Coherent coupling between optical fields and solid-state spins is essential for building a spin–photon interface and exchanging quantum information. The nitrogen-vacancy (NV) center, a solid-state defect center in diamond, is a promising qubit system for its relatively high-temperature spin coherence. Here, we study the coherent coupling between the photonic spin texture (PST) and the quantum polarization cloud (phase shift) of NV centers spanning a temperature range from liquid nitrogen (77 K) to room temperature (295 K). We show that by optimizing the laser power and frequency detuning, it is possible to maintain coherence in NV–photon interaction even in this nonideal limit. The coherent NV–photon interaction in our experiment is encoded in the quantum phase shift of the NV center spin qubit, which can be read out using the Hahn-echo magnetometry technique. Our approach of studying light–matter interaction at an elevated temperature can build an unexplored regime of spin–photon interface, which has potential applications in diverse quantum applications.
Coherent coupling between optical fields and solid-state spins is essential for building a spin–photon interface and exchanging quantum information. The nitrogen-vacancy (NV) center, a solid-state defect center in diamond, is a promising qubit system for its relatively high-temperature spin coherence. Here, we study the coherent coupling between the photonic spin texture (PST) and the quantum polarization cloud (phase shift) of NV centers spanning a temperature range from liquid nitrogen (77 K) to room temperature (295 K). We show that by optimizing the laser power and frequency detuning, it is possible to maintain coherence in NV–photon interaction even in this nonideal limit. The coherent NV–photon interaction in our experiment is encoded in the quantum phase shift of the NV center spin qubit, which can be read out using the Hahn-echo magnetometry technique. Our approach of studying light–matter interaction at an elevated temperature can build an unexplored regime of spin–photon interface, which has potential applications in diverse quantum applications.
The nitrogen vacancy (NV) center in diamond is a unique quantum system that combines solid state spin qubits with coherent optical transitions. The spin states of the NV center can be initialized, read out, and controlled with RF fields at room temperature. It can be coupled to other spin systems in the environment while at the same time maintaining an extraordinary degree of quantum coherence. Experiments utilizing the NV center's spin states have led to a wide range of demonstrations from quantum error correction to high-sensitivity magnetometry. This thesis, however, focuses on creating an interface between NV centers and light in the visible domain by making use of its optical transitions. Such an interface connects the quantum system consisting of NV centers and nuclear spins to photons, which can then be used to both manipulate the spin qubits themselves or transport quantum information over large distances.
Abstract Photonic spin texture (PST), the spatial distribution of the spin angular momentum of light, is connected to unique properties of light, such as optical skyrmions and topological optical N-invariants. There has been recent progress on the generation and manipulation of PST using various methodologies. However, a challenge remains for the sub-wavelength characterization of PST. Here, we demonstrate nitrogen–vacancy (NV) centers in diamond as nanoscale quantum sensors for imaging the PST of a beam with orbital angular momentum. Leveraging the coherent interaction between photon spin and NV center electron spin at cryogenic temperature (77 K), and using the Hahn-echo magnetometry technique, we experimentally demonstrate the imprinting of the PST on the quantum phase shift of NV centers. Our work can lead to the development of a quantum imaging platform capable of characterization of the spin texture of light at sub-wavelength scales.
The nitrogen-vacancy (NV) center in diamond has garnered great interest over the past decade as its electronic spin shows promise as a quantum bit (qubit) and nanoscale sensor. Consisting of a substitutional nitrogen adjacent to a vacant site within the carbon lattice of diamond, this defect exhibits millisecond-long spin coherence times extending beyond room temperature, spin-dependent optical addressability, coupling to intrinsic and nearby nuclear spins, and it can be controlled and manipulated through electrical, magnetic, and optical means. In particular, at cryogenic temperatures (T < 25 K), the NV center's excited state becomes sharp and optically resolvable, providing a solid-state quantum optical testbed. In this thesis, I describe several experiments that explore this quantum optical interface to facilitate the development of a photonic network of single spins linked and controlled by light. We begin by exploring how electric fields tune the orbital levels within the NV center through the DC Stark effect, finding a surprising photo-induced field that aids in the ability to tune multiple NV centers' optical transitions to degeneracy. We then develop techniques to fully control the spin state of the NV center by coupling through a lambda system, an energy configuration consisting of two lower levels coupled to one of higher energy. When a lambda system is optically driven, the spin becomes trapped in a dark state, or the eigenstate of the system that is not coupled to the light fields through destructive interference, forming the basis for the various types of control demonstrated. We demonstrate arbitrary-basis initialization and readout of the spin state through coherent population trapping, as well as the ability to rotate about any arbitrary basis through stimulated Raman transitions. Combining these techniques, we measure the NV center's spin coherence through a completely optical measurement. We then extend these lambda system techniques to adiabatically move the dark state in trajectories around the Bloch sphere. Such trajectories accumulate a quantum mechanical phase that depends only on the geometry of the path enclosed, not on the energetics or time of the interaction. We characterize the interaction, measure this phase, known as Berry phase, and explore the limits of its control and resilience to noise. Finally, we demonstrate another all-optical control technique that uses strong ultrafast pulses of light to transfer the spin between the ground and excited states, deriving spin manipulation from the excited state dynamics. This technique also provides time-resolved spectroscopy of the excited state and its various decay and decoherence mechanisms. These experiments advance the progress toward the development of photonic networks coupling and controlling defects through light-matter interactions.
