Equilibrium phases of dipolar lattice bosons in the presence of random diagonal disorder

Ultracold gases offer an unprecedented opportunity to engineer disorder and interactions in a controlled manner. In an effort to understand the interplay between disorder, dipolar interaction and quantum degeneracy, we study two-dimensional hard-core dipolar lattice bosons in the presence of on-site bound disorder. Our results are based on large-scale path-integral quantum Monte Carlo simulations by the Worm algorithm. We study the ground state phase diagram at fixed half-integer filling factor for which the clean system is either a superfluid at lower dipolar interaction strength or a checkerboard solid at larger dipolar interaction strength. We find that, even for weak dipolar interaction, superfluidity is destroyed in favor of a Bose glass at relatively low disorder strength. Interestingly, in the presence of disorder, superfluidity persists for values of dipolar interaction strength for which the clean system is a checkerboard solid. At fixed disorder strength, as the dipolar interaction is increased, superfluidity is destroyed in favor of a Bose glass. As the interaction is further increased, the system eventually develops extended checkerboard patterns in the density distribution. Due to the presence of disorder, though, grain boundaries and defects, responsible for a finite residual compressibility, are present in the density distribution. Finally, we study the robustness of the superfluid phase against thermal fluctuations

Metabolic studies in patients undergoing thoracic surgery.

1. The metabolic changes following thoracic surgery in three groups of patients, (oesophageal cancer, lung cancer and hiatus hernia) have been studied. 2. Fasting levels of plasma glucose in patients with tumours of the lung or oesophagus were within the normal range and were no different from those found in patients with hiatus hernia, before operation. 3. Hyperglycaemia occurred after oesophagectomy, oesophago-gastrectomy and herniorrhapy. Operations of the lung, such as pneumonectomy or lobectomy did not lead to an immediate rise in blood sugar Level after surgery. 4. Post-operative hyperglycaemia was accompanied by the fall in the levels of plasma glucogenic amino acids. Evidence is presented in support of the idea that post-operative hyperglycaemia is the result of increased glucose production rather than the decrease in glucose utilization. 5. In contrast to the plasma insulin concentrations which remained unchanged immediately after surgery, the Levels of plasma 11-hydroxy-corticosteroids rose immediately after operation and that was accompanied by the same rise in the Levels of plasma FFA. 6. Plasma insulin concentration rose significantly and the rise was not proportional to the level of blood glucose on the second post-operative day. Since the urinary excretion of ketone bodies was also high on the same day, there was evidence of postoperative insulin resistance. 7. Elevated plasma levels of glucagon coincided with hyperglycaemia in oesophageal cancer patients but did not occur in lung cancer patients in whom there was no hyperglycaemia. 8. The plasma free tryptophan level in patients with oesophageal or lung cancer tended to be lower than in patients with hiatus hernia. Furthermore, the concentration of plasma free tryptophan rose after surgery and this rise was associated with a fall in the level of plasma total tryptophan. 9. There was no significant correlation between the level of plasma tryptophan and the rate of urinary excretion of N'-methylnicotinamide (NMN) in patients with oesophageal cancer. The significance of these findings has been discussed in relation to the metabolism of tryptophan. 10. The concentration of copper in the plasma was found to be elevated in patients with oesophageal cancer. Thoracic surgery was not associated with a consistent change in the level of plasma copper. 11. There was a transient fall in the level of plasma zinc after operation and this was associated with a similar fall in urinary excretion in hiatus hernia and oesophageal cancer. 12. Urinary levels of cyclic AMP or GMP in patients with tumours of the lung or oesophagus were no different from those found in patients with hiatus hernia. Cyclic GMP increased after surgery, and was higher in patients with malignancy than in patients with hiatus hernia. 13. Post-operative parenteral nutrition prevented the fall of plasma amino acids and led to a rise of plasma albumin. It also diminished the urinary losses of nitrogen on the second post-operative day

