Entanglement production in chaotic quantum dots subject to spin-orbit coupling

We study numerically the production of orbital and spin entangled states in chaotic quantum dots for non-interacting electrons. The introduction of spin-orbit coupling permit us to identify signatures of time-reversal symmetry correlations in the entanglement production previously unnoticed, resembling weak-(anti)localization quantum corrections to the conductance. We find the entanglement to be strongly dependent on spin-orbit coupling, showing universal features for broken time-reversal and spin-rotation symmetries.Comment: 6 pages; extended versio

Dipole oscillations of confined lattice bosons in one dimension

We study the dynamics of a non-integrable system comprising interacting cold bosons trapped in an optical lattice in one-dimension by means of exact time-dependent numerical DMRG techniques. Particles are confined by a parabolic potential, and dipole oscillations are induced by displacing the trap center of a few lattice sites. Depending on the system parameters this motion can vary from undamped to overdamped. We study the dipole oscillations as a function of the lattice displacement, the particle density and the strength of interparticle interactions. These results explain the recent experiment C.D. Fertig et al., Phys. Rev. Lett. 94, 120403 (2005).Comment: 4 pages, 3 figure

Parity dependent Josephson current through a helical Luttinger liquid

We consider a superconductor-two dimensional topological insulator- superconductor junction (S-2DTI-S) and study how the 2{\pi}- and 4{\pi}-periodic Josephson currents are affected by the electron-electron interaction. In the long-junction limit the supercurrent can by evaluated by modeling the system as a helical Luttinger liquid coupled to superconducting reservoirs. After having introduced bosonization in the presence of the parity constraint we turn to consider the limit of perfect and poor interfaces. For transparent interfaces, where perfect Andreev reflections occur at the boundaries, the Josephson current is marginally affected by the interaction. On the contrary, if strong magnetic scatterers are present in the weak link, the situation changes dramatically. Here Coulomb interaction plays a crucial role both in low and high temperature regimes. Furthermore, a phase-shift of Josephson current can be induced by changing the direction of the magnetization of the impurity

Density-of-states of many-body quantum systems from tensor networks

We present a technique to compute the microcanonical thermodynamical properties of a manybody quantum system using tensor networks. The Density Of States (DOS), and more general spectral properties, are evaluated by means of a Hubbard-Stratonovich transformation performed on top of a real-time evolution, which is carried out via numerical methods based on tensor networks. As a consequence, the free energy and thermal averages can be also calculated. We test this approach on the one-dimensional Ising and Fermi-Hubbard models. Using matrix product states, we show that the thermodynamical quantities as a function of temperature are in very good agreement with the exact results. This approach can be extended to higher-dimensional system by properly employing other types of tensor networks.Comment: 8 pages, 7 figure

Superfluid density and quasi-long-range order in the one-dimensional disordered Bose-Hubbard model

We study the equilibrium properties of the one-dimensional disordered Bose-Hubbard model by means of a gauge-adaptive tree tensor network variational method suitable for systems with periodic boundary conditions. We compute the superfluid stiffness and superfluid correlations close to the superfluid to glass transition line, obtaining accurate locations of the critical points. By studying the statistics of the exponent of the power-law decay of the correlation, we determine the boundary between the superfluid region and the Bose glass phase in the regime of strong disorder and in the weakly interacting region, not explored numerically before. In the former case our simulations are in agreement with previous Monte Carlo calculations.Comment: 18 pages, 12 figures; some references and two appendices added; appearing in New Journal of Physics focus issue "Strongly Interacting Quantum Gases in One Dimension

Unconstrained Tree Tensor Network: An adaptive gauge picture for enhanced performance

We introduce a variational algorithm to simulate quantum many-body states based on a tree tensor network ansatz which releases the isometry constraint usually imposed by the real-space renormalization coarse-graining: This additional numerical freedom, combined with the loop-free topology of the tree network, allows one to maximally exploit the internal gauge invariance of tensor networks, ultimately leading to a computationally flexible and efficient algorithm able to treat open and periodic boundary conditions on the same footing. We benchmark the novel approach against the 1D Ising model in transverse field with periodic boundary conditions and discuss the strategy to cope with the broken translational invariance generated by the network structure. We then perform investigations on a state-of-the-art problem, namely the bilinear-biquadratic model in the transition between dimer and ferromagnetic phases. Our results clearly display an exponentially diverging correlation length and thus support the most recent guesses on the peculiarity of the transition.Comment: 11 pages, 13 figure

Efficiency of quantum controlled non-Markovian thermalization

We study optimal control strategies to optimize the relaxation rate towards the fixed point of a quantum system in the presence of a non-Markovian dissipative bath. Contrary to naive expectations that suggest that memory effects might be exploited to improve optimal control effectiveness, non-Markovian effects influence the optimal strategy in a non trivial way: we present a necessary condition to be satisfied so that the effectiveness of optimal control is enhanced by non-Markovianity subject to suitable unitary controls. For illustration, we specialize our findings for the case of the dynamics of single qubit amplitude damping channels. The optimal control strategy presented here can be used to implement optimal cooling processes in quantum technologies and may have implications in quantum thermodynamics when assessing the efficiency of thermal micro-machines.Comment: 7 pages, 3 figure