The nitrogen-vacancy (NV) center in diamond has emerged as a versatile atom-like system, finding diverse applications at both ambient and cryogenic temperatures. At room temperature, the NV center's spin-triplet electronic ground state has a long coherence time and can be read out and initialized using nonresonant optical excitation, which has enabled a wide range of metrology and quantum information applications. At cryogenic temperatures, the NV center exhibits a variety of narrow, atom-like optical transitions, which has made the NV center a promising platform for quantum optics applications. We use coherent optical manipulation of the NV center at cryogenic temperatures to probe its internal dynamics and aspects of its interactions with its environment.\nFirst, we investigate the intersystem crossing (ISC) process, which is a spin-dependent nonradiative decay mechanism that enables the electronic spin state to be optically initialized and read out at room temperature. We measure the ISC rates from different excited states as well as the rate at which interactions with phonons redistribute population between these states. Based on these measurements, we develop a theoretical model that unifies the phonon-induced mixing and ISC mechanisms. We find that our model is in excellent agreement with experiment and that it can be used to predict unknown elements of the NV center's electronic structure.\nSecond, we investigate a novel method of using coherent optical manipulation of the NV center's electronic spin to control a nearby nuclear spin. Coherent interactions between the NV center and nearby nuclear spins have enabled the development of NV center-based, multi-qubit quantum registers, but these techniques have generally required the application of microwave or radio-frequency radiation. We demonstrate control of the nuclear spin using an all-optical Raman technique and theoretically evaluate the extent to which the intrinsic physics of the NV center limits the coherence of this Raman-based manipulation technique.
Among the possible defects that can occur in diamonds, one that draws attention is the nitrogen-vacancy (NV) center.Studied since the early 90s, in recent years, they became one of the most promising platforms for field applications of quantum technology at room temperature, especially for quantum sensing.They are sensitive to electric and magnetic fields, temperature, and strain, making these nanosensors a versatile platform for many applications.The NV center's spin state is easy to read and manipulate by optical means, and, most interestingly, it works well at room temperature, which facilitates its use.The great challenge to implement quantum protocols and quantum algorithms is the coherence time of the quantum states.The NV center stands out for having relatively high coherence times at room temperature.This dissertation presents measurements to characterize the electron spin coherence of NV centers in an ultrapure sample of diamond designed for quantum sensing applications.These measurements combine optical e magnetic resonance techniques.For that, a method was implemented using a conventional CCD camera and a clever imaging protocol, making it possible to perform various pulsed microwave experiments on the electron spin, such as Rabi oscillations and Hahn spin-echo, which were used for determining the characteristic relaxation times (T 1 and T 2 ).Results show that this system provides at least two readily accessible qubits that can be used in quantum protocols even at room temperature.
The nitrogen-vacancy (NV) center in diamond is an ideal candidate for quantum sensing because of its excellent spin coherence property as well as the possibility for optical initialization and readout. Previous studies, on the other hand, have typically been conducted at low or room temperature. The inability to fully understand the coherence properties of the NV center at high temperatures limits NV's further applications. We systematically investigate the coherence properties of NV center ensemble at temperatures ranging from 300 K to 600 K in this paper. Coherence time T2 decreases rapidly from $184\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\text{s}$ at 300 K to $30\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\text{s}$ at 600 K due to the interaction with paramagnetic impurities. At all experiment temperatures, both single-quantum and double-quantum transitions exhibit a T5 relaxation rate, which is attributed to the two-phonon Raman process. Nonetheless, the inhomogeneous dephasing time T2∗ and thermal-echo decoherence time TTE remain almost unchanged at temperature up to 600 K. A thermal-echo-based thermometer is demonstrated to have a sensitivity of 41mK/Hz at 450 K. These findings will pave the way for NV-based high-temperature sensing and provide a more comprehensive understanding of solid-state qubit decoherence.