Compact Electron Paramagnetic Resonance on a Chip Spectrometer Using a Single Sided Permanent Magnet.

Electron paramagnetic resonance (EPR) spectroscopy provides information about the physical and chemical properties of materials by detecting paramagnetic states. Conventional EPR measurements are performed in high resonator using large electromagnets which limits the available space for operando experiments. Here we present a solution toward a portable EPR sensor based on the combination of the EPR-on-a-Chip (EPRoC) and a single-sided permanent magnet.

Microwave field mapping for EPR-on-a-chip experiments.

Electron paramagnetic resonance-on-a-chip (EPRoC) devices use small voltage-controlled oscillators (VCOs) for both the excitation and detection of the EPR signal, allowing access to unique sample environments by lifting the restrictions imposed by resonator-based EPR techniques. EPRoC devices have been successfully used at multiple frequencies (7 to 360 gigahertz) and have demonstrated their utility in producing high-resolution spectra in a variety of spin centers. To enable quantitative measurements using EPRoC devices, the spatial distribution of the field produced by the VCOs must be known.

Managing Excess Lead Iodide with Functionalized Oxo-Graphene Nanosheets for Stable Perovskite Solar Cells.

Stability issues could prevent lead halide perovskite solar cells (PSCs) from commercialization despite it having a comparable power conversion efficiency (PCE) to silicon solar cells. Overcoming drawbacks affecting their long-term stability is gaining incremental importance. Excess lead iodide (PbI ) causes perovskite degradation, although it aids in crystal growth and defect passivation.

Highly efficient p-i-n perovskite solar cells that endure temperature variations.

Daily temperature variations induce phase transitions and lattice strains in halide perovskites, challenging their stability in solar cells. We stabilized the perovskite black phase and improved solar cell performance using the ordered dipolar structure of β-poly(1,1-difluoroethylene) to control perovskite film crystallization and energy alignment. We demonstrated p-i-n perovskite solar cells with a record power conversion efficiency of 24.

Optical and Spin Properties of NV Center Ensembles in Diamond Nano-Pillars.

Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations.

Rapid-scan electron paramagnetic resonance using an EPR-on-a-Chip sensor.

Electron paramagnetic resonance (EPR) spectroscopy is the method of choice to investigate and quantify paramagnetic species in many scientific fields, including materials science and the life sciences. Common EPR spectrometers use electromagnets and microwave (MW) resonators, limiting their application to dedicated lab environments. Here, novel aspects of voltage-controlled oscillator (VCO)-based EPR-on-a-Chip (EPRoC) detectors are discussed, which have recently gained interest in the EPR community.

Interdependence of photon upconversion performance and antisolvent processing in thin-film halide perovskite-sensitized triplet-triplet annihilators.

We prepared triplet-triplet annihilation photon upconverters combining thin-film methylammonium lead iodide (MAPI) perovskite with a rubrene annihilator in a bilayer structure. Excitation of the perovskite film leads to delayed, upconverted photoluminescence emitted from the annihilator layer, with triplet excitation of the rubrene being driven by carriers excited in the perovskite layer. To better understand the connections between the semiconductor properties of the perovskite film and the upconversion efficiency, we deliberately varied the perovskite film properties by modifying two spin-coating conditions, namely, the choice of antisolvent and the antisolvent dripping time, and then studied the resulting photon upconversion performance with a standard annihilator layer.

Engineering preferentially-aligned nitrogen-vacancy centre ensembles in CVD grown diamond.

Here we report a method for improving the magnetic field sensitivity of an ensemble of Nitrogen-Vacancy (NV) centres in C-enriched diamond aligned along the [111] crystal axis. The preferentially-aligned NV centres are fabricated by a Plasma Enhanced Chemical Vapour Deposition (PECVD) process and their concentration is quantitatively determined by analysing the confocal microscopy images. We further observe that annealing the samples at high temperature (1500 °C) in vacuum leads to a conversion of substitutional nitrogen into NV centres.

Robust optical polarization of nuclear spin baths using Hamiltonian engineering of nitrogen-vacancy center quantum dynamics.

Dynamic nuclear polarization (DNP) is an important technique that uses polarization transfer from electron to nuclear spins to achieve nuclear hyperpolarization. Combining efficient DNP with optically polarized nitrogen-vacancy (NV) centers offers promising opportunities for novel technological applications, including nanoscale nuclear magnetic resonance spectroscopy of liquids, hyperpolarized nanodiamonds as magnetic resonance imaging contrast agents, and the initialization of nuclear spin-based diamond quantum simulators. However, none of the current realizations of polarization transfer are simultaneously robust and sufficiently efficient, making the realization of the applications extremely challenging.

Submillihertz magnetic spectroscopy performed with a nanoscale quantum sensor.

Precise timekeeping is critical to metrology, forming the basis by which standards of time, length, and fundamental constants are determined. Stable clocks are particularly valuable in spectroscopy because they define the ultimate frequency precision that can be reached. In quantum metrology, the qubit coherence time defines the clock stability, from which the spectral linewidth and frequency precision are determined.

Fluorescent Nanodiamond-Gold Hybrid Particles for Multimodal Optical and Electron Microscopy Cellular Imaging.

