Fast machine-learning online optimization of ultra-cold-atom experiments.

We apply an online optimization process based on machine learning to the production of Bose-Einstein condensates (BEC). BEC is typically created with an exponential evaporation ramp that is optimal for ergodic dynamics with two-body s-wave interactions and no other loss rates, but likely sub-optimal for real experiments. Through repeated machine-controlled scientific experimentation and observations our 'learner' discovers an optimal evaporation ramp for BEC production. In contrast to previous work, our learner uses a Gaussian process to develop a statistical model of the relationship between the parameters it controls and the quality of the BEC produced. We demonstrate that the Gaussian process machine learner is able to discover a ramp that produces high quality BECs in 10 times fewer iterations than a previously used online optimization technique. Furthermore, we show the internal model developed can be used to determine which parameters are essential in BEC creation and which are unimportant, providing insight into the optimization process of the system.

High-speed spiral imaging technique for an atomic force microscope using a linear quadratic Gaussian controller.

This paper demonstrates a high-speed spiral imaging technique for an atomic force microscope (AFM). As an alternative to traditional raster scanning, an approach of gradient pulsing using a spiral line is implemented and spirals are generated by applying single-frequency cosine and sine waves of slowly varying amplitudes to the X and Y-axes of the AFM's piezoelectric tube scanner (PTS). Due to these single-frequency sinusoidal input signals, the scanning process can be faster than that of conventional raster scanning. A linear quadratic Gaussian controller is designed to track the reference sinusoid and a vibration compensator is combined to damp the resonant mode of the PTS. An internal model of the reference sinusoidal signal is included in the plant model and an integrator for the system error is introduced in the proposed control scheme. As a result, the phase error between the input and output sinusoids from the X and Y-PTSs is reduced. The spirals produced have particularly narrow-band frequency measures which change slowly over time, thereby making it possible for the scanner to achieve improved tracking and continuous high-speed scanning rather than being restricted to the back and forth motion of raster scanning. As part of the post-processing of the experimental data, a fifth-order Butterworth filter is used to filter noises in the signals emanating from the position sensors and a Gaussian image filter is used to filter the images. A comparison of images scanned using the proposed controller (spiral) and the AFM PI controller (raster) shows improvement in the scanning rate using the proposed method.

Pulsed quantum cascade laser-based CRDS substance detection: real-time detection of TNT.

This paper presents experimental results from a pulsed quantum cascade laser based cavity ringdown spectrometer used as a high-throughput detection system. The results were obtained from an optical cavity with 99.8% input and output coupling mirrors that was rapidly swept (0.2s to 7s sweep times) between 1582.25 cm(-1) (6.3201µm) and 1697.00 cm(-1) (5.8928µm). The spectrometer was able to monitor gas species over the pressure range 585 torr to 1µtorr, and the analysis involves a new digital data processing system that optimises the processing speed and minimises the data storage requirements. In this approach we show that is it not necessary to make direct measurements of the ringdown time of the cavity to obtain the system dynamics. Furthermore, we show that correct data processing is crucial for the ultimate implementation of a wideband IR spectrometer that covers a range similar to that of commercial Fourier transform infrared instruments.

High-speed cycloid-scan atomic force microscopy.

A key hurdle in achieving high scan speeds in atomic force microscopes is that the probe is required to be scanned over the sample in a zig-zag raster pattern. The fast axis of the AFM scanner must track a signal that contains frequencies beyond its mechanical bandwidth. Consequently, fast raster scans generate distortions in the resulting image. We propose a smooth cycloid-like scan pattern that allows us to achieve scan speeds much higher than a raster scan. We illustrate how the proposed method can be implemented on a commercial AFM with minimal modifications.

Homodyne locking of a squeezer.

We report on the successful implementation of an approach to locking the frequencies of an optical parametric oscillator (OPO)-based squeezed-vacuum source and its driving laser. The technique allows the simultaneous measurement of the phase shifts induced by a cavity, which may be used for the purposes of frequency locking, as well as the simultaneous measurement of the sub-quantum-noise-limited (sub-QNL) phase quadrature output of the OPO. The homodyne locking technique is cheap, easy to implement, and has the distinct advantage that subsequent homodyne measurements are automatically phase locked. The homodyne locking technique is also unique in that it is a sub-QNL frequency discriminator.

Multiple pregnancies with single intrauterine demise. Description of twenty-eight pregnancies.

METHODS: Retrospective study of multiple pregnancies and deliveries with single intrauterine demise, in a five years' study period. RESULTS: Of a total of 13,840 deliveries in the study period, 355 represented multiple pregnancies with two or more fetuses from conception: 310 twin pregnancies and 45 triplets or higher. Twenty-eight multiple pregnancies were complicated by single intrauterine death: in six cases (group A) as first trimester spontaneous fetal loss, in nine cases (group B) due to selective fetal reduction, and in thirteen pregnancies as spontaneous intrauterine demise occurring in the second or third trimester (group C). In group A, no specific cause of death was proven. In group C, four cases of death were caused by twin transfusion syndrome, three cases by severe intrauterine growth retardation, four cases by placental insufficiency, one case by placental abruption striking one of the twins, whereas the last death was undefined. In group A, mean gestational age at delivery was 33 completed weeks. In group C, five monochorionic pregnancies were delivered at median gestational age 30 weeks and seven dichorionic pregnancies at 34 weeks (the chorionicity was indefinite in one case). The neonatal complications of the forty-two live born babies included prematurity problems only, except for one case of congenital anemia in a transfusion syndrome donor twin. None of the mothers showed signs of intravascular coagulopathy. CONCLUSION: The main problem for the surviving twin was prematurity - not the sibling's death.