Nonequilibrium dynamics of spin-boson models from phase space methods

An accurate description of the nonequilibrium dynamics of systems with coupled spin and bosonic degrees of freedom remains theoretically challenging, especially for large system sizes and in higher than one dimension. Phase space methods such as the Truncated Wigner Approximation (TWA) have the advantage of being easily scalable and applicable to arbitrary dimensions. In this work we adapt the TWA to generic spin-boson models by making use of recently developed algorithms for discrete phase spaces [Schachenmayer, PRX 5, 011022 (2015)]. Furthermore we go beyond the standard TWA approximation by applying a scheme based on the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy of equations [Pucci, PRB 93, 174302 (2016)] to our coupled spin-boson model. This allows in principle to study how systematically adding higher order corrections improves the convergence of the method. To test various levels of approximation we study an exactly solvable spin-boson model which is particularly relevant for trapped-ion arrays. Using TWA and its BBGKY extension we accurately reproduce the time evolution of a number of one- and two-point correlation functions in several dimensions and for arbitrary number of bosonic modes.Comment: 10+5 pages, 5 figure

Equilibrium Phases of Tilted Dipolar Lattice Bosons

The recent advances in creating nearly degenerate quantum dipolar gases in optical lattices are opening the doors for the exploration of equilibrium physics of quantum systems with anisotropic and long-range dipolar interactions. In this paper we study the zero- and finite-temperature phase diagrams of a system of hard-core dipolar bosons at half-filling, trapped in a two-dimensional optical lattice. The dipoles are aligned parallel to one another and tilted out of the optical lattice plane by means of an external electric field. At zero-temperature, the system is a superfluid at all tilt angles $\theta$ provided that the strength of dipolar interaction is below a critical value $V_c(\theta)$. Upon increasing the interaction strength while keeping $\theta$ fixed, the superfluid phase is destabilized in favor of a checkerboard or a stripe solid depending on the tilt angle. We explore the nature of the phase transition between the two solid phases and find evidence of a micro-emulsion phase, following the Spivak-Kivelson scenario, separating these two solid phases. Additionally, we study the stability of these quantum phases against thermal fluctuations and find that the stripe solid is the most robust, making it the best candidate for experimental observation.Comment: 7 pages, 6 figure

Influence of monolayer contamination on electric-field-noise heating in ion traps

Electric field noise is a hinderance to the assembly of large scale quantum computers based on entangled trapped ions. Apart from ubiquitous technical noise sources, experimental studies of trapped ion heating have revealed additional limiting contributions to this noise, originating from atomic processes on the electrode surfaces. In a recent work [A. Safavi-Naini et al., Phys. Rev. A 84, 023412 (2011)] we described a microscopic model for this excess electric field noise, which points a way towards a more systematic understanding of surface adsorbates as progenitors of electric field jitter noise. Here, we address the impact of surface monolayer contamination on adsorbate induced noise processes. By using exact numerical calculations for H and N atomic monolayers on an Au(111) surface representing opposite extremes of physisorption and chemisorption, we show that an additional monolayer can significantly affect the noise power spectrum and either enhance or suppress the resulting heating rates.Comment: 8 pages, 5 figure

Breast-Lesion Characterization using Textural Features of Quantitative Ultrasound Parametric Maps

© 2017 The Author(s). This study evaluated, for the first time, the efficacy of quantitative ultrasound (QUS) spectral parametric maps in conjunction with texture-analysis techniques to differentiate non-invasively benign versus malignant breast lesions. Ultrasound B-mode images and radiofrequency data were acquired from 78 patients with suspicious breast lesions. QUS spectral-analysis techniques were performed on radiofrequency data to generate parametric maps of mid-band fit, spectral slope, spectral intercept, spacing among scatterers, average scatterer diameter, and average acoustic concentration. Texture-analysis techniques were applied to determine imaging biomarkers consisting of mean, contrast, correlation, energy and homogeneity features of parametric maps. These biomarkers were utilized to classify benign versus malignant lesions with leave-one-patient-out cross-validation. Results were compared to histopathology findings from biopsy specimens and radiology reports on MR images to evaluate the accuracy of technique. Among the biomarkers investigated, one mean-value parameter and 14 textural features demonstrated statistically significant differences (p < 0.05) between the two lesion types. A hybrid biomarker developed using a stepwise feature selection method could classify the legions with a sensitivity of 96%, a specificity of 84%, and an AUC of 0.97. Findings from this study pave the way towards adapting novel QUS-based frameworks for breast cancer screening and rapid diagnosis in clinic