The efficiency of collecting photons from optically active defect centres in bulk diamond is greatly reduced by refraction and reflection at the diamond-air interface. We report on the fabrication and measurement of a geometrical solution to the problem; integrated solid immersion lenses (SILs) etched directly into the surface of diamond. An increase of a factor of 10 was observed in the saturated count-rate from a single negatively charged nitrogen-vacancy (NV − ) within a 5 µm diameter SIL compared with NV − s under a planar surface in the same crystal. A factor of 3 reduction in background emission was also observed due to the reduced excitation volume with a SIL present. Such a system is potentially scalable and easily adaptable to other defect centres in bulk diamond.The ability to address single defect centres in diamond using confocal microscopy allows optical access to these single 'atom like' systems trapped within a macro-scale solid. The negatively charged nitrogenvacancy centre (NV − ) is of particular interest for applications such as single photon generation [1,2], nanoscale magnetometery [3], and fundamental investigations of spin interactions and entanglement at room temperature [4][5][6]. Other defect centres that exhibit single photon emission have also been identified (e.g. the nickel-related 'NE8' [7], the silicon-vacancy [8], and chromium related centres [9]), but the search continues for other defect centres with spin properties like those of the NV − centre [10]. The high refractive index of diamond causes refraction of the emitted light at the diamond-air interface, reducing the possible angular collection of a microscope objective. Thus the NV − photon collection efficiency is severely reduced. This is a problem regardless of the application, or of the particular defect centre of interest. Here we report on the fabrication and measurement of hemispherical integrated solid immersion lenses (SILs) etched directly into the surface of diamond. These structures eliminate surface refraction, thus increasing the numerical aperture (NA) of the microscope system. This allows a substantial increase in the resolution and background rejection of our system, along with a strong enhancement in NV − photon collection efficiency. Moreover, this geometrical solution can easily be applied to other defect centres in bulk diamond which emit at different wavelengths [11].The photon collection efficiency from NV − centres in diamond has previously been improved by using NV − centres located within nanocrystals small enough that the centres effectively emit into free space [2,12], or nanophotonic structures such as nanowires which guide emission towards collection [13]. Photon collection is increased by a factor of up to about 5 in the former case and 10 in the latter. However with the NV − centres positioned so close to the surface, local strain, impurities and other surface effects have been shown to degrade the stability, and spin coherence time of the NV − centre [14,15], so a solution which improves the p...

No abstract

Xenon-129 biosensors offer an attractive alternative to conventional MRI contrast agents due to the chemical shift sensitivity and large nuclear magnetic signal of hyperpolarized (129)Xe. Here, we report the first enzyme-responsive (129)Xe NMR biosensor. This compound was synthesized in 13 steps by attaching the consensus peptide substrate for matrix metalloproteinase-7 (MMP-7), an enzyme that is upregulated in many cancers, to the xenon-binding organic cage, cryptophane-A. The final coupling step was achieved on solid support in 80-92% yield via a copper (I)-catalyzed [3+2] cycloaddition. In vitro enzymatic cleavage assays were monitored by HPLC and fluorescence spectroscopy. The biosensor was determined to be an excellent substrate for MMP-7 (K(M) = 43 microM, V(max) = 1.3 x 10(-)(8) M s(-1), k(cat)/K(M) = 7,200 M(-1) s(-1)). Enzymatic cleavage of the tryptophan-containing peptide led to a dramatic decrease in Trp fluorescence, lambda(max) = 358 nm. Stern-Volmer analysis gave an association constant of 9000 +/- 1,000 M(-1) at 298 K between the cage and Trp-containing hexapeptide under enzymatic assay conditions. Most promisingly, (129)Xe NMR spectroscopy distinguished between the intact and cleaved biosensors with a 0.5 ppm difference in chemical shift. This difference most likely reflected a change in the electrostatic environment of (129)Xe, caused by the cleavage of three positively charged residues from the C-terminus. This work provides guidelines for the design and application of new enzyme-responsive (129)Xe NMR biosensors.

Recent deep learning approaches have achieved impressive performance on speech enhancement and separation tasks. However, these approaches have not been investigated for separating mixtures of arbitrary sounds of different types, a task we refer to as universal sound separation, and it is unknown how performance on speech tasks carries over to non-speech tasks. To study this question, we develop a dataset of mixtures containing arbitrary sounds, and use it to investigate the space of mask-based separation architectures, varying both the overall network architecture and the framewise analysis-synthesis basis for signal transformations. These network architectures include convolutional long short-term memory networks and time-dilated convolution stacks inspired by the recent success of time-domain enhancement networks like ConvTasNet. For the latter architecture, we also propose novel modifications that further improve separation performance. In terms of the framewise analysis-synthesis basis, we explore both a short-time Fourier transform (STFT) and a learnable basis, as used in ConvTasNet. For both of these bases, we also examine the effect of window size. In particular, for STFTs, we find that longer windows (25-50 ms) work best for speech/non-speech separation, while shorter windows (2.5 ms) work best for arbitrary sounds. For learnable bases, shorter windows (2.5 ms) work best on all tasks. Surprisingly, for universal sound separation, STFTs outperform learnable bases. Our best methods produce an improvement in scale-invariant signal-todistortion ratio of over 13 dB for speech/non-speech separation and close to 10 dB for universal sound separation.

We demonstrate a cavity-enhanced room-temperature magnetic field sensor based on nitrogen-vacancy centers in diamond. Magnetic resonance is detected using absorption of light resonant with the 1042 nm spin-singlet transition. The diamond is placed in an external optical cavity to enhance the absorption, and significant absorption is observed even at room temperature. We demonstrate a magnetic field sensitivity of 2.5  nT/Hz, and project a photon shot-noise-limited sensitivity of 70  pT/Hz for a few mW of infrared light, and a quantum projection-noise-limited sensitivity of 250  fT/Hz for the sensing volume of ∼90  μm×90  μm×200  μm.

Single-molecule switching (SMS) microscopy is a super-resolution method capable of producing images with resolutions far exceeding that of the classical diffraction limit. However, like all optical microscopes, SMS microscopes are sensitive to, and often limited by, specimen-induced aberrations. Adaptive optics (AO) has proven beneficial in a range of microscopes to overcome the limitations caused by aberrations. We report here on new AO methods for SMS microscopy that enable the feedback correction of specimeninduced aberrations. The benefits are demonstrated through two-dimensional and three-dimensional STORM imaging. We expect that this advance will broaden the scope of SMS microscopy by enabling deep-cell and tissue-level imaging.

Large arrays of uniform, precisely tunable, open-access optical microcavities with mode volumes as small as 2.2 μm(3) are reported. The cavities show clear Hermite-Gauss mode structure and display finesses up to 460, in addition to quality (Q) factors in excess of 10,000. The cavities are attractive for use in quantum optics applications, such as single atom detection and efficient single photon sources, and have potential to be extended for experiments in the strong coupling regime.

As one of the most powerful tools in the biological investigation of cellular structures and dynamic processes, fluorescence microscopy has undergone extraordinary developments in the past decades. The advent of super-resolution techniques has enabled fluorescence microscopy – or rather nanoscopy – to achieve nanoscale resolution in living specimens and unravelled the interior of cells with unprecedented detail. The methods employed in this expanding field of microscopy, however, are especially prone to the detrimental effects of optical aberrations. In this review, we discuss how super-resolution microscopy techniques based upon single-molecule switching, stimulated emission depletion and structured illumination each suffer from aberrations in different ways that are dependent upon intrinsic technical aspects. We discuss the use of adaptive optics as an effective means to overcome this problem.