Reentrant Phenomenon in Quantum Phase Diagram of Optical Boson Lattice

We calculate the location of the quantum phase transitions of a bose gas trapped in an optical lattice as a function of effective scattering length a_{\eff} and temperature $T$. Knowledge of recent high-loop results on the shift of the critical temperature at weak couplings is used to locate a {\em nose} in the phase diagram above the free Bose-Einstein critical temperature $T_c^{(0)}$, thus predicting the existence of a reentrant transition {\em above} $T_c^{(0)}$, where a condensate should form when {\em increasing} a_{\eff}. At zero temperature, the transition to the normal phase produces the experimentally observed Mott insulator.Comment: Author Information under http://www.physik.fu-berlin.de/~kleinert/institution.htm

Variational Cluster Perturbation Theory for Bose-Hubbard models

We discuss the application of the variational cluster perturbation theory (VCPT) to the Mott-insulator--to--superfluid transition in the Bose-Hubbard model. We show how the VCPT can be formulated in such a way that it gives a translation invariant excitation spectrum -- free of spurious gaps -- despite the fact that if formally breaks translation invariance. The phase diagram and the single-particle Green function in the insulating phase are obtained for one-dimensional systems. When the chemical potential of the cluster is taken as a variational parameter, the VCPT reproduces the dimension dependence of the phase diagram even for one-site clusters. We find a good quantitative agreement with the results of the density-matrix renormalization group when the number of sites in the cluster becomes of order 10. The extension of the method to the superfluid phase is discussed.Comment: v1) 10 pages, 6 figures. v2) Final version as publishe

Revealing Superfluid--Mott-Insulator Transition in an Optical Lattice

We study (by an exact numerical scheme) the single-particle density matrix of $\sim 10^3$ ultracold atoms in an optical lattice with a parabolic confining potential. Our simulation is directly relevant to the interpretation and further development of the recent pioneering experiment by Greiner et al. In particular, we show that restructuring of the spatial distribution of the superfluid component when a domain of Mott-insulator phase appears in the system, results in a fine structure of the particle momentum distribution. This feature may be used to locate the point of the superfluid--Mott-insulator transition.Comment: 4 pages (12 figures), Latex. (A Latex macro is corrected

Aberrant promoter hypermethylation of RAR-β in endometrial carcinoma- an Indian study.

Endometrial cancer is the seventh most common cancer in women worldwide with and age standardized rate of 8.4 per 100,000 women. Epigenetic alterations such as promoter hypermethylation of TSGs are known to be early events in carcinogenesis. The aim of the present study, we assessed the aberrant promoter hypermethylation pattern of RAR-β in 78 endometrial cancer samples. Methods: DNA was isolated from endometrial carcinoma samples and normal tissues and aberrant promoter hypermethylation was assessed using nested and methylation specific PCR. Chi square test was used for statistical analysis and a p-value<0.05 was considered to be statistically significant. Results: 40 of the 78 (51.28%) endometrial carcinoma sample showed aberrant hypermethylation of RAR-β gene. Methylation status in each histological subtype, grade and stage of the disease was also assessed. Conclusion: Aberrant hypermethylation is an important early epigenetic alteration that occurs during tumorigenesis. The Data shown here reports that promoter hypermethylation of RAR-β occurs in endometrial carcinoma and therefore could be used as a potential marker for early diagnosis and prognosis of the disease

Assessment of Promoter hypermethylation of APC and BRCA1 in endometrial cancer.

Introduction: Endometrial cancer is one of the most common cancers in women worldwide. The underlying cause of endometrial tumorigenesis remains elusive. Several genetic and epigenetic alterations are known to be involved in the carcinogenesis of endometrial carcinoma. One important and early epigenetic alteration that is attributed to endometrial carcinoma is the aberrant promoter hypermethylation of gene promoters. In this study, we have assessed the aberrant promoter hypermethylation of APC and BRCA1 in 78 endometrial cancer samples. Methods: Histologically confirmed tumour tissue samples were obtained post-surgery and DNA was extracted. The DNA was subjected to sodium bisulfite conversion and used as a template for a polymerase chain reaction. The PCR was performed using a nested PCR followed by methylation specific PCR. Results: A 33.33% and 46.15% methylation frequency was observed for APC and BRCA1 genes respectively. A higher percentage of methylation was observed in stage IV for APC (66.66%) and in stage II for BRCA1 (88.88%). Conclusion: Aberrant promoter hypermethylation is an early event in endometrial carcinoma and can serve as a useful molecular marker for diagnosis and prognosis of the disease along with existing screening modalities

