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The defence will be in English.
Abstract: Acoustic wave devices are widely used in modern electronics and are becoming important components in quantum technologies due to their compactness, low crosstalk, and ability to couple to many quantum systems. This coupling is mainly achieved through piezoelectricity, which links electrical signals to mechanical motion. However, existing microwave-to-acoustic transducers typically suffer from either low efficiency or limited bandwidth. This thesis focuses on optimizing piezoelectric coupling between superconducting microwave circuits and acoustic waves in thin lithium niobate films. To achieve this, nanofabrication techniques were developed to integrate superconducting circuits with suspended acoustic structures. The work demonstrates high-performance piezoelectric transducers operating close to the theoretical limits imposed by material properties. By using SQUID arrays to match impedances, the devices achieve both large bandwidth and high efficiency. Using unidirectional transducers, we demonstrate unprecedented efficiency-bandwidth products of 440 MHz, with maximum efficiency of 62% at 5.7 GHz. Moreover, leveraging the flux dependence of SQUIDs, we realize transducers with in-situ tunability across nearly an octave around 5.5 GHz. A detailed analysis identifies the main loss mechanisms limiting performance. Additionally, the thesis presents a design for circuit quantum acoustodynamics, integrating a transmon circuit directly into an acoustic resonator. Simulations predict ultra-strong coupling between the transmon and the acoustic modes. Preliminary experimental data on such devices will be presented.
