Ultrasensitive quantum detection of external weak signals at the nanoscale levels can be implemented in a variety of forms. Here we discuss different feedback control algorithms for the sensing scenario based on the semiclassical Tavis-Cummings model for nitrogen-vacancy (NV) centers located in the diamond. In the frame of this model, the sensing elements are considered as non-interacting two-level quantum systems, distribute in-homogeneously due to heterogeneous local magnetic and strain environments. The dynamical system of ordinary differential equations corresponding to the model contains the set of control parameters: the detunings between the drive frequency and the cavity frequency and between the drive frequency and NV transition frequency, as well as the relaxation coefficients. Correspondingly, it opens a gate for developing feedback control algorithms for tracking the cavity field, the income signal, and the reflection signal in the model sensing system. To study the principal features of algorithmic feedback we formulate the simplified ’toy model’ for the Tavis-Cummings system and investigate alternative schemes of feedback (gradient methods, target attractor methods) to compare their pros and cons for effective control for nitrogen-vacancy-cavity quantum sensing based on different choices of the control parameter set. This work was supported by the Research Fund of Abdullah Gül University; Project Number: BAP FBA-2023-176 ’Geribesleme kontrol algoritmaları ile kubit tabanlı sensörlerin verimliliğinin artırılması’. The paper was presented at PhysCon2024.
Ultrasensitive quantum detection of external weak signals at the nanoscale levels can be implemented in a variety of forms. Here we discuss different feedback control algorithms for the sensing scenario based on the semiclassical Tavis-Cummings model for nitrogen-vacancy (NV) centers located in the diamond. In the frame of this model, the sensing elements are considered as non-interacting two-level quantum systems, distribute in-homogeneously due to heterogeneous local magnetic and strain environments. The dynamical system of ordinary differential equations corresponding to the model contains the set of control parameters: the detunings between the drive frequency and the cavity frequency and between the drive frequency and NV transition frequency, as well as the relaxation coefficients. Correspondingly, it opens a gate for developing feedback control algorithms for tracking the cavity field, the income signal, and the reflection signal in the model sensing system. To study the principal features of algorithmic feedback we formulate the simplified ’toy model’ for the Tavis-Cummings system and investigate alternative schemes of feedback (gradient methods, target attractor methods) to compare their pros and cons for effective control for nitrogen-vacancy-cavity quantum sensing based on different choices of the control parameter set. This work was supported by the Research Fund of Abdullah Gül University; Project Number: BAP FBA-2023-176 ’Geribesleme kontrol algoritmaları ile kubit tabanlı sensörlerin verimliliğinin artırılması’. The paper was presented at PhysCon2024.
Here we discuss as an important particular case the hybrid quantum electromagnetic sensor represented by a nitrogen-vacancy (NV) ensemble of N gt;gt; 1 centers in the doped diamond coupled to a high-quality factor dielectric resonator. The existing NV ensemble-based devices exhibit sensitivities that are several orders of magnitude away from theoretical limits. On the one hand, improvements in spin dephasing time, readout accuracy, and properties of the base diamond material can significantly improve the quality of operation of a quantum sensor. On the other hand, sensing optimization schemes also significantly affect its performance. We focus on the application of feedback to control the response in the cavity quantum electromagnetic sensor. We use the standard Tavis-Cummings model for the system and then introduce control over the target attractor method. In this model they are considered to be noninteracting two-level systems with transition frequencies wj, distributed inhomogeneously due to heterogeneous local magnetic and strain environments as well as hyperfine coupling with 14N nuclear spins. We adopted an operator form of closed-loop algorithm to the semi-classical Tavis-Cummings model in its ‘weak microwave drive’ limit. We used here target attractor Kolesnikov’s formulation of feedback to track the sensor response r or, alternatively, the reflected signal to the input drive field. In both cases, we achieve the tracking goal in the exponentially fast convergence.
In recent years, the field of quantum sensing has garnered increasing attention due to its potential to revolutionize various scientific and technological domains. Among the different quantum sensors, the nitrogen-vacancy (NV) color center in diamond stands out for its ease of use, ability to be read out and initialized with a laser, and long coherence times even at room temperature. Over the past years, numerous quantum control sequences have been developed to successfully deploy NV sensors in diverse situations, such as measuring nearby spin clusters, classical AC signals, and static magnetic fields. However, the NV center faces limitations when coupling to high frequency signals. More specifically, as the frequency of the target signal increases, stronger driving fields over NVs are needed, ultimately reaching the limits of current experimental capabilities. In this thesis, we propose several protocols to address this high-frequency problem in different scenarios.
