Millikelvin cryo-CMOS – qubit (co)-integration for scalable superconducting qubit control

Quantum computing is today one of the most promising future technologies that can keep up with the raising humanities’ computation needs as well as offer new information processing paradigms, some of which we cannot even fully grasp today. In the last three decades an enormous progress towards quantum computing was made by both university and private research groups, leading to demonstrations of basic quantum algorithms [1], quantum error correction [2] and quantum supremacy [3]. Currently we are on a path of scaling prototypical quantum computers beyond 100 qubits, with projections reaching ~1000 qubits in a quantum computer using known methodology [4]. Going beyond that, towards fault tolerant quantum computing, would require drastically new concepts in qubit fabrication, control, and input-output (I/O) signal routing.

In superconducting quantum technology, and other quantum technologies, each qubit requires dedicated control instrumentation and at least one signal wire between room temperature and qubit’s operating temperature, which is normally at 10 millikelvin in a dilution refrigerator. This represents a scaling bottleneck for qubit control and I/O wiring. For example, a state-of-the-art dilution refrigerator does not have enough cooling power (~10 µW) and volume (~1 m³) to support millions of RF coaxial cables between RT and 10 mK stages. A promising solution to the wiring problem and later to qubit control is using specially designed ultra-low power cryo-CMOS electronics that can operate at millikelvin. Our initial work on multiplexers [5] has shown that co-placement of superconducting qubits and cryo-electronics is in principle possible, however, for practical applications power consumption must still be significantly reduced.

Within the proposed PhD topic, a student, supported by imec experts, would explore fundamental limits of cryo-CMOS electronics based on FDSOI or similar technologies at millikelvin temperature, explore ultra-low power integrated circuits designs and packaging methods that would render cryo-electronics compatible with superconducting qubits and enable scalable operations such as qubit control, read-out, qubit-qubit interaction, etc.

We are seeking a highly motivated and skilled student that would be willing to undertake this challenge and make a difference in the interdisciplinary field of cryo-electronic and superconducting qubit technology. Strong background in electrical engineering, circuit design microwave technology is highly desired. Understanding of physics, quantum mechanics and heat-flow modelling is beneficial. The student would spend a large part of his/her work designing cryo-CMOS and superconducting qubit circuits (35%), perform classical and quantum device characterization (45%), and literature study and dissemination (20%).

[1] Harrigan, et al., Nature Physics 17, 332–36 (2021).

[2] Krinner, et al., Nature 605,669–74 (2022).

[3] Arute, et al., Nature 574, 505–10 (2019).

[4] Cho A., Science News, doi:10.1126/science.abe8122 (2022).