The negatively charged nitrogen-vacancy (NV) defect in diamond has established itself as a promising quantum sensing platform with applications in nuclear magnetic resonance at the nanoscale. Still, control protocols are not yet optimized to work in all imaginable regimes. We present the NV-ERC technique, which has demonstrated efficient initialization and readout of the double quantum transition with no leakage to any third level thanks to an effective Raman coupling. The protocol is especially useful in the low-field regime and for high-frequency sensing applications. Based on this insight, we propose a scheme to perform fast single qubit gates in the double quantum transition. We study its robustness with respect to pulse-timing errors resulting from faulty identification of system parameters or phase-control limitations. We demonstrate that the technique can also be implemented in the presence of unknown electric or strain fields.
The negatively charged nitrogen-vacancy (NV) defect in diamond has established itself as a promising quantum sensing platform with applications in nuclear magnetic resonance at the nanoscale. Still, control protocols are not yet optimized to work in all imaginable regimes. We present the NV-ERC technique, which has demonstrated efficient initialization and readout of the double quantum transition with no leakage to any third level thanks to an effective Raman coupling. The protocol is especially useful in the low-field regime and for high-frequency sensing applications. Based on this insight, we propose a scheme to perform fast single qubit gates in the double quantum transition. We study its robustness with respect to pulse-timing errors resulting from faulty identification of system parameters or phase-control limitations. We demonstrate that the technique can also be implemented in the presence of unknown electric or strain fields.
Microwave control of the negatively charged nitrogen-vacancy (NV) defect in diamond is usually based on a two-level approximation of its ground state that is only valid in the regime of high bias magnetic fields or low microwave power. We present the NV-ERC technique, which has demonstrated efficient initialization and readout of the double quantum transition with no leakage to any third level, thanks to an effective Raman coupling. The protocol may be used in the low-field regime and for high-frequency sensing. Furthermore, we propose a scheme to perform fast single-qubit gates in the double quantum transition, consisting of pulse trains of constant frequency and intensity. We analyze its robustness with respect to pulse-timing errors resulting from inaccurate identification of system parameters or phase-control limitations. We also demonstrate that the technique can be implemented in the presence of unknown electric or strain fields.
Abstract We present a scheme for the implementation of fast arbitrary qubit gates in the ground state of the negatively charged nitrogen-vacancy (NV) defect in diamond. The protocol is especially useful for sensing in two regimes: on the one hand, in the low-field limit where the Zeeman splitting of the NV-center is smaller than the MW Rabi frequency; on the other hand, for the detection of high-frequency signals, comparable to the Zeeman splitting of the NV center. It constitutes an extension to the NV-ERC technique, which has demonstrated efficient initialization and readout of the double quantum transition with no leakage to any third level thanks to an effective Raman coupling. Here we derive a full theoretical framework of the scheme, identifying the complete unitary associated to the approach, and more specifically the relevant basis transformation for each of two characteristic pulse durations. Based on this insight, we propose a scheme to perform fast single qubit gates in the double quantum transition. We study its robustness with respect to pulse-timing errors resulting from faulty identification of system parameters or phase-control limitations. We finally demonstrate that the technique can also be implemented in the presence of unknown electric or strain fields and numerically test its effectiveness in a Hahn echo sequence in the high-frequency or low-field regime.
We present a scheme for the implementation of fast arbitrary qubit gates in the ground state of the negatively charged nitrogen-vacancy (NV) defect in diamond [1]. The protocol is especially useful for sensing in two regimes: on the one hand, in the low-field limit where the Zeeman splitting of the NV-center is smaller than the MW Rabi frequency; on the other hand, for the detection of high-frequecy signals, comparable to the Zeeman splitting of the NV-center. It constitutes an extension to the NV-ERC technique [2, 3], which has demonstrated efficient initialization and readout of the double quantum transition with no leakage to any third level thanks to an effective Raman coupling. Here we derive a full theoretical framework of the scheme, identifying the complete unitary associated to the approach, and more specifically the relevant basis transformation for each of two characteristic pulse durations. Based on this insight, we propose a scheme to perform fast single qubit gates in the double quantum transition. We study its robustness with respect to pulse-timing errors resulting from faulty identification of system parameters or phase-control limitations. We finally demonstrate that the technique can also be implemented in the presence of unknown electric or strain fields and numerically test its effectiveness in a Hahn echo sequence in the high-frequency or low-field regime.
