KEYWORDSNitrogen-vacancy center, diamond, spin-mechanical interaction, nanomechancial sensing, NEMS 2 ABSTRACT Nanomechanical sensors and quantum nanosensors are two rapidly developing technologies that have diverse interdisciplinary applications in biological and chemical analysis and microscopy.For example, nanomechanical sensors based upon nanoelectromechanical systems (NEMS) have demonstrated chip-scale mass spectrometry capable of detecting single macromolecules, such as proteins. Quantum nanosensors based upon electron spins of negatively-charged nitrogen-vacancy (NV) centers in diamond have demonstrated diverse modes of nanometrology, including single molecule magnetic resonance spectroscopy. Here, we report the first step towards combining these two complementary technologies in the form of diamond nanomechanical structures containing NV centers. We establish the principles for nanomechanical sensing using such nano-spinmechanical sensors (NSMS) and assess their potential for mass spectrometry and force microscopy. We predict that NSMS are able to provide unprecedented AC force images of cellular biomechanics and to, not only detect the mass of a single macromolecule, but also image its distribution. When combined with the other nanometrology modes of the NV center, NSMS potentially offer unparalleled analytical power at the nanoscale. TEXTNanomechanical sensors based upon nanoelectromechanical systems (NEMS) are a burgeoning nanotechnology with diverse microscopy and analytical applications in biology and chemistry. Two applications with particular promise are force microscopy in geometries that transcend the constraints of conventional atomic force microscopy (AFM) 1-3 and on-chip mass spectrometry with single molecule sensitivity. [4][5][6] Another burgeoning nanotechnology is quantum nanosensors based upon the electron spin of the NV center in diamond. The NV center has been 3 used to locate single elementary charges, 7 to perform thermometry within living cells 8 and to realize nanoscale MRI in ambient conditions. 9-11 However, there is yet to be a nanosensing application of the NV center that exploits its susceptibility to local mechanical stress/ strain.Here, we propose that the mechanical susceptibility of the NV center's electron spin can be exploited together with the extreme mechanical properties of diamond nanomechanical structures to realize nano-spin-mechanical sensors (NSMS) that outperform the best available technology. Such NSMS will be capable of both high-sensitivity nanomechanical sensing and the quantum nanosensing of electric fields, magnetic fields and temperature. NSMS will thereby constitute the unification of two burgeoning nanotechnologies and have the potential to perform such unparalleled analytical feats as mass-spectrometry and MRI of single molecules. As the first step towards realizing NSMS, we report the complete characterization of the spin-mechanical interaction of the NV center. We use this to establish the design and operating principles of diamond NSMS and to perfor...

In this work, we present a method for targeted and maskless fabrication of single silicon vacancy (V Si ) defect arrays in silicon carbide (SiC) using focused ion beam. Firstly, we studied the photoluminescence (PL) spectrum and optically detected magnetic resonance (ODMR) of the generated defect spin ensemble, confirming that the synthesized centers were in the desired defect state. Then we investigated the fluorescence properties of single V Si defects and our measurements indicate the presence of a photostable single photon source. Finally, we find that the Si ++ ion to V Si defect conversion yield increases as the implanted dose decreases. The reliable production of V Si defects in silicon carbide could pave the way for its applications in quantum photonics and quantum information processing. The resolution of implanted V Si defects is limited to a few tens of nanometers, defined by the diameter of the ion beam.Silicon carbide (SiC) is a technologically mature semiconductor material, which can be grown as inch-scale high-quality single crystal wafers and has been widely used in microelectronics systems and high-power electronics, etc. In recent years, some defects in SiC have been successfully implemented as solid state quantum bit 1-8 and quantum photonics 9-11 . They meet essential requirements for spin-based quantum information processing such as optical initialization, readout and microwave control of the spin state, which are similar as the nitrogen vacancy (NV) centers in diamond. 12 In particular, silicon vacancy (V Si ) defect in 4H-SiC has increasingly attracted attention owing to its excellent features, such as non-blinking single photon emission and long spin coherence times which persist up to room temperature (about 160 µs). 3,5,13 These remarkable properties have been exploited in many applications in quantum photonics, 9,10 and quantum metrological studies such as high sensitivity magnetic sensing 14,15 and temperature sensing. 16 The V Si defect consists of a vacancy on a silicon site which exhibits a C 3v symmetry in 4H-SiC. 3,5 In order to extend its applications in quantum information science, it is essential to develop the technique of scalable efficient generation of single V Si defect arays in 4H-SiC. Since the collected fluorescence rate of a single V Si defect is modest with only about 10 kcps, 3,5,17 it is required to couple with some photonic devices to improve the counts towards the construction of photonics networks. 3,9,10,17,20 However, in order to realize the mode-maximum of photonic devices, it is necessary to place the V Si defects relative to the optimal position with sub-wavelength-scale precision. Previously there are three methods to generate V Si defect: the electron irradiation, neutron irradiation, and carbon implantation, however, these methods either can't control the position of the V Si defect, or need a electron beam lithography (EBL) pre-fabricated photoresist patterned mask, 3,5,9,17 which is not convenient for coupling to pre-fabricated photonic devices...

