Out of equilibrium correlations in the XY chain

We study the transversal XY spin-spin correlations in the non-equilibrium steady state constructed in \cite{AP03} and prove their spatial exponential decay close to equilibrium

Quasi-one-dimensional anisotropic Heisenberg model in a transverse magnetic field

The phase diagram of weakly coupled $XXZ$ chains in a transverse magnetic field is studied using the mean-field approximation for the interchain coupling and known exact results for an effective one-dimensional model. Results are applied to the quasi-one-dimensional antiferromagnet $Cs_{2}CoCl_{4}$ and the value of interchain interaction in this compound is estimated.Comment: 4 pages, 2 figure

Out of equilibrium correlation functions of quantum anisotropic XY models: one-particle excitations

We calculate exactly matrix elements between states that are not eigenstates of the quantum XY model for general anisotropy. Such quantities therefore describe non equilibrium properties of the system; the Hamiltonian does not contain any time dependence. These matrix elements are expressed as a sum of Pfaffians. For single particle excitations on the ground state the Pfaffians in the sum simplify to determinants.Comment: 11 pages, no figures; revtex. Minor changes in the text; list of refs. modifie

Polymer multilayer tattooing for enhanced DNA vaccination

DNA vaccines have many potential benefits but have failed to generate robust immune responses in humans. Recently, methods such as in vivo electroporation have demonstrated improved performance, but an optimal strategy for safe, reproducible, and pain-free DNA vaccination remains elusive. Here we report an approach for rapid implantation of vaccine-loaded polymer films carrying DNA, immune-stimulatory RNA, and biodegradable polycations into the immune-cell-rich epidermis, using microneedles coated with releasable polyelectrolyte multilayers. Films transferred into the skin following brief microneedle application promoted local transfection and controlled the persistence of DNA and adjuvants in the skin from days to weeks, with kinetics determined by the film composition. These ‘multilayer tattoo’ DNA vaccines induced immune responses against a model HIV antigen comparable to electroporation in mice, enhanced memory T-cell generation, and elicited 140-fold higher gene expression in non-human primate skin than intradermal DNA injection, indicating the potential of this strategy for enhancing DNA vaccination.Howard Hughes Medical Institute (Investigator)Ragon Institute of MGH, MIT, and HarvardNational Institutes of Health (U.S.) (NIH AI095109)United States. Dept. of Defense. Institute for Soldier Nanotechnologies (contract W911NF-07-D-0004)United States. Dept. of Defense. Institute for Soldier Nanotechnologies (contract W911NF-07-0004

Critical properties of Sudden Quench Dynamics in the anisotropic XY Model

We study the zero temperature quantum dynamical critical behavior of the anisotropic XY chain under a sudden quench in a transverse field. We demonstrate theoretically that both quench magnetic susceptibility and two-particle quench correlation can be used to describe the dynamical quantum phase transition (QPT) properties. Either the quench magnetic susceptibility or the derivative of correlation functions as a function of initial magnetic field $a$ exhibits a divergence at the critical points when final magnetic field $b$ is fixed. A special case that final magnetic field $b$ is just at the critical point is discussed separately. Some of the critical exponents of the dynamical QPT are obtained and the long-range correlation of the quench system is analyzed. We also compare our result with that of the static QPT.Comment: published on EPJ

Study of Loschmidt Echo for a qubit coupled to an XY-spin chain environment

We study the temporal evolution of a central spin-1/2 (qubit) coupled to the environment which is chosen to be a spin-1/2 transverse XY spin chain. We explore the entire phase diagram of the spin-Hamiltonian and investigate the behavior of Loschmidt echo(LE) close to critical and multicritical point(MCP). To achieve this, the qubit is coupled to the spin chain through the anisotropy term as well as one of the interaction terms. Our study reveals that the echo has a faster decay with the system size (in the short time limit) close to a MCP and also the scaling obeyed by the quasiperiod of the collapse and revival of the LE is different in comparison to that close to a QCP. We also show that even when approached along the gapless critical line, the scaling of the LE is determined by the MCP where the energy gap shows a faster decay with the system size. This claim is verified by studying the short-time and also the collapse and revival behavior of the LE at a quasicritical point on the ferromagnetic side of the MCP. We also connect our observation to the decoherence of the central spin.Comment: Accepted for publication in EPJ

