Broadband loop gap resonator for nitrogen vacancy centers in diamond.

We present an S-band tunable loop gap resonator (LGR), which provides strong, homogeneous, and directionally uniform broadband microwave (MW) drive for nitrogen-vacancy (NV) ensembles. With 42 dBm of input power, the composite device provides drive field amplitudes approaching 5 G over a circular area ≳50 mm2 or cylindrical volume ≳250 mm3. The wide 80 MHz device bandwidth allows driving all NV Zeeman resonances for bias magnetic fields below 20 G. The device realizes percent-scale MW drive inhomogeneity; we measure a fractional root-mean-square inhomogeneity σ rms = 1.6% and a peak-to-peak variation σ pp = 3% over a circular area of 11 mm2 and σ rms = 3.2% and σ pp = 10.5% over a larger 32 mm2 circular area. We demonstrate incident MW power coupling to the LGR using two methodologies: a printed circuit board-fabricated exciter antenna for deployed compact bulk sensors and an inductive coupling coil suitable for microscope-style imaging. The inductive coupling coil allows for approximately 2π steradian combined optical access above and below the device, ideal for envisioned and existing NV imaging and bulk sensing applications.

In-vacuum scattered light reduction with black cupric oxide surfaces for sensitive fluorescence detection.

We demonstrate a simple and easy method for producing low-reflectivity surfaces that are ultra-high vacuum compatible, may be baked to high temperatures, and are easily applied even on complex surface geometries. Black cupric oxide (CuO) surfaces are chemically grown in minutes on any copper surface, allowing for low-cost, rapid prototyping, and production. The reflective properties are measured to be comparable to commercially available products for creating optically black surfaces. We describe a vacuum apparatus which uses multiple blackened copper surfaces for sensitive, low-background detection of molecules using laser-induced fluorescence.

Magneto-optical trapping of a diatomic molecule.

Laser cooling and trapping are central to modern atomic physics. The most used technique in cold-atom physics is the magneto-optical trap (MOT), which combines laser cooling with a restoring force from radiation pressure. For a variety of atomic species, MOTs can capture and cool large numbers of particles to ultracold temperatures (less than ∼1 millikelvin); this has enabled advances in areas that range from optical clocks to the study of ultracold collisions, while also serving as the ubiquitous starting point for further cooling into the regime of quantum degeneracy. Magneto-optical trapping of molecules could provide a similarly powerful starting point for the study and manipulation of ultracold molecular gases. The additional degrees of freedom associated with the vibration and rotation of molecules, particularly their permanent electric dipole moments, allow a broad array of applications not possible with ultracold atoms. Spurred by these ideas, a variety of methods has been developed to create ultracold molecules. Temperatures below 1 microkelvin have been demonstrated for diatomic molecules assembled from pre-cooled alkali atoms, but for the wider range of species amenable to direct cooling and trapping, only recently have temperatures below 100 millikelvin been achieved. The complex internal structure of molecules complicates magneto-optical trapping. However, ideas and methods necessary for creating a molecular MOT have been developed recently. Here we demonstrate three-dimensional magneto-optical trapping of a diatomic molecule, strontium monofluoride (SrF), at a temperature of approximately 2.5 millikelvin, the lowest yet achieved by direct cooling of a molecule. This method is a straightforward extension of atomic techniques and is expected to be viable for a significant number of diatomic species. With further development, we anticipate that this technique may be employed in any number of existing and proposed molecular experiments, in applications ranging from precision measurement to quantum simulation and quantum information to ultracold chemistry.

Laser radiation pressure slowing of a molecular beam.

We demonstrate deceleration of a beam of neutral strontium monofluoride molecules using radiative forces. Under certain conditions, the deceleration results in a substantial flux of detected molecules with velocities ≲50 m/s. Simulations and other data indicate that the detection of molecules below this velocity is greatly diminished by transverse divergence from the beam. The observed slowing, from ∼140 m/s, corresponds to scattering ≳10(4) photons. We also observe longitudinal velocity compression under different conditions. Combined with molecular laser cooling techniques, this lays the groundwork to create slow and cold molecular beams suitable for trap loading.

A bright, slow cryogenic molecular beam source for free radicals.

We demonstrate and characterize a cryogenic buffer gas-cooled molecular beam source capable of producing bright beams of free radicals and refractory species. Details of the beam properties (brightness, forward velocity distribution, transverse velocity spread, rotational and vibrational temperatures) are measured under varying conditions for the molecular species SrF. Under typical conditions we produce a beam of brightness 1.2 × 10(11) molecules/sr/pulse in the X(2)Σ(+)(v = 0, N(rot) = 0) state, with 140(m/s) forward velocity and a rotational temperature of ≈ 1 K. This source compares favorably to other methods for producing beams of free radicals and refractory species for many types of experiments. We provide details of construction that may be helpful for others attempting to use this method.

Pulse-dose application of chelated copper to a river for Didymosphenia geminata control: effects on macroinvertebrates and fish.

