Purification of a single-photon nonlinearity.

Single photon nonlinearities based on a semiconductor quantum dot in an optical microcavity are a promising candidate for integrated optical quantum information processing nodes. In practice, however, the finite quantum dot lifetime and cavity-quantum dot coupling lead to reduced fidelity. Here we show that, with a nearly polarization degenerate microcavity in the weak coupling regime, polarization pre- and postselection can be used to restore high fidelity. The two orthogonally polarized transmission amplitudes interfere at the output polarizer; for special polarization angles, which depend only on the device cooperativity, this enables cancellation of light that did not interact with the quantum dot. With this, we can transform incident coherent light into a stream of strongly correlated photons with a second-order correlation value up to 40, larger than previous experimental results, even in the strong-coupling regime. This purification technique might also be useful to improve the fidelity of quantum dot based logic gates.

Polarization-preserving confocal microscope for optical experiments in a dilution refrigerator with high magnetic field.

We present the design and operation of a fiber-based cryogenic confocal microscope. It is designed as a compact cold-finger that fits inside the bore of a superconducting magnet, and which is a modular unit that can be easily swapped between use in a dilution refrigerator and other cryostats. We aimed at application in quantum optical experiments with electron spins in semiconductors and the design has been optimized for driving with and detection of optical fields with well-defined polarizations. This was implemented with optical access via a polarization maintaining fiber together with Voigt geometry at the cold finger, which circumvents Faraday rotations in the optical components in high magnetic fields. Our unit is versatile for use in experiments that measure photoluminescence, reflection, or transmission, as we demonstrate with a quantum optical experiment with an ensemble of donor-bound electrons in a thin GaAs film.

Fetal general movements and brain sonography in a population at risk for preterm birth.

BACKGROUND: General movements (GMs) assessed three months post term are related to brain injury and neurological outcome. AIMS: To study GMs in fetuses and their predictive value for echogenicity changes in the fetal brain. STUDY DESIGN: Prospective study of fetal GMs (classified as normal or abnormal) and echogenicity changes in the periventricular, basal ganglia/thalami area, and ventricular system (classified as absent, mild or moderate). SUBJECTS: 121 fetuses from pregnancies affected by hypertensive disorders and/or preterm labour, at risk for preterm birth (26-34weeks gestational age). OUTCOME MEASURES: Prevalence of abnormal GMs, GM parameters (amplitude, speed and complexity), and moderate echogenicity changes in the fetal brain (periventricular >or=IB, intraventricular grade II/III, and basal ganglia/thalamus locally increased). Predictive values of GMs for clinical parameters and moderate echogenicity changes. RESULTS: GMs were abnormal in 58%, with amplitude affected in 96%, and speed and complexity in 59%. Abnormal GMs correlated with oligohydramnios (p=0.002) and hypertensive disorders (p=0.015). Echogenicity changes of the brain were absent, mild and moderate in 27%, 39% and 31%, respectively. The sensitivity of GMs for moderate echogenicity changes in the three areas combined was 0.65, and the periventricular area 0.85, specificity both 0.44, negative predictive values 0.73 and 0.96 respectively. CONCLUSIONS: Qualitative abnormal GMs are frequent in fetuses of compromised pregnancies, and correlate with hypertensive disorders and oligohydramnios. The amplitude of GMs was most frequently affected. Abnormal GMs relate to moderate echogenicity changes especially in the periventricular area of the fetal brain, while normal GMs predict absence of moderate echogenicity changes.

Oblique abdominal muscle activity in standing and in sitting on hard and soft seats.

The activity of the oblique abdominal muscles was investigated with the trunk in unconstrained, symmetrical and static postures. Electromyographic recordings in six healthy subjects revealed that in all subjects the activity of both the internal and the external obliques is significantly higher in unconstrained standing than in supine posture. Activity of the internal oblique was higher than that of the external oblique abdominal. The sacrospinal, gluteus maximus and biceps femoris muscles showed practically no activity in unconstrained erect posture. During unconstrained sitting both oblique abdominals are active. In most subjects the activity of the oblique abdominals was significantly smaller when sitting on a soft car seat than when sitting on an office chair with a hard seat. The possibility is discussed that contraction of the oblique abdominals in unconstrained standing and sitting may help in stabilizing the basis of the spine and particularly the sacroiliac joints. During standing and sitting the oblique abdominal muscles apparently have a significant role in sustaining gravity loads. RELEVANCE: Back pain and pelvic pain are often experienced in prolonged standing and sitting postures. In these postures the oblique abdominals are shown to be active. The present study gains clinical significance by the studies showing relatively small oblique abdominal muscle strength in patients with low back pain. A soft seat may be helpful in treatment and prevention, because it substitutes oblique abdominal muscle activity.