We describe an all-optical scheme for spin manipulation in the ground-state triplet of the negatively charged nitrogen-vacancy (NV) center in diamond. Virtual optical excitation from the ${}^{3}{A}_{2}$ ground state into the ${}^{3}E$ excited state allows for spin rotations by virtue of the spin-spin interaction in the two-fold orbitally degenerate excited state. We derive an effective Hamiltonian for optically induced spin-flip transitions within the ground state spin triplet due to off-resonant optical pumping. Furthermore, we investigate the spin qubit formed by the Zeeman sublevels with spin projection ${m}_{S}=0$ and ${m}_{S}=\ensuremath{-}1$ along the NV axis around the ground state level anticrossing with regard to full optical control of the electron spin.
We describe an all-optical scheme for spin manipulation in the ground-state triplet of the negatively charged nitrogen-vacancy (NV) center in diamond. Virtual optical excitation from the 3A2 ground state into the 3E excited state allows for spin rotations by virtue of the spin-spin interaction in the two-fold orbitally degenerate excited state. We derive an effective Hamiltonian for optically induced spin-flip transitions within the ground state spin triplet due to off-resonant optical pumping. Furthermore, we investigate the spin qubit formed by the Zeeman sublevels with spin projection mS=0 and mS=\ensuremath−1 along the NV axis around the ground state level anticrossing with regard to full optical control of the electron spin.
Optically addressable spin defects in solid-state materials have shown great potential for applications ranging from metrology to quantum information processing. Many of these experiments require a detailed understanding of the full Hamiltonian dynamics in order to develop precise quantum control. Here we use picosecond resonant optical pulses to investigate the coherent orbital and spin dynamics of the nitrogen-vacancy (NV) center in diamond, over timescales spanning six orders of magnitude. We implement an ultrafast optical pump-probe technique to study the NV center’s orbital-doublet, spin-triplet excited state at cryogenic temperatures (T < 20 K), where the excited state becomes stable and optically coherent with the ground state. This technique, coupled with optical polarization selection rules, allows us to probe the coherent orbital dynamics of the NV center’s excited state [1]. These experiments reveal dynamics on femtosecond to nanosecond timescales due to the interplay between the ground and excited state orbital levels. This all-optical technique also provides a method to dynamically control the spin state of the NV center by harnessing the excited state structure. Through studying the spin dynamics of the NV center with coherent pulses of light, we are able to rotate the spin state on sub-nanosecond timescales. Furthermore, by tuning the excited-state spin Hamiltonian with an external magnetic eld, we demonstrate arbitrary-axis spin rotations through controlled unitary evolution of the spin state. Extending this to the full excited-state manifold, we develop a time-domain quantum tomography technique to precisely map the NV center’s excited state Hamiltonian. These techniques generalize to other systems and can be a powerful tool in characterizing and controlling qubits in other optically addressable spin systems.
We propose an approach for an optical qubit rotation in the negatively charged nitrogen vacancy (NV) center in diamond. The qubit is encoded in the ground degenerate states at a relatively low-temperature limit. The basic idea of the rotation procedure is the non-Abelian geometric phase in an adiabatic passage, which is produced by the non-adiabatic transition between the two degenerate dark states. The feasibility is based on the success of modeling the NV center as an excited-doublet four-level atom. By applying two pump and two Stokes laser pulses, we found that the behavior of the adiabatic passage depends crucially on the applied intensity of each applied laser field and the detunings between the laser frequencies and their corresponding atomic transition. Particularly, a non-adiabatic transition appears when the applied pump and Stokes laser pulses are off resonance with their corresponding atomic transition.
The negatively charged nitrogen-vacancy defect $({\text{NV}}^{\ensuremath{-}})$ in diamond has attracted much attention in recent years in qubit and biological applications. The negative charge is donated from nearby nitrogen donors that could limit or stem the successful application of ${\text{NV}}^{\ensuremath{-}}$. In this study, we identify the neutral nitrogen-vacancy defect (NV0) by ab initio supercell calculations through the comparison of the measured and calculated hyperfine tensors of the 4A2 excited state. Our analysis shows that (i) the spin state can be selectively occupied optically, (ii) the electron spin state can be manipulated by time-varying magnetic field, and (iii) the spin state may be read out optically. Based on this NV0 is a hope for realizing qubit in diamond without the need of nitrogen donors. In addition, we propose that NV0 may be more sensitive magnetometer than the ultrasensitive ${\text{NV}}^{\ensuremath{-}}$.
The nitrogen vacancy (NV) center in diamond is promising as an electron spin qubit due to its long-lived coherence and optical addressability. The ground state is a spin triplet with two levels $({m}_{s}=\ifmmode\pm\else\textpm\fi{}1)$ degenerate at zero magnetic field. Polarization-selective microwave excitation is an attractive method to address the spin transitions independently since this allows operation down to zero magnetic field. Using a resonator designed to produce circularly polarized microwaves, we have investigated the polarization selection rules of the NV center. We first apply this technique to NV ensembles in [100]- and [111]-oriented samples. Next, we demonstrate an imaging technique, based on optical polarization dependence, which allows rapid identification of the orientations of many single NV centers. Finally, we test the microwave polarization selection rules of individual NV centers of known orientation.
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.