Controlling the dynamics of targeted quantum correlations is a central goal across many disciplines of quantum science. For applications in nanoscale quantum sensing, nitrogen-vacancy (NV) centers in diamond have recently emerged as a leading platform due to their atom-like nature, exquisite magnetic sensitivity and well-developed coherent control techniques under ambient conditions. However, harnessing the entanglement structure required to improve this sensitivity beyond the standard quantum limit (SQL) from the native dipolar interactions between NV centers is challenging due to their strong positional disorder, three-dimensional geometry and low-fidelity readout. Coupled tightly to proof of principle experimental demonstrations, this thesis provides a theoretical blueprint to realize practical, entanglement-enhanced quantum sensing in the solid-state via far-from-equilibrium dynamics of dense ensembles of NV centers in diamond. Our most fundamental contribution is to identify a universal mechanism exploiting the thermalization of long-wavelength spin textures to generate scalable spin squeezing in the absence of finite temperature symmetry breaking. We further develop a novel sensing protocol based on asymmetric time-reversal capable of rapidly breaking the SQL without high-fidelity readout. Challenging long-standing beliefs in the field, these results open the door to a new era of entanglement-enhanced sensing under ambient conditions, with applications ranging from nanoscale imaging of biological structures to covariance magnetometry of exotic quantum materials.
Controlling the dynamics of targeted quantum correlations is a central goal across many disciplines of quantum science. For applications in nanoscale quantum sensing, nitrogen-vacancy (NV) centers in diamond have recently emerged as a leading platform due to their atom-like nature, exquisite magnetic sensitivity and well-developed coherent control techniques under ambient conditions. However, harnessing the entanglement structure required to improve this sensitivity beyond the standard quantum limit (SQL) from the native dipolar interactions between NV centers is challenging due to their strong positional disorder, three-dimensional geometry and low-fidelity readout. Coupled tightly to proof of principle experimental demonstrations, this thesis provides a theoretical blueprint to realize practical, entanglement-enhanced quantum sensing in the solid-state via far-from-equilibrium dynamics of dense ensembles of NV centers in diamond. Our most fundamental contribution is to identify a universal mechanism exploiting the thermalization of long-wavelength spin textures to generate scalable spin squeezing in the absence of finite temperature symmetry breaking. We further develop a novel sensing protocol based on asymmetric time-reversal capable of rapidly breaking the SQL without high-fidelity readout. Challenging long-standing beliefs in the field, these results open the door to a new era of entanglement-enhanced sensing under ambient conditions, with applications ranging from nanoscale imaging of biological structures to covariance magnetometry of exotic quantum materials.
Solid-state spin defects, particularly the nitrogen-vacancy (NV) center in diamond, have emerged as powerful platforms for exploring quantum many-body physics and quantum metrology. Their exceptional coherence properties and strong dipolar interactions offer unique opportunities to simulate complex quantum dynamics and engineer entangled states for enhanced sensing beyond the standard quantum limit. However, achieving scalable entanglement in these systems is notoriously difficult due to intrinsic disorder and the complex nature of long-range dipole-dipole interactions. This thesis presents both theoretical and experimental advancements in harnessing quantum dynamics in interacting spin ensembles for quantum-enhanced metrology. A central result is the experimental realization of spin squeezing in a dense ensemble of NV centers, demonstrating a clear path toward overcoming classical limits in solid-state platforms. To further formalize and scale these phenomena, this work develops theoretical frameworks for generating robust spin squeezing under realistic experimental conditions. We show that finite-temperature easy-plane magnetism can be actively leveraged to create scalable squeezed states for the dipolar spin systems on regular lattices. Building upon this, we further extend the result to spatially disordered quantum dipoles. We demonstrate that strongly coupled spin pairs suppress squeezing through dynamical heating, and we propose a selective shelving protocol to mitigate this problem. Furthermore, we also propose a universal protocol for quantum-enhanced sensing that exploits information scrambling, utilizing the natural, scrambling dynamics of strongly interacting many-body systems to effectively amplify weak external signals. Together, the findings detailed in this thesis establish a foundational paradigm for controlling and utilizing solid-state spin ensembles, paving the way for entanglement-enhanced quantum sensors.
Many-body dynamics constitutes a promising approach for creating correlations between quantum particles which can be used for applications in sensing and metrology. However, utilizing this potential for substantial gains in practical settings is a challenging task with only a very few applications realized to date. Here, we demonstrate an approach to nanoscale magnetic sensing enabled by strongly interacting electronic spins in a room temperature solid. By coherently controlling collective many-body dynamics of a dipolar ensemble of ∼104 nitrogen-vacancy (NV) centres in diamond with pulsed magnetic field gradients, we demonstrate practical metrological gain up to 7.9(2)dB for magnetic signal detection and 8.8(3)dB for magnetic noise sensing, fully accounting for experimental overheads. Finally, we combine these methods to demonstrate a momentum-space-resolved sensing modality that enables detection of spatially correlated magnetic noise at continuously tunable length scales down to 50 nanometers. These observations open the door toward practical applications of interaction-enhanced quantum sensors for nanoscale biological imaging and material characterization.
