Cryo-CMOS circuits for quantum computing

Quantum computers use quantum mechanical principles like superposition and entanglement to perform calculations in parallel on large amounts of data. This way they promise significant speedups of complex algorithms like prime factorization or data base searches. In a quantum computer the classical binary bits are replaced by quantum particles (qubits) at extremely low cryogenic temperatures. Interaction with these qubits requires conventional digital and analog control circuits (ADCs, DACs, LNAs, oscillators, etc.). However, today’s control circuits operate at room temperature, requiring long cables to connect them to the qubits at cryogenic temperatures. This interconnection strategy is only feasible for a limited number of qubits, whereas practical quantum algorithms require thousands or even millions of qubits. In order to obtain a more scalable solution the control circuits should be placed close to the qubits and hence they should also operate at cryogenic temperatures. This research aims to implement these control circuits in standard CMOS at cryogenic temperatures (cryo-CMOS). In order to enable reliable circuit design, several challenges must be overcome. For example, well-established cryo-CMOS device models are not yet available, and there has not yet been much research on noise and mismatch at cryogenic temperatures. Furthermore, the control circuits must meet stringent requirement in terms of accuracy and speed, while the dissipated power needs to be minimal in order not to exceed the cooling capabilities of the cryogenic refrigerator. In order to fulfil these challenging conditions, it is necessary to investigate how the specific properties of cryo-CMOS can best be used in circuit design.