Perfect state distinguishability and computational speedups with postselected closed timelike curves

Bennett and Schumacher's postselected quantum teleportation is a model of closed timelike curves (CTCs) that leads to results physically different from Deutsch's model. We show that even a single qubit passing through a postselected CTC (P-CTC) is sufficient to do any postselected quantum measurement, and we discuss an important difference between "Deutschian" CTCs (D-CTCs) and P-CTCs in which the future existence of a P-CTC might affect the present outcome of an experiment. Then, based on a suggestion of Bennett and Smith, we explicitly show how a party assisted by P-CTCs can distinguish a set of linearly independent quantum states, and we prove that it is not possible for such a party to distinguish a set of linearly dependent states. The power of P-CTCs is thus weaker than that of D-CTCs because the Holevo bound still applies to circuits using them regardless of their ability to conspire in violating the uncertainty principle. We then discuss how different notions of a quantum mixture that are indistinguishable in linear quantum mechanics lead to dramatically differing conclusions in a nonlinear quantum mechanics involving P-CTCs. Finally, we give explicit circuit constructions that can efficiently factor integers, efficiently solve any decision problem in the intersection of NP and coNP, and probabilistically solve any decision problem in NP. These circuits accomplish these tasks with just one qubit traveling back in time, and they exploit the ability of postselected closed timelike curves to create grandfather paradoxes for invalid answers.Comment: 15 pages, 4 figures; Foundations of Physics (2011

Entanglement between a qubit and the environment in the spin-boson model

The quantitative description of the quantum entanglement between a qubit and its environment is considered. Specifically, for the ground state of the spin-boson model, the entropy of entanglement of the spin is calculated as a function of $\alpha$, the strength of the ohmic coupling to the environment, and $\epsilon$, the level asymmetry. This is done by a numerical renormalization group treatment of the related anisotropic Kondo model. For $\epsilon=0$, the entanglement increases monotonically with $\alpha$, until it becomes maximal for $\alpha \lim 1^-$. For fixed $\epsilon>0$, the entanglement is a maximum as a function of $\alpha$ for a value, $\alpha = \alpha_M < 1$.Comment: 4 pages, 3 figures. Shortened version restricted to groundstate entanglemen

Irreversible Quantum Baker Map

We propose a generalization of the model of classical baker map on the torus, in which the images of two parts of the phase space do overlap. This transformation is irreversible and cannot be quantized by means of a unitary Floquet operator. A corresponding quantum system is constructed as a completely positive map acting in the space of density matrices. We investigate spectral properties of this super-operator and their link with the increase of the entropy of initially pure states.Comment: 4 pages, 3 figures include

Magnetic and quantum entanglement properties of the distorted diamond chain model for azurite

We present the results of magnetic properties and entanglement of the distorted diamond chain model for azurite using pure quantum exchange interactions. The magnetic properties and concurrence as a measure of pairwise thermal entanglement have been studied by means of variational mean-field like treatment based on Gibbs-Bogoliubov inequality. Such a system can be considered as an approximation of the natural material azurite, Cu3(CO3)2(OH)2. For values of exchange parameters, which are taken from experimental results, we study the thermodynamic properties, such as azurite specific heat and magnetic susceptibility. We also have studied the thermal entanglement properties and magnetization plateau of the distorted diamond chain model for azurite

Communicating Josephson Qubits

We propose a scheme to implement a quantum information transfer protocol with a superconducting circuit and Josephson charge qubits. The information exchange is mediated by an L-C resonator used as a data bus. The main decoherence sources are analyzed in detail.Comment: 4 pages, 2 figure

Covariance of Antiproton Yield and Source Size in Nuclear Collisions

We confront for the first time the widely-held belief that combined event-by-event information from quark gluon plasma signals can reduce the ambiguity of the individual signals. We illustrate specifically how the measured antiproton yield combined with the information from pion-pion HBT correlations can be used to identify novel event classes.Comment: 8 pages, 5 figures, improved title, references and readability; results unchange