The NV-ERC technique for control of the NV ground state exploits the spin-1 nature of the system to best initialize the double-quantum transition. It has been proven to be a crucial control strategy for low field or high frequency sensing. Beyond initialization and readout, the scheme to perform 𝜋 rotations in the transition was inefficient for low intensity pulses. We present a complete theoretical picture of the strategy and demonstrate a mechanism for fast arbitrary unitaries in the double quantum transition. We show it is a robust approach with respect to pulse strength inaccuracies even in the presence of unexpected electric or strain fields.
Shallow nitrogen-vacancy (NV) centers are promising candidates for high-precision sensing applications; these defects, when positioned a few nanometers below the surface, provide an atomic-scale resolution along with substantial sensitivity. However, the dangling bonds and impurities on the diamond surface result in a complex environment which reduces the sensitivity and is unique to each shallow NV center. To avoid the environment's detrimental effect, we apply feedback-based quantum optimal control. We first show how a direct search can improve the initialization and readout process. In a second step, we optimize microwave pulses for pulsed optically detected magnetic resonance (ODMR) and Ramsey measurements. Throughout the sensitivity optimizations, we focus on robustness against errors in the control field amplitude. This feature not only protects the protocols' sensitivity from drifts but also enlarges the sensing volume. The resulting ODMR measurements produce sensitivities below $1\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{T}$ ${\mathrm{Hz}}^{\ensuremath{-}\frac{1}{2}}$ for an 83% decrease in control power, increasing the robustness by approximately one third. The optimized Ramsey measurements produce sensitivities below 100 nT ${\mathrm{Hz}}^{\ensuremath{-}\frac{1}{2}}$ giving a twofold sensitivity improvement. Being on par with typical sensitivities obtained via single NV magnetometry, the complementing robustness of the presented optimization strategy may provide an advantage for other NV-based applications.
Quantum technologies are transitioning from proof-of-principle experiments to practical everyday applications. As this transition unfolds, it remains unclear which quantum system will offer the most suitable platform for specific tasks. While many candidate systems offer excellent control and demonstrate rapid progress, they often require demanding operating conditions such as cryogenic temperatures down to the millikelvin range. The nitrogen-vacancy (N-V) center in diamond is a notable exception. This optically active defect allows full control of its electronic spin state at room temperature and maintains long coherence times under ambient conditions, a prerequisite for many applications. This accessibility makes the N-V center uniquely suited for translating fundamental quantum concepts into deployable technologies. The applicability of N-V centers in quantum sensing, quantum control, and quantum simulation is the central focus of this thesis. After an introductory overview of the field, the thesis introduces the experimental and theoretical concepts that are necessary to understand the presented results. It proceeds to show how the operating regime of N-V centers as sensors for AC magnetic fields and nuclear spins can be extended to low and zero magnetic bias fields. Many commonly used sensing protocols require a magnetic bias field, which can alter the investigated dynamics or may be infeasible to apply due to experimental constraints. This work describes how established sensing protocols can be adjusted for operation under these conditions, and presents novel sensing protocols that enable the detection of AC magnetic fields and nuclear spins in a regime where conventional protocols fail. These results highlight that precise control of the underlying quantum system is a must. Such control can be optimized using quantum optimal control, which allows one to improve the underlying gate operations in a closed-loop, black-box manner, provided a figure of merit can be found which reliably evaluates the gate-set's performance. As this performance can depend on the specific application, the following part of this thesis defines and benchmarks several figures of merit for closed-loop optimal control using an ensemble of N-V centers. The strengths and limitations of these figures of merit are discussed, and the dependence of the optimization performance on several control and experimental parameters is analyzed. The achieved results are applicable to a broad range of other physical platforms, and can serve as a reference for experimental groups that aim to optimize their gate operations using optimal control. Building upon these insights into quantum control, the next part of this thesis presents the fabrication, control, and application of a room-temperature quantum simulator based on thin nuclear spin layers in diamond. A detailed assessment of the growth process is provided, and the dynamics that allow nearby N-V centers to initialize and read out the nuclear spins are thoroughly investigated. Furthermore, the nuclear spin layer is employed to create and study discrete time-crystalline order. The results demonstrate a scalable route for exploring quantum many-body phenomena under ambient conditions. The thesis concludes with a summary and discussion of all results and provides an outlook on future work based on these findings. In conclusion, this thesis demonstrates and expands the versatile use of N-V centers in diamond for quantum sensing, control, and simulation, highlighting their potential as a practical platform for future quantum technologies.