Quantum correlations in topological quantum phase transitions

We study the quantum correlations in a 2D system that possesses a topological quantum phase transition. The quantumness of two-body correlations is measured by quantum discord. We calculate both the correlation of two local spins and that of an arbitrary spin with the rest of the lattice. It is notable that local spins are classically correlated, while the quantum correlation is hidden in the global lattice. This is different from other systems which are not topologically orderd. Moreover, the mutual information and global quantum discord show critical behavior in the topological quantum phase transition.Comment: 6 pages, 3 figure

Quantum phase transitions in a two-dimensional quantum XYX model: Ground-state fidelity and entanglement

A systematic analysis is performed for quantum phase transitions in a two-dimensional anisotropic spin 1/2 anti-ferromagnetic XYX model in an external magnetic field. With the help of an innovative tensor network algorithm, we compute the fidelity per lattice site to demonstrate that the field-induced quantum phase transition is unambiguously characterized by a pinch point on the fidelity surface, marking a continuous phase transition. We also compute an entanglement estimator, defined as a ratio between the one-tangle and the sum of squared concurrences, to identify both the factorizing field and the critical point, resulting in a quantitative agreement with quantum Monte Carlo simulation. In addition, the local order parameter is "derived" from the tensor network representation of the system's ground state wave functions.Comment: 4+ pages, 3 figure

Quantum refrigerator driven by current noise

We proposed a scheme to implement a self-contained quantum refrigerator system composed of three rf-SQUID qubits, or rather, flux-biased phase qubits. The three qubits play the roles of the target, the refrigerator and the heat engine respectively. We provide different effective temperatures for the three qubits, by imposing external current noises of different strengths. The differences of effective temperatures give rise to the flow of free energy and that drives the refrigerator system to cool down the target. We also show that the efficiency of the system approaches the Carnot efficiency.Comment: 5 pages, 1 figur

Experimental realization of large-alphabet quantum key distribution protocol using orbital angular momentum entanglement

We experimentally demonstrate a quantum key distribution (QKD) protocol using photon pairs entangled in orbit angular momentum (OAM). In our protocol, Alice and Bob modulate their OAM states on each entangled pair with spatial light modulators (SLMs), respectively. Alice uses a fixed phase hologram in her SLM, while Bob designs $N$ different suitable phase holograms and uses them to represent his $N$-based information in his SLM. With coincidences, Alice can fully retrieve the key stream sent by Bob without information reconciliation or privacy amplification. We report the experiment results with N=3 and the sector states with OAM eigenmodes l=1 and l=-1. Our experiment shows that the coincidence rates are in relatively distinct value regions for the three different key elements. Alice could recover fully Bob's keys by the protocol. Finally, we discuss the security of the protocol both form the light way and against the general attacks

Exotic Gapless Mott Insulators of Bosons on Multi-Leg Ladders

We present evidence for an exotic gapless insulating phase of hard-core bosons on multi-leg ladders with a density commensurate with the number of legs. In particular, we study in detail a model of bosons moving with direct hopping and frustrating ring exchange on a 3-leg ladder at $\nu=1/3$ filling. For sufficiently large ring exchange, the system is insulating along the ladder but has two gapless modes and power law transverse density correlations at incommensurate wave vectors. We propose a determinantal wave function for this phase and find excellent comparison between variational Monte Carlo and density matrix renormalization group calculations on the model Hamiltonian, thus providing strong evidence for the existence of this exotic phase. Finally, we discuss extensions of our results to other $N$-leg systems and to $N$-layer two-dimensional structures.Comment: 5 pages, 4 figures; v3 is the print version; supplemental material attache

Reactive oxygen species drive herpes simplex virus (HSV)-1-induced proinflammatory cytokine production by murine microglia

Abstract Background Production of reactive oxygen species (ROS) and proinflammatory cytokines by microglial cells in response to viral brain infection contributes to both pathogen clearance and neuronal damage. In the present study, we examined the effect of herpes simplex virus (HSV)-1-induced, NADPH oxidase-derived ROS in activating mitogen-activated protein kinases (MAPKs) as well as driving cytokine and chemokine expression in primary murine microglia. Methods Oxidation of 2', 7'-dichlorodihydrofluorescin diacetate (H2DCFDA) was used to measure production of intracellular ROS in microglial cell cultures following viral infection. Virus-induced cytokine and chemokine mRNA and protein levels were assessed using real-time RT-PCR and ELISA, respectively. Virus-induced phosphorylation of microglial p38 and p44/42 (ERK1/2) MAPKs was visualized using Western Blot, and levels of phospho-p38 were quantified using Fast Activated Cell-based ELISA (FACE assay). Diphenyleneiodonium (DPI) and apocynin (APO), inhibitors of NADPH oxidases, were used to investigate the role of virus-induced ROS in MAPK activation and cytokine, as well as chemokine, production. Results Levels of intracellular ROS were found to be highly elevated in primary murine microglial cells following infection with HSV and the majority of this virus-induced ROS was blocked following DPI and APO treatment. Correspondingly, inhibition of NADPH oxidase also decreased virus-induced proinflammatory cytokine and chemokine production. In addition, microglial p38 and p44/42 MAPKs were found to be phosphorylated in response to viral infection and this activation was also blocked by inhibitors of NADPH oxidase. Finally, inhibition of either of these ROS-induced signaling pathways suppressed cytokine (TNF-α and IL-1β) production, while chemokine (CCL2 and CXCL10) induction pathways were sensitive to inhibition of p38, but not ERK1/2 MAPK. Conclusions Data presented herein demonstrate that HSV infection induces proinflammatory responses in microglia through NADPH oxidase-dependent ROS and the activation of MAPKs.</p

Analysis of Stress State of Bolts Under Different Anchorage Qualities

A series of pull-out tests were conducted in order to study the stress states of bolts under different anchorage qualities and to simulate the influence of quality defects in empty-slurry and low-strength mortar anchorage in actual engineering. The tests mainly investigated strain characteristics at different positions of the bolts and the effects of strains at the same positions under different anchorage conditions. The research led to the following conclusions: (1) under ultimate bearing capacity, the strain values decayed the fastest along the length of the bolt in the full-length anchorage, the strain values decayed the slowest in the empty-slurry and low-strength mortar anchorage, and the decaying speed of strains in the empty-slurry mortar anchorage was between that of the above two kinds of anchorages; (2) at almost 50% of the ultimate bearing capacity, the strain values were slightly different between the empty-slurry and low-strength mortar anchorage and the empty-slurry anchorage. Obvious differences in strain values occurred when the bolts were continued to be loaded. The strain values of the full-length anchorage bolts were different from those of the other two kinds of anchorages; (3) from the analysis of stress variation characteristics, the safety reserve was the highest for the full-length anchorage under the condition of ultimate bearing capacity, followed by the empty-slurry mortar anchorage, while the safety reserve was the lowest for the empty-slurry and low-strength mortar anchorage. However, in terms of uniformity of force and utilization of the material, the result was reverse