Nonperturbative and perturbative treatments of parametric heating in atom traps

We study the quantum description of parametric heating in harmonic potentials both nonperturbatively and perturbatively, having in mind atom traps. The first approach establishes an explicit connection between classical and quantum descriptions; it also gives analytic expressions for properties such as the width of fractional frequency parametric resonances. The second approach gives an alternative insight into the problem and can be directly extended to take into account nonlinear effects. This is specially important for shallow traps.Comment: 12 pages, 2 figure

All-optical 3D atomic loops generated with Bessel light fields

The propagation invariance of Bessel beams as well as their transversal structure are used to perform a comparative analysis of their effect on cold atoms for four different configurations and combinations thereof. We show that, even at temperatures for which the classical description of the atom center of mass motion is valid, the interchange of momentum, energy and orbital angular momentum between light and atoms yields efficient tools for all-optical trapping, transporting and, in general, manipulating the state of motion of cold atoms.Comment: 13 pages, 9 figure

Properties of Squeezed-State Excitations

The photon distribution function of a discrete series of excitations of squeezed coherent states is given explicitly in terms of Hermite polynomials of two variables. The Wigner and the coherent-state quasiprobabilities are also presented in closed form through the Hermite polynomials and their limiting cases. Expectation values of photon numbers and their dispersion are calculated. Some three-dimensional plots of photon distributions for different squeezing parameters demonstrating oscillatory behaviour are given.Comment: Latex,35 pages,submitted to Quant.Semiclassical Op

The Uncertainty Relation in "Which-Way" Experiments: How to Observe Directly the Momentum Transfer using Weak Values

A which-way measurement destroys the twin-slit interference pattern. Bohr argued that distinguishing between two slits a distance s apart gives the particle a random momentum transfer \wp of order h/s. This was accepted for more than 60 years, until Scully, Englert and Walther (SEW) proposed a which-way scheme that, they claimed, entailed no momentum transfer. Storey, Tan, Collett and Walls (STCW) in turn proved a theorem that, they claimed, showed that Bohr was right. This work reviews and extends a recent proposal [Wiseman, Phys. Lett. A 311, 285 (2003)] to resolve the issue using a weak-valued probability distribution for momentum transfer, P_wv(\wp). We show that P_wv(\wp) must be wider than h/6s. However, its moments can still be zero because P_wv(\wp) is not necessarily positive definite. Nevertheless, it is measurable in a way understandable to a classical physicist. We introduce a new measure of spread for P_wv(\wp): half of the unit-confidence interval, and conjecture that it is never less than h/4s. For an idealized example with infinitely narrow slits, the moments of P_wv(\wp) and of the momentum distributions are undefined unless a process of apodization is used. We show that by considering successively smoother initial wave functions, successively more moments of both P_wv(\wp) and the momentum distributions become defined. For this example the moments of P_wv(\wp) are zero, and these are equal to the changes in the moments of the momentum distribution. We prove that this relation holds for schemes in which the moments of P_wv(\wp) are non-zero, but only for the first two moments. We also compare these moments to those of two other momentum-transfer distributions and \hat{p}_f-\hat{p}_i. We find agreement between all of these, but again only for the first two moments.Comment: 14 pages, 6 figures, submitted to J. Opt.

Cladding mode coupling in highly localized fiber Bragg gratings: modal properties and transmission spectra

The spectral characteristics of a fiber Bragg grating (FBG) with a transversely inhomogeneous refractive index profile, differs con- siderably from that of a transversely uniform one. Transmission spectra of inhomogeneous and asymmetric FBGs that have been inscribed with focused ultrashort pulses with the so-called point-by-point technique are investigated. The cladding mode resonances of such FBGs can span a full octave in the spectrum and are very pronounced (deeper than 20dB). Using a coupled-mode approach, we compute the strength of resonant coupling and find that coupling into cladding modes of higher azimuthal order is very sensitive to the position of the modification in the core. Exploiting these properties allows precise control of such reflections and may lead to many new sensing applications.Comment: Submission to OE, 16 pages, 6 figure

Intravenous immunoglobulin to prevent myasthenic crisis after thymectomy and other procedures can be omitted in patients with well-controlled myasthenia gravis