Simulation of gauge transformations on systems of ultracold atoms

We show that gauge transformations can be simulated on systems of ultracold atoms. We discuss observables that are invariant under these gauge transformations and compute them using a tensor network ansatz that escapes the phase problem. We determine that the Mott-insulator-to-superfluid critical point is monotonically shifted as the induced magnetic flux increases. This result is stable against the inclusion of a small amount of entanglement in the variational ansatz.Comment: 14 pages, 6 figure

Phase diagram of two-component bosons on an optical lattice

We present a theoretical analysis of the phase diagram of two--component bosons on an optical lattice. A new formalism is developed which treats the effective spin interactions in the Mott and superfluid phases on the same footing. Using the new approach we chart the phase boundaries of the broken spin symmetry states up to the Mott to superfluid transition and beyond. Near the transition point, the magnitude of spin exchange can be very large, which facilitates the experimental realization of spin-ordered states. We find that spin and quantum fluctuations have a dramatic effect on the transition making it first order in extended regions of the phase diagram. For Mott states with even occupation we find that the competition between effective Heisenberg exchange and spin-dependent on--site interaction leads to an additional phase transition from a Mott insulator with no broken symmetries into a spin-ordered insulator

Mean-field phase diagram of disordered bosons in a lattice at non-zero temperature

Bosons in a periodic lattice with on-site disorder at low but non-zero temperature are considered within a mean-field theory. The criteria used for the definition of the superfluid, Mott insulator and Bose glass are analysed. Since the compressibility does never vanish at non-zero temperature, it can not be used as a general criterium. We show that the phases are unambiguously distinguished by the superfluid density and the density of states of the low-energy exitations. The phase diagram of the system is calculated. It is shown that even a tiny temperature leads to a significant shift of the boundary between the Bose glass and superfluid

Thermometry with spin-dependent lattices

We propose a method for measuring the temperature of strongly correlated phases of ultracold atom gases confined in spin-dependent optical lattices. In this technique, a small number of "impurity" atoms--trapped in a state that does not experience the lattice potential--are in thermal contact with atoms bound to the lattice. The impurity serves as a thermometer for the system because its temperature can be straightforwardly measured using time-of-flight expansion velocity. This technique may be useful for resolving many open questions regarding thermalization in these isolated systems. We discuss the theory behind this method and demonstrate proof-of-principle experiments, including the first realization of a 3D spin-dependent lattice in the strongly correlated regime.Comment: 22 pages, 8 figures v2: Several references added; Section on heating rates updated to include dipole fluctuation terms; Section added on the limitations of the proposed method. To appear in New Journal of Physic

Vortex Pinning and the Non-Hermitian Mott Transition

The boson Hubbard model has been extensively studied as a model of the zero temperature superfluid/insulator transition in Helium-4 on periodic substrates. It can also serve as a model for vortex lines in superconductors with a magnetic field parallel to a periodic array of columnar pins, due to a formal analogy between the vortex lines and the statistical mechanics of quantum bosons. When the magnetic field has a component perpendicular to the pins, this analogy yields a non-Hermitian boson Hubbard model. At integer filling, we find that for small transverse fields, the insulating phase is preserved, and the transverse field is exponentially screened away from the boundaries of the superconductor. At larger transverse fields, a ``superfluid'' phase of tilted, entangled vortices appears. The universality class of the transition is found to be that of vortex lines entering the Meissner phase at H_{c1}, with the additional feature that the direction of the tilted vortices at the transition bears a non-trivial relationship to the direction of the applied magnetic field. The properties of the Mott Insulator and flux liquid phases with tilt are also discussed.Comment: 20 pages, 12 figures included in text; to appear in Physical Review