Circuit QED and sudden phase switching in a superconducting qubit array

Superconducting qubits connected in an array can form quantum many-body systems such as the quantum Ising model. By coupling the qubits to a superconducting resonator, the combined system forms a circuit QED system. Here, we study the nonlinear behavior in the many-body state of the qubit array using a semiclassical approach. We show that sudden switchings as well as a bistable regime between the ferromagnetic phase and the paramagnetic phase can be observed in the qubit array. A superconducting circuit to implement this system is presented with realistic parameters .Comment: 4 pages, 3 figures, submitted for publication

6-OHDA generated ROS induces DNA damage and p53- and PUMA-dependent cell death

<p>Abstract</p> <p>Background</p> <p>Parkinson's disease (PD) is characterized by the selective loss of dopaminergic neurons in the substantia nigra (SN), resulting in tremor, rigidity, and bradykinesia. Although the etiology is unknown, insight into the disease process comes from the dopamine (DA) derivative, 6-hydroxydopamine (6-OHDA), which produces PD-like symptoms. Studies show that 6-OHDA activates stress pathways, such as the unfolded protein response (UPR), triggers mitochondrial release of cytochrome-c, and activates caspases, such as caspase-3. Because the BH3-only protein, Puma (p53-upregulated mediator of apoptosis), is activated in response to UPR, it is thought to be a link between cell stress and apoptosis.</p> <p>Results</p> <p>To test the hypothesis that Puma serves such a role in 6-OHDA-mediated cell death, we compared the response of dopaminergic neurons from wild-type and <it>Puma</it>-null mice to 6-OHDA. Results indicate that Puma is required for 6-OHDA-induced cell death, in primary dissociated midbrain cultures as well as <it>in vivo</it>. In these cultures, 6-OHDA-induced DNA damage and p53 were required for 6-OHDA-induced cell death. In contrast, while 6-OHDA led to upregulation of UPR markers, loss of ATF3 did not protect against 6-OHDA.</p> <p>Conclusions</p> <p>Together, our results indicate that 6-OHDA-induced upregulation of <it>Puma </it>and cell death are independent of UPR. Instead, p53 and DNA damage repair pathways mediate 6-OHDA-induced toxicity.</p

Canonical and kinetic forms of the electromagnetic momentum in an ad hoc quantization scheme for a dispersive dielectric

An ad hoc quantization scheme for the electromagnetic field in a weakly dispersive, transparent dielectric leads to the definition of canonical and kinetic forms for the momentum of the electromagnetic field in a dispersive medium. The canonical momentum is uniquely defined as the operator that generates spatial translations in a uniform medium, but the quantization scheme suggests two possible choices for the kinetic momentum operator, corresponding to the Abraham or the Minkowski momentum in classical electrodynamics. Another implication of this procedure is that a wave packet containing a single dressed photon travels at the group velocity through the medium. The physical significance of the canonical momentum has already been established by considerations of energy and momentum conservation in the atomic recoil due to spontaneous emission, the Cerenkov effect, the Doppler effect, and phase matching in nonlinear optical processes. In addition, the data of the Jones and Leslie radiation pressure experiment is consistent with the assignment of one ?k unit of canonical momentum to each dressed photon. By contrast, experiments in which the dielectric is rigidly accelerated by unbalanced electromagnetic forces require the use of the Abraham momentum.Comment: 21 pages, 1 figure, aip style, submitted to PR

Physical aspects of oracles for randomness, and Hadamard's conjecture

We analyze the physical aspects and origins of currently proposed oracles for (absolute) randomness.Comment: 10 pages, 3 figures. arXiv admin note: substantial text overlap with arXiv:1405.140

Fostering online learning at the workplace : a scheme to identify and analyse collaboration processes in asynchronous discussions

Research has shown that providing participants with high‐quality learning material is not sufficient to help them profit most from online education. The level of interaction among participants is another key determinant for learning outcomes. However, merely proposing interaction does not automatically lead to fruitful discussion and collaboration. Specifically, social presence and facilitation activities add value to online discussions. In Murphy's collaboration framework, social presence represents the basis of successful online collaboration from which more reflective discussions and co‐construction can evolve. In this paper, an adjusted version of this framework was applied in a workplace learning context. The content analysis of 1170 comments in an online course for careers practitioners of a public employment service showed that the extended framework generated deeper insights into the dynamics of online discussions. The results show that involvement in collaborative learning at the workplace was supported by a high social presence and influenced by course topic and tasks. Facilitation played an important role in creating a sympathetic sense of community and stimulating co‐creation processes