Photon tunneling through absorbing dielectric barriers

Using a recently developed formalism of quantization of radiation in the presence of absorbing dielectric bodies, the problem of photon tunneling through absorbing barriers is studied. The multilayer barriers are described in terms of multistep complex permittivities in the frequency domain which satisfy the Kramers--Kronig relations. From the resulting input--output relations it is shown that losses in the layers may considerably change the photon tunneling times observed in two-photon interference experiments. It is further shown that for sufficiently large numbers of layers interference fringes are observed that cannot be related to a single traversal time.Comment: 17 pages LaTeX, 9 figures (PS) include

Generation of long-living entanglement between two separate atoms

A scheme for non-conditional generation of long-living maximally entangled states between two spatially well separated atoms is proposed. In the scheme, $\Lambda$-type atoms pass a resonator-like equipment of dispersing and absorbing macroscopic bodies giving rise to body-assisted electromagnetic field resonances of well-defined heights and widths. Strong atom-field coupling is combined with weak atom-field coupling to realize entanglement transfer from the dipole-allowed transitions to the dipole-forbidden transitions, thereby the entanglement being preserved when the atoms depart from the bodies and from each other. The theory is applied to the case of the atoms passing by a microsphere.Comment: 13 pages, 5 figure

Atomic entanglement near a realistic microsphere

We study a scheme for entangling two-level atoms located close to the surface of a dielectric microsphere. The effect is based on medium-assisted spontaneous decay, rigorously taking into account dispersive and absorptive properties of the microsphere. We show that even in the weak-coupling regime, where the Markov approximation applies, entanglement up to 0.35 ebits between two atoms can be created. However, larger entanglement and violation of Bell's inequality can only be achieved in the strong-coupling regime.Comment: 16 pages, 4 figures, Late

Spontaneous Decay in the Presence of Absorbing Media

After giving a summary of the basic-theoretical concept of quantization of the electromagnetic field in the presence of dispersing and absorbing (macroscopic) bodies, their effect on spontaneous decay of an excited atom is studied. Various configurations such as bulk material, planar half space media, spherical cavities, and microspheres are considered. In particular, the influence of material absorption on the local-field correction, the decay rate, the line shift, and the emission pattern are examined. Further, the interplay between radiative losses and losses due to material absorption is analyzed. Finally, the possibility of generating entangled states of two atoms coupled by a microsphere-assisted field is discussed.Comment: 32 pages, 15 eps figures, contribution to Recent Research Developments in Optics, to be published by Research Signpos

Instagram i njegov utjecaj na fotografiju danas

Cilj ovog rada je analizirati povijest i razvoj digitalne fotografije i mobilne aplikacije Instagram. Područje rada je istraživanje funkcioniranja aplikacije te dodataka unutar nje koji omogućavaju obradu i ureĎivanje fotografija. Istraživanje će se provesti pomoću online ankete na postojećim korisnicima i onima koji to još uvijek nisu. Na osnovu dobivenih rezultata ispitanika pobliže se odreĎuje demografija populacije koja ju koristi i za koju svrhu. Prema svim dobivenim parametrima zaključuje se o prednosti suvremene digitalne fotografije koja posljednjih godina vodi glavnu riječ u fotografskoj industriji , gdje je klasična fotografija godinama bila bez konkurencije

Spatio-temporal representations during eye movements and their neuronal correlates

During fast ballistic eye movements, so-called saccades, our visual perception undergoes a range of distinct changes. Sensitivity to luminance contrasts is reduced (saccadic suppression) and the localization of stimuli can be shifted in the direction of a saccade or is compressed around the saccade target. The temporal order of two stimuli can be perceived as inverted and the duration in between can be underestimated. The duration of a target change close to the saccade target can be overestimated, when the change occurs during the saccade (chronostasis). In my thesis I investigated the spatial and temporal profiles of peri-saccadic changes in human visual perception and explored how these might result from changes in neural activity of the macaque middle temporal area (MT). I found that peri-saccadic contrast sensitivity was only reduced by a constant factor across space when the data was analyzed in retinal coordinates (as opposed to screen coordinates), indicating that saccadic suppression occurs in an eye-centered frame of reference. I demonstrated that the found variations of saccadic suppression with the location of the stimulus appear to cause variations in the spatio-temporal pattern of another peri-saccadic misperception: chronostasis. I was able to show that, unlike previously assumed, the saccadic overestimation of time is not a spatially localized disturbance of time perception but instead spans across the whole visual field. I further determined that chronostasis is not dependent on the eye movement itself, but is rather a consequence of the visual stimulation induced by it. This result clearly segregates chronostasis from other peri-saccadic perceptual changes like saccadic suppression and the compression of space. To relate these findings to a potential neuronal basis of saccadic suppression and time perception, I measured neuronal responses of single cells in MT of an awake behaving macaque. The results provide relevant insight into the processing of stationary stimuli and pairs of stimuli during fixation and saccades in MT. Responses to the second of a pair of stimuli were strongly suppressed and response latencies increased even at onset asynchronies of about 100ms. The increase in latency is an important difference to the temporal dynamics previously reported in other brain areas as the frontal eye field in the frontal cortex and the superior colliculus in the midbrain. During saccades, response latencies to single high luminance stimuli remained unchanged. For stimuli shown during the second half of the saccade, the average responses were reduced. By comparison with responses to single stimuli at different luminance levels during fixation, I was able to show that the peri-saccadic response reduction found in MT quantitatively fit to what could be expected from known psychophysical measurements of peri-saccadic contrast sensitivity. Responses that were already reduced due to a preceding stimulus were however not subject to further reductions, indicating a possible interaction of these two response modulations. Saccadic suppression occurs in an eye-centered frame of reference with changes in perception compatible to changes in single cell activity in the macaque monkey MT. The peri-saccadic overestimation of time is influenced by saccadic suppression and the saccade-induced visual changes, but is not dependent on eye-movement related signals

Noise from metallic surfaces -- effects of charge diffusion

Non-local electrodynamic models are developed for describing metallic surfaces for a diffusive metal. The electric field noise at a distance z_0 from the surface is evaluated and compared with data from ion chips that show anomalous heating with a noise power decaying as z_0^{-4}. We find that high surface diffusion can account for the latter result.Comment: 16 pages, 2 figures. Revised version focusing on charge diffusing and anomalous heatin