Dicke-state preparation through global transverse control of Ising-coupled qubits

We consider the problem of engineering the two-excitation Dicke state $|D^{3}_{2}\rangle$ in a three-qubit system with all-to-all Ising-type qubit-qubit interaction, which is also subject to global transverse (Zeeman-type) control fields. The theoretical underpinning for our envisioned state-preparation scheme, in which $|000\rangle$ is adopted as the initial state of the system, is provided by a Lie-algebraic result that guarantees state-to-state controllability of this system for an arbitrary choice of initial- and final states that are invariant with respect to permutations of qubits. This scheme is envisaged in the form of a pulse sequence that involves three instantaneous control pulses, which are equivalent to global qubit rotations, and two Ising-interaction pulses of finite durations between consecutive control pulses. The design of this pulse sequence -- whose total duration is $T\approx 0.95\:\hbar/J$, where $J$ is the Ising-coupling strength -- leans heavily on the concept of the symmetric sector, a four-dimensional, permutationally-invariant subspace of the three-qubit Hilbert space. We demonstrate the feasibility of the proposed state-preparation scheme by carrying out a detailed numerical analysis of its robustness to systematic errors, i.e. deviations from the optimal values of the eight parameters that characterize the underlying pulse sequence. Finally, we discuss how our proposed scheme can be generalized for engineering Dicke states in systems with $N \ge 4$ qubits. For the sake of illustration, we describe the preparation of the two-excitation Dicke state $|D^{4}_{2}\rangle$ in a four-qubit system.Comment: extended version, accepted for publication in Phys. Rev.

Multiple-Resampling Receiver Design for OFDM Over Doppler-Distorted Underwater Acoustic Channels

Cataloged from PDF version of article.In this paper, we focus on orthogonal frequency-divisionmultiplexing (OFDM) receiver designs for underwater acoustic (UWA) channels with user- and/or path-specific Doppler scaling distortions. The scenario is motivated by the cooperative communications framework, where distributed transmitter/receiver pairs may experience significantly different Doppler distortions, as well as by the single-user scenarios, where distinct Doppler scaling factors may exist among different propagation paths. The conventional approach of front–end resampling that corrects for common Doppler scalingmay not be appropriatein such scenarios, rendering a post-fast-Fourier-transform (FFT) signal that is contaminated by user- and/or path-specific intercarrier interference. To counteract this problem, we propose a family of front–end receiver structures thatutilizemultiple-resampling (MR)branches,eachmatched to the Doppler scaling factor of a particular user and/or path. Following resampling, FFT modules transform the Doppler-compensated signals into the frequency domain for further processing through linear or nonlinear detection schemes. As part of the overall receiver structure, a gradient–descent approachis also proposed to refine the channel estimates obtained by standard sparse channel estimators. The effectiveness and robustness of the proposed receivers are demonstrated via simulations, as well as emulations based on real data collected during the 2010 Mobile Acoustic Communications Experiment (MACE10, Martha’s Vineyard, MA) and the 2008 Kauai Acomms MURI (KAM08, Kauai, HI) experiment

Entanglement dynamics of two qubits under the influence of external kicks and Gaussian pulses

We have investigated the dynamics of entanglement between two spin-1/2 qubits that are subject to independent kick and Gaussian pulse type external magnetic fields analytically as well as numerically. Dyson time ordering effect on the dynamics is found to be important for the sequence of kicks. We show that "almost-steady" high entanglement can be created between two initially unentangled qubits by using carefully designed kick or pulse sequences

Bank credit risk and macro-prudential policies: role of counter-cyclical capital buffer

This paper investigates the impact of macro-prudential policy (proxied by the counter-cyclical capital buffer (CCyB)) on bank credit risk during uncertain times, as banking sector stability is crucial in promoting financial intermediation. Using a unique daily data set consisting of 4939 credit default swaps (CDS) of 70 banks from 25 countries over the period 2010–2019, we find that CCyB tightening decreases bank-level CDS spreads, while CCyB loosening increases CDS spreads. This heterogeneous effect of CCyB arises due to its asymmetric effect on the capital ratio (i.e., the equity-to-total assets ratio) of banks. Tightening CCyB significantly increases capital, whereas loosening CCyB does not impact capital. Thus, the risks that emanate from the banking sector during periods of heightened uncertainty and financial distress can be significantly dampened when CCyB regulation is enabled. Consequently, macro-prudential policies for banks to hold higher levels of capital during good times are justified to contain financial market risks during downturns

Relationships between livelihoods, well-being, and marine protected areas : evidence from a community survey, Watamu Marine National Park and Reserve, Kenya

