Magnetic phase transition in coherently coupled Bose gases in optical lattices

We describe the ground state of a gas of bosonic atoms with two coherently coupled internal levels in a deep optical lattice in a one dimensional geometry. In the single-band approximation this system is described by a Bose-Hubbard Hamiltonian. The system has a superfluid and a Mott insulating phase which can be either paramagnetic or ferromagnetic. We characterize the quantum phase transitions at unit filling by means of a density matrix renormalization group technique and compare it with a mean-field approach. The presence of the ferromagnetic Ising-like transition modifies the Mott lobes. In the Mott insulating region the system maps to the ferromagnetic spin-1/2 XXZ model in a transverse field and the numerical results compare very well with the analytical results obtained from the spin model. In the superfluid regime quantum fluctuations strongly modify the phase transition with respect to the well established mean-field three dimensional classical bifurcation.Comment: 6 pages, 3 figure

EXTREME EVENT: HEAVY SNOWFALL ON THE TRENTINO REGION ON 11 MARCH 2004

an extreme event of heavy snowfall occurred in the last 11 march 2004 in many regions of the north Italy. It was one of the most important events of snowfall in the winter season 2003-2004 and it was really unusual for the period. The possibility of snowfall at the lower levels was forecasted two days before but the quantity of the precipitation was generally underestimated by the models. This event caused many problems to the civil protection and to the public above all in the traffic and the increasing avalanche risk

Effects of Environmental Enrichment on Learning a Discrimination Task by Captive White-spotted Bamboo Sharks (Chiloscyllium plagiosum)

It has been demonstrated experimentally that several species of sharks are capable of learning by association but no studies have investigated the effects of environmental enrichment on sharks’ learning abilities. The main objective of this study was to test the hypothesis that environmental enrichment would improve learning performance in captivity of white-spotted bamboo sharks (Chiloscyllium plagiosum). During training and testing with a food reward before environmental enrichment, the sharks appeared to associate a discriminative stimulus (black vs. white tile) with food, but they did not discriminate between the tiles without a food reward. After a 68-d non-testing period followed by 10 d of exposure to enrichment objects (two plastic hula hoops) in the sharks’ tank, the experiment was repeated with the same result. There were no statistically significant differences in learning and memory before and after environmental enrichment. This negative result may have resulted from 1) small sample size (N=2 sharks), 2) ineffective enrichment objects, 3) insufficient time for enrichment effects to occur, or 4) inability of this species to learn a discrimination task. Future studies on enrichment should include larger sample sizes within species, multiple species of sharks, and testing with different enrichment objects

Spontaneous Peierls dimerization and emergent bond order in one-dimensional dipolar gases

We investigate the effect of dipolar interactions in one-dimensional systems in connection with the possibility of observing exotic many-body effects with trapped atomic and molecular dipolar gases. By combining analytical and numerical methods, we show how the competition between short- and long-range interactions gives rise to frustrating effects which lead to the stabilization of spontaneously dimerized phases characterized by a bond ordering. This genuine quantum order is sharply distinguished from Mott and spin-density-wave phases, and can be unambiguously probed by measuring nonlocal order parameters via in situ imaging techniques

Observation of a Spinning Top in a Bose-Einstein Condensate

Boundaries strongly affect the behavior of quantized vortices in Bose-Einstein condensates, a phenomenon particularly evident in elongated cigar-shaped traps where vortices tend to orient along a short direction to minimize energy. Remarkably, contributions to the angular momentum of these vortices are tightly confined to the region surrounding the core, in stark contrast to untrapped condensates where all atoms contribute $\hbar$. We develop a theoretical model and use this, in combination with numerical simulations, to show that such localized vortices precess in an analogous manner to that of a classical spinning top. We experimentally verify this spinning-top behavior with our real-time imaging technique that allows for the tracking of position and orientation of vortices as they dynamically evolve. Finally, we perform an in-depth numerical investigation of our real-time expansion and imaging method, with the aim of guiding future experimental implementation, as well as outlining directions for its improvement.Comment: 10 pages, 7 figure

