Characterization and Design of a Cryogenic CMOS Receiver for Superconducting and Spin Qubit Readout

Abstract

Quantum computers hold a promise to solve intractable problems that can not be solved with classical computers. In quantum computers, information is processed in qubits as opposed to bits. The proper operation of qubits requires them to be operated in a quantum state; hence they need to be cooled down to temperatures well below <1K. Using qubits and their quantum mechanical property, quantum computers can achieve exponential speedup in solving certain computing problems compared to classical computers. However, this can only be achieved by employing thousands of qubits. At the current state of play, quantum computers are still far from practical. The current state-of-the-art solution dictates that each qubit needs multiple interconnects towards room temperature and requires bulky room temperature instruments for qubit readout and control. Clearly, this current solution will not scale well for a quantum computer with many qubits. In an effort to solve this issue, it has been proposed to realize dedicated integrated circuits for control and readout of the qubits and operate them closer to the qubits' operating temperature to enable scalability.
The thesis presents the implementation of an integrated RF receiver for spin and superconducting qubit readout applications. The work aims to replace the bulky room temperature electronics with an integrated solution that operates at 4K to enable scalability and simplification of the quantum computing architecture. The receiver has been designed in the TSMC 40nm CMOS technology and has been characterized in room temperature and 4K. The measured performance shows that the receiver features a gain of 58 dB and a minimum double-sideband noise figure of 0.6 dB at 4K with an operating frequency of 6-8 GHz; a comparable performance to the current state-of-the-art room temperature electronics used for qubit readout. Moreover, this work demonstrates a qubit readout experiment with the integrated receiver in both room temperature and 4K. The qubit readout experiment shows a comparable qubit readout performance with the integrated receiver at room temperature. However, due to oscillation problems, a degradation in qubit readout performance with the chip operating at 4K is observed.