Funding information: UK Global Challenges Research Fund and Scottish Funding Council (projects 'Community Capabilities and Marine Protected Area Governance' and 'Mitigation of the effects of COVID-19 crisis in coastal Kenya XFC092').At a time of massive expansion of Marine Protected Areas, there is a need to learn more about their sustainability and success. This study draws on a framework which operationalizes three-dimensions of well-being: material, relational, and subjective, in order to measure the range of benefits and disbenefits experienced by local communities from protected areas. 308 respondents from two coastal Kenyan villages adjacent to the Watamu Marine National Reserve participated in a telephone survey in June and July 2020. The study recorded varying levels of dependency on the marine environment for the livelihoods of residents. A key finding of this study was that benefits reported by participants consistently exceeded disbenefits. A principal components analysis identified that the number of benefits and disbenefits experienced explained the most variance within the dataset. The benefits and disbenefits reported contributed to each dimension of human well-being. The highest ranked benefits reported contributed to subjective well-being (‘better health’, and ‘ability to enjoy a clean and healthy creek and ocean’), and the most frequently reported disbenefits related to relational and material well-being (for instance ‘increased conflict and social tension’ ‘increased poverty’, ‘fewer supplies of food’). Practical local conservation efforts can address relational disbenefits through better partnership working, and material disbenefits by supporting pro-conservation, alternative livelihoods. The findings demonstrate the relevance of understanding social trends for marine protected area governance and management. The paper offers insights into how fundamental relations between protected marine environments, livelihoods, and well-being may affect the perceptions and success of conservation initiatives amongst local communities.Publisher PDFPeer reviewe

Microstructure and properties of 308LSI steel obtained by deposition of metal wire

Shaped metal deposition (SMD) is a relatively new technology of additive manufacturing, which creates near-net shaped components by joining metallic materials by melting the area of a welding joint in high vacuum in the range from 10-3 to 10-6 mbar. In the present study, the main mechanical properties including micro-hardness and tensile properties were investigated. Single bead walls were deposited. Test pieces were machined from the deposited walls according to the National standard of Russia Federation for the mechanical tests. The tensile properties also showed dependence on the direction of the test carried out. All the examined tensile properties of the as deposited samples are close-matched properties of the as cast material

A review of recent perspectives on biomechanical risk factors associated with anterior cruciate ligament injury

There is considerable evidence to support a number of biomechanical risk factors associated with non-contact anterior cruciate ligament (ACL) injury. This paper aimed to review these biomechanical risk factors and highlight future directions relating to them. Current perspectives investigating trunk position and relationships between strength, muscle activity and biomechanics during landing/cutting highlight the importance of increasing hamstring muscle force during dynamic movements through altering strength, muscle activity, muscle length and contraction velocity. In particular, increased trunk flexion during landing/cutting and greater hamstring strength are likely to increase hamstring muscle force during landing and cutting which have been associated with reduced ACL injury risk. Decision making has also been shown to influence landing biomechanics and should be considered when designing tasks to assess landing/cutting biomechanics. Coaches should therefore promote hamstring strength training and active trunk flexion during landing and cutting in an attempt to reduce ACL injury risk.Peer reviewe

Trajectories of exposure and vulnerability of small islands to climate change

The authors thank the funding and logistical supports for the Back to the Future workshop (France, October 8–10, 2013) provided by the Corderie Royale de Rochefort, the Regional Council of Poitou-Charentes, the Conservatoire du Littoral, the Fondation de France, the Club Méditerranée, the Communautés d'agglomération de La Rochelle et du Pays Rochefortais, and the Université populaire du Littoral Charentais 17 and the French National Research Agency (CapAdapt project, ANR-2011-JSH1-004 01 and STORISK project, ANR-15-CE03-0003).This article advocates for a dynamic and comprehensive understanding of vulnerability to climate-related environmental changes in order to feed the design of adaptation future pathways. It uses the trajectory of exposure and vulnerability (TEV) approach that it defines as ‘storylines of driving factors and processes that have influenced past and present territorial system exposure and vulnerability to impacts associated with climate variability and change.’ The study is based on the analysis of six peer-reviewed Pacific island case studies covering various geographical settings (high islands vs low-lying reef islands, urban vs rural) and hazards associated with climate variability and change; that addressed the interactions between natural and anthropogenic driving factors; and adopted multidecadal past-to-present approaches. The findings emphasize that most urban and rural reef and high islands have undergone increasing exposure and vulnerability as a result of major changes in settlement and demographic patterns, lifestyles and economies, natural resources availability, and environmental conditions. The article highlights three generic and successive periods of change in the studied islands’ TEV: from geopolitical and political over the colonization-to-political independence period; to demographic, socio-economic, and cultural from the 1960s to the 1980s; culminating in the dominance of demographic, socio-economic, cultural, and environmental drivers since the 1980s. Based on these empirical insights, the article emphasizes the existence of anthropogenic-driven path-dependency effects in TEV, thus arguing for the analysis of the temporal dimensions of exposure and vulnerability to be a prerequisite for science to be able to inform policy- and decision-making processes toward robust adaptation pathways.PostprintPeer reviewe