Diamond-based microelectromechanical systems (MEMS) enable direct coupling between the quantum states of nitrogen-vacancy (NV) centers and the phonon modes of a mechanical resonator. One example, diamond high-overtone bulk acoustic resonators (HBARs), feature an integrated piezoelectric transducer and support high-quality factor resonance modes into the GHz frequency range. The acoustic modes allow mechanical manipulation of deeply embedded NV centers with long spin and orbital coherence times. Unfortunately, the spin-phonon coupling rate is limited by the large resonator size, > 100 µm, and thus strongly-coupled NV electron-phonon interactions remain out of reach in current diamond BAR devices. Here, we report the design and fabrication of a semi-confocal HBAR (SCHBAR) device on diamond (silicon carbide) with 1 arXiv:1906.06309v1 [cond-mat.mes-hall] 14 Jun 2019 f · Q > 10 12 (> 10 13 ). The semi-confocal geometry confines the phonon mode laterally below 10 µm. This drastic reduction in modal volume enhances defect center electronphonon coupling. For the native NV centers inside the diamond device, we demonstrate mechanically driven spin transitions and show a high strain-driving efficiency with a Rabi frequency of (2π)2.19(14) MHz/V p , which is comparable to a typical microwave antenna at the same microwave power.Defect-based qubits are attractive platforms for solid state quantum technologies. 1 The leading examples are the nitrogen-vacancy (NV) 2 center and the silicon-vacancy (SiV) 3 center in diamond, and the divacancy center 4 and the silicon vacancy center (V Si ) 5 in silicon carbide (SiC). Hybrid quantum systems based on these defect qubits are particularly interesting because they interface the qubit spin to photons or phonons and thus potentially enable the transport of quantum information. For sensing applications, they offer unconventional modalities of quantum control which is a resource for extending the coherence time and thus sensitivity. Coupling spins to mechanical motion could also enable new quantum-enhanced sensors of motion, such as inertial sensing. 6,7 Although solid state spin-photon entanglement has been demonstrated in recent years 8 and has been used to build quantum networks, 9 defect-based spin-mechanical systems have yet to operate at the single phonon quantum level because they are limited by weak electronphonon coupling, g, in existing devices. Considering g ∝ 1/V , where V is the modal volume, one approach to strengthening the coupling is to engineer small mode volume mechanical resonators with high quality factors. Ultimately, defect-based spin-mechanical systems may enable new sensing applications and control of phonon states at the quantum level. 10Defect-based spin-mechanical systems can be classified into two categories: 1) micro-beam resonator systems 11-13 and 2) micro-electromechanical systems (MEMS) 14-17 with integrated thin-film piezoelectric transducers. While the first category minimizes the resonator fabrication to a single material, i.e., diamond, SiC, etc., high...

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Silicon carbide (SiC) excels in its outstanding mechanical properties, which are widely studied in microelectromechanical systems. Recently, the mechanical tuning of color centers in 4H-SiC has been demonstrated, broadening its application in quantum spintronics. The strain generated in a mechanical resonator can be used to manipulate the quantum state of the color center qubit. This work reports a lateral overtone mechanical resonator fabricated from a semi-insulating bulk 4H-SiC wafer. An aluminum nitride piezoelectric transducer on SiC is used to drive the resonance. The resonator shows a series of modes with quality factors (Q) above 3000. An acoustic reflector positioned at the anchor shows a 22% improvement in Q at 300 MHz resonance and suppresses the overtone modes away from it. This monolithic SiC resonator allows optical access to the SiC color centers from both sides of the wafer, enabling a convenient setup in quantum measurements.

We demonstrate that a nitrogen-vacancy (NV) center in diamond can be used as a nanoscale quantum sensor for detecting photonic spin density (PSD). This opens a new frontier for studying exotic phases of photons as well as future on-chip applications.

A method to envisage trap density in the semiconductor bandgap near the semiconductor/oxide interface of nanoscale silicon junctionless transistors (JLTs) is presented. JLTs are fabricated in a bottom-up fabrication technique using in situ highly doped nanowires grown by low pressure chemical vapor deposition. Low-frequency noise characterization of JLTs biased in saturation is conducted at different gate biases. The noise spectrum indicates either a Lorentzian or 1/f noise depending on the gate bias. Analysis of the results indicates very low trap densities in the order of 1016 cm−3eV−1. Low trap densities in these devices are associated with their simple fabrication technique, in situ oxide formation, and the absence of semiconductor junction and the ion implantation step in the process. A simple analysis of the low-frequency noise data leads to the density of the traps and their energy within the semiconductor bandgap and their location from the Si/SiO2 interface.