Entanglement in a simple quantum phase transition

What entanglement is present in naturally occurring physical systems at thermal equilibrium? Most such systems are intractable and it is desirable to study simple but realistic systems which can be solved. An example of such a system is the 1D infinite-lattice anisotropic XY model. This model is exactly solvable using the Jordan-Wigner transform, and it is possible to calculate the two-site reduced density matrix for all pairs of sites. Using the two-site density matrix, the entanglement of formation between any two sites is calculated for all parameter values and temperatures. We also study the entanglement in the transverse Ising model, a special case of the XY model, which exhibits a quantum phase transition. It is found that the next-nearest neighbour entanglement (though not the nearest-neighbour entanglement) is a maximum at the critical point. Furthermore, we show that the critical point in the transverse Ising model corresponds to a transition in the behaviour of the entanglement between a single site and the remainder of the lattice.Comment: 14 pages, 7 eps figure

Magnetic and quadrupolar order in a one-dimensional ferromagnet with cubic crystal-field anisotropy

The zero temperature phase diagram of a one-dimensional S=2 Heisenberg ferromagnet with single-ion cubic anisotropy is studied numerically using the density-matrix renormalization group method. Evidence is found that although the model does not involve quadrupolar couplings, there is a purely quadrupolar phase for large values of the anisotropy. The phase transition between the magnetic and quadrupolar phases is continuous and it seems to be characterized by Ising critical exponents.Comment: 11 pages, 7 figures, REVTeX, accepted in Phys. Rev. B (scheduled on June 99

Generation of Effector Memory T Cell-Based Mucosal and Systemic Immunity with Pulmonary Nanoparticle Vaccination

Many pathogens infiltrate the body and initiate infection via mucosal surfaces. Hence, eliciting cellular immune responses at mucosal portals of entry is of great interest for vaccine development against mucosal pathogens. We describe a pulmonary vaccination strategy combining Toll-like receptor (TLR) agonists with antigen-carrying lipid nanocapsules [interbilayer-crosslinked multilamellar vesicles (ICMVs)], which elicit high-frequency, long-lived, antigen-specific effector memory T cell responses at multiple mucosal sites. Pulmonary immunization using protein- or peptide-loaded ICMVs combined with two TLR agonists, polyinosinic-polycytidylic acid (polyI:C) and monophosphoryl lipid A, was safe and well tolerated in mice, and led to increased antigen transport to draining lymph nodes compared to equivalent subcutaneous vaccination. This response was mediated by the vast number of antigen-presenting cells (APCs) in the lungs. Nanocapsules primed 13-fold more T cells than did equivalent soluble vaccines, elicited increased expression of mucosal homing integrin α4β7+, and generated long-lived T cells in both the lungs and distal (for example, vaginal) mucosa strongly biased toward an effector memory (TEM) phenotype. These TEM responses were highly protective in both therapeutic tumor and prophylactic viral vaccine settings. Together, these data suggest that targeting cross-presentation–promoting particulate vaccines to the APC-rich pulmonary mucosa can promote robust T cell responses for protection of mucosal surfaces.Howard Hughes Medical Institute (Investigator)National Institutes of Health (U.S.) (AI095109)United States. Dept. of Defense (contract W911NF-07-D-0004)Bill & Melinda Gates FoundationRagon Institute of MGH, MIT, and HarvardNational Cancer Institute (U.S.)David H. Koch Institute for Integrative Cancer Research at MIT (Koch Institute Support (core) Grant P30-CA14051

Density-Matrix Spectra of Solvable Fermionic Systems

We consider non-interacting fermions on a lattice and give a general result for the reduced density matrices corresponding to parts of the system. This allows to calculate their spectra, which are essential in the DMRG method, by diagonalizing small matrices. We discuss these spectra and their typical features for various fermionic quantum chains and for the two-dimensional tight-binding model.Comment: 12 pages and 9 figure