A 1-h pulse-dose of a chelated Cu formulation (Gemex™; New Zealand) was applied to a river to test efficacy against the invasive mat-forming diatom Didymosphenia geminata (didymo) and to provide information on nontarget species effects that could not be adequately predicted from laboratory and experimental mesocosm studies. Intensive sampling allowed characterization of doses achieved at multiple downstream locations, and concurrent application of rhodamine dye allowed quantification of dispersion, adsorption, and dilution processes. The target dose of 10 to 20 mg Cu/L for 60 min was achieved at least 0.9 km downstream at sites with contrasting levels of didymo mat development. Adsorptive losses of Gemex were 12%/km where didymo was mostly nonvisible and approximately 36%/km where substantial didymo mats were present. At 0.9 km downstream, Cu concentrations peaked at 12 mg/L, and didymo was <5% viable (down from 65-72%) for ≥21 d posttreatment. Viability data indicate that elimination of nonvisible infestations is possible and that suppression of early-stage infestations (≤40% cover, ≤4.5 mm thick) could be achieved after repeated applications. After a single Gemex application, no significant accumulation of Cu was noted in the sediments six weeks posttreatment, but Cu concentrations remained high in algal mats (109-367 mg/kg dry wt). Long-term effects on the nontarget algal, invertebrate, or fish communities were minimal, although significant localized trout mortalities, not predicted by prior laboratory exposures, occurred on the treatment day. Extended Gemex exposure in low-hardness waters might have caused the mortalities, although changes in chelated Cu speciation also possibly contributed. The present study integrates effects on resident biota with dosage data, including changes in pH, in a natural waterway.

Laser cooling of a diatomic molecule.

It has been roughly three decades since laser cooling techniques produced ultracold atoms, leading to rapid advances in a wide array of fields. Laser cooling has not yet been extended to molecules because of their complex internal structure. However, this complexity makes molecules potentially useful for a wide range of applications. For example, heteronuclear molecules possess permanent electric dipole moments that lead to long-range, tunable, anisotropic dipole-dipole interactions. The combination of the dipole-dipole interaction and the precise control over molecular degrees of freedom possible at ultracold temperatures makes ultracold molecules attractive candidates for use in quantum simulations of condensed-matter systems and in quantum computation. Also, ultracold molecules could provide unique opportunities for studying chemical dynamics and for tests of fundamental symmetries. Here we experimentally demonstrate laser cooling of the polar molecule strontium monofluoride (SrF). Using an optical cycling scheme requiring only three lasers, we have observed both Sisyphus and Doppler cooling forces that reduce the transverse temperature of a SrF molecular beam substantially, to a few millikelvin or less. At present, the only technique for producing ultracold molecules is to bind together ultracold alkali atoms through Feshbach resonance or photoassociation. However, proposed applications for ultracold molecules require a variety of molecular energy-level structures (for example unpaired electronic spin, Omega doublets and so on). Our method provides an alternative route to ultracold molecules. In particular, it bridges the gap between ultracold (submillikelvin) temperatures and the ∼1-K temperatures attainable with directly cooled molecules (for example with cryogenic buffer-gas cooling or decelerated supersonic beams). Ultimately, our technique should allow the production of large samples of molecules at ultracold temperatures for species that are chemically distinct from bialkalis.

Radiative force from optical cycling on a diatomic molecule.

We demonstrate a scheme for optical cycling in the polar, diatomic molecule strontium monofluoride (SrF) using the X2Sigma+ --> A2Pi(1/2) electronic transition. SrF's highly diagonal Franck-Condon factors suppress vibrational branching. We eliminate rotational branching by employing a quasicycling N = 1 --> N' = 0 type transition in conjunction with magnetic field remixing of dark Zeeman sublevels. We observe cycling fluorescence and deflection through radiative force of an SrF molecular beam using this scheme. With straightforward improvements our scheme promises to allow more than 10(5) photon scatters, possibly enabling the direct laser cooling of SrF.

Habitat-specific variation and performance trade-offs in shell armature of New Zealand mudsnails.

Studies documenting phenotypic variation among populations show that ecological performance in one activity is sometimes traded off against another. Identifying environment-specific costs and benefits associated with performance trade-offs is fundamental to knowing how conflicting selection pressures shape phenotype-environment matching in populations. We studied phenotypic variation in shell armature (spininess) of the New Zealand mudsnail, Potamopyrgus antipodarum (Gray), and explored how this variability relates to performance trade-offs between flow resistance and predator deterrence. Smooth- and spiny-shell morphotypes exist in populations in New Zealand streams and lakes, but the patterns and correlates of spatial variation of these phenotypes, and the possible hydrodynamical constraints and antipredatory benefits associated with spiny shell armature, are unknown. Samples from 11 rivers and nine lakes on the South Island showed that, on average, nearly 70% of snails in streams were smooth-shelled, whereas >80% of snails in lakes were spiny, suggesting dissimilar selective pressures between habitats. A laboratory flume experiment revealed that spines collected seston (i.e., suspended algae) at current speeds <40 cm/s, making spiny morphs more prone to flow-induced dislodgment than smooth morphs. However, a fish feeding experiment showed that one benefit of spines on shells was a decrease in predation risk from the common bully (Gobiomorphus cotidianus), a widespread predator of mudsnails in both streams and lakes. All snails egested by bullies were dead, further suggesting that these fishes may exert strong lethal effects on mudsnail populations in nature. Spine expression in lakes also appeared to be temperature related. We conclude that functional trade-offs between risk of flow-induced dislodgment and risk of fish predation affect shell armature frequencies of Potamopyrgus in freshwater habitats.

The relative effectiveness of four methods of teaching practical scientific skills to secondary school students.

The investigation compares the effectiveness of four methods of teaching students how to perform two practical scientific skills. The methods commonly used combinations of four different modes of communication. Method W uses written instructions only. Method WG has these written instructions supplemented with graphics. Method WGS adds spoken instructions to the combination used in Method WG, and Method WGSD also includes a video-recorded demonstration of the practical task. After teaching random groups (N = 20) of students aged 14-15 years with one of the methods, their effectiveness was assessed in terms of the students' performance on test exercises which required the students to carry out these tasks. The results showed that the methods involving the use of spoken instructions (i.e. WGS and WGSD) were significantly worse than those that did not use spoken instructions. The use of graphics also had no significant beneficial effect, and the demonstration had a significant positive effect only in one task.