Low-noise high-frequency electronics for quantum computers

Dr. Fabian Thome and Felix Heinz from Fraunhofer IAF are developing cryogenic high-frequency electronics for existing quantum computer concepts in the EU-funded joint project “SEQUENCE”. The motivation is to scale up established quantum computer architectures, which is only possible by means of compact and extremely low-noise electronics.

Neither of you are (quantum) physicists, how did you get involved in this project?

Thome — Quantum computing has long since ceased to be an exclusive research field for quantum physicists and has become an interdisciplinary one. Ultimately, the current goal of scaling quantum computers (QCs), which have been proven to work today, relies heavily on electrotechnical components—and this is where we, as high-frequency engineers, come into play.

Heinz — We both have our scientific background in the research of cryogenic and ultra-low-noise amplifiers. Until a few years ago, this was truly a niche topic, typically applied in radio astronomy. However, since the first functional QCs emerged, there has been a whole new interest in this research area. Cryogenic and low-noise electronics are needed for reading out and controlling qubits.

What is your role in the project? 

Thome — In this project, we at Fraunhofer IAF are researching high-frequency technologies with which we have already gained a lot of experience, such as mHEMTs and MOSHEMTs. We want to optimize these with regard to their use in QCs. To do this, we need to further reduce the noise of the established technologies and make the components more compact so that the electronics can work closer to the sensitive and cooled qubits. As IAF’s project manager of “SEQUENCE”, I’m mainly research low-noise amplifiers.

Heinz — I am primarily responsible for cryogenic measurements and noise modeling. I research different technologies at extremely low temperatures and describe their behaviors with electrical models for CAD systems. Based on this, I design ultra-low noise circuits optimized for cryogenic operations.

What research questions would you like to pursue next?

Thome — An exciting topic that has not yet been exhaustively studied is the frequency scaling of QCs. Today, QCs use low-noise amplifiers in the frequency range of about 5 GHz as central components in their readout circuits. However, it is theoretically possible to increase this frequency. On the one hand, this could improve the performance of the systems, and on the other hand, it would allow us to exploit more synergies that go beyond quantum computing. One example are future satellite systems, in which low-noise amplifiers could be used at an operating temperature of about -220 °C.

Heinz — The chase for increasingly low-noise high-frequency electronics will remain an exciting question even after “SEQUENCE”. In this project, we will certainly take a big step in that regard, but it will not be the end. Furthermore, I am interested in novel integration concepts and multifunctional electronics for scalable QCs.