Mental health academics in rural and remote Australia

Context: The significant impact of mental ill health in rural and remote Australia has been well documented. Included among innovative approaches undertaken to address this issue has been the Mental Health Academic (MHA) project, established in 2007. Funded by the Australian Government (Department of Health), this project was established as a component of the University Departments of Rural Health (UDRH) program. All 11 UDRHs appointed an MHA. Although widely geographically dispersed, the MHAs have collaborated in various ways. The MHA project encompasses a range of activities addressing four key performance indicators. These activities, undertaken in rural and remote Australia, aimed to increase access to mental health services, promote awareness of mental health issues, support students undertaking mental health training and improve health professionals' capacity to recognise and address mental health issues. MHAs were strategically placed within the UDRHs across the country, ensuring an established academic base for the MHAs' work was available immediately. Close association with each local rural community was recognised as important. For most MHAs this was facilitated by having an established clinical role in their local community and actively engaging with the community in which they worked. In common with other rural health initiatives, some difficulties were experienced in the recruitment of suitable MHAs, especially in more remote locations. The genesis of this article was a national meeting of the MHAs in 2014, to identify and map the different types of activities MHAs had undertaken in their regions. These activities were analysed and categorised by the MHAs. These categories have been used as a guiding framework for this article. Issues: The challenge to increase community access to mental health services was addressed by (i) initiatives to address specific access barriers, (ii) supporting recruitment and retention of rural mental health staff, (iii) developing the skills of the existing workforce and (iv) developing innovative approaches to student placements. Strategies to promote awareness of mental health issues included workshops in rural and remote communities, specific suicide prevention initiatives and targeted initiatives to support the mental health needs of Indigenous Australians. The need for collaboration between the widely dispersed MHAs was identified as important to bridge the rural divide, to promote project cohesiveness and ensure new ideas in an emerging setting are readily shared and to provide professional support for one another as mental health academics are often isolated from academic colleagues with similar mental health interests. Lessons learned: The MHA project suggests that an integrated approach can be taken to address the common difficulties of community awareness raising of mental health issues, increasing access to mental health services, workforce recruitment and retention (access), and skill development of existing health professionals (access and awareness). To address the specific needs and circumstances of their community, MHAs have customised their activities. As in other rural initiatives, one size was found not to fit all. The triad of flexibility, diversity and connectedness (both to local community and other MHAs) describes the response identified as appropriate by the MHAs. The breadth of the MHA role to provide university sponsored educational activities outside traditional student teaching meant that the broader health workforce benefited from access to mental health training that would not otherwise have occurred. Provision of these additional educational opportunities addressed not only the need for increased education regarding mental health but also reduced the barriers commonly faced by rural health professionals in accessing quality professional development

Observables suitable for restricting the fidelity to multipartite maximally entangled states

We present a class of observables which are suitable for determining the fidelity of a state to the multipartite Greenberger-Horne-Zeilinger (GHZ) state. Given an expectation value of an observable belonging to the class, we give a simple formula that gives a lower bound and an upper bound for the fidelity. Applying the formula to the GHZ-state preparation experiment by Pan {\it et al}. {[Nature (London) {\bf 403}, 515 (2000)]}, we show that the observed state lies outside of the class of biseparable mixed three-qubit states. We also show that for this class of operators, adopting the principle of minimum variance {[Phys. Rev. A {\bf 60}, 4338 (1999)]} in the state estimation always results in the state with the minimum fidelity.Comment: 6 page

Multiple tier fuel cycle studies for waste transmutation.

As part of the U.S. Department of Energy Advanced Accelerator Applications Program, a systems study was conducted to evaluate the transmutation performance of advanced fuel cycle strategies. Three primary fuel cycle strategies were evaluated: dual-tier systems with plutonium separation, dual-tier systems without plutonium separation, and single-tier systems without plutonium separation. For each case, the system mass flow and TRU consumption were evaluated in detail. Furthermore, the loss of materials in fuel processing was tracked including the generation of new waste streams. Based on these results, the system performance was evaluated with respect to several key transmutation parameters including TRU inventory reduction, radiotoxicity, and support ratio. The importance of clean fuel processing ({approx}0.1% losses) and inclusion of a final tier fast spectrum system are demonstrated. With these two features, all scenarios capably reduce the TRU and plutonium waste content, significantly reducing the radiotoxicity; however, a significant infrastructure (at least 1/10 the total nuclear capacity) is required for the dedicated transmutation system

Topological Defects and CMB anisotropies : Are the predictions reliable ?

We consider a network of topological defects which can partly decay into neutrinos, photons, baryons, or Cold Dark Matter. We find that the degree-scale amplitude of the cosmic microwave background (CMB) anisotropies as well as the shape of the matter power spectrum can be considerably modified when such a decay is taken into account. We conclude that present predictions concerning structure formation by defects might be unreliable.Comment: 14 pages, accepted for publication in PR