Spin manipulated nanoscopy with nitrogen vacancy centres in nanodiamonds

Nowadays, fluorescence microscopy has become the imaging technique mainly employed for medical and biological applications in vitro and in vivo. A light beam is absorbed by an organic or inorganic specimen and subsequently re-radiated. This physical phenomenon is called fluorescence of phosphorescence. It is possible to reconstruct morphological and structural images of biological samples by staining them with fluorescent dyes. The increasing application of fluorescence microscopy has led to the development of super-resolution techniques, able to visualise fine details of biological structures, beyond the diffraction limit. The far-field super-resolution techniques mainly used are stimulated emission depletion (STED), ground state depletion (GSD) and single molecules localisation techniques such as stochastic optical reconstruction microscopy (STORM) and photoactivated localisation microscopy (PALM). These techniques have all achieved lateral (x-y) resolution down to tens of nanometers, allowing single molecule super-resolution imaging. Fluorescent nanoparticles are indispensable candidates for optical imaging. Negatively charged nitrogen vacancy (NV- ) centres in nanodiamonds (NDs) have attracted significant interest due to their outstanding optical and magnetic properties. In the recent years super-resolution fluorescence imaging with NDs has substantially improved our ability to comprehend subcellular processes. In particular, optically detected magnetic resonance (ODMR) of the single electron spin of NV- centres at room temperature has enabled a new all-optical imaging approach to measure magnetic fields of complex biological systems. Therefore, the ability to readout the magnetic sensitive NV- electron spin at the nanoscale is of paramount importance for super-resolution optical magnetic imaging. STED microscopy has provided nanoscale resolution combined with spin readout of individual NV- centres in NDs. However, this super-resolution method based on scanning mechanism is not suitable for magnetic imaging of dynamical processes of living cells such as neuronal firing. On the other hand, the wide-field view of the STORM-spin methods allows for parallel acquisition and imaging of cellular dynamics from multiple NV- centres. The aim of this thesis is to demonstrate a novel super-resolution technique called spin manipulated nanoscopy that enables imaging and spin readout of single NV- centres in blinking NDs. The method is applied for super-resolution optical imaging of magnetic fields generated from biological cells. Fluorescence intermittency or blinking is observed after reducing the size of NDs with an oxidation process at 450°C for 2 h and 30 min at 600°C or at 600°C for 2h. With the effect of oxidation not widely investigated, we study the opto-magnetic properties of NV- centres in blinking NDs. We demonstrate first evidence of the ODMR spectrum in blinking NDs. We find that at the ODMR frequency the fluorescence of NV- centres exhibits intermittence that confirms the blinking phenomenon. Further, with an oxidation at 600°C for 2 h we observe a reduction of the ODMR linewidth which improves the magnetic sensitivity of NDs to small magnetic fields. Super-resolution imaging based on blinking localisation in conjunction with ODMR has not been researched in NV- centres in nanoparticle form. A super-resolution method, called spin manipulated nanoscopy, is developed to image single NV- centres in blinking NDs. The method combines wide-field localisation with nanoscale spin manipulation at the ODMR frequency. For the first time the NV- magnetic sensitive spin in blinking NDs is imaged based on spin manipulated microscopy. The maximum transverse resolution of 34 nm is achieved. Further, two collectively blinking NV- centres are resolved based on spin manipulated microscopy. Two adjacent fluorescent features are imaged at 23 nm distance, peak to peak. Finally, we investigate the magnetic capabilities of NDs by measuring local magnetic fields from iron oxide magnetic nanoparticles (MNPs). MNPs are then implemented to label the membrane of biological cells. We apply spin manipulated nanoscopy with blinking NDs for nanoscale reconstruction of magnetic fields generated from magnetically labelled biological cells. The maximum transverse resolution of 25 nm is achieved. The magnetic sensitivity achieved is 16 μT√Hz . The presented method adds a greater value for the application of NDs as biomarkers for superresolved magnetic imaging in life scienc

Bound state dynamics in the long-range spin- ½ XXZ model

Experimental platforms based on trapped ions, cold molecules, and Rydberg atoms have made possible the investigation of highly nonlocal spin-1/2 Hamiltonians with long-range couplings. Here, we study the effects of such nonlocal couplings in the long-range spin-1/2 XXZ Heisenberg Hamiltonian. We calculate explicitly the two-spin energy spectrum, which describes all possible energetic configurations of two spins pointing in a specific direction embedded in a background of spins with opposite orientation. For fast decay of the spin-spin couplings, we find that the two-spin energy spectrum is characterized by well-defined discrete values, corresponding to bound states, separated by a set of continuum states describing the scattering region. In the deep long-range regime instead, the bound states disappear as they get incorporated by the scattering region. The presence of two-spin bound states results to be crucial to determine both two- and many-spin dynamics. On one hand, radically different two-spin spreadings can be observed by tuning the decay of the spin couplings. On the other hand, two-spin bound states enable the dynamical stabilization of effective antiferromagnetic states in the presence of ferromagnetic couplings. Finally, we propose a novel scheme based on a trapped-ion quantum simulator to experimentally realize the long-range XXZ model and to study its out-of-equilibrium properties