CR-110 and Esorb-230 absorptive dielectric fillings along with experimental data at room and cryogenic temperatures and up to 70 GHz presented. The filter cut-off frequencies between 1 to 10 GHz are set by the filter length, and the roll-off is material dependent. The relative dielectric permittivity and magnetic permeability for the Esorb-230 material in the pair-breaking frequency range from 75 to 110 GHz are measured, and the filter properties in this frequency range are calculated. The filter contribution to the noise photon flux implies a dramatic reduction, proving their usefulness for experiments with superconducting quantum systems.