Topological spin liquids: Robustness under perturbations

We study the robustness of the paradigmatic kagome Resonating Valence Bond (RVB) spin liquid and its orthogonal version, the quantum dimer model. The non-orthogonality of singlets in the RVB model and the induced finite length scale not only makes it difficult to analyze, but can also significantly affect its physics, such as how much noise resilience it exhibits. Surprisingly, we find that this is not the case: The amount of perturbations which the RVB spin liquid can tolerate is not affected by the finite correlation length, making the dimer model a viable model for studying RVB physics under perturbations. Remarkably, we find that this is a universal phenomenon protected by symmetries: First, the dominant correlations in the RVB are spinon correlations, making the state robust against doping with visons. Second, reflection symmetry stabilizes the spin liquid against doping with spinons, by forbidding mixing of the initially dominant correlations with those which lead to the breakdown of topological order.Comment: v2: accepted versio

The Relationship between Sex Role Stereotypes, Domestic Violence Training, History of Law Enforcement Involvement, and Law Enforcement Officer\u27s Perceptions of a Domestic Violence Incident

This study examined how police officers perceptions of a domestic violence situation are influenced by sex role stereotypes, domestic violence training and history of police intervention. Participants were police officers employed in sheriff\u27s departments or city police departments. Officers received several surveys and a vignette describing a domestic violence scene. Officers were given one of two vignettes, one describing a situation in which there have been previous calls to the address and one in which this is the first call and were then asked several questions to assess their perceptions. Sex role stereotypes were assessed using the Sex Role Egalitarianism Scale. Results indicated a positive correlation between perceptions of the incident and scores on the sex role questionnaire. There was a significant difference between officers who received the first time call vignette and officers who received the repeated calls vignette on their scores on the marital roles subscale of the sex role questionnaire. Future research is needed to expand these results

The Relationship between Sex Role Stereotypes, Domestic Violence Training, History of Law Enforcement Involvement, and Law Enforcement Officer\u27s Perceptions of a Domestic Violence Incident

This study examined how police officers perceptions of a domestic violence situation are influenced by sex role stereotypes, domestic violence training and history of police intervention. Participants were police officers employed in sheriff\u27s departments or city police departments. Officers received several surveys and a vignette describing a domestic violence scene. Officers were given one of two vignettes, one describing a situation in which there have been previous calls to the address and one in which this is the first call and were then asked several questions to assess their perceptions. Sex role stereotypes were assessed using the Sex Role Egalitarianism Scale. Results indicated a positive correlation between perceptions of the incident and scores on the sex role questionnaire. There was a significant difference between officers who received the first time call vignette and officers who received the repeated calls vignette on their scores on the marital roles subscale of the sex role questionnaire. Future research is needed to expand these results

Optimal squeezing and entanglement from noisy Gaussian operations

We investigate the creation of squeezing via operations subject to noise and losses and ask for the optimal use of such devices when supplemented by noiseless passive operations. Both single and repeated uses of the device are optimized analytically and it is proven that in the latter case the squeezing converges exponentially fast to its asymptotic optimum, which we determine explicitly. For the case of multiple iterations we show that the optimum can be achieved with fixed intermediate passive operations. Finally, we relate the results to the generation of entanglement and derive the maximal two-mode entanglement achievable within the considered scenario.Comment: 4 pages; accepted version (minor changes), Journal-ref adde

The computational difficulty of finding MPS ground states

We determine the computational difficulty of finding ground states of one-dimensional (1D) Hamiltonians which are known to be Matrix Product States (MPS). To this end, we construct a class of 1D frustration free Hamiltonians with unique MPS ground states and a polynomial gap above, for which finding the ground state is at least as hard as factoring. By lifting the requirement of a unique ground state, we obtain a class for which finding the ground state solves an NP-complete problem. Therefore, for these Hamiltonians it is not even possible to certify that the ground state has been found. Our results thus imply that in order to prove convergence of variational methods over MPS, as the Density Matrix Renormalization Group, one has to put more requirements than just MPS ground states and a polynomial spectral gap.Comment: 5 pages. v2: accepted version, Journal-Ref adde

Quantum entanglement theory in the presence of superselection rules

Superselection rules severly constrain the operations which can be implemented on a distributed quantum system. While the restriction to local operations and classical communication gives rise to entanglement as a nonlocal resource, particle number conservation additionally confines the possible operations and should give rise to a new resource. In [Phys. Rev. Lett. 92, 087904 (2004), quant-ph/0310124] we showed that this resource can be quantified by a single additional number, the superselection induced variance (SiV) without changing the concept of entanglement. In this paper, we give the results on pure states in greater detail; additionally, we provide a discussion of mixed state nonlocality with superselection rules where we consider both formation and distillation. Finally, we demonstrate that SiV is indeed a resource, i.e., that it captures how well a state can be used to overcome the restrictions imposed by the superselection rule.Comment: 16 pages, 5 figure

Nonlocal resources in the presence of Superselection Rules

Superselection rules severely alter the possible operations that can be implemented on a distributed quantum system. Whereas the restriction to local operations imposed by a bipartite setting gives rise to the notion of entanglement as a nonlocal resource, the superselection rule associated with particle number conservation leads to a new resource, the \emph{superselection induced variance} of local particle number. We show that, in the case of pure quantum states, one can quantify the nonlocal properties by only two additive measures, and that all states with the same measures can be asymptotically interconverted into each other by local operations and classical communication. Furthermore we discuss how superselection rules affect the concepts of majorization, teleportation and mixed state entanglement.Comment: 4 page

Die österreichische Zulieferindustrie im Lichte des europäischen Integrationsprozesses. Eine empirische Untersuchung am Beispiel der Maschinen- und Stahlbau- sowie der Elektro- und Elektronikindustrie.

Series: Research Reports of the Institute for Economic Geography and GIScienc