Many modern sensing, processing, and fabrication technologies depend upon the sequential scanning of laser light. Due to inertial, thermal, and electrical limitations, the speed of a typical laser deflector is inversely related to its optical invariant and therefore the number of resolvable spots it can address. Passive optical systems have been developed that can effectively double the optical invariant and maximum throughput of a single deflector. We present a method for increasing the effective optical invariant beyond 2× by repeated relaying of the deflected beam onto the deflector in an optical loop created within a cavity. We use this Relayed-Loop Optically Amplified Deflection (ReLOAD) approach to accomplish 8× amplification of electro-optical (EO) deflection, a deflection technology with unparalleled speed, but limited optical invariant. Using ReLOAD, we demonstrate 10 kHz frame rate imaging, 1 MHz line scan rate, and μs step times across an addressable space well beyond the capabilities of typical electro-optical deflectors.

BACKGROUND:Perception and behavior require coordinated activity of thousands of neurons operating in networks that span millimeters of brain area. In vivo calcium imaging approaches have proven exceptionally powerful for examining the structure of these networks at large scales, and optogenetics can allow for causal manipulations of large populations of neurons. However, realizing the full potential of these techniques requires the ability to simultaneously measure and manipulate distinct circuit elements on the scale of millimeters.NEW METHOD:We describe an opto-macroscope, an artifact-free, all-optical system capable of delivering patterned optogenetic stimulation with high spatial and temporal resolution across millimeters of brain while simultaneously imaging functional neural activity.RESULTS:We find that this approach provides direct manipulation of cortical regions ranging from hundreds of microns to several millimeters in area, allowing for the perturbation of individual brain areas or networks of functional domains. Using this system we find that spatially complex endogenous networks in the developing ferret visual cortex can be readily reactivated by precisely designed patterned optogenetic stimuli.COMPARISON WITH EXISTING METHODS:Our opto-macroscope extends current all-optical optogenetic approaches which operate on a cellular scale with multiphoton stimulation, and are poorly suited to investigate the millimeter-scale of many functional networks. It also builds upon other mesoscopic optogenetic techniques that lack simultaneous optical readouts of neural activity.CONCLUSIONS:The large-scale all-optical capabilities of our system make it a powerful new tool for investigating the contribution of cortical domains and brain areas to the functional neural networks that underlie perception and behavior.

Significance: The development of genetically encoded fluorescent indicators of neural activity with millisecond dynamics has generated demand for ever faster two-photon (2P) imaging systems, but acoustic and mechanical beam scanning technologies are approaching fundamental limits. We demonstrate that potassium tantalate niobate (KTN) electro-optical deflectors (EODs), which are not subject to the same fundamental limits, are capable of ultrafast two-dimensional (2D) 2P imaging in vivo. Aim: To determine if KTN-EODs are suitable for 2P imaging, compatible with 2D scanning, and capable of ultrafast in vivo imaging of genetically encoded indicators with millisecond dynamics. Approach: The performance of a commercially available KTN-EOD was characterized across a range of drive frequencies and laser parameters relevant to in vivo 2P microscopy. A second KTN-EOD was incorporated into a dual-axis scan module, and the system was validated by imaging signals in vivo from ASAP3, a genetically encoded voltage indicator. Results: Optimal KTN-EOD deflection of laser light with a central wavelength of 960 nm was obtained up to the highest average powers and pulse intensities tested (power: 350 mW; pulse duration: 118 fs). Up to 32 resolvable spots per line at a 560 kHz line scan rate could be obtained with single-axis deflection. The complete dual-axis EO 2P microscope was capable of imaging a 13 mu m by 13 mu m field-of-view at over 10 kHz frame rate with similar to 0.5 mu m lateral resolution. We demonstrate in vivo imaging of neurons expressing ASAP3 with high temporal resolution. Conclusions: We demonstrate the suitability of KTN-EODs for ultrafast 2P cellular imaging in vivo, providing a foundation for future high-performance microscopes to incorporate emerging advances in KTN-based scanning technology.

