High quality micro-and nano-mechanical resonators are widely used in sensing, communications and timing, and have future applications in quantum technologies and fundamental studies of quantum physics. Crystalline thin-films are particularly attractive for such resonators due to their prospects for high quality, intrinsic stress and yield strength, and low dissipation. However, when grown on a silicon substrate, interfacial defects arising from lattice mismatch with the substrate have been postulated to introduce additional dissipation. Here, we develop a new backside etching process for single crystal silicon carbide microresonators that allows us to quantitatively verify this prediction. By engineering the geometry of the resonators and removing the defective interfacial layer, we achieve quality factors exceeding a million in silicon carbide trampoline resonators at room temperature, a factor of five higher than without the removal of the interfacial defect layer. We predict that similar devices fabricated from ultrahigh purity silicon carbide and leveraging its high yield strength, could enable room temperature quality factors as high as 6 × 10 9 .

We demonstrate a single-mode phononic waveguide that enables robust propagation of mechanical waves. The waveguide is a highly-stressed silicon nitride membrane that supports the propagation of out-of-plane modes. In direct analogy to rectangular microwave waveguides, there exists a band of frequencies over which only the fundamental mode is allowed to propagate, while multiple modes are supported at higher frequencies. We directly image the mode profiles using optical heterodyne vibration measurement, showing good agreement with theory. In the single-mode frequency band, we show low-loss propagation (∼ 1 dB/cm) for a ∼ 5 MHz mechanical wave. This design is well suited for phononic circuits interconnecting elements such as non-linear resonators or optomechanical devices for signal processing, sensing or quantum technologies.

Nanomechanical resonators have applications in a wide variety of technologies ranging from biochemical sensors to mobile communications, quantum computing, inertial sensing, and precision navigation. The quality factor of the mechanical resonance is critical for many applications. Until recently, mechanical quality factors rarely exceeded a million. In the past few years however, new methods have been developed to exceed this boundary. These methods involve careful engineering of the structure of the nanomechanical resonator, including the use of acoustic bandgaps and nested structures to suppress dissipation into the substrate, and the use of dissipation dilution and strain engineering to increase the mechanical frequency and suppress intrinsic dissipation. Together, they have allowed quality factors to reach values near a billion at room temperature, resulting in exceptionally low dissipation. This review aims to provide a pedagogical introduction to these new methods, primarily targeted to readers who are new to the field, together with an overview of the existing state‐of‐the‐art, what may be possible in the future, and a perspective on the future applications of these extreme‐high quality resonators.

In this paper we investigate a hybrid quantum system comprising a mechanical oscillator coupled via magnetic induced electromotive force to an LC resonator. We derive the Lagrangian and Hamiltonian for this system and find that the interaction can be described by a charge-momentum coupling with a strength that has a strong geometry dependence. We focus our study on a mechanical resonator with a thin-film magnetic coating which interacts with a nanofabricated planar coil. We determine that the coupling rate between these two systems can enter the strong and ultrastrong coupling regimes with experimentally feasible parameters. This magnetomechanical configuration allows for a range of applications including electromechanical state transfer and weak-force sensing.

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Micro and nanomechanical systems play an important role in modern science and technology.They are indispensable for precision sensing, navigation and communication. Over the past decade, the rapid advances in nano-fabrication and measurement science have enabled quantum control of mechanical devices by integrating them to optical and microwave cavities, in the growing field of quantum optomechanics. However, experiments in quantum optomechanics at room temperature still face significant challenges. Perhaps the most demanding condition to perform experiments of this nature is reducing noise level due to coupling of the device to its environment through mechanical vibrations, phonons. In this thesis, we engineer micromechanical devices that confine mechanical excitations, decoupling them from their environment. The engineered design of these resonators combines a built-in suspended phononic low pass filter with a trampoline design made of top quality SiC single crystal. Results with quality factors Q ∼ 4 × 10 8 show the efficiency of these resonators. This is the largest Q for a system of its kind with such a large mesoscopic mode size ∼ 0.5 mm 2 and resonance frequency f ∼ 220 kHz.The ultra-high Q mechanical resonators we developed can be used for quantum optomechanics experiments at room temperature.Similar to electrons, phonons propagate through material and are characterized by their dispersion relation. By engineering the properties of the material it is possible to confine and guide phonons through phononic channels. The importance of guided phonons relies on the fact that guided signals are the back-bone of all communication systems. The existing platforms for mechanical channels rely on the inclusion of phononic crystals for phonon confinement. However, phononic crystals base their functionality on acoustic interference, limiting its scalability. In this thesis, we designed, fabricated and characterized the basic components for a phononic circuitry platform based on highly stressed Si 3 N 4 membranes on Si. These phononic waveguides share a similar mathematical framework with to photonic waveguides. Our phononic waveguides are single mode for a range of frequencies. In this region, the guided mode experiences low dissipation. We also show that there is a cut-off frequency at which the excitations cannot propagate, completely analogous to the photonic case. This phononic "wires" could in principle be used as the fundamental element for mechanics based communication networks.In the last chapter of this thesis, we propose a magnetomechanical system, where the mechanical system couples through the momentum to an electromagnetic field. By coupling the momentum to an electromagnetic field, it is possible to perform non-demolition measurement protocols that allow us to measure directly the position of the oscillator. By enhancing the coupling between the mechanics and the electromagnetic field we predict that the ground state of the two systems get entangled. We designed a system that can achieve coupling rates as...