RESUMEN

We propose a method of cooling nuclear spin systems of solid-state nanostructures by applying a time-dependent magnetic field synchronized with spin fluctuations. Optical spin noise spectroscopy is considered a method of fluctuation control. Depending on the mutual orientation of the oscillating magnetic field and the probe light beam, cooling might be either provided by dynamic spin polarization in an external static field or result from population transfer between spin levels without build-up of a net magnetic moment ("true cooling").

RESUMEN

Migratory birds are known to be sensitive to external magnetic field (MF). Much indirect evidence suggests that the avian magnetic compass is localized in the retina. Previously, we showed that changes in the MF direction could modulate retinal responses in pigeons. In the present study, we performed similar experiments using the traditional model animal to study the magnetic compass, European robins. The photoresponses of isolated retina were recorded using ex vivo electroretinography (ERG). Blue- and red-light stimuli were applied under an MF with the natural intensity and two MF directions, when the angle between the plane of the retina and the field lines was 0° and 90°, respectively. The results were separately analysed for four quadrants of the retina. A comparison of the amplitudes of the a- and b-waves of the ERG responses to blue stimuli under the two MF directions revealed a small but significant difference in a- but not b-waves, and in only one (nasal) quadrant of the retina. The amplitudes of both the a- and b-waves of the ERG responses to red stimuli did not show significant effects of the MF direction. Thus, changes in the external MF modulate the European robin retinal responses to blue flashes, but not to red flashes. This result is in a good agreement with behavioural data showing the successful orientation of birds in an MF under blue, but not under red illumination.

Asunto(s)

RESUMEN

Migratory birds can detect the direction of the Earth's magnetic field using the magnetic compass sense. However, the sensory basis of the magnetic compass still remains a puzzle. A large body of indirect evidence suggests that magnetic compass in birds is localized in the retina. To confirm this point, an evidence of visual signals modulation by magnetic field (MF) should be obtained. In a previous study we showed that MF inclination impacts the amplitude of ex vivo electroretinogram (ERG) recorded from isolated pigeon retina. Here we present the results of an analysis of putative MF effect on one component of ERG, the photoreceptor's response, isolated from the total ERG by adding sodium aspartate and barium chloride to the perfusion solution. Photoresponses were recorded from isolated retinae of domestic pigeons Columba livia. The retinal samples were placed in MF that was modulated by three pairs of orthogonal Helmholtz coils. Light stimuli (blue and red) were applied under two inclinations of MF, 0° and 90°. In all the experiments, preparations from two parts of retina were used, red field (with dominant red-sensitive cones) and yellow field (with relatively uniform distribution of cone color types). In contrast to the whole retinal ERG, we did not observe any effect of MF inclination on either amplitude or kinetics of pharmacologically isolated photoreceptor responses to blue or red half-saturating flashes. A possible explanations of these results could be that magnetic compass sense is localized in retinal cells other than photoreceptors, or that photoreceptors do participate in magnetoreception, but require some processing of compass information in other retinal layers, so that only whole retina signal can reflect the response to changing MF.

Asunto(s)

RESUMEN

Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new - magnetometric - potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This "optical field" is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates.