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Register a new userNonlinear coupling of phononic resonators induced by surface acoustic waves
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The rising need for hybrid physical platforms has triggered a renewed interest for the development of agile radio-frequency phononic circuits with complex functionalities. The combination of travelling waves with resonant mechanical elements appears as an appealing means of harnessing elastic vibration. In this work, we demonstrate that this combination can be further enriched by the occurrence of elastic non-linearities induced travelling surface acoustic waves (SAW) interacting with a pair of otherwise linear micron-scale mechanical resonators. Reducing the resonator gap distance and increasing the SAW amplitude results in a frequency softening of the resonator pair response that lies outside the usual picture of geometrical Duffing non-linearities. The dynamics of the SAW excitation scheme allows further control of the resonator motion, notably leading to circular polarization states. These results paves the way towards versatile high-frequency phononic-MEMS/NEMS circuits fitting both classical and quantum technologies.
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We present a theoretical framework allowing to properly address the nature of surface-like eigenmodes in a hypersonic surface phononic crystal, a composite structure made of periodic metal stripes of nanometer size and periodicity of 1 micron, deposited over a semi-infinite silicon substrate. In surface-based phononic crystals there is no distinction between the eigenmodes of the periodically nanostructured overlayer and the surface acoustic modes of the semi-infinite substrate, the solution of the elastic equation being a pseudo-surface acoustic wave partially localized on the nanostructures and radiating energy into the bulk. This problem is particularly severe in the hypersonic frequency range, where semi-infinite substrates surface acoustic modes strongly couple to the periodic overlayer, thus preventing any perturbative approach. We solve the problem introducing a surface-likeness coefficient as a tool allowing to find pseudo-surface acoustic waves and to calculate their line shapes. Having accessed the pseudo-surface modes of the composite structure, the same theoretical frame allows reporting on the gap opening in the now well-defined pseudo-SAW frequency spectrum. We show how the filling fraction, mass loading and geometric factors affect both the frequency gap, and how the mechanical energy is scattered out of the surface waveguiding modes.
We investigate the performance of microwave-frequency phononic crystal resonators fabricated on thin-film lithium niobate for integration with superconducting quantum circuits. For different design geometries at millikelvin temperatures, we achieve mechanical internal quality factors $Q_i$ above $10^5 - 10^6$ at high microwave drive power, corresponding to $5times10^6$ phonons inside the resonator. By sweeping the defect size of resonators with identical mirror cell designs, we are able to indirectly observe signatures of the complete phononic bandgap via the resonators internal quality factors. Examination of quality factors temperature dependence shows how superconducting and two-level system (TLS) loss channels impact device performance. Finally, we observe an anomalous low-temperature frequency shift consistent with resonant TLS decay and find that material choice can help to mitigate these losses.
We report the design and fabrication of diamond spin-mechanical resonators embedded in a two-dimensional (2D) phononic crystal square lattice. The rectangular resonator features GHz in-plane compression modes protected by the phononic band gap of the square lattice. A membrane-in-bulk approach is developed for the fabrication of the suspended 2D structure. This approach overcomes the limitations of the existing approaches, which are either incompatible with the necessary high-temperature thermal annealing or unsuitable for 2D structures with the required feature size. Graded soft oxygen etching, with the etching rate decreased gradually to below 1 nm/minute, is used to remove defective surface layers damaged by reactive ion etching. Combining the graded etching with other established surface treatment techniques reduces the optical linewidth of nitrogen vacancy centers in resonators with a thickness below 1 micron to as narrow as 330 MHz.
Recently, the concept of valley pseudospin, labeling quantum states of energy extrema in momentum space, has attracted enormous attention because of its potential as a new type of information carrier. Here, we present surface acoustic wave (SAW) waveguides, which utilize and transport valley pseudospins in two-dimensional SAW phononic crystals (PnCs). In addition to a direct visualization of the valley-dependent states excited from the corresponding chiral sources, the backscattering suppression of SAW valley-dependent edge states transport is observed in sharply curved interfaces. By means of band structure engineering, elastic wave energy in the SAW waveguides can be transported with remarkable robustness, which is very promising for new generations of integrated solid-state phononic circuits with great versatility.
Surface acoustic wave (SAW) is utilized in diverse fields ranging from physics, engineering, to biology, for transducing, sensing and processing various signals. Optical imaging of SAW provides valuable information since the amplitude and the phase of the displacement field can be measured locally with the resolution limited by the spot size of the optical beam. So far, optical imaging techniques rely on modulation of optical path, phase, or diffraction associated with SAW. Here, we report experiments showing that SAW can be imaged with an optical polarimetry. Since the amount of polarization rotation can be straightforwardly calibrated when polarimeters work in the shot-noise-limited regime, the polarimetric imaging of SAW is beneficial for quantitative studies of SAW-based technologies.
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