Heralded phase-contrast imaging using an orbital angular momentum phase-filter

We utilise the position and orbital angular momentum (OAM) correlations between the signal and idler photons generated in the down-conversion process to obtain ghost images of a phase object. By using an OAM phase filter, which is non-local with respect to the object, the images exhibit isotropic edge-enhancement. This imaging technique is the first demonstration of a full-field, phase-contrast imaging system with non-local edge enhancement, and enables imaging of phase objects using significantly fewer photons than standard phase-contrast imaging techniques

Properties of Hot Stars in the Wolf-Rayet galaxy NGC5253 from ISO Spectroscopy

ISO-SWS spectroscopy of the WR galaxy NGC5253 is presented, and analysed to provide estimates of its hot young star population. Our approach differs from previous investigations in that we are able to distinguish between the regions in which different infrared fine-structure lines form, using complementary ground-based observations. The high excitation nebular [SIV] emission is formed in a very compact region, which we attribute to the central super-star-nucleus, and lower excitation [NeII] nebular emission originates in the galactic core. We use photo-ionization modelling coupled with the latest theoretical O-star flux distributions to derive effective stellar temperatures and ionization parameters of Teff>38kK, logQ=8.25 for the compact nucleus, with Teff=35kK, logQ<8 for the larger core. Results are supported by more sophisticated calculations using evolutionary synthesis models. We assess the contribution that Wolf-Rayet stars may make to highly ionized nebular lines (e.g. [OIV]). From our Br(alpha) flux, the 2" nucleus contains the equivalent of approximately 1000 O7V star equivalents and the starburst there is 2-3Myr old; the 20" core contains about 2500 O7V star equivalents, with a representative age of 5Myr. The Lyman ionizing flux of the nucleus is equivalent to the 30 Doradus region. These quantities are in good agreement with the observed mid-IR dust luminosity of 7.8x10^8 L(sun) Since this structure of hot clusters embedded in cooler emission may be common in dwarf starbursts, observing a galaxy solely with a large aperture may result in confusion. Neglecting the spatial distribution of nebular emission in NGC5253, implies `global' stellar temperatures (or ages) of 36kK (4.8Myr) and 39kK (2.9 or 4.4Myr) from the observed [NeIII/II] and [SIV/III] line ratios, assuming logQ=8.Comment: 16 pages, 7 figures, uses mn.sty, to appear in MNRA

Imaging with a small number of photons

Low-light-level imaging techniques have application in many diverse fields, ranging from biological sciences to security. We demonstrate a single-photon imaging system based on a time-gated inten- sified CCD (ICCD) camera in which the image of an object can be inferred from very few detected photons. We show that a ghost-imaging configuration, where the image is obtained from photons that have never interacted with the object, is a useful approach for obtaining images with high signal-to-noise ratios. The use of heralded single-photons ensures that the background counts can be virtually eliminated from the recorded images. By applying techniques of compressed sensing and associated image reconstruction, we obtain high-quality images of the object from raw data comprised of fewer than one detected photon per image pixel.Comment: 9 pages, 4 figure

Static and dynamic traversable wormhole geometries satisfying the Ford-Roman constraints

It was shown by Ford and Roman in 1996 that quantum field theory severely constrains wormhole geometries on a macroscopic scale. The first part of this paper discusses a wide class of wormhole solutions that meet these constraints. The type of shape function used is essentially generic. The constraints are then discussed in conjunction with various redshift functions. Violations of the weak energy condition and traversability criteria are also considered. The second part of the paper analyzes analogous time-dependent (dynamic) wormholes with the aid of differential forms. It is shown that a violation of the weak energy condition is not likely to be avoidable even temporarily.Comment: 16 pages AMSTe

Resolution limits of quantum ghost imaging

Quantum ghost imaging uses photon pairs produced from parametric downconversion to enable an alternative method of image acquisition. Information from either one of the photons does not yield an image, but an image can be obtained by harnessing the correlations between them. Here we present an examination of the resolution limits of such ghost imaging systems. In both conventional imaging and quantum ghost imaging the resolution of the image is limited by the point-spread function of the optics associated with the spatially resolving detector. However, whereas in conventional imaging systems the resolution is limited only by this point spread function, in ghost imaging we show that the resolution can be further degraded by reducing the strength of the spatial correlations inherent in the downconversion process

Self-energy and critical temperature of weakly interacting bosons

Using the exact renormalization group we calculate the momentum-dependent self-energy Sigma (k) at zero frequency of weakly interacting bosons at the critical temperature T_c of Bose-Einstein condensation in dimensions 3 <= D < 4. We obtain the complete crossover function interpolating between the critical regime k << k_c, where Sigma (k) propto k^{2 - eta}, and the short-wavelength regime k >> k_c, where Sigma (k) propto k^{2 (D-3)} in D> 3 and Sigma (k) \propto ln (k/k_c) in D=3. Our approach yields the crossover scale k_c on the same footing with a reasonable estimate for the critical exponent eta in D=3. From our Sigma (k) we find for the interaction-induced shift of T_c in three dimensions Delta T_c / T_c approx 1.23 a n^{1/3}, where a is the s-wave scattering length and n is the density.Comment: 4 pages,1 figur