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was funded by a Fondo de Investigación Sanitaria (FIS-FEDER) (grants PI16-01673 and PI19/00593) and an Interlaken Research Award Programme (2012-12094537).Background: Myasthenic crisis (MC) is a potentially life-threatening complication of myasthenia gravis. Its precipitating factors include surgical procedures, particularly thymectomy. The role of preoperative intravenous immunoglobulin (IVIg) in preventing MC in patients scheduled for thymectomy and other surgery with general anaesthesia is unknown. Our objective was to test the hypothesis that preoperative IVIg is effective in preventing myasthenic crisis in patients with myasthenia gravis scheduled for surgery under general anaesthesia, including thymectomy. Methods: A prospective, randomized, double-blind, single-centre study was conducted over a 4-year period. The treatment group received IVIg, 0.4 g/kg/day preoperatively for 5 consecutive days, and the placebo group received saline solution under the same conditions. The two groups were age-matched, with similar functional status, and Myasthenia Gravis Foundation of America class. All patients had well-controlled myasthenia gravis with minimal manifestations before surgery. The primary outcome measured was MC. Intubation times, time in the recovery room, number of postoperative complications, and days of hospitalization were the secondary outcomes measured. Results: A total of 47 patients were randomized, 25 to the IVIg group and 22 to placebo. There were 19 men and 28 women, with a mean age of 58.6 years, mean body mass index of 27.8 kg/m, and mean acetylcholine receptor antibodies of 12.9 nmol/l. The mean forced vital capacity was 84.4%. The mean quantitative myasthenia gravis sum score was 6.3. Ten patients (five in each arm) had a history of MC. Thymectomy was performed in 16 patients. Only one patient in the placebo group presented with MC requiring non-invasive ventilation (but no reintubation) for 6 days. Neither differences between groups in the univariate analysis nor risk factors for MC in the multivariate analysis were found. Conclusions: Preoperative IVIg to prevent MC does not appear to be justified in well-controlled myasthenia gravis patients. This study provides class I evidence that preparation with IVIg to prevent MC is not necessary in well-controlled myasthenia gravis patients scheduled for surgery with general anaesthesia

Intravenous immunoglobulin to prevent myasthenic crisis after thymectomy and other procedures can be omitted in patients with well-controlled myasthenia gravis

Immunoglobulin; Myasthenia; ThymectomyInmunoglobulina; Miastenia; TimectomíaImmunoglobulina; Miastènia; TimectomiaBACKGROUND: Myasthenic crisis (MC) is a potentially life-threatening complication of myasthenia gravis. Its precipitating factors include surgical procedures, particularly thymectomy. The role of preoperative intravenous immunoglobulin (IVIg) in preventing MC in patients scheduled for thymectomy and other surgery with general anaesthesia is unknown. Our objective was to test the hypothesis that preoperative IVIg is effective in preventing myasthenic crisis in patients with myasthenia gravis scheduled for surgery under general anaesthesia, including thymectomy. METHODS: A prospective, randomized, double-blind, single-centre study was conducted over a 4-year period. The treatment group received IVIg, 0.4 g/kg/day preoperatively for 5 consecutive days, and the placebo group received saline solution under the same conditions. The two groups were age-matched, with similar functional status, and Myasthenia Gravis Foundation of America class. All patients had well-controlled myasthenia gravis with minimal manifestations before surgery. The primary outcome measured was MC. Intubation times, time in the recovery room, number of postoperative complications, and days of hospitalization were the secondary outcomes measured. RESULTS: A total of 47 patients were randomized, 25 to the IVIg group and 22 to placebo. There were 19 men and 28 women, with a mean age of 58.6 years, mean body mass index of 27.8 kg/m2, and mean acetylcholine receptor antibodies of 12.9 nmol/l. The mean forced vital capacity was 84.4%. The mean quantitative myasthenia gravis sum score was 6.3. Ten patients (five in each arm) had a history of MC. Thymectomy was performed in 16 patients. Only one patient in the placebo group presented with MC requiring non-invasive ventilation (but no reintubation) for 6 days. Neither differences between groups in the univariate analysis nor risk factors for MC in the multivariate analysis were found. CONCLUSIONS: Preoperative IVIg to prevent MC does not appear to be justified in well-controlled myasthenia gravis patients. This study provides class I evidence that preparation with IVIg to prevent MC is not necessary in well-controlled myasthenia gravis patients scheduled for surgery with general anaesthesia.This work was funded by a Fondo de Investigacion Sanitaria (FIS-FEDER) (grants PI16-01673 and PI19/00593) and an Interlaken Research Award Programme (2012-12094537