Quantum-Enhanced Sensing in Solid-State and Molecular Spin Systems

Building new tools capable of studying phenomena beyond the reach of current technologies always brings exciting opportunities. In recent decades, quantum systems have emerged as attractive candidates for realizing advantages in computing, communication, and sensing. Quantum sensors harness the small and fragile nature of qubits, which can perform some of the most precise measurements in the world. The development of better quantum sensors will lead to breakthroughs in both the study of fundamental physics—such as many-body problems in condensed matter systems—and applications including nuclear magnetic resonance and thermometry in living biological samples. Pushing resolution and sensitivity to the next level lies at the heart of this field. This dissertation mainly discusses how to improve the performance of quantum sensors through both experimental and theoretical approaches. Chapter 1 introduces the experimental efforts toward a hybrid quantum sensor that couples shallow nitrogen-vacancy centers in diamond with rare-earth ions. Details of the experimental setup—a confocal microscope integrated into a dilution refrigerator—are provided. Chapter 2 presents a novel molecular qubit that tethered on the surface of a 2D material, which we experimentally discovered to reduce the distance between the sensor and the target of interest. Chapter 3 discusses a protocol for leveraging dipolar interactions, which are ubiquitous among spin-qubit systems, to generate metrologically useful entangled states that improve sensitivity beyond the classical limit. Chapter 4 takes a broader perspective, examining the foundations of solving many-body quantum spin dynamics without using the Schrödinger equation.