A broad effort is underway to understand and harness the interaction between superconductors and spin-active color centers with an eye on hybrid quantum devices and novel imaging modalities of superconducting materials. Most work, however, overlooks the interplay between either system and the environment created by the color center host. Here we use a diamond scanning probe to investigate the spin dynamics of a single nitrogen-vacancy (NV) center proximal to a superconducting film. We find that the presence of the superconductor increases the NV spin coherence lifetime, a phenomenon we tentatively rationalize as a change in the electric noise due to a superconductor-induced redistribution of charge carriers near induced redistribution of charge carriers near the NV. We then build on these findings to demonstrate transverse-relaxation-time-weighted imaging of the superconductor film. These results shed light on the dynamics governing the spin coherence of shallow NVs, and promise opportunities for new forms of noise spectroscopy and imaging of superconductors.

The silicon vacancy (SiV) center in diamond is typically found in three stable charge states, SiV0, SiV-, and SiV2-, but studying the processes leading to their formation is challenging, especially at room temperature, due to their starkly different photoluminescence rates. Here, we use confocal fluorescence microscopy to activate and probe charge interconversion between all three charge states under ambient conditions. In particular, we witness the formation of SiV0 via the two-step capture of diffusing, photogenerated holes, a process we expose both through direct SiV0 fluorescence measurements at low temperatures and confocal microscopy observations in the presence of externally applied electric fields. In addition, we show that continuous red illumination induces the converse process, first transforming SiV0 into SiV- and then into SiV2-. Our results shed light on the charge dynamics of SiV and promise opportunities for nanoscale sensing and quantum information processing.

Charge control of color centers in semiconductors promises opportunities for novel forms of sensing and quantum information processing. Here, we articulate confocal fluorescence microscopy and magnetic resonance protocols to induce and probe charge transport between discrete sets of engineered nitrogen-vacancy (NV) centers in diamond, down to the level of individual defects. In our experiments, a "source" NV undergoes optically-driven cycles of ionization and recombination to produce a stream of photo-generated carriers, one of which we subsequently capture via a "target" NV several micrometers away. We use a spin-to-charge conversion scheme to encode the spin state of the source color center into the charge state of the target, in the process allowing us to set an upper bound to carrier injection from other background defects. We attribute our observations to the action of unscreened Coulomb potentials producing giant carrier capture cross-sections, orders of magnitude greater than those typically attained in ensemble measurements. Besides their fundamental interest, these results open intriguing prospects in the use of free carriers as a quantum bus to mediate effective interactions between paramagnetic defects in a solid-state chip.

Color centers in hexagonal boron nitride (hBN) are presently attracting broad interest as a novel platform for nanoscale sensing and quantum information processing. Unfortunately, their atomic structures remain largely elusive and only a small percentage of the emitters studied thus far has the properties required to serve as optically addressable spin qubits. Here, we use confocal fluorescence microscopy at variable temperature to study a new class of point defects produced via cerium ion implantation in thin hBN flakes. We find that, to a significant fraction, emitters show bright room-temperature emission, and good optical stability suggesting the formation of Ce-based point defects. Using density functional theory (DFT) we calculate the emission properties of candidate emitters, and single out the CeVB center - formed by an interlayer Ce atom adjacent to a boron vacancy - as one possible microscopic model. Our results suggest an intriguing route to defect engineering that simultaneously exploits the singular properties of rare-earth ions and the versatility of two-dimensional material hosts.

Control of the dynamics of mechanical resonators is central to quantum science and metrology applications. Optomechanical control of diamond resonators is attractive owing to the excellent physical properties of diamond and its ability to host electronic spins that can be coherently coupled to mechanical motion. Using a confocal microscope, we demonstrate tunable amplification and damping of the motion of a diamond nanomechanical resonator. Observation of both normal-mode cooling from room temperature to 80 K and amplification into self-oscillations with 60 mu W of optical power is observed via waveguide optomechanical readout. This system is promising for quantum spin optomechanics, as it is predicted to enable optical control of stress-spin coupling with rates of approximately 1 MHz (100 THz) to ground (excited) states of diamond nitrogen-vacancy centers.

