(A) cryogenic-MEMS switch for modulating a circulator in quantum computer readout circuit

Abstract

A quantum computer is an emerging candidate to solve various problems that require large computational power, by processing data through qubits and quantum algorithms with higher speed exceeding conventional supercomputers. Since superconducting qubits must be located in a cryogenic environment to maintain their quantum state, microwave circuits for controlling and measuring them must operate stably in a cryogenic environment as well. A circulator is an essential component that is placed very adjacent to qubits, to protect sensitive qubits from external energy and signals. Normally, circulators used in a quantum computer are composed of magnets and ferrites, thereby they occupy most of the volume of a cryogenic circuit and cannot be integrated on a chip. Therefore, numerous previous studies have been conducted on compact spatio-temporal modulation circulators without magnets, but a variable capacitor, which is a modulation element, has been unable to operate at a very low temperature due to the free carrier freeze-out phenomenon of semiconductors. In this thesis, we demonstrated a MEMS switch capable of stable cryogenic operation and showed its feasibility of implementation as a modulation element of a spatio-temporal modulation circulator for application to a quantum computer.