Electronic structure of the N-V center in diamond: Experiments

Excited-State Lifetime of NV Centers for All-Optical Magnetic Field Sensing

We investigate the magnetic field-dependent fluorescence lifetime of microdiamond powder containing a high density of nitrogen-vacancy centers. This constitutes a non-intensity quantity for robust, all-optical magnetic field sensing. We propose a fiber-based setup in which the excitation intensity is modulated in a frequency range up to 100MHz. The change in magnitude and phase of the fluorescence relative to B=0 is recorded where the phase shows a maximum in magnetic contrast of 5.8∘ at 13MHz. A lock-in amplifier-based setup utilizing the change in phase at this frequency shows a 100 times higher immunity to fluctuations in the optical path compared to the intensity-based approach. A noise floor of 20μT/Hz and a shot-noise-limited sensitivity of 0.95μT/Hz were determined.

Materials Innovations for Quantum Technology Acceleration: A Perspective

A broad perspective of quantum technology state of the art is provided and critical stumbling blocks for quantum technology development are identified. Innovations in demonstrating and understanding electron entanglement phenomena using bulk and low-dimensional materials and structures are summarized. Correlated photon-pair generation via processes such as nonlinear optics is discussed. Application of qubits to current and future high-impact quantum technology development is presented. Approaches for realizing unique qubit features for large-scale encrypted communication, sensing, computing, and other technologies are still evolving; thus, materials innovation is crucially important. A perspective on materials modeling approaches for quantum technology acceleration that incorporate physics-based AI/ML, integrated with quantum metrology is discussed.

Microwave Passive Direction-Finding Method Based on NV Color Center in Diamond

In this study, we established a passive direction-finding scheme based on microwave power measurement: Microwave intensity was detected using microwave-frequency proportion integration differentiation control and coherent population oscillation effect converting the change in microwave resonance peak intensity into a shift of the microwave frequency spectrum, for which the minimum microwave intensity resolution was -20 dBm. The direction angle of the microwave source was calculated using the weighted global least squares method of microwave field distribution. This lay in the 12~26 dBm microwave emission intensity range, and the measurement position was in the range of (-15°~15°). The average angle error of the angle measurement was 0.24°, and the maximum angle error was 0.48°. In this study, we established a microwave passive direction-finding scheme based on quantum precision sensing, which measures the microwave frequency, intensity, and angle in a small space and has a simple system structure, small equipment size, and low system power consumption. In this study, we provide a basis for the future application of quantum sensors in microwave direction measurements.

Resonant Degenerate Four-Wave Mixing at the Defect Energy Levels of 2D Organic-Inorganic Hybrid Perovskite Crystals

Two-dimensional organic-inorganic lead halide perovskites are generating great interest due to their optoelectronic characteristics such as high solar energy conversion efficiency and a tunable direct band gap in the visible regime. However, the presence of defect states within the two-dimensional crystal structure can affect these properties, resulting in changes to their band gap emission as well as the emergence of nonlinear optical phenomena. Here, we have investigated the effects of the presence of defect states on the nonlinear optical phenomena of the 2D hybrid perovskite (BA)₂(MA)₂Pb₃Br₁₀. When two pulses, one narrowband pump pulse centered at 800 nm and one supercontinuum pulse with bandwidth from 800-1100 nm, are incident on a perovskite flake, degenerate four-wave mixing (FWM) occurs, with peaks corresponding to the energy levels of the defect states present within the crystal. The longer carrier lifetime of the defect state, in comparison to that of virtual transitions that take place in nonresonant FWM processes, allows for a larger population of electrons to be excited by the second pump photon, resulting in increased FWM signal at the defect energy levels. The quenching of the two-photon luminescence as flake thickness increases is also observed and attributed to the increased presence of defects within the flake at larger thicknesses. This technique shows the potential of detecting defect energy levels in crystals using FWM for a variety of optoelectronic applications.

Low-field microwave-mediated optical hyperpolarization in optically pumped diamond

The emergence of a new class of optically polarizable electronic spins in diamond, nitrogen vacancy (NV) defect centers, has opened interesting new avenues for dynamic nuclear polarization. Here we review methods for the room-temperature hyperpolarization of lattice ¹³C nuclei using optically pumped NV centers, focusing particular attention to a polarization transfer via rotating-frame level anti-crossings. We describe special features of this optical DNP mechanism at low-field, in particular, its deployability to randomly oriented diamond nanoparticles. In addition, we detail methods for indirectly obtaining high-resolution NV ESR spectra via hyperpolarization readout. These mechanistic features provide perspectives for interesting new applications exploiting the optically generated ¹³C hyperpolarization.

