AB
A. Bruno
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Quantum-limited parametric amplifiers have become increasingly interesting and relevant with the progressing field of quantum computing. However, currently it is still challenging to fabricate these complex devices. In this thesis, we developed cross type Josephson junctions (JJs), lumped element LC resonators, lumped element Josephson parametric amplifiers (JPAs) and Josephson traveling wave parametric amplifiers (JTWPAs). We found and resolved several fabrication issues however we suspect that both the JPA and JTWPA suffered from microshorts in the circuits during the cryogenic measurements. Nevertheless, we managed to measure the resonance frequency of the JPA and have noticed the flux focusing effect when we flux tune it. We preformed room temperature measurements on over 300 JJs and calculated the relative standard deviation (RSD) for various JJ sizes. We found the spread of 30 fabricated resonators and a rough estimate of their Q factors. The JTWPAs developed are non-degenerate four wave mixing amplifiers that use the resonant phase matching (RPM) technique to reduce the phase mismatch problem. The transmission through the measured JTWPA showed 50 dB loss probably caused by presumably a short from the transmission line to ground. However, when the JTWPA was driven with a pump we observed 20 dB increase in transmission in some frequency bands.
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Quantum-limited parametric amplifiers have become increasingly interesting and relevant with the progressing field of quantum computing. However, currently it is still challenging to fabricate these complex devices. In this thesis, we developed cross type Josephson junctions (JJs), lumped element LC resonators, lumped element Josephson parametric amplifiers (JPAs) and Josephson traveling wave parametric amplifiers (JTWPAs). We found and resolved several fabrication issues however we suspect that both the JPA and JTWPA suffered from microshorts in the circuits during the cryogenic measurements. Nevertheless, we managed to measure the resonance frequency of the JPA and have noticed the flux focusing effect when we flux tune it. We preformed room temperature measurements on over 300 JJs and calculated the relative standard deviation (RSD) for various JJ sizes. We found the spread of 30 fabricated resonators and a rough estimate of their Q factors. The JTWPAs developed are non-degenerate four wave mixing amplifiers that use the resonant phase matching (RPM) technique to reduce the phase mismatch problem. The transmission through the measured JTWPA showed 50 dB loss probably caused by presumably a short from the transmission line to ground. However, when the JTWPA was driven with a pump we observed 20 dB increase in transmission in some frequency bands.
For quantum computing with superconducting qubits, fabricating transmon qubits with increased coherence time is crucial, especially in view of multi-qubit quantum processors. The fabrication process, geometries and materials used to fabricate a transmon qubit are similar to the fabrication of CPW resonators. However, due to shorter fabrication time and straightforward measurement scheme of the latter, finding a way to increase the internal quality factor Qi in a CPW resonator is a quick way to gain insight into methods to increase the coherence time of a transmon qubit. The main goal of this research is to characterize the Qi at cryogenic temperature and single photon level of CPW resonators that are fabricated with novel surface treatments and etching techniques. The highest Qi is observed for resonators etched using Deep Reactive Ion Etching and HDMS surface treatment, which reached ∼106 at single photon level. This is comparable to the highest Qi reported in literature so far.
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For quantum computing with superconducting qubits, fabricating transmon qubits with increased coherence time is crucial, especially in view of multi-qubit quantum processors. The fabrication process, geometries and materials used to fabricate a transmon qubit are similar to the fabrication of CPW resonators. However, due to shorter fabrication time and straightforward measurement scheme of the latter, finding a way to increase the internal quality factor Qi in a CPW resonator is a quick way to gain insight into methods to increase the coherence time of a transmon qubit. The main goal of this research is to characterize the Qi at cryogenic temperature and single photon level of CPW resonators that are fabricated with novel surface treatments and etching techniques. The highest Qi is observed for resonators etched using Deep Reactive Ion Etching and HDMS surface treatment, which reached ∼106 at single photon level. This is comparable to the highest Qi reported in literature so far.