The Nitrogen-Vacancy (NV) defect in diamond is a unique quantum system that offers precision sensing of nanoscale physical quantities beyond the current state-of-the-art. Here we present a method to controllably encode the interactions in the population of the spin states, thereby introducing a way to control the sensitivity of a single spin as a continuum in contrast to free-evolution based methods. By adopting this feature we demonstrate high-accuracy NV magnetometry without 2pi ambiguities, enhance the dynamic range by a factor of 4*10^3 achieve interaction times exceeding 2 ms in off-the-shelf diamond. We perform nuclear spin-noise spectroscopy in the frequency domain by dynamically controlling the NV spin's sensitivity piecewise and in a smooth manner thereby precluding harmonic artefacts and undesired interactions. On a broader perspective dynamical sensitivity control provides an elegant handle on the inherent dynamics of quantum systems, while offering decisive advantages for NV centre applications notably in quantum controls and single molecule NMR/MRI.
The Nitrogen-Vacancy (NV) defect in diamond is a unique quantum system that offers precision sensing of nanoscale physical quantities beyond the current state-of-the-art. Here we present a method to controllably encode the interactions in the population of the spin states, thereby introducing a way to control the sensitivity of a single spin as a continuum in contrast to free-evolution based methods. By adopting this feature we demonstrate high-accuracy NV magnetometry without 2pi ambiguities, enhance the dynamic range by a factor of 4*10^3 achieve interaction times exceeding 2 ms in off-the-shelf diamond. We perform nuclear spin-noise spectroscopy in the frequency domain by dynamically controlling the NV spin's sensitivity piecewise and in a smooth manner thereby precluding harmonic artefacts and undesired interactions. On a broader perspective dynamical sensitivity control provides an elegant handle on the inherent dynamics of quantum systems, while offering decisive advantages for NV centre applications notably in quantum controls and single molecule NMR/MRI.
Abstract The Nitrogen-Vacancy (NV) defect in diamond is a unique quantum system that offers precision sensing of nanoscale physical quantities at room temperature beyond the current state-of-the-art. The benchmark parameters for nanoscale magnetometry applications are sensitivity, spectral resolution, and dynamic range. Under realistic conditions the NV sensors controlled by conventional sensing schemes suffer from limitations of these parameters. Here we experimentally show a new method called dynamical sensitivity control (DYSCO) that boost the benchmark parameters and thus extends the practical applicability of the NV spin for nanoscale sensing. In contrast to conventional dynamical decoupling schemes, where π pulse trains toggle the spin precession abruptly, the DYSCO method allows for a smooth, analog modulation of the quantum probe’s sensitivity. Our method decouples frequency selectivity and spectral resolution unconstrained over the bandwidth (1.85 MHz–392 Hz in our experiments). Using DYSCO we demonstrate high-accuracy NV magnetometry without |2π| ambiguities, an enhancement of the dynamic range by a factor of 4 · 103, and interrogation times exceeding 2 ms in off-the-shelf diamond. In a broader perspective the DYSCO method provides a handle on the inherent dynamics of quantum systems offering decisive advantages for NV centre based applications notably in quantum information and single molecule NMR/MRI.
The nitrogen-vacancy (NV) center in diamond is a quantum defect in diamond with unique properties for use in high-sensitive, high-resolution quantum sensors of magnetic fields. One of the most interesting and challenging application of NV quantum sensors is nanoscale magnetic resonance imaging (nano-MRI), which would enable to address single biomolecules. To this goal, improving the sensitivity of the NV sensor is a crucial task. Here, we present a quantum optimal control method that optimizes the sensitivity of NV sensor to specific weak magnetic signals with biologically-relevant, complex spectrum. The method, based on the mapping of the sensing problem on a problem of energy optimization of an Ising chain, allows us to improve sensitivity by three orders of magnitude compared to standard control sequences.