Soon after the first measurements of nuclear magnetic resonance in a condensed-matter system, Bloch 1 predicted the presence of statistical fluctuations proportional to 1/ √ N in the polarization of an ensemble of N spins. Such spin noise 2 has recently emerged as a critical ingredient for nanometre-scale magnetic resonance imaging 3-6 . This prominence is a consequence of present magnetic resonance imaging resolutions having reached less than (100 nm) 3 , a size scale at which statistical spin fluctuations begin to dominate the polarization dynamics. Here, we demonstrate a technique that creates spin order in nanometre-scale ensembles of nuclear spins by harnessing these fluctuations to produce polarizations both larger and narrower than the thermal distribution. This method may provide a route to enhancing the weak magnetic signals produced by nanometre-scale volumes of nuclear spins or a way of initializing the nuclear hyperfine field of electron-spin qubits in the solid state.Spin noise is a phenomenon present in all spin ensembles that begins to exceed the mean thermal polarization as the size of the ensemble shrinks. These fluctuations have a random amplitude and phase and have been observed in a wide variety of nuclear spin systems including in liquids by conventional nuclear magnetic resonance 7,8 (NMR) and in the solid state using a superconducting quantum interference device 2 , by force-detected magnetic resonance 9 or by nitrogen-vacancy magnetometry 4,5 . In addition to finding applications in nanometre-scale magnetic resonance imaging (MRI), spin noise has been used in MRI specially adapted for the investigation of extremely delicate specimens, in which external radiofrequency irradiation is not desired 10 . Through the hyperfine interaction, nuclear spin noise also sets limits on the coherence of electron spin qubits in the solid state [11][12][13][14][15] . Various efforts to mitigate these nuclear field fluctuations by hyperfinemediated nuclear state preparation have been developed, both in quantum dots [16][17][18][19][20] and in nitrogen-vacancy centres in diamond 21 . We report on a manipulation and initialization technique that applies to arbitrary nanometre-scale samples; that is, it does not require specialized structures providing a controllable electronic spin and a strong hyperfine interaction. Rather, our technique requires a detector sensitive enough to resolve nuclear spin noise and the ability to apply radiofrequency electromagnetic pulses.Conventional NMR and MRI techniques rely on manipulating the mean thermal polarization to produce signals. Statistical nuclear polarization fluctuations exceed the mean thermal polarization below a critical number of spins N c = 3/(I (I + 1))(k B T /hγ B 0 ) 2 , where I is the spin quantum number, k B is the Boltzmann constant, T is the temperature, γ is the gyromagnetic ratio and B 0 is The end of the nanowire, which is affixed to an ultrasensitive cantilever, is positioned 100 nm away from the nanomagnet. Below the nanomagnet, a microwire radiof...

