Charles F. de las Casas

Fluorescence thermometry enhanced by the quantum coherence of single spins in diamond

We demonstrate fluorescence thermometry techniques with sensitivities approaching 10 mK⋅Hz−1/2 based on the spin-dependent photoluminescence of nitrogen vacancy (NV) centers in diamond. These techniques use dynamical decoupling protocols to convert thermally induced shifts in the NV centers spin resonance frequencies into large changes in its fluorescence. By mitigating interactions with nearby nuclear spins and facilitating selective thermal measurements, these protocols enhance the spin coherence times accessible for thermometry by 45-fold, corresponding to a 7-fold improvement in the NV center’s temperature sensitivity. Moreover, we demonstrate these techniques can be applied over a broad temperature range and in both finite and near-zero magnetic field environments. This versatility suggests that the quantum coherence of single spins could be practically leveraged for sensitive thermometry in a wide variety of biological and microscale systems.

Three-dimensional localization of spins in diamond using 12C implantation

We demonstrate three-dimensional localization of a single nitrogen-vacancy (NV) center in diamond by combining nitrogen doping during growth with a post-growth 12C implantation technique that facilitates vacancy formation in the crystal. We show that the NV density can be controlled by the implantation dose without necessitating increase of the nitrogen incorporation. By implanting a large 12C dose through nanoscale apertures, we can localize an individual NV center within a volume of (∼180 nm)3 at a deterministic position while repeatedly preserving a coherence time (T2) > 300 μs. This deterministic position control of coherent NV centers enables integration into NV-based nanostructures to realize scalable spin-sensing devices as well as coherent spin coupling mediated by photons and phonons.

Isolated Spin Qubits in SiC with a High-Fidelity Infrared Spin-to-Photon Interface

The divacancies in SiC are a family of paramagnetic defects that show promise for quantum communication technologies due to their long-lived electron spin coherence and their optical addressability at near-telecom wavelengths. Nonetheless, a high-fidelity spin-photon interface, which is a crucial prerequisite for such technologies, has not yet been demonstrated. Here, we demonstrate that such an interface exists in isolated divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that divacancies in 4H-SiC have minimal undesirable spin mixing, and that the optical linewidths in our current sample are already similar to those of recent remote entanglement demonstrations in other systems. Moreover, we find that 3C-SiC divacancies have a millisecond Hahn-echo spin coherence time, which is among the longest measured in a naturally isotopic solid. The presence of defects with these properties in a commercial semiconductor that can be heteroepitaxially grown as a thin film on Si shows promise for future quantum networks based on SiC defects. DOI:https://doi.org/10.1103/PhysRevX.7.021046 Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Published by the American Physical Society

Engineered Micro- and Nanoscale Diamonds as Mobile Probes for High-Resolution Sensing in Fluid

The nitrogen-vacancy (NV) center in diamond is an attractive platform for quantum information and sensing applications because of its room temperature operation and optical addressability. A major research effort focuses on improving the quantum coherence of this defect in engineered micro- and nanoscale diamond particles (DPs), which could prove useful for high-resolution sensing in fluidic environments. In this work we fabricate cylindrical diamonds particles with finely tuned and highly reproducible sizes (diameter and height ranging from 100 to 700 and 500 nm to 2 μm, respectively) using high-purity, single-crystal diamond membranes with shallow-doped NV centers. We show that the spin coherence time of the NV centers in these particles exceeds 700 μs, opening the possibility for the creation of ultrahigh sensitivity micro- and nanoscale sensors. Moreover, these particles can be efficiently transferred into a water suspension and delivered to the region to probe. In particular, we introduce a DP suspension inside a microfluidic circuit and control position and orientation of the particles using an optical trapping apparatus. We demonstrate a DC magnetic sensitivity of 9 μT/√Hz in fluid as well as long-term trapping stability (>30 h), which paves the way toward the use of high-sensitivity pulse techniques on contactless probes manipulated within biological settings.

Long-range spin wave mediated control of defect qubits in nanodiamonds

The nitrogen-vacancy (NV) center in diamond has been extensively studied in recent years for its remarkable quantum coherence properties that make it an ideal candidate for room temperature quantum computing and quantum sensing schemes. However, these schemes rely on spin-spin dipolar interactions, which require the NV centers to be within a few nanometers from each other while still separately addressable, or to be in close proximity of the diamond surface, where their coherence properties significantly degrade. Here we demonstrate a method for overcoming these limitations using a hybrid yttrium iron garnet (YIG)-nanodiamond quantum system constructed with the help of directed assembly and transfer printing techniques. We show that YIG spin-waves can amplify the oscillating field of a microwave source by more than two orders of magnitude and efficiently mediate its coherent interactions with an NV center ensemble. These results demonstrate that spinwaves in ferromagnets can be used as quantum buses for enhanced, long-range qubit interactions, paving the way to ultra-efficient manipulation and coupling of solid state defects in hybrid quantum networks and sensing devices.

Stark tuning and electrical charge state control of single divacancies in silicon carbide

Neutrally charged divacancies in silicon carbide (SiC) are paramagnetic color centers whose long coherence times and near-telecom operating wavelengths make them promising for scalable quantum communication technologies compatible with existing fiber optic networks. However, local strain inhomogeneity can randomly perturb their optical transition frequencies, which degrades the indistinguishability of photons emitted from separate defects, and hinders their coupling to optical cavities. Here we show that electric fields can be used to tune the optical transition frequencies of single neutral divacancy defects in 4H-SiC over a range of several GHz via the DC Stark effect. The same technique can also control the charge state of the defect on microsecond timescales, which we use to stabilize unstable or non-neutral divacancies into their neutral charge state. Using fluorescence-based charge state detection, we show both 975 nm and 1130 nm excitation can prepare its neutral charge state with near unity efficiency.