The recent decade has witnessed exciting developments in quantum science and technology. Quantum sensing is a rapidly growing branch, which exploits the fragility of quantum systems to detect small external signals. The extreme control at the single-atom level and the remarkably long coherence time of engineered quantum systems enable unprecedented sensitivity and precision, beating the performance of classical techniques. The nitrogen-vacancy (NV) center in diamond is one of the most promising quantum sensors. Its unique advantages have attracted considerable attention, including a long spin coherence time throughout a broad temperature range, nanoscale resolution limited by the sensor-sample distance, convenient optical control of its spin states and remarkably versatile sensing capabilities. Its properties are well studied under a bias magnetic field oriented along its quantization axis. However, its sensing capabilities in the presence of an off-axis magnetic field are much less explored. My research aims to unlock the full potential of NV quantum sensor by developing new sensing modalities under a magnetic field acting perpendicular to the NV axis, and furthermore, integrating them into a scanning probe microscope. In this dissertation, I will report our progress toward building a scanning NV multimodal quantum imaging platform, which will open up exciting opportunities in measuring nanoscale phenomena. The first chapter provides an introduction to the background of quantum sensing with NV centers, followed by a discussion on its basic properties and established sensing techniques. The second and third chapters are dedicated to two experiments performed under a perpendicular magnetic field where traditional NV magnetometry based on the Zeeman effect fails. In the second chapter, I will introduce a new sensing strategy that uses the entanglement between the electron and nuclear spins to restore the magnetic field sensitivity under this unfavored condition. This allows us to sense small changes in the magnetic field angle relative to the NV axis, and to detect anisotropic magnetic noise in the local environment. In the third chapter, I will present our latest development of scanning NV electrometry, where a single NV at the apex of a diamond scanning probe images external alternating (AC) and direct (DC) electric fields with sub-100 nm resolution. In the last chapter, I will discuss our efforts on four experiments that were left unfinished. I will present the results we have achieved, analyze the challenges that we faced and propose potential solutions to overcome them.
This thesis investigates the theoretical foundations, material properties, and experimental realization of quantum sensors based on the Nitrogen-Vacancy (NV) centers in diamond, a solid-state system that combines quantum coherence with room-temperature operability. The first chapter introduces the principles of quantum sensing, outlining the fundamental definitions, operating protocols, and physical processes underlying the quantum measurement paradigm. Emphasis is placed on the quantum sensing Hamiltonian and the distinction between various classes of quantum sensors. The second chapter focuses on diamond as a host material and on the NV center as a quantum defect. The electronic structure, optical transitions, and spin properties of the NV center are analyzed in detail. Several techniques of NV-based magnetometry are presented, including continuouswave and pulsed optically detected magnetic resonance (ODMR). The discussion also addresses coherence times (T1, T2, and T∗2 ) and methods of diamond synthesis together with NV-center generation through irradiation and annealing. Chapter three develops the physical theory describing the NV center. The Hamiltonian formalism includes spin-spin, hyperfine, and quadrupolar interactions, as well as couplings to external magnetic fields. The chapter further introduces the Bloch sphere representation, magnetic resonance phenomena, and models of lightmatter interaction, ranging from the semiclassical to the fully quantum Rabi framework. A seven-level rate-equation model is proposed to capture the spin dynamics and optical cycling processes of the NV center. The fourth chapter reports the experimental results. After describing materials and methods, several ODMR-based vector magnetometry experiments are presented, highlighting different spectral regimes and the dependence of resonance features on the external magnetic field geometry. Additional studies demonstrate temperature sensing and microwave-free magnetometry techniques for mapping magnetic field distributions. Sensitivity analysis and calibration procedures are also discussed.
Recent great progress in studying theoretical and especially experimental properties of BoseEinstein condensate (BEC) creates a new era in developing and designing principally novel types of quantum devices, including quantum sensors for measuring nonlinear interactions, external electrical and magnetic fields, and other physical characteristics with high sensitivity. Here we discuss the application of feedback control over a quantum sensor based on the Bose-Einstein condensate trapped in twodimensional ring potential. For a weakly interacting regime, the dynamics of such a system are modeled by three coupled complex differential master equations containing the parameter of interaction and the chemical potential parameter. The last one plays the role of control variable in sensing protocol for twobody interaction. The goal of control is to minimize the effects of the higher energy levels in BEC by driving their corresponding matrix density elements. The control algorithm is designed as Kolesnikov’s feedback forming an artificial target attractor in the dynamical system. We re-formulate Kolesnikov’s approach in the operator form to adapt it to quantum engineering processes. The control approach proposed here can be efficiently extended to different sensing protocols for detecting external magnetic fields, rotational components, and other physical characteristics of BEC interacting with the environment.
Recent great progress in studying theoretical and especially experimental properties of Bose Einstein condensate (BEC) creates a new era in developing and designing principally novel types of quantum devices, including quantum sensors for measuring nonlinear interactions, external electrical and magnetic fields, and other physical characteristics with high sensitivity. Here we discuss the application of feedback control over a quantum sensor based on the Bose-Einstein condensate trapped in two dimensional ring potential. For a weakly interacting regime, the dynamics of such a system are modeled by three coupled complex differential master equations containing the parameter of interaction and the chemical potential parameter. The last one plays the role of control variable in sensing protocol for two body interaction. The goal of control is to minimize the effects of the higher energy levels in BEC by driving their corresponding matrix density elements. The control algorithm is designed as Kolesnikov’s feedback forming an artificial target attractor in the dynamical system. We re-formulate Kolesnikov’s approach in the operator form to adapt it to quantum engineering processes. The control approach proposed here can be efficiently extended to different sensing protocols for detecting external magnetic fields, rotational components, and other physical characteristics of BEC interacting with the environment.