Electronic spins of nitrogen vacancy (NV) centers in diamond constitute a promising system for micro- and nano-scale magnetic sensing, due to their operation under ambient conditions, ease of placement in close proximity to sensing targets, and biological compatibility. At high densities, the electronic spins interact through dipolar coupling, which typically limits but can also potentially enhance sensing performance. Here we report the experimental demonstration of many-body signal amplification in a solid-state, room temperature quantum sensor. Our approach utilizes time-reversed two-axis-twisting interactions, engineered through dynamical control of the quantization axis and Floquet engineering in a two-dimensional ensemble of NV centers. Strikingly, we observe that the optimal amplification occurs when the backward evolution time equals twice the forward evolution time, in sharp contrast to the conventional Loschmidt echo. These observations can be understood as resulting from an underlying time-reversed mirror symmetry of the microscopic dynamics, providing key insights into signal amplification and opening the door towards entanglement-enhanced practical quantum sensing.
Solid-state spin ensembles have emerged as a leading platform for micro- and nanoscale sensing, combining high sensitivity, nanoscale spatial resolution, and operation under ambient conditions. At high spin densities, magnetic dipole–dipole interactions typically limit sensing performance by reducing coherence, but can in principle be harnessed to enhance sensitivity. Realizing such interaction-enhanced sensing in practice, however, remains challenging due to the intrinsic anisotropy of dipolar interactions and the random spatial distribution of spins. This thesis presents a series of experimental works that culminate in a practical interaction-enhanced magnetometer based on ensembles of nitrogen-vacancy (NV) centers in diamond. Our approach is based on collective, one-axis-twisting-like (OAT-like) dynamics engineered from native dipolar interactions using controlled nanoscale spin textures, in combination with a dressed-state qubit encoding that significantly extends the sensor coherence time. These results open the door to practical deployment of interaction-enhanced quantum sensors for nanoscale biological imaging and material characterization.
In modern-day quantum metrology, quantum sensors are widely employed to detect weak magnetic fields or nanoscale signals. Quantum devices, exploiting quantum coherence, are inevitably connected to physical constants and can achieve accuracy, repeatability, and precision approaching fundamental limits. As a result, these sensors have shown utility in a wide range of research domains spanning both science and technology. A rapidly emerging quantum sensing platform employs atomic-scale defects in crystals. In particular, magnetometry using nitrogen-vacancy (NV) color centers in diamond has garnered increasing interest. NV systems possess a combination of remarkable properties, optical addressability, long coherence times, and biocompatibility. Sensors based on NV centers excel in spatial resolution and magnetic sensitivity. These diamond-based sensors promise comparable combination of high spatial resolution and magnetic sensitivity without cryogenic operation. The above properties of NV magnetometers promise increasingly integrated quantum measurement technology, as a result, they have been extensively developed with various protocols and find use in numerous applications spanning materials characterization, nuclear magnetic resonance (NMR), condensed matter physics, paleomagnetism, neuroscience and living systems biology, and industrial vector magnetometry. In this chapter, NV centers are explored for magnetic sensing in a number of contexts. In general, we introduce novel regimes for magnetic-field probes with NV ensembles. Specifically, NV centers are developed for sensitive magnetometers for applications where microwaves (MWs) are prohibitively invasive and operations need to be carried out under zero ambient magnetic field. The primary goal of our discussion is to improve the utility of these NV center-based magnetometers.
The study of quantum mechanics, together with the ability to coherently control and manipulate quantum systems in the lab has led to a myriad of discoveries and real world applications. In this thesis we present experiments demonstrating precise control of an individual long-lived spin qubit as well as sensing applications for biology and investigation of quantum many-body dynamics.\n\nStable quantum bits, capable both of storing quantum information for macroscopic time scales and of integration inside small portable devices, are an essential building block for an array of potential applications. In the second chapter of this thesis we demonstrate high-fidelity control of a solid-state qubit, which preserves its polarization for several minutes and features coherence lifetimes exceeding 1 second at room temperature.\n\nSensitive probing of temperature variations on nanometer scales is an outstanding challenge in many areas of modern science and technology. In chapter three we show how nitrogen vacancy centers in diamond can be used as a robust, high sensitivity temperature probe. We furthermore demonstrate biological compatibility by introducing nano-sized diamonds into living cells and measuring externally induced sub-cellular temperature gradients.\n\nUnderstanding the dynamics of interacting many-body quantum systems with on-site potential disorder has proven one of the biggest challenges in quantum physics to investigate both in theory and experiment. In chapter four we demonstrate how coherent control techniques can be utilized to probe the many-body dynamics of a strongly interacting NV spin ensemble. Specifically, we show how a long-range interacting dipolar spin system exhibits characteristically slow thermalization in the presence of tunable disorder.\n\nThe presented works offer up many new areas to investigate, including complex quantum many-body effects of large, disordered spin systems, as well as applications of NV centers as bio-compatible nano-scale temperature probes.