As a demand from developing nanotechnology and quantum information technology based on mesoscopic material, quantum sensors with better spatial resolution and sensitivity are required. \n \nHowever, few material meets the requirements of nanoscale sensors including stability and small size. Single spin of Nitrogen-Vacancy(NV) centers in diamond crystal is one kind of the ideal quantum sensors for magnetometry that has been investigated in recent years. It provides a potential way to study the dynamics in a mesoscopic system with high sensitivity at room temperature. This thesis proposes a theoretical method to realize spin interaction detection based on NV centers on an atomic force-microscopy(AFM) tip. To realize this method, a robust control on NV centers and target electron spins at zero magnetic field is necessary. A pulse control technique for NV centers is proposed to realize transitions between two degenerate states at zero magnetic field, which is an important part of the sensing method. The key to realizing this transition is a circularly polarized microwave pulse generated by two parallel wires. Combined with optimal control techniques, this pulse can achieve a gate fidelity over 99.95% theoretically.
Quantum sensing has witnessed rapid development and transition from laboratories to practical applications in the past decade. Applications of quantum sensors, ranging from nanotechnologies to biosensing, are expected to benefit from quantum sensors' unprecedented spatial resolution and sensitivity. Solid-state spin systems are particularly attractive platforms for quantum sensing technologies because room temperature operation is viable while reaching the quantum limits of sensitivity. Among various solid-state spin systems, nitrogen-vacancy (NV) centers in diamond demonstrated high-fidelity initialization, coherent control, and high contrast readout of the electron spin state. However, electron spin coherence due to noise from the surrounding spin bath and this environment effect limits the sensitivity of NV centers. Thus, a critical task in NV center-based quantum sensing is sensitivity enhancement through coherence protection. Several strategies, such as dynamical decoupling techniques, feedback control, and nuclear spin-assisted sensing protocols, have been developed and realized for this task. Among these strategies, nuclear spin-assisted protocols have demonstrated greater enhancement of electron spin coherence. In addition, the electron and nuclear spin pair of an NV center in diamond naturally allows the application of the nuclear spin-assisted sensitivity enhancement protocol. Owing to long nuclear coherence times, further enhancement of sensitivity can be achieved by exploiting active nuclear spins (e.g., 14N, 13C) in the proximity of an NV center as memory ancillas when coupled with the NV center. Here, we review the spin properties of NV centers, mechanisms of the nuclear spin-assisted protocol and its gate variation, and the status of quantum sensing applications in high-resolution nuclear spin spectroscopy, atomic imaging, and magnetic field sensing. We discuss the potential for commercialization, current challenges in sensitivity enhancement, and conclude with future research directions for promoting the development of nuclear spin-assisted protocol and its integration into industrial applications.
Synthetic diamond has recently emerged as a candidate material for a number of quantum applications, including quantum information processing and quantum sensing. In this talk, I will show how single nitrogen-vacancy (NV) color centers can be created near the diamond surface and used as nanoscale sensors of electric and magnetic fields. I will also demonstrate novel dynamical decoupling techniques allowing to improve the sensitivity of diamond quantum sensors and discuss applications of small-scale quantum registers for nanoscale NMR. Applications of NV centers for hyperpolarisation of nuclear spins and application of optical spin polarization in MRI will be presented.
Abstract Quantum sensors based on nitrogen vacancy (NV) defects in diamond have a demonstrated capability to detect nuclear magnetic resonance (NMR) spectra from proximate molecular nuclei, thereby promising an alternative with higher sensitivity to conventional NMR spectrometers for micro-scale samples. Fluorescence-based readout of these sensors is limited by higher shot noise due to the small number of emitters and photoionisation induced instabilities, meaning there is still significant scope to maximise their sensitivity and temporal resolution. In this work, we demonstrate a new readout protocol based on parameter fitting to a precise model of the NV photo-physics, thereby demonstrating an improvement of 36% in sensitivity and 85% gain in measurement speed. Whereas typical approaches to improvement involve expensive diamond material, and optical and microwave engineering, our method can be readily implemented into existing NV quantum sensing protocols.