While the study of space-charge potentials has a long history, present models are largely based on the notion of steady state equilibrium, ill-suited to describe wide band gap semiconductors with moderate to low concentrations of defects. Here we build on color centers in diamond both to locally inject carriers into the crystal and probe their evolution as they propagate in the presence of external and internal potentials. We witness the formation of metastable charge patterns whose shape---and concomitant field---can be engineered through the timing of carrier injection and applied voltages. With the help of previously crafted charge patterns, we unveil a rich interplay between local and extended sources of space-charge field, which we then exploit to show space-charge-induced carrier guiding.

We articulate confocal microscopy and electron spin resonance to implement spin-to-charge conversion in a small ensemble of nitrogen-vacancy (NV) centers in bulk diamond and demonstrate charge conversion of neighboring defects conditional on the NV spin state. We build on this observation to show time-resolved NV spin manipulation and ancilla-charge-aided NV spin state detection via integrated measurements. Our results hint at intriguing opportunities in the development of novel measurement strategies in fundamental science and quantum spintronics as well as in the search for enhanced forms of color-center-based metrology down to the limit of individual point defects.

Although chemical vapor deposition (CVD) is one of the preferred routes to synthetic diamond crystals, a full knowledge of the point defects produced during growth is still incomplete. Here we exploit the charge and spin properties of nitrogen vacancy (NV) centers in type-1b CVD diamond to expose an optically and magnetically dark point defect, so far virtually unnoticed despite an abundance comparable to (if not greater than) that of substitutional nitrogen. Indirectly detected photoluminescence spectroscopy indicates a donor state 1.6 eV above the valence band, although the defect's microscopic structure and composition remain elusive. Our results may prove relevant to the growing set of applications that rely on CVD-grown single-crystal diamond.

Color centers in wide bandgap semiconductors are attracting broad attention as platforms for quantum technologies relying on room-temperature single-photon emission (SPE), and for nanoscale metrology applications building on the centers' response to electric and magnetic fields. Here, we demonstrate room-temperature SPE from defects in cubic boron nitride (cBN) nanocrystals, which we unambiguously assign to the cubic phase using spectrally resolved Raman imaging. These isolated spots show photoluminescence (PL) spectra with zero-phonon lines (ZPLs) within the visible region (496-700 nm) when subject to sub-bandgap laser excitation. Second-order autocorrelation of the emitted photons reveals antibunching with $g^{2}$ ~ 0.2 and a decay constant of 2.75 ns that is further confirmed through fluorescence lifetime measurements. The results presented herein prove the existence of optically addressable isolated quantum emitters originating from defects in cBN, making this material an interesting platform for opto-electronic devices and quantum applications.

Abstract Integration of quantum emitters in photonic structures is an important step in the broader quest to generate and manipulate on-demand single photons via compact solid-state devices. Unfortunately, implementations relying on material platforms that also serve as the emitter host often suffer from a tradeoff between the desired emitter properties and the photonic system practicality and performance. Here, we demonstrate “pick and place” integration of a Si3N4 microdisk optical resonator with a bright emitter host in the form of ∼20-nm-thick hexagonal boron nitride (hBN). The film folds around the microdisk maximizing contact to ultimately form a hybrid hBN/Si3N4 structure. The local strain that develops in the hBN film at the resonator circumference deterministically activates a low density of defect emitters within the whispering gallery mode volume of the microdisk. These conditions allow us to demonstrate cavity-mediated out-coupling of emission from defect states in hBN through the microdisk cavity modes. Our results pave the route toward the development of chip-scale quantum photonic circuits with independent emitter/resonator optimization for active and passive functionalities.

We demonstrate coupling of hBN defect emission to Si3N4 microdisk cavities and high-Q plasmonic surface lattice resonances by exploiting the topography of the photonic elements to engineer strain-activated color centers within the element’s field-mode.