[1] Development of a high quality thin diamond membrane with em- bedded nitrogen-vacancy centers for hybrid spin-mechanical quan- tum systems S. Ali Momenzadeh †,* , Felipe Fávaro de Oliveira † , Philipp Neumann † , D. D. Bhaktavatsala Rao †, § , Andrej Denisenko † , Morteza Amjadi ¶ , Sen Yang † , Neil B. Manson ‡ , Marcus W. Doherty ‡, ** , and Jörg Wrachtrup †, § † 3 rd Institute of Physics, Research Center SCoPE and IQST, University of Stuttgart, 70569 Stuttgart, Germany § Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany ¶ Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany ‡ Laser Physics Centre, Research School of Physics and Engineering, Australian National University, Australian Cap- ital Territory 0200, Australia ABSTRACT: Hybrid quantum systems (HQSs) have attracted several research interests in the last years. In this Letter, we report on the design, fabrication, and characterization of a novel diamond architecture for HQSs that consists of a high quality thin circular diamond membrane with embedded near-surface nitrogen-vacancy centers (NVCs). To demonstrate this architecture, we employed the NVCs by means of their optical and spin interfaces as nanosensors of the motion of the membrane under static pressure and in-resonance vibration, as well as the residual stress of the membrane. Driving the membrane at its fundamental resonance mode, we observed coupling of this vibrational mode to the spin of the NVCs by Hahn echo signal. Our realization of this architecture will enable futuristic HQS-based applications in diamond piezome- try and vibrometry, as well as spin-mechanical and mechanically mediated spin-spin coupling in quantum information science. KEYWORDS: hybrid quantum systems, nitrogen-vacancy center, thin circular diamond membrane, harmonic oscilla- tor, Hahn echo There have been several recent proposals 1-2 to exploit mechanical degrees of freedom to control and couple nitrogen-vacancy centers (NVCs) for applications in quantum information science 1-4 and nano-force sens- ing 5-6 . For example, mechanical motions of diamond microcantilevers have been detected via the electron- ic spins of NVCs 7-9 . Such proposals rely on the incor- poration of NVCs into well-characterized nano/micro-mechanical structures that behave ac- cording to simple models from continuum mechan- ics. However, the realization of such ideal structures, free from complications like residual stress, is a sig- nificant challenge yet to be achieved. Thus, a vital first step is to comprehensively characterize these factors and their influence on the performance of the structures. Furthermore, unlike other materials such as SiN 10 , the manufacturing of large, homogenous, and high-quality thin diamond membranes for the simple, robust and scalable fabrication of diamond nano/micro-mechanical structures is yet to be demonstrated. In this Letter, we report a novel approach to the sys- tematic design, fabrication, and characterization of a circular diamond membrane (hereinafter will be mentioned shortly as “membrane”) incorporating NVCs at the average depth of ≈20 nm. The mem- brane has a diameter of ≈1.1 mm, a thickness of ≈1.2 μm and surface roughness of ≈0.4 nm. To examine the mechanical properties of the membrane, we em- ployed the confocal microscopy technique that uses the fluorescence point spread function (PSF) of indi- vidual embedded NVCs as nanosensors to measure the deflection of the membrane under an applied pressure. In this way, and by applying the theory of thin membranes 11 we have inferred an effective thickness of ≈1.2 µm and average radial residual stress of 54 MPa. By means of the spin-mechanical coupling of the NVCs, we employed them as nano- probes for the motion of the membrane under ap- plied static pressure (DC) and in-resonance vibration (AC), as well as residual stress. In this way, we ob- served ≈2.3 MHz of spin resonance frequency shift under 1 bar of applied DC pressure, and coupling of