There is a continuous demand for imaging probes offering excellent performance in various microscopy techniques for comprehensive investigations of cellular processes by more than one technique. Fluorescent nanodiamond-gold nanoparticles (FND-Au) constitute a new class of "all-in-one" hybrid particles providing unique features for multimodal cellular imaging including optical imaging, electron microscopy, and, and potentially even quantum sensing. Confocal and optical coherence microscopy of the FND-Au allow fast investigations inside living cells via emission, scattering, and photothermal imaging techniques because the FND emission is not quenched by AuNPs.

Quantum Metrology Enhanced by Repetitive Quantum Error Correction.

We experimentally demonstrate the protection of a room-temperature hybrid spin register against environmental decoherence by performing repeated quantum error correction whilst maintaining sensitivity to signal fields. We use a long-lived nuclear spin to correct multiple phase errors on a sensitive electron spin in diamond and realize magnetic field sensing beyond the time scales set by natural decoherence. The universal extension of sensing time, robust to noise at any frequency, demonstrates the definitive advantage entangled multiqubit systems provide for quantum sensing and offers an important complement to quantum control techniques.

Toward Optimized Surface δ-Profiles of Nitrogen-Vacancy Centers Activated by Helium Irradiation in Diamond.

The negatively charged nitrogen-vacancy (NV) center in diamond has been shown recently as an excellent sensor for external spins. Nevertheless, their optimum engineering in the near-surface region still requires quantitative knowledge in regard to their activation by vacancy capture during thermal annealing. To this aim, we report on the depth profiles of near-surface helium-induced NV centers (and related helium defects) by step-etching with nanometer resolution.

Accelerated 2D magnetic resonance spectroscopy of single spins using matrix completion.

Two dimensional nuclear magnetic resonance (NMR) spectroscopy is one of the major tools for analysing the chemical structure of organic molecules and proteins. Despite its power, this technique requires long measurement times, which, particularly in the recently emerging diamond based single molecule NMR, limits its application to stable samples. Here we demonstrate a method which allows to obtain the spectrum by collecting only a small fraction of the experimental data.

Germanium-Vacancy Single Color Centers in Diamond.

Atomic-sized fluorescent defects in diamond are widely recognized as a promising solid state platform for quantum cryptography and quantum information processing. For these applications, single photon sources with a high intensity and reproducible fabrication methods are required. In this study, we report a novel color center in diamond, composed of a germanium (Ge) and a vacancy (V) and named the GeV center, which has a sharp and strong photoluminescence band with a zero-phonon line at 602 nm at room temperature.

DNA-Based Self-Assembly of Fluorescent Nanodiamonds.

As a step toward deterministic and scalable assembly of ordered spin arrays we here demonstrate a bottom-up approach to position fluorescent nanodiamonds (NDs) with nanometer precision on DNA origami structures. We have realized a reliable and broadly applicable surface modification strategy that results in DNA-functionalized and perfectly dispersed NDs that were then self-assembled in predefined geometries. With optical studies we show that the fluorescence properties of the nitrogen-vacancy color centers in NDs are preserved during surface modification and DNA assembly.

Optical depth localization of nitrogen-vacancy centers in diamond with nanometer accuracy.

Precise positioning of nitrogen-vacancy (NV) centers is crucial for their application in sensing and quantum information. Here we present a new purely optical technique enabling determination of the NV position with nanometer resolution. We use a confocal microscope to determine the position of individual emitters along the optical axis.

Nanoscale detection of a single fundamental charge in ambient conditions using the NV- center in diamond.

Single charge nanoscale detection in ambient conditions is a current frontier in metrology that has diverse interdisciplinary applications. Here, such single charge detection is demonstrated using two nitrogen-vacancy (NV) centers in diamond. One NV center is employed as a sensitive electrometer to detect the change in electric field created by the displacement of a single electron resulting from the optical switching of the other NV center between its neutral (NV(0)) and negative (NV(-)) charge states.

High-fidelity spin entanglement using optimal control.

Precise control of quantum systems is of fundamental importance in quantum information processing, quantum metrology and high-resolution spectroscopy. When scaling up quantum registers, several challenges arise: individual addressing of qubits while suppressing cross-talk, entangling distant nodes and decoupling unwanted interactions. Here we experimentally demonstrate optimal control of a prototype spin qubit system consisting of two proximal nitrogen-vacancy centres in diamond.

Diamond nanophotonics.

We demonstrate the coupling of single color centers in diamond to plasmonic and dielectric photonic structures to realize novel nanophotonic devices. Nanometer spatial control in the creation of single color centers in diamond is achieved by implantation of nitrogen atoms through high-aspect-ratio channels in a mica mask. Enhanced broadband single-photon emission is demonstrated by coupling nitrogen-vacancy centers to plasmonic resonators, such as metallic nanoantennas.

Tuning a spin bath through the quantum-classical transition.

We study decoherence of a single nitrogen-vacancy (NV) center induced by the 13C nuclear spin bath of diamond. By comparing Hahn-Echo experiments on single and double-quantum transitions of the NV triplet ground state we demonstrate that this bath can be tuned into two different regimes. At low magnetic fields, the nuclei behave as a quantum bath which causes decoherence by entangling with the NV central spin.

Charge state manipulation of qubits in diamond.

The nitrogen-vacancy (NV) centre in diamond is a promising candidate for a solid-state qubit. However, its charge state is known to be unstable, discharging from the qubit state NV(-) into the neutral state NV(0) under various circumstances. Here we demonstrate that the charge state can be controlled by an electrolytic gate electrode.