Cryo-CMOS Circuits and Systems for Scalable Quantum Computing

Quantum computing holds a promise to achieve unprecedented computation power and to solve problems today intractable. State-of-the-art quantum processors consist of arrays of quantum bits (qubits) operating at a very low base temperature, typically a few tens of mK. The qubit states degrade naturally after a certain time, upon loss of quantum coherence. For proper operation, a fault-tolerant quantum computer with millions of qubits requires massive yet very precise control electronics for the manipulation and read-out of individual qubits. While few qubits (~10) in today’s quantum processors can be easily connected to a room-temperature controller; however, it appears extremely challenging, if not impossible, to manage the thousands of qubits required in practical quantum algorithms. CMOS operating at cryogenic temperatures down to 4K (cryo-CMOS) allows for a closer system integration, thus promising a scalable solution to enable future quantum computers. In this presentation, a cryogenic control system is proposed, along with the required specifications, for the interface of the classical electronics with the quantum processor. To prove the advantages of such a system, the functionality of key circuit blocks is experimentally demonstrated. First, the characterization of nanometer CMOS transistors of different aspect ratios at deep-cryogenic temperatures (4 K and 100 mK) is presented for two standard CMOS technologies (40 nm and 160 nm). A detailed understanding of the device physics at those temperatures was developed and captured in an augmented MOS11/PSP model. Second, the characteristic properties of cryo-CMOS are exploited to design a noise-canceling low-noise amplifier for spin-qubit RF-reflectometry read-out, and a class-F digitally controlled oscillator required to manipulate the state of qubits. A detailed analysis of the measurement results over temperature is also presented. Finally, the advantages and disadvantages of designing CMOS circuits at cryogenic temperatures are investigated.