Photon-assisted tunneling and charge transport in hybrid circuits

Abstract

Photonic dissipation and charge sensing are two crucial topics of modern quantum circuit dynamics. Quantum circuits operating at low powers reaching few-photon level require precise control over losses to be a workhorse of quantum information processing. Contrastingly, qubit manipulation demands reliable reset protocols. Although charge sensing is considered as a mature diagnostic device in mesoscopic physics, high-frequency charge pumping requires much more sensitive detectors to reveal faster electron dynamics. In all of the topics discussed in this thesis, a multitude of device materials and parameters are explored, consisting of superconductors, normal metals, insulators, field-induced two-dimensional electron gas conductors, and quantum dots. The variety of the mentioned "components" forms the investigated hybrid nanostructures. In this thesis, the control of the coupling between a superconducting resonator and a dissipative reservoir is investigated. One convenient control method is to employ a normal-metal–insulator–superconductor junction, which functions as a voltage-tunable heat sink that is compatible with superconducting circuit technology. The heat sink is found to modulate the fundamental frequency of a resonator, a signature of a broadband Lamb shift in a microwave circuit. Also, the heat sink can be operated as an accurate thermal microwave source that can be used to calibrate the total gain of an arbitrary amplification chain. Another method, as demonstrated in an experiment, is to couple two resonators capacitively with one of the resonators that was intentionally engineered with a low-quality factor. This highly-dissipative resonator has an integrated magnetic-field-sensitive superconducting quantum interference device that enables the tunability of the resonator natural frequency. Matching the resonances of both resonators then allows to increase the dissipation in the high-quality resonator. This work also investigates electric current metrology realized through semiconductor field-effect transistor quantum dot pumps. In one aspect, we integrated a high-sensitivity superconducting Josephson-junction-based charge sensor with a silicon quantum dot architecture to examine the noise properties of the system. By studying the noise statistics, we are able to determine the dominant noise mechanism surrounding these pumps thus paving the way to the development of better detectors. In another aspect, the portability of a quantum dot single-electron pump is verified, where we have demonstrated that the relative uncertainty of the quantized current created by the same device is within 1.30 ppm regardless of the location of the experiment.