Jahn-Teller-induced femtosecond electronic depolarization dynamics of the nitrogen-vacancy defect in diamond

Single-photon emission from the nitrogen-vacancy defect in diamond constitutes one of its many proposed applications. Owing to its doubly degenerate ³E electronic excited state, photons from this defect can be emitted by two optical transitions with perpendicular polarization. Previous measurements have indicated that orbital-selective photoexcitation does not, however, yield photoluminescence with well-defined polarizations, thus hinting at orbital-averaging dynamics even at cryogenic temperatures. Here we employ femtosecond polarization anisotropy spectroscopy to investigate the ultrafast electronic dynamics of the ³E state. We observe subpicosecond electronic dephasing dynamics even at cryogenic temperatures, up to five orders of magnitude faster than dephasing rates suggested by previous frequency- and time-domain measurements. Ab initio molecular dynamics simulations assign the ultrafast depolarization dynamics to nonadiabatic transitions and phonon-induced electronic dephasing between the two components of the ³E state. Our results provide an explanation for the ultrafast orbital averaging that exists even at cryogenic temperatures.

Understanding ultrafast dynamics of excited states of nitrogen-vacancy helps its manipulation for technological applications. Here the authors use polarization anisotropy spectroscopy and molecular dynamics to investigate sub-picosecond dephasing dynamics, identifying the origin of orbital averaging effects.

Efficient mode conversion in an optical nanoantenna mediated by quantum emitters

Converting signals at low intensities between different electromagnetic modes is an asset for future information technologies. In general, slightly asymmetric optical nanoantennas enable the coupling between bright and dark modes that they sustain. However, the conversion efficiency might be very low. Here, we show that the additional incorporation of a quantum emitter allows us to tremendously enhance this efficiency. The enhanced local density of states cycles the quantum emitter between its upper and lower level at an extremely high rate, hence converting the energy very efficiently. The process is robust with respect to possible experimental tolerances, and adds a new ingredient to be exploited while studying and applying coupling phenomena in optical nanosystems.

Ultrafast optical control of orbital and spin dynamics in a solid-state defect

Atom-scale defects in semiconductors are promising building blocks for quantum devices, but our understanding of their material-dependent electronic structure, optical interactions, and dissipation mechanisms is lacking. Using picosecond resonant pulses of light, we study the coherent orbital and spin dynamics of a single nitrogen-vacancy center in diamond over time scales spanning six orders of magnitude. We develop a time-domain quantum tomography technique to precisely map the defect's excited-state Hamiltonian and exploit the excited-state dynamics to control its ground-state spin with optical pulses alone. These techniques generalize to other optically addressable nanoscale spin systems and serve as powerful tools to characterize and control spin qubits for future applications in quantum technology.

Optical superradiance from nuclear spin environment of single-photon emitters

We show that superradiant optical emission can be observed from the polarized nuclear spin ensemble surrounding a single-photon emitter such as a single quantum dot or nitrogen-vacancy center. The superradiant light is emitted under optical pumping conditions and would be observable with realistic experimental parameters.

Symmetric Double-Well Potential Model and Its Application to Vibronic Spectra: Studies of Inversion Modes of Ammonia and Nitrogen-Vacancy Defect Centers in Diamond

In this paper, we have studied the vibronic transitions between two symmetric double-well potentials by proposing a model Hamiltonian consisting of a harmonic oscillator and a parturition described by a Gaussian function that leads to a double minima potential with a barrier between the two energy minima. Making use of the contour integral form of Hermite polynomials, we present a new formula that can calculate Franck-Condon factors of the system rigorously. The simulated vibronic spectra of ammonia and the negatively charged nitrogen-vacancy center in diamond are presented as an application of the formula.

Raman-excited spin coherences in nitrogen-vacancy color centers in diamond

Raman-excited spin coherences were experimentally observed in nitrogen-vacancy (N-V) diamond color centers by means of nondegenerate four-wave mixing and electromagnetically induced transparency. The maximal absorption suppression was found to be 17%, which corresponds to 70% of what is possible given the random geometric orientation of the N-V center in diamond. In the context of quantum computing in solids, this level of transparency represents efficient preparation of quantum bits, as well as the ability to perform arbitrary single-quantum-bit rotations.