Robust optimal quantum gates for Josephson charge qubits

Quantum optimal control theory allows to design accurate quantum gates. We employ it to design high-fidelity two-bit gates for Josephson charge qubits in the presence of both leakage and noise. Our protocol considerably increases the fidelity of the gate and, more important, it is quite robust in the disruptive presence of 1/f noise. The improvement in the gate performances discussed in this work (errors of the order of 10^{-3}-10^{-4} in realistic cases) allows to cross the fault tolerance threshold.Comment: 4 pages, 4 figure

Life Cycle Data Network: Handbook for data developers and providers

After its debut in the European Commission’s Integrated Product Policy (COM (2003)302) as the “best framework for assessing the potential environmental impacts of products”, Life Cycle Thinking (LCT) and Assessment (LCA) has become increasingly used in support of community policies and business. Focus has been primarily on establishing agreed methods, both within Europe and internationally. The EC’s European Platform on Life Cycle Assessment (EPLCA) has continued to address the equally essential issue of data availability, coherence, and quality assurance. LCA has become an important approach to boost smart, sustainable and inclusive growth in the EU. As an example, in the context of the Europe 2020 Flagship Initiative “A Resource Efficient Europe” , and the “Single Market for Green Products Communication” and related European Commission Recommendation for the Product Environmental Footprint (PEF) Guide and the Organisation Environmental Footprint (OEF) Guides . These methodologies reflect a vital milestone in the aim to increase coherence and quality in the assessment of environmental performance of products and organisations. Other prominent applications include in support of the Waste Framework Directive, the Eco-design Directive, EU Ecolabel and EU GPP, the Raw Materials Initiative, the bio economy strategy, as well as providing a more advanced basis for indicators and targets accounting for the burdens of EU imports and exports to help focus policies and research funding. Life Cycle Thinking is essential in modern decision making in business and policy. Commonly implemented through Life Cycle Assessment, it is increasingly necessary to quantify the benefits and burdens associated with products, both goods and services, that occur in their supply chains, during use, as well as at the end-of-their lives. This helps to avoid the shifting of burdens between different geographic regions, generations and impacts. Within this framework, the EPLCA, developed by the JRC, together with DG-Environment, represents the reference point for data and methods essential to implementing Life Cycle based approaches. The EPLCA promotes the availability of data and information, with a focus on coherence and quality assurance. Although methodology development is advancing fast, the availability of coherent, quality-assured life cycle data and studies still represents a major challenge to mainstream the use of LCA and associated environmental footprint methods in business and in policy. To date, the EPLCA has facilitated several notable developments: - The Life Cycle Data Network (LCDN); launched in early 2014, aims at providing a globally usable infrastructure for consistent and quality assured life cycle data. - The European Reference Life Cycle Database (ELCD); comprises of Life Cycle emissions and resource consumption Inventory (LCI) data from front-running EU-level business associations and other sources for key materials, energy carriers, transport, and waste management, to be used as source for secondary data. - The Resource Directory (RD); provides a structured repository for several types of life cycle-based documents and studies, as well as a world-wide list of life cycle support software packages and databases from suppliers/developers, and service providers. - The Reviewer Registry (RR): provides a list of potential reviewers for different LCA schemes, and automatically assess the eligibility of single reviewers and reviewers’ teams, according to different levels of compliance. This guide provides comprehensive instructions on how to utilize the Life Cycle Data Network (LCDN) for publishing LCA data. It summarizes how to orchestrate the various tools in order to guide the data developers through the entire process from generation of a dataset to publication on the LCDN. Further and more detailed documentation for the individual steps can be found in the annexes to this technical report. In principle, the following steps are required in order to publish data on the LCDN and therefore covered in this document: 1. Prepare data (export from an LCA modelling tool) 2. Technical validation of the data 3. Set up a node for participation in the LCDN. 4. Upload of the data to the node 5. Publication of the data on the LCDN Beyond that, a detailed guidance on how document different ILCD-EL aspects, in three commonly used LCA software in Europe (Namely: GaBi , OpenLCA and SimaPro ), is also provided in this document. This document is providing some examples, taking into account some the above mentioned LCA software, because are the most commonly used and widespread in Europe, this does NOT imply any recommendation or endorsement from the JRC or the European Commission. An exemplary dataset was used to provide an overview and understanding of how to address some compliance issues, in different software. Some general guiding principles that apply to all of the software are summarized, along with a short review of discrepancies found when exporting the dataset in ILCD format using the individual LCA software. The editable compliance elements are explained individually, showing some screenshots of different software tools. Finally a set of slides, resuming the content of this guide, is provided in annex II.JRC.D.1-Bio-econom

Dynamical versus static imperfections in quantum computers(6) Approaches from mathematical science and quantum information, Chaos and Nonlinear Dynamics in Quantum-Mechanical and Macroscopic Systems)

この論文は国立情報学研究所の電子図書館事業により電子化されました。We study the effects of imperfections in a spin model of a quantum computer. We identify different regimes, ranging from low-frequency fluctuations, where the imperfections can be considered static, to the high-frequency case, where the imperfections are purely dynamical and their effects are shown to be completely wiped out