As the number of spins in an ensemble is reduced, the statistical fluctuations in its polarization eventually exceed the mean thermal polarization. This transition has now been surpassed in a number of recent nuclear magnetic resonance experiments, which achieve nanometer-scale detection volumes. Here, we measure nanometer-scale ensembles of nuclear spins in a KPF 6 sample using magnetic resonance force microscopy. In particular, we investigate the transition between regimes dominated by thermal and statistical nuclear polarization. The ratio between the two types of polarization provides a measure of the number of spins in the detected ensemble.In recent decades, the drive for technological advancement coupled with an interest in understanding underlying microscopic interactions has led to rapid growth in the number of studies related to nanometerscale phenomena. The research area broadly known as nanoscience and nanotechnology brings together a diverse range of topics including surface science, semiconductor physics, and molecular self-assembly. In many systems, physical phenomena at the nanometer-scale are strikingly different from their behavior at the macroscale. In particular, the reduced dimensionality of nanometerscale samples can manifest itself in either thermal or quantum effects not observed in larger systems. For example, behavior ranging from the Brownian motion 1 to the quantization of conductance 2 emerge as measurement length scales are reduced.The development of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) with nanometer-scale resolution has been a particularly captivating goal in nanoscience, due to its potential impact. As the only non-destructive, chemically-selective, and truly three-dimensional imaging technique, MRI is an indispensable tool in a broad array of fields including medicine, biology, physics, and materials science. Conventional inductively-detected MRI, however, is limited to a detection volume of a few µm 3 . 3 The extension of this resolution down to a few nm 3 and eventually to atomic resolution has been a long-standing goal. 4 The capability to image molecules atom-by-atom, thus allowing the mapping of the three-dimensional atomic structure of unknown macro-molecules would be revolutionary. While the latter goal has not yet been achieved, a few experiments in the last few years have demonstrated nanometer-scale MRI (nanoMRI). 5-7 Two techniques, magnetic resonance force microscopy (MRFM) first, and nitrogen-vacancy (NV) magnetometry shortly thereafter, have both detected NMR in nanometer-scale detection volumes. 8-10 Although so far only MRFM techniques have produced 3D images of nuclear spin density, a) martino.poggio@unibas.ch; http://poggiolab.unibas.ch/ e.g. virus particles and hydrocarbon layers, 5-7 NV magnetometry has achieved a higher sensitivity 11 and initial imaging experiments 12-14 have recently been made. In addition, NV magnetometry appears particularly promising given its ability to work under ambient conditions, while high-sensitivi...

We use a quantum point contact (QPC) as a displacement transducer to measure and control the low-temperature thermal motion of a nearby micromechanical cantilever. The QPC is included in an active feedback loop designed to cool the cantilever's fundamental mechanical mode, achieving a squashing of the QPC noise at high gain. The minimum achieved effective mode temperature of 0.2 K and the displacement resolution of 10 −11 m/ √ Hz are limited by the performance of the QPC as a one-dimensional conductor and by the cantilever-QPC capacitive coupling. [5]. The displacement imprecision of some of these measurements approaches the standard quantum limit on position detection [6], i.e. the limit set by quantum mechanics to the precision of continuously measuring position. Such exquisite resolution has enabled recent experiments measuring quantum states of mechanical motion in a resonator [7][8][9].It naturally follows that with such fine measurement resolution comes equally fine control of the mechanical motion, enabling both tuning of a resonator's linear dynamic range [10] and manipulation of its time response [11]. In fact, such conditions allow for the application of active feedback cooling [11] as a method for preparing a mechanical oscillator near its quantum ground state. Unlike side-band cooling, which has recently been used to cool high-frequency resonators into their ground state [8,9], feedback cooling is particularly well-suited to the ultra-soft low-frequency cantilevers typically used in sensitive force measurements. The minimum phonon occupation number achieved by this method depends only on the detector's displacement imprecision and the resonator's thermal noise [11]. As a result, a widely applicable transduction scheme with low displacement imprecision has the potential to prepare resonators in quantum states of mechanical motion.Here we investigate one such technique: the use of a quantum point contact (QPC) as a sensitive detector of cantilever displacement [12]. The QPC transducer works by virtue of the strong dependence of its conductance on disturbances of the nearby electric field by an object's motion. In particular, a QPC is advantageous due to its versatility as an off-board detector, its applicability to nanoscale oscillators, and its potential to achieve quantum-limited detection [13,14]. Most other displace- Figure 1: Schematic diagram of the experimental setup. In the red loop, the motion of the cantilever is transduced by a quantum point contact and amplified by an optimal controller, before being sent to a piezoelectric element mechanically coupled to the cantilever. The motion is also independently detected by an out-of-loop fiber interferometer, shown in blue. ment detection schemes require the functionalization of mechanical resonators with electrodes, magnets, or mirrors [5]. These requirements tend to compete with the small resonator mass and high quality factor necessary to achieve low thermal noise and high coupling strength to